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Stefano CONTI
Professore Associato
Dipartimento di Scienze Chimiche e Geologiche - Sede Dipartimento di Scienze Chimiche e Geologiche
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Pubblicazioni
2024
- The transition from normal marine to evaporitic conditions recorded in a cold seep environment: The Messinian succession of Northern Italy
[Articolo su rivista]
Conti, S.; Argentino, C.; Bojanowki, M.; Fioroni, C.; Giunti, S.; Kremer, B.; Fontana, D.
abstract
2023
- A multidisciplinary approach in recognizing seep-carbonates: A case study from the Loiano Formation (late Eocene) in the northern Apennines (Italy)
[Articolo su rivista]
Conti, S.; Panini, F.; Patteri, P.; Rondelli, R.; Malferrari, D.
abstract
2023
- Paleoecology of a new Gyrolithes ichnospecies as a component of a compound trace fossil from the Middle Miocene Marnoso-arenacea Formation (northern Apennines, Italy)
[Articolo su rivista]
Conti, S.; Serventi, P.
abstract
2022
- Messinian seep-carbonates marking the transition to the evaporite
deposits in the Romagna sector of the northern Apennines (Italy)
[Articolo su rivista]
Conti, S.; Fioroni, C.; Serventi, P.; Fontana, D.
abstract
2022
- Petrographic features to formere presence of gas hydrate in ancient seep carbonates: preliminary observations of moderm and fossil material
[Relazione in Atti di Convegno]
Giunti, S.; Bohrmann, G.; Conti, S.; Dela Pierre, F.; Fontana, D.; Martire, L.; Natalicchio, M.; Wetzel, A.; Bojanowski, M.
abstract
2021
- Biomarker constraints on Mediterranean climate and ecosystem transitions during the Early-Middle Miocene
[Articolo su rivista]
Salocchi, Aura C.; Krawielicki, Julia; Eglinton, Timothy I.; Fioroni, Chiara; Fontana, Daniela; Conti, Stefano; Picotti, Vincenzo
abstract
2021
- Gas Hydrate destabilization and sea-level changes: insights from Miocene seep carbonate deposits of the northern Apennines (Italy).
[Relazione in Atti di Convegno]
Fontana, D.; Conti, S.; Fioroni, C.; Argentino, C.
abstract
2021
- Miocene Seep-Carbonates of the Northern Apennines (Emilia to Umbria, Italy): An Overview.
[Articolo su rivista]
Conti, S; Argentino, C; Fioroni, C; Salocchi, Ac; Fontana, D
abstract
2021
- Trace fossils in seep-impacted sediments as a tool to decipher the origin
of fine-grained intervals of the Marnoso-arenacea turbidite succession
(Miocene, northern Apennines, Italy)
[Articolo su rivista]
Conti, S.; Baucon, A.; Serventi, P.; Argentino, C.; Fontana, D.
abstract
The Marnoso-arenacea turbidite succession outcropping in northern Italy is one of the most studied deep-water
systems worldwide due to its excellent exposure. Despite the well-established sedimentology of the arenaceous
succession, the origin of fine-grained intervals within the Marnoso-arenacea Fm is reconsidered in the light of
methane-rich fluid expulsion, in particular as seep-carbonates are present. Fine-grained intervals are marked
by limited vertical and lateral extent, in the order of 102 m and 103 m respectively, and are often associated
with small-scale sediment deformation. In this study, we conduct a detailed sedimentological and stratigraphic
investigation of the well-exposed Prati Piani fine-grained interval (Serravallian in age) with particular focus on
the characterization of trace fossils and seep-carbonates. Trace fossils interpreted as Thalassinoides are widespread
throughout the interval and form a complex network testifying long-lasting burrowing activity of decapod
crustaceans. Seep-carbonates crop out at different stratigraphic levels and form meter-sized blocks with
δ13C from−33.2‰ to−18.2‰. The occurrence of aragonite cements and fossil chemosymbiotic fauna indicates
episodic carbonate precipitation close to the paleo-seafloor. Although crustaceans have been frequently reported
grazing microbial mats atmodern seeps and leaving a 13C-depleted isotopic signature in trace fossils, in our study
we found only one slightly depleted δ13C value (−9.5‰,) allowing us to exclude preferential authigenesis. Moreover,
burrows are filled by detrital fine-grained sediments and hemipelagic micrite that may have diluted the
methane-related signature. The association between in situ seep-carbonates and well-preserved trace fossils is
of use to interpret the interval as formed by fine-grained sedimentation draping a thrust-related anticline. In
this model, the stratigraphically- and laterally-confined deformed zones affecting the Prati Piani interval reflect
in-situ soft-sediment deformation and small-scale slumping induced by fluid seepage along the ridge, consistent
with present-day observations from several continental margins worldwide.
© 2021
2020
- Preservation of 34S-enriched sulfides in fossil sulfate-methane transition zones: new evidence from Miocene outcrops of the northern Apennines (Italy)
[Articolo su rivista]
Argentino, C.; Johnson, J. E.; Conti, S.; Fioroni, C.; Fontana, D.
abstract
We provide new evidence of the preservation of 34S-enriched signals in methane seep-impacted sediments from two onshore Miocene outcrops located in the northern Apennines (Italy). Selected outcrops include methane-derived authigenic carbonates (MDAC) with δ13C composition between − 42.3 and − 18.2‰. MDACs contain chemosynthetic clams and abundant pyrite indicative of formation close to or within a shallow sulfate-methane transition zone (SMTZ). This study aims to evaluate the relative contributions of background organic matter mineralization and anaerobic oxidation of methane (AOM) to sulfate consumption and to gain insight into the transport process (i.e., diffusion, advection) controlling the depth of the SMTZ. Host sediments were investigated by CHN elemental analysis coupled with total sulfur (TS) and sulfur isotopic measurements on bulk samples. Total organic carbon (TOC) measurements reveal a consistent and low amount of organic carbon (TOC< 0.5%), with no notable difference between the underlying turbidites and the stratigraphic intervals hosting the MDACs. The TS/TOC ratio of most samples is well above the baseline value of deposition under normal marine conditions, suggesting the excess TS here is due to enhanced sulfate reduction. The samples show bulk δ34S values commonly enriched (> 0‰ and up to + 17.1‰), which is characteristic of sulfides precipitated in association with AOM. We propose that advection of methane-rich fluids was responsible for maintaining the shallow depth of the studied paleo-SMTZs. AOM at paleo-SMTZ positions in the investigated seep-impacted sediments resulted in excess bicarbonate and sulfide production, favoring solid-phase MDAC and iron sulfide precipitation.
2019
- A deep fluid source of radiogenic Sr and highly dynamic seepage conditions recorded in Miocene seep carbonates of the northern Apennines (Italy)
[Articolo su rivista]
Argentino, C.; Lugli, F.; Cipriani, A.; Conti, S.; Fontana, D.
abstract
The 87Sr/86Sr, REE and MoU systematics were investigated in Miocene seep carbonates formed on accretionary ridges at the front of the northern Apennine wedge. Here we evaluate fluid sources, seepage intensity and redox conditions during carbonate precipitation. Micrite matrix and early calcite cements lining cavities are the main authigenic carbonate phases and show negligible diagenetic alteration. Their AOM-related (anaerobic oxidation of methane) origin is evident from δ13C values ranging from −38.7‰ to −25.7‰. The 87Sr/86Sr ratios in carbonates vary between 0.708659 and 0.709132. Most micrite values fall within the range of Middle Miocene seawater (Langhian, MNN5a biozone), in agreement with the biostratigraphy of the host sediments, thus reflecting precipitation of seep carbonates close to the seafloor. Highly radiogenic 87Sr/86Sr ratios, of early calcite cements and micrite from conduit-rich facies at the base of carbonate bodies, likely derived from the interaction of fluids with detrital clays during the fault-controlled upward migration through the underlying terrigenous turbidite successions. Strong Mo and U enrichments in carbonates, with MoEF and UEF up to 233.5 and 86.6 respectively, coupled with (Mo/U)EF ratios ranging between 0.7 and 9.7, indicate dynamic redox conditions, episodically sulfidic and restricted to porewaters. This interpretation is also supported by enrichments in MREE of micrites and a general absence of negative Ce anomalies. These new data provide an indirect indication of rates and temporal variability of AOM at fossil methane seeps developed on a thrust related anticline and help to constrain the complex interaction between fluid migration pathways, seepage intensity and environmental conditions as observed in modern seep analogues.
2019
- Biostratigraphic distribution of Miocene carbonates associated with gas hydrates in the northern Apennines (Italy) and their relationship with sea-level lowering
[Abstract in Atti di Convegno]
Fioroni, Chiara; Argentino, Claudio; Conti, Stefano; Fontana, Daniela
abstract
Gas hydrates are widespread in modern continental margins and their stability is related to temperature, pressure and availability of gas and water. Their sensitivity to tectonic activity and climate is still poorly constrained and more efforts are needed to understand how they respond to these forcing processes. Gas hydrates are frequently associated with carbonates, called clathrites, that may form bodies of large dimension and are marked by geochemical indicators such as 13C-depleted and enriched 18O values.
A number of Miocene seep-carbonates outcrop in different geological settings of the northern Apennines (Italy) (Argentino et al., 2019a), showing characters suggesting paleo-gas hydrate occurrence and then can be considered as clathrites. Our biostratigraphic investigation on the sediment enclosing gas-hydrate associated carbonates has shown that they are roughly concentrated in three main intervals: in the Langhian (subzone MNN5a), in the upper Serravallian-lower Tortonian (subzone MNN6b to zone MNN7) and the upper Tortonian-lowermost Messinian (zones MNN10 and MNN11). By comparing seep distributions with 3rd order eustatic curves of Haq et al. (1987), they seem to match phases of sea-level lowering.
The relationship among gas hydrate destabilization, climate change, sea-level variations, tectonic activity and fluid circulation, is particularly challenging in the fossil record. In the examined carbonates, a drop in the hydraulic pressure on the plumbing system during sea-level lowering would have shifted the base of the gas hydrate stability zone into shallower depths, inducing gas-hydrate destabilization. The uplift of the different sectors of the wedge-top foredeep system during tectonic migration could have increased the effect of the concomitant eustatic sea-level drop, reducing the hydrostatic load on the seafloor and inducing gas-hydrate decomposition.
In this view, a precise biostratigraphic framework of paleo-clathrites in the sedimentary record may help to shed light into gas-hydrates long-term evolution and their relation with sea level changes and tectonics.
2019
- Evidences for Paleo-Gas Hydrate Occurrence: What We Can Infer for the Miocene of the Northern Apennines (Italy)
[Articolo su rivista]
Argentino, C.; Conti, S.; Fioroni, C.; Fontana, D.
abstract
The occurrence of seep-carbonates associated with shallow gas hydrates is increasingly
documented in modern continental margins but in fossil sediments the recognition of gas hydrates
is still challenging for the lack of unequivocal proxies. Here, we combined multiple field and
geochemical indicators for paleo-gas hydrate occurrence based on present-day analogues to
investigate fossil seeps located in the northern Apennines. We recognized clathrite-like structures such
as thin-layered, spongy and vuggy textures and microbreccias. Non-gravitational cementation fabrics
and pinch-out terminations in cavities within the seep-carbonate deposits are ascribed to irregularly
oriented dissociation of gas hydrates. Additional evidences for paleo-gas hydrates are provided by
the large dimensions of seep-carbonate masses and by the association with sedimentary instability
in the host sediments. We report heavy oxygen isotopic values in the examined seep-carbonates up
to +6h that are indicative of a contribution of isotopically heavier fluids released by gas hydrate
decomposition. The calculation of the stability field of methane hydrates for the northern Apennine
wedge-foredeep system during the Miocene indicated the potential occurrence of shallow gas
hydrates in the upper few tens of meters of sedimentary column.
2019
- Fluid expulsion in accretionary wedges: what can we learn from
Miocene seep carbonates (Emilia and Tuscan Apennines, Italy)
[Capitolo/Saggio]
Fontana, D.; Conti, S.; Argentino, C.; Fioroni, C.
abstract
Seepage of hydrocarbon-rich fluids is a common process
in accre onary wedges where tectonic thickening and
underpla ng generate pore-fluid overpressures and
induce fluid migra on (Bohrmann et al., 2002; Gill et al.,
2005; Ding et al., 2010; Crutchley et al., 2015; Klaucke et
al., 2015). The migra on and expulsion of methane-rich
fluids promote the precipita on of a variety of authigenic
minerals on the seafloor or within the sediments, i.e.
carbonates (aragonite, calcite, dolomite), sulfides and
sulphates, forming crusts, concre ons and build-ups.
Reduced compounds in the fluids also sustain peculiar
microbial consor a and macrofaunal communi es
(Teichert et al., 2005; Campbell, 2006) (Fig. 1).
It is widely recognized that the most reliable indicators of
fossil cold seeps are the anomalously nega ve carbon
13 isotope composi on of the carbonates, with d C values as
low as -60‰ VPDB (Judd and Hovland, 2009), the peculiar
chemosynthe c bivalves (Lucinidae and Vesicomyidae)
and specific biomarkers (e.g. Taviani, 2014; Peckmann et
al., 2002; Grillenzoni et al., 2017).
In the northern Apennine orogenic belt, several outcrops
of authigenic carbonates tes fy for Miocene seepage
ac vity (Terzi et al., 1994; Dela Pierre et al., 2010; Con et
al., 2017). These carbonates show highly depleted d13C
signatures and host large chemosynthe c bivalve
assemblages (mainly giant lucinids)(Grillenzoni et al.,
2017), thus tes fying a long and complex history of
methane-rich fluid ven ng on the sea floor. Apenninic
carbonate deposits bearing fossil chemosynthe c fauna
have been found in various domains and basin types, from
wedge-top basins to the slope of the accre onary wedge,
and in the inner foredeep (Con and Fontana, 1999;
Argen no et al., 2019a) (Figs 2, 3).
In the following, we summarize and describe the main
features of the Apennine seep carbonates, from field
observa ons to geochemical features.
2019
- Formation of tubular carbonate conduits at Athina mud volcano, eastern
Mediterranean Sea
[Articolo su rivista]
Tamborrinoa, L.; Himmlerb, T.; Elvert, M.; Conti, S.; Gualtieri, A.; Fontana, D.; Bohrmann, G.
abstract
Tubular carbonate conduits (TCC) represent the termination of fluid plumbing systems in environments of hydrocarbon
seepage and play a relevant role in the discharge of methane from sub-seafloor sediments to the water
column. However, the biogeochemical reactions and biological activities involved in their formation are not fully
understood. To address this, TCC samples were collected with a remotely operated vehicle from the seabed on
the SW flank of the Athina mud volcano in the eastern Mediterranean Sea. Petrographic, mineralogical, stable
carbon and oxygen isotope and lipid biomarker analyses were performed to elucidate the formation processes of
the tubular carbonates. Clotted and fibrous aragonite form the internal lining of the cavities, while the outer
portion of the tubes is formed by micritic Mg-calcite cementing hemipelagic sediment. 13C-depleted Mg-calcite
and aragonite (as low as −14.4‰ V-PDB) and lipid biomarkers (archaeol, −89.8‰ V-PDB) indicate that carbonate
precipitation was influenced by sulfate-dependent anaerobic oxidation of methane (AOM). AOM locally
enhances aragonite precipitation, thereby facilitating early lithification of the conduits within the mud volcano
sediments. The size and morphology of the TCC comparable with the buried portion of tubeworm colonies found
in the proximity of the sampling site. However, our results suggest that TCC likely formed by the action of
burrowing organism rather than being mineralizations of the tubeworm colonies. This study provides new insights
into the interpretation and understanding of TCC, highlighting the role of macrofaunal activity in the
formation of migration pathways for hydrocarbon-rich fluids on the flank of a mud volcano
2019
- Methane-derived authigenic carbonates on accretionary ridges: Miocene case studies in the northern Apennines (Italy) compared with modern submarine counterparts
[Articolo su rivista]
Argentino, C.; Conti, S.; Crutchley, J. C.; Fioroni, C.; Fontana, D.; Johnson, J. E.
abstract
We present new field data from three outcrops of Miocene methane-derived authigenic carbonates in the
foredeep of the northern Apennines that contain chemosynthetic fauna and record a long history (∼1 Ma) of
shallow fluid seepage linked to seafloor anaerobic oxidation of methane. The studied outcrops show similar
features in terms of carbonate morphology, facies, spatial distribution and lateral and vertical contacts with the
enclosing sediments. Methane-derived carbonates occur in two structural positions: 1) on the slope of the accretionary
wedge in hemipelagites draping buried thrust-related anticlines, and 2) at the leading edge of the
deformation front in the inner foredeep, within fault-related anticlines standing above the adjacent deep seafloor
as intrabasinal ridges. We compare fossil seeps with two extensively investigated modern analogues: the
Hikurangi Margin, offshore New Zealand and Hydrate Ridge, on the Cascadia margin, offshore the U.S.A. These
analogues share a similar compressive structural setting and are marked by the presence of variably extensive
and voluminous methane-derived carbonate bodies and chemosynthetic fauna on the present-day seafloor. The
comparison allows us to propose a model for the evolution of fluid seeps on thrust-related ridges. At the deformation
front, uplift and geometry of the anticlinal ridges are controlled by the growth of splay faults, mostly
blind, connected to the basal detachment, favoring the migration of fluids toward the incipient anticline. Fold
development generates extensional stresses in the hinge zone of the anticline, promoting the development of
normal faults; fluid migration pathways and seafloor seeps shift from the forelimb toward the crest of the ridge
as the structures evolve. In the slope setting, far from the deformation front, thrust faults and extensional faults
in buried anticlines remain the main fluid migration pathways to sustain seepage at the seafloor. After reaching a
mature stage within the wedge, the structure is less active and buried in the slope environment of the evolved
2018
- Constraining the fluid source of Miocene seep carbonates using radiogenic Sr isotopes (Corella outcrop, northern Apennines, Italy)
[Abstract in Atti di Convegno]
Argentino, Claudio; Lugli, Federico; Cipriani, Anna; Conti, Stefano; Fioroni, Chiara; Fontana, Daniela
abstract
Analisi isotopiche e biostratigrafiche su corpi carbonatici metanoderivati dell'Appennino settentrionale
2018
- Highly dinamic redox condition and fluid source identification in seep impacted sediments revealed by Mo-U enrichments, 87Sr/86SR and REE pattern (Miocene, Mugello outcrops, northern Apennines)
[Abstract in Atti di Convegno]
Argentino, C.; Lugli, F.; Cipriani, A.; Conti, S.; Fioroni, C.; Fontana, D.
abstract
cold seeps have been increasingly identified.....
2017
- Correlating shelf carbonate evolutive phases with fluid expulsion episodes in the foredeep (Miocene, northern Apennines, Italy)
[Articolo su rivista]
Conti, Stefano; Fioroni, Chiara; Fontana, Daniela
abstract
In the Miocene of the northern Apennines of Italy, evolutionary phases of shallow-water carbonates in
wedge-top basins are coeval with methane-rich fluid expulsion episodes in the inner foredeep. We
identified four main correlative events, primarily controlled by synsedimentary tectonics, sediment input
and climate cooling: 1) a Burdigalian tectonic phase determined the onset of shelfal sedimentation in
wedge-top areas and is correlated with an important episode of fluid expulsion in marly sediments of the
inner foredeep (Croce di Moggiona seep-carbonates); 2) the decrease of shelfal carbonate production and
the increase of detrital input in the Early Langhian correspond with a second important episode of seepcarbonate
precipitation in the inner foredeep (Castagno d'Andrea); 3) the demise of the carbonate shelf
and the coeval expulsion of methane-rich fluids in the inner foredeep (Vicchio and M. Citerna seepcarbonates)
at the Langhian/Serravallian boundary approximate the Mi3b cooling event. The lower
temperatures, associated with increased siliciclastic weathering, led to the crisis of shallow-water carbonate
production whereas the pressure drop due to the eustatic fall may have triggered the gas-charged
fluid expulsion; 4) the tectonic-related uplift of frontal sectors of the wedge-top basin led to the wide
erosion of the Burdigalian-Langhian carbonates and caused the precipitation of authigenic seepcarbonates
(Deruta seep) both in the slope and the adjacent foredeep.
2017
- MIOCENE SEDIMENTARY INSTABILITIES ASSOCIATED WITH
METHANE DERIVED AUTHIGENIC CARBONATES: A NEW CASE
STUDY FROM THE NORTHERN APENNINES (PALAZZUOLO
OUTCROPS, ITALY)
[Abstract in Atti di Convegno]
Argentino, Claudio; Johnson, Joel; Conti, Stefano; Fioroni, Chiara; Fontana, Daniela
abstract
Northern Apennines (Italy) host several outcrops of methane derived seep carbonates often associated
with sedimentary instabilities such as intraformational slumps, extraformational slides and diapiric
processes. Despite the vast body of literature on seep-deposits from the Monferrato to the Umbro-Tuscan
sectors of the mountain chain, only a few studies focus on the interplay between paleomethane seepage and
sedimentary instabilities (Conti and Fontana, 2002) because of the lack of good exposures.
In this study we investigate an outcrop located in the Mugello area of the Tuscan Apennines (Prati
Piani di Palazzuolo) characterized by the co-occurrence of methane derived authigenic carbonates,
chemosynthetic fauna and slump-like structures. The examined outcrop consists of several carbonate blocks
with max length of 3.5 m enclosed in a 100 m thick pelitic interval, interpreted as sedimentation above a
structural high in the inner foredeep at the front of the Middle Miocene accretionary wedge.
The blocks are mainly located at the base of the pelitic interval and have the same strike as the
enclosing sediments. At various levels, pelitic sediments show soft sediment deformation structures (folds,
slumps). Within the slumps, we sampled some concretions (silty-carbonate in composition).
The δ13C value in the carbonates ranges between -18.2‰ and -33.22‰, confirming they are methane
derived (AOM-related in origin). Pelites surrounding the carbonate blocks (in situ or transported for a short
distance. Isotopic δ18O values are comprised between -4.31‰ and 0.87‰. The concretions are slightly
depleted in 13C (-5.47‰; -10.95‰).
Preliminary data suggest the presence of a seepage system active before the onset of the instability
and able to sustain chemosynthetic communities at the seafloor. The interstitial overpressures might have
reduced the shear strength of the fine-grained sediments and constituted an important preconditioning factor
for diapiric or mass-transport structures. However, this conclusion is still speculative and needs further
investigation.
2017
- Miocene phosphatic hardgrounds of the Mediterranean and their biotic assemblage: new insights from the "Aturia level" of the Salento Peninsula (S. Italy)
[Abstract in Atti di Convegno]
Vescogni, Alessandro; Bosellini, Francesca Romana; Vertino, Agostina; Harzhauser, Mathias; Mandic, Oleg; Cipriani, Anna; Conti, Stefano; Remitti, Francesca
abstract
From the late Oligocene to the late Miocene, the central Mediterranean area was interested by an
extensive deposition of phosphate-rich sediments. They are usually represented by 10-20 cm thick,
sub-horizontal hardgrounds, made of phosphatic sediments arranged into thin layers separated by
erosion surfaces. Macrofossils are very abundant, their assemblage composed of colonial and solitary
corals, molluscs, echinoderms, brachiopods, bryozoans and fish teeth.
In the past decades, the Mediterranean phosphatic deposits have been the subject of several studies,
mainly aimed to understand their depositional processes and the mechanisms leading to
phosphogenesis. In particular, the formation of these sediments has been recently interpreted as
associated to the occurrence of a complex system of upwelling currents, flowing into the central
Mediterranean from the deeper, eastern region of the basin. However, most of the contributions
mainly relies on stratigraphic, sedimentary and geochemical features, whereas the macrofossil
assemblage, despite its abundance and diversity, has never been analyzed in detail. The main goal of
this study is thus a thorough investigation, mainly from a palaeontological/palaeoecological
perspective, of the phosphatic deposits of the Salento Peninsula (named “Aturia” level). Special
attention is given to the coral and mollusc associations, particularly sensitive to changes in the main
environmental stressors and representing the most abundant biotic components of the phosphatic
deposits.
The Salento Aturia level is up to 25 cm in thickness and made of several phosphatic layers separated
by erosion surfaces. Microstratigraphic and microfacies analyses allow to identify two distinct facies.
A coral rudstone, about 7-10 cm thick, constitutes the base of the hardground, while on the top lies a
detrital rudstone, made of the succession of thinner layers mainly composed of phosphatic fragments.
Most of the macrofossils are concentrated within the coral rudstone and particularly abundant are
corals, associated to molluscs and to a lesser amount to brachiopods, echinoderms, bryozoans,
serpulids and fish teeth.
The coral assemblage is composed at least by 16 taxa belonging to 4 families, represented in order of
2017
- Miocene seep-impacted sediments and authigenic carbonates of the Mugello area (northern Apennines, Italy): new insights from facies, stable isotopes and CHN analyses
[Poster]
Argentino, Claudio; Johnson, J. E.; Conti, Stefano; Fioroni, Chiara; Fontana, Daniela
abstract
Reconstructing seepage dynamics and geochemical conditions that created massive authigenic carbonate precipitation and sustained chemosynthetic fauna on the seafloor at the studied site during the Langhian period of the Miocene.
2017
- Mud diapirs originated from mud-rich mass transport deposits: exhumed field cases and modern analogues
[Abstract in Atti di Convegno]
Pini, Gian Andrea; Conti, S.; Festa, A.; Fontana, D.; Lucente, C. C.; Ogata, K
abstract
sedimentary instability
2017
- Paleoenvironmental evolution in a high-stressed cold-seep system (Vicchio Marls, Miocene, northern Apennines, Italy)
[Articolo su rivista]
Grillenzoni, Claudia; Monegatti, Paola; Turco, Elena; Conti, Stefano; Fioroni, Chiara; Fontana, Daniela; Salocchi, AURA CECILIA
abstract
Excellent exposures of Miocene seep-carbonates enclosed in marine marly sediments (Vicchio outcrops in the
northern Apennines, Italy) offer the opportunity to highlight the evolution of a fossil seep ecosystem and the
response of benthic communities to high-stressed environmental conditions. For this purpose, seep-related facies
and molluscs within carbonate bodies have been studied, coupled with benthic foraminiferal assemblages and
carbon and oxygen isotopes in the enclosing marls. The integrated planktonic foraminiferal and calcareous
nannofossil biostratigraphy has allowed us to constrain the seepage within well-calibrated bioevents and to
stress the relationships with paleoclimatic and paleoceanographic variations during the middle Miocene in the
Mediterranean area. Our biostratigraphic data indicate that the onset of the seepage approximates the Mi3b
cooling event (13.82 Ma) and the seepage system lasts for 400 kyr. The evolution of the Vicchio cold-seep system
passes through four phases: (1) The onset of the seepage, characterized by a pervasive flow of methane-rich
fluids, is inferred by δ13C depletion of marly sediments and by prevailing benthic foraminifera indicative of
suboxic conditions at the sea-floor. (2) The methane flow becomes focused causing the precipitation of wide
pinnacle-like carbonate bodies which contain giants lucinids. Enclosing marls indicate well-oxygenated conditions,
possibly enhanced by paleoceanographic variations connected to the Mi3b cooling event. (3) The appearance
of the vesicomyid Christineconcha cf. C. regab and the absence of lucinids in seep-carbonates suggest
stable methane-rich fluid emissions; higher flow rates locally favoured the flourishment of bacterial mats.
Benthic foraminifera show abundance peaks of organic matter depending taxa. (4) The reduced intensity of
methane-rich fluid flows favours the precipitation of stratiform carbonate bodies along strike; the macrofauna is
characterized by the presence of both Vesicomyidae and giant lucinids. Foraminiferal assemblages in the enclosing
marls indicate the restoration of well-oxygenated conditions.
2017
- RECONSTRUCTING SEEPAGE DYNAMICS OF A MIOCENE SYSTEM
THROUGH SEDIMENTOLOGICAL AND GEOCHEMICAL
CHARACTERIZATION OF AUTHIGENIC CARBONATES AND HOST
SEDIMENTS (CORELLA, NORTHERN APENNINES, ITALY)
[Abstract in Atti di Convegno]
Argentino, Claudio; Johnson, Joel; Conti, Stefano; Fioroni, Chiara; Fontana, Daniela
abstract
New data from facies, stable isotopes (C and O) and CHN analyses on seep-impacted sediments and
authigenic carbonates provided insights into dynamics and geochemical background conditions at a Miocene
seepage system (Corella outcrops, northern Apennines, Italy).
The examined outcrops comprise 4 lenticular carbonate bodies with maximum length of 200 m and
thickness up to 12 m. These carbonates strike parallel to the bedding of the enclosing sediments and show
lateral pinch out terminations. Chemosynthetic fauna (mainly Lucinids and Vesycomids) are very common
and forms local concentrations of disarticulated or articulated shells; veins and conduits crosscut the
carbonate bodies. Microfacies show mottled micrite including clotted textures related to bacterial activity
and framboids of pyrite (rosette-like features observed at SEM). δ13C values of the carbonates (micrites and
sparry cement filling veins) range between -42.32‰ to -26.63‰ and are indicative of AOM. The δ18O range
between -5.67‰ to 1.13‰ (average -0.96‰) and is close to the Miocene seawater signature and therefore
considered unaffected by significative diagenetic alteration. The host sediments at the top of the carbonates
body is depleted in 13C compared to normal marine carbonates and range between -8.40‰ to -4.75‰ and
δ18O is comprised between -3.50‰ and 1.68‰. CHN analyses on the enclosing sediments revealed low TOC
values in the range 0.21-0.72% with an average of 0.37%, similar to other Miocene foredeep successions of
the northern Apennines. The atomic C/N ratio ranges from 8.93 to 14.05 (avg. 10.84) suggesting minor
admixture of land-derived and marine organic carbon.
We suggest, based on field data, geotectonic setting, and geochemical analysis, that a blind fault,
rooted in the underlyingTertiary turbidites, acted as a pathway for deep methane-rich fluids. Advective fluid
flow resulted in a shallow, near seafloor sulfate-methane transition zone (SMTZ), resulting in the anaerobic
oxidation of methane and the precipitation of massive authigenic carbonate. The presence and preservation
of chemosynthetic fauna throughout the authigenic carbonate body indicates much of the advective fluid
flow breached the seafloor, resulting in methane seepage that helped sustain these chemosynthetic
organisms
2017
- STRONTIUM ISOTOPE STRATIGRAPHY AS A CONTRIBUTION FOR DATING
MIOCENE SHELF CARBONATES (S. MARINO FM., NORTHERN APENNINES)
[Articolo su rivista]
Argentino, Claudio; Reghizzi, Matteo; Conti, Stefano; Fioroni, Chiara; Fontana, Daniela; Salocchi, AURA CECILIA
abstract
This paper provides new data on strontium isotope stratigraphy applied to the Miocene heterozoan
shelfal carbonates of the S. Marino Fm. (Marecchia Valley, northern Apennines). Sr isotopic analyses were
carried out on oyster shells, bryozoans and bulk-rocks from the lower-middle carbonate portion of the section.
In the upper part of the succession that shows evidence of detrital influx, 87Sr/86Sr analyses were performed on
foraminifera tests, separating planktonic and benthic forms. Results were compared with calcareous nannofossil
biostratigraphic data from the same levels, in order to test the reliability of Sr dating in mixed carbonate-siliciclastic
sediments. Mean ages obtained from oysters range between 16.9 Ma and 16.3 Ma. Very similar results are obtained
using bryozoans (16.5 Ma to 16.1 Ma) and bulk-rocks (16.8 Ma to 16.2 Ma). These results allow to better constrain
the age of the massive carbonate shelf, referable to the upper Burdigalian. In the upper carbonate-siliciclastic portion
of the shelf, numerical ages obtained from planktonic and benthic foraminifera are in good agreement with
nannofossil biozones (mean ages respectively around 15.3 Ma and 14.5 Ma) although they display wide confidence
intervals. These wide age uncertainties depend on the slow rate of change of marine 87Sr/86Sr through time that
characterizes the interval between ~15 and ~13.5 Ma.
2016
- Authigenic carbonates as tracers of methane-rich fluid emission into the sea floor: fossil examples (Miocene, northern Apennines, Italy) compared to modern analogues
[Abstract in Atti di Convegno]
Argentino, Claudio; Conti, Stefano; Fontana, Daniela; Grillenzoni, Claudia; Mecozzi, Silvia
abstract
Cold seepage is a worldwide widespread process recognized in different marine settings of both active and passive continental margins. Authigenic carbonates, deriving from anaerobic oxidation of methane, can be used as tracers for ancient hydrocarbon-rich fluid emissions. Seep-carbonates of the northern Apennines mainly formed during the Miocene, commonly located in the inner part of the foredeep, at the deformation front of the accretionary prism. They are concentrated in two different depositional settings: - in pelitic intervals included in Langhian-Serravallian basin-plain turbidites; - in slope hemipelagites (Burdigalian to Messinian) capping turbidites in proximity to the deformational fronts. Although many of these bodies have been studied yet, significant outcrops still have to be investigated. This study will focus on seep carbonates in the Tuscan-Romagna Apennines (Moggiona). Carbonate bodies have lenticular to stratiform morphologies extending along strike and concordant with the attitude of the enclosing marls. Dimensions vary from 10 to 40 m wide and from 3 to 8 m thick. Carbonates are very rich in lucinid-like clams; at the base, numerous conduits filled with coquina debris and breccias are present, as well as dense irregular networks of carbonate-filled veins and extensional fractures. Carbonates are depleted in δ13C ranging from -40.22 to -19.28‰ V-PDB. The comparison between fossil and modern methane-derived carbonates may allow a better definition of the evolution of the seepage system, and relationships with synsedimentary instability (intraformational slumps and extraformational slides) and diapiric processes
2016
- Depositional history of the Epiligurian wedge-top basin in the Val Marecchia area
(northern Apennines, Italy): a revision of the Burdigalian-Tortonian succession
[Articolo su rivista]
Conti, Stefano; Fioroni, Chiara; Fontana, Daniela; Grillenzoni, Claudia
abstract
The Burdigalian-Tortonian Epiligurian succession in the Val Marecchia area comprehends different
lithostratigraphic units deposited in a wedge-top basin during the northeastern migration of the
thrust belt. The succession includes shallow-water carbonates passing to mixed carbonatesiliciclastic
and to fine-grained pelitic sediments, capped by fluvio-deltaic coarse-grained deposits.
Detailed field work and stratigraphy has allowed to characterize depositional units and
unconformities and to delineate the sedimentary and tectonic evolution of the basin. Tectonics
exerted a primary control at different stages. During the Burdigalian, a general uplift of the area
allowed the onset of shelfal carbonate sedimentation on underlying Ligurian and Epiligurian deepwater
sediments. At the Serravallian the sedimentation was influenced by the thrust reactivations
which caused a marked asymmetry in the basin geometry and fill. The subsidence increase in the
rear part of the basin determined the deposition of a thick succession of relatively deep fine-grained
sediments (up to 800 m water-depth) (Serravallian, MNN6a through MNN6b subzones based on
nannofossil biostratigraphy) and fossiliferous clays (lower Tortonian, biozones MNN8b-MNN9).
Conversely, uplift is activated in the frontal part of the basin, causing the partial erosion of the
Burdigalian–Langhian shallow-water carbonates. A relevant amount of this carbonate detritus is
delivered to the foredeep, supplying the Marnoso-arenacea Fm. A general uplift of the area in the
late Tortonian leads to the deposition of fluvio-deltaic conglomerates supplied by emerged rear
sectors of the basin.
2015
- Factors controlling the evolution of a wedge-top temperate-type carbonate platform in the Miocene of the northern Apennines (Italy)
[Articolo su rivista]
Fontana, Daniela; Conti, Stefano; Fioroni, Chiara; Grillenzoni, Claudia
abstract
An integrated study including stratigraphy, composition and biostratigraphy was performed on temperate-type shallow-water carbonates of early middle Miocene age deposited in a wedge-top basin within the Apenninic chain (Romagna-Tuscan area). The succession rests unconformably on the deep-water sediments of allochthonous Ligurian units and is represented by up to 350 m thick carbonates and mixed siliciclastic-carbonate rocks. Two main units are recognized, each characterized by a distinct facies association. The basal unit (upper Burdigalian) consists of rhodalgal rudstones and packstones of shelf environment, dominated by echinoids, bryozoans, coralline algae and benthic foraminifera, deposited in temperate conditions and showing a transgressive pattern. It gradually passes into mixed carbonate-siliciclastic shallow water-facies, (Langhian in age) characterized by an increase in terrigenous components and planktonic and benthic taxa. Sediment starvation during the Langhian is suggested by the occurrence of glaucony-rich packstones with abundant planktonic foraminifera. The succession grades upwards into upper Langhian-lower Serravallian planktonic foraminifera-rich marls. Increasing detrital discharge and water depth up section result in drowning of the carbonate shelf. Debris-flow deposits including material of extraformational origin are intercalated at different levels, in particular from the uplifting south-western margins, close to the Ligurian thrusts. The inception and demise of these temperate rhodalgal-foramol carbonate sediments located in a wedge-top Epiligurian basins is primarily controlled by synsedimentary tectonics, which in turn affects relative sea-level rise, and nutrient and detrital input. In particular, tectonics controlled the initial stage of the transgression, determining the configuration of the basin, subdivided in narrow submerged palaeotopographic lows and relatively elevated areas. Synsedimentary tectonics related to the thrust migration was also the main controlling factor in the demise of carbonate sedimentation, through the combined effect of two processes: increasing the subsidence of the basin, and triggering the terrigenous discharge from the erosion of the uplifted Apenninic relieves
2015
- History of Miocene temperate-type carbonate shelf in a compressive setting (northern Apennines), constrained by a chemostratigraphycal, microfacies and compositional study
[Abstract in Rivista]
Salocchi, AURA CECILIA; Nereo, P.; Fontana, Daniela; Conti, Stefano; Grillenzoni, Claudia; Argentino, Claudio
abstract
A detailed chemostratigraphic study associated with microfacies and compositional analysis has been performed on a early middle Miocene shallow-water shelf deposited on a wedge-top basin in the northern Apennines. More than 140 samples were collected in the representative outcrop of Torriana (Val Marecchia valley, Romagna Apennines) in order to identify factors controlling the inception and crisis of the shelf. The succession is constituted by 100 m thick mixed siliciclastic-carbonate rocks, unconformably overlying the allochthonous Ligurian units. The evolution of the carbonate shelf passed true four main phases, as shown by the detailed microfacies and compositional study, that evidence the progressive decrease of the carbonate productivity, gradually replaced by detrital sedimentation. The basal portion consists of rhodalgal rudstones and grainstones dominated by echinoids, bryozoans, coralline algae and benthic foraminifera. The progressive increase of terrigenous components and planktonic and benthic taxa marks the gradual transition to a mixed carbonate-siliciclastic shallow water-facies. The top of the succession is characterized by fine-grained sediments rich in glaucony. The main factors controlling the evolution of the shelf are increased subsidence of the basin, related to the thrust migration, and terrigenous contributions from the erosion of the rising Apennines areas. The stable isotope study show that the carbonate production has been influenced not only by regional factors, but also by a global fertility event, as the Monterey Event, recorded in the Mediterranean during the late Burdigalian - Serravallian.
2015
- Inception and crisis of a Miocene temperate-type carbonate shelf in a compressive setting (northern Apennines)
[Abstract in Atti di Convegno]
Salocchi, AURA CECILIA; Fontana, Daniela; Conti, Stefano; Fioroni, Chiara; Grillenzoni, Claudia; Argentino, Claudio
abstract
A detailed study including stratigraphy and composition has been performed on shallow-water carbonates of early-middle Miocene age deposited in a wedge-top basin in the northern Apennines. In the representative outcrop of Torriana (Val Marecchia valley, Romagna Apennines) more than 140 samples were collected in order to identify factors controlling the inception and crisis of the shelf.
The succession unconformably rests on the allochthonous Ligurian units and is constituted by up to 100 m thick carbonates and mixed siliciclastic-carbonate rocks. The basal portion consists of rhodalgal rudstones and grainstones dominated by echinoids, bryozoans, coralline algae and benthic foraminifera. It gradually passes into mixed carbonate-siliciclastic shallow water-facies, characterized by an increase in terrigenous components and planktonic and benthic taxa. The occurrence of glaucony-rich packstones with abundant planktonic foraminifera marks the transition to the upper fine-grained sediments.
Results of a detailed compositional study evidence four main phases in the platform evolution, and a progressive decreasing of the carbonate productivity, gradually replaced by detrital sedimentation.
Regional factors linked to the Apenninic tectonics seem to primarily support the eu- to mesotrophic conditions in the examined carbonate shelf. However this time interval (late Burdigallian - Serravallian) is characterized by the global fertility event, the Monterey Event, recorded also in the Mediterranean. The stable isotope study shows that this global event also influenced the carbonate production.
The inception and demise of these temperate rhodalgal-foramol carbonate sediments located in a wedge-top basin is primarily controlled by synsedimentary tectonics related to the thrust migration, through the combined effect of two processes: increasing the subsidence of the basin, and triggering the terrigenous discharge from the erosion of the uplifted Apenninic areas.
2015
- Miocene carbonate shelf in the northern Apennines (S. Marino Fm): insights from microfacies, petrography and strontium isotopes
[Abstract in Atti di Convegno]
Argentino, Claudio; Salocchi, AURA CECILIA; Fontana, Daniela; Reghizzi, M; Grillenzoni, Claudia; Conti, Stefano
abstract
A detailed stratigraphic study associated with microfacies and strontium analysis has been performed on middle Miocene shallowwater
carbonates developed in a wedge-top basin in the northern Apennines. More than 140 samples were collected in the
representative outcrop of Torriana (Marecchia valley, Romagna Apennines). It covers the entire carbonate succession from the
basal unconformity on Ligurian units to the terrigenous-rich sediments that mark the demise of the shelf. The modal analysis
allowed to quantify the main framework components: an intrabasinal carbonate fraction (biogenic), a terrigenous fraction (largely
siliciclastic) and an authigenic intrabasinal component mainly constituted by glauconitic grains.
The carbonate succession starts with massive carbonates consisting of rudstones and grainstones dominated by bryozoans and
echinoids. The basal few meters are rich in rhodolithes. The succession passes to planar-bedded grainstones to packstones with the
same fossiliferous composition. The upper part is characterized by low angle cross-bedded grainstones to packstones with high
detrital content, that gradually passes to mixed siliciclastic-carbonate sediments and finegrained hybrid arenites. An overall
increase of the terrigenous input to the basin and the progressive deepening from a shallow shelf to outer shelf-slope environment
caused the drowning of the shelf, marked by relatively high concentration of glauconitic grains. Our data indicate an almost
exclusive intrabasinal supply during deposition of the basal portion. A vertical evolution is documented by a progressive increase
in the terrigenous supply that replaces the bioclastic fraction.
Preliminary 87Sr/86Sr data obtained from 7 carbonate samples allowed us to obtain absolute ages for the lower massive portion of
the succession. For each sample we analyzed mollusk shells, bryozoans and bulk rock. Results indicate ages between 16,52-15,91
Ma, corresponding to the Burdigalian-lower Langhian interval. Comparing the values obtained from mollusk shells, bryozoans and
bulk rock from samples at the same stratigraphic level, we observe similar results.
This, according to petrographic analysis, permitted us to suppose a low diagenetic imprint of the rock.
2014
- Cold-seep carbonates as tracers for the evolution of the platform-basin system in the Miocene of the northern Apennines (Italy)
[Abstract in Atti di Convegno]
Salocchi, AURA CECILIA; Fontana, Daniela; Conti, Stefano; Fioroni, Chiara; Grillenzoni, Claudia
abstract
The peculiar methane-derived carbonates enclosed in pelitic and marly deposits of the Miocene inner foredeep
in the northern Apennines are useful tracers for an evaluation of tectonic and sedimentary processes in the
Miocene shelf-slope-basin system in a compressive geodynamic context. The carbonate precipitation is related
to emissions of hydrocarbon-rich fluids and it is controlled by: - tectonic events (tectonics constrains the
plumbing system, with faults and fractures serving as conduits and channelling water and methane up to the
seafloor); - climatic events (carbonate formation seems to correlate with cold periods and sea-level low-stand).
The correlation between methane-derived carbonates and climate during the Miocene in the northern Apennines
has been suggested by recent results (Fontana et al,. 2013) of a sedimentological and biostratigraphic study of
seep-carbonates and the enclosing hemipelagic Vicchio marls. The study suggests a correlation between the
carbonate precipitation and the middle Miocene cooling event (Mi3b). The ascent and emission of methane-rich
fluids may have been triggered by the pressure drop due to the eustatic fall. A detailed study of the δ18O record
of carbonates and δ13C of total organic matter in enclosing marls has been performed in order to verify a
correlative trend in correspondence of the climatic cooling event. A palaeocological study has allowed to check
the influence of these stressed environmental conditions on benthic foraminifera assemblages. Therefore
morphological, textural, biostratigraphic, geochemical studies could allow to characterize seep-carbonates
related to climatic event. Results of this study could contribute to the reconstruction of transgressive-regressive
events in the adjacent temperate-type carbonate platforms, as well as the definition of modes and rates of the
demise of carbonate deposition and the onset of clastic sedimentation.
The identification of cold phases and lowering of sea level in slope-basinal deposits and their detailed timing,
may be an useful and innovative tool for correlation with coeval shallow-water successions, and for the
reconstruction of the evolution of the Miocene platform-basin system in the compressive setting of the northern
Apennines.
2014
- Relationships between seep-carbonates, mud volcanism and basin geometry in the Late Miocene of the northern Apennines of Italy: the Montardone mélange
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela; Claudio Corrado, Lucente; Gian Andrea, Pini
abstract
The Montardone mélange (Mm) is a chaotic, block-in-matrix unit outcropping in the Montebaranzone syncline in the northern Apennines. The Mm occurs in the uppermost part of the Termina Fm, the Middle-Late Miocene interval of a succession deposited in a wedge-top slope basin (Epiligurian succession). The Mm is closely associated with bodies of authigenic carbonates, characterized by negative values of δ13C (from -18.22 to -39.05 ‰ PDB) and chemosyntethic benthic fauna (lucinid and vesicomyd bivalves). In this paper we propose that the Mm is a mud volcano originated by the post-depositional reactivation and rising of a stratigraphically lower mud-rich mass-transport body (Canossa-Val Tiepido sedimentary mélange or olistostrome) triggered by fluid overpressure. We base our conclusion on: 1) the Mm pierces the entire Termina Fm and older Epiligurian units and represents the direct continuation of the underlying Canossa-Val Tiepido mélange; 2) the geometry and facies distribution of the Montebaranzone sandstone body, which are compatible with a confined basin controlled by the rising of the Mm; 3) the systematic presence of large-scale (lateral extension 300-400 m) seep-carbonates associated with the mélange, suggesting a persistent gas-enriched fluid vent from the ascending overpressured mud; 4) blocks and clasts sourced from the Mm, hosted by the authigenic carbonates, conveyed by ascending mud and gas-enriched fluids.
The Mm represents one of the few fossil examples of reactivation of a basin-scale sedimentary mélange (olistostrome); a three-stage model showing mechanisms of Mm raising is proposed.
2014
- Tectonic and climatic control on deposition of seep-carbonates: the case of middle-late Miocene Salsomaggiore Ridge (Northern Apennines, Italy)
[Articolo su rivista]
Artoni, Andrea; Conti, Stefano; Turco, Elena; Iaccarino, Silvia
abstract
Seep-carbonates are generally related to hydrocarbon seepage on continental margins. Modern cold seeps are abundant in actively deforming tectonic settings, suggesting that tectonics is one of the major controlling factor on fluid emissions. Hydrocarbon seepages are considered major geological sources of atmospheric methane, one of the most important green-house gases, and therefore may also be related to climate changes. However, the cause-effect relationship between seepage and climate changes is debated and the interplay between tectonics and climate change in forcing seepage is not clearly understood. Miocene seep-carbonates, formed in a collisional setting such as that of the Salsomaggiore area of the Northern Apennines (Italy), provide an opportunity to assess accumulation and release of methane in response to tectonics and climate change along a convergent margin. A new stratigraphic framework indicates that the studied seep-carbonates, related to fluid emissions of various intensities and to sediment destabilization events, were coeval with both local and regional tectonic pulses. In addition, planktonic foraminifer biostratigraphy reveals that deposition of these seep-carbonates is late Serravallian-early Tortonian in age and partially coeval with the Miller’s global cooling event Mi 5. It could be also established that the seep-carbonates were deposited in two stages with different seepage modalities. During the first stage, local tectonic pulses at the onset of the Mi5 event may have produced slow seepage, whereas during the second stage regional tectonics and more extreme climatic conditions (coolest peak of Mi5 event) may have resulted in a fast and
2014
- The evolution of the Miocene platform-basin system in the northern Apennines: what can we learn from seep-carbonates?
[Abstract in Rivista]
Grillenzoni, G.; Conti, Stefano; Fioroni, Chiara; Fontana, Daniela; Salocchi, A.
abstract
Cold seep-carbonates documenting the expulsion of fluids enriched in methane have been identified in a variety of
basin margins and tectonic-sedimentary settings. A number of geological factors influences methane seep activity, but
primarily regional and local tectonics, mainly at the deformation front of accretionary prism and inner foredeep.
Tectonics constrains the fluid circulation system, with faults and fractures serving as conduits and channelling water
and methane up to the seafloor. Recent studies suggest that seep-carbonates occurrence is also controlled by climatic
changes and their formation seems to correlate with cold periods and sea level low-stand. A drop of the hydraulic
pressure on the plumbing system during sea level lowering in glacial phase could increase methane flows at seeps,
inducing carbonate precipitation. The correlation between methane-derived carbonates and climate has been recently
suggested for the Miocene of the northern Apennines by means of a sedimentological and biostratigraphic study of
seep-carbonates and the enclosing hemipelagic marls (Vicchio Formation) (Fontana et al., 2013). The study suggests a
correlation between the carbonate precipitation and the middle Miocene glacial cooling event (Mi3b). The triggering of
the ascent and emission of methane-rich fluids may be related to the eustatic fall and in turn to the water pressure
drop. A detailed stratigraphic and biostratigraphic study of seep-carbonates and enclosing marls in foredeep deposits of
the Tuscan-Romagna Apennines has allowed a precise dating of seepage in slope and basinal successions. The analysis
of the δ18O and δ13C records of carbonates, δ13Corg excursion of organic matter and TOC on the marls enclosing the
authigenic carbonates has been performed in order to verify a correlative trend in correspondence of the climatic
cooling event. A paleoecological study on benthic foraminifera assemblages has also allowed to detail these peculiar
environments. The events defined from this study in basinal deposits have been correlated with depositional changes
and discontinuity surfaces in the adjacent temperate-type carbonate platforms, and have contributed to the definition of
modes and rates of the demise of carbonate deposition. The identification of cold phases and lowering of sea level in
slope-basinal deposits and their detailed timing, may be a useful tool for correlation between deep depositional setting
and coeval shallow-water successions. This approach may also provide important constrains in the reconstruction of the
evolution of the Miocene platform-basin system in this complex compressive setting of the northern Apennines.
Fontana D., Conti S., Grillenzoni C., Mecozzi S., Petrucci F. & Turco E. 2013. Evidence of climatic control on
hydrocarbon seepage in the Miocene of the northern Apennines:
2013
- Evidence of climatic control on hydrocarbon seepage in the Miocene of the northern Apennines: The case study of the Vicchio Marls
[Articolo su rivista]
Fontana, Daniela; Conti, Stefano; Grillenzoni, Claudia; Mecozzi, S.; Petrucci, F.; Turco, E.
abstract
The Vicchio outcrop in the Tuscan Apennines contains excellent exposures of a Miocene methane-derived carbonate system, made up of more than 80 carbonate bodies enclosed in marly sediments. Facies analysis, composition and a detailed biostratigraphic study of the carbonates and enclosing Vicchio Marls allowed us to document the role of climatic changes and eustasy on seepage in these ancient deposits. Results of our study indicate that the stratigraphic horizon bearing seep-carbonates is constrained by two planktonic foraminiferal events, the Acme End (AE) of Turborotalita cf. T.quinqueloba (13.75Ma) and the Acme1 Beginning (A1B) of Paragloborotalia siakensis (13.32Ma), encompassing about 400,000 years. The AE of T. cf. T.quinqueloba approximates the mid-Miocene global cooling event (Mi3b), as defined by the δ18O maxima (13.78Ma). The glacio-eustatic sea level drop associated with this cooling event is estimated to be approximately 60m. Assuming that the highest rates of glacio-eustatic sea level fall coincide with δ18O maxima, the timing of the seepage onset (at about 13.75Ma) is concomitant with the phase of sea level-lowering. The ascent and emission of methane-rich fluids may have been triggered by pressure drop due to the eustatic fall associated with the Mi3b event. The moderate intensity of fluid expulsion is suggested by the lack of brecciation, by the scarcity of detrital particles in the carbonates and by the pervasive occurrence of carbonate in the enclosing marls. This type of seepage differs from focused fault-confined fluid flows, typical of other tectonically controlled Apenninic seep-carbonates. © 2013 Elsevier Ltd.
2013
- Seep-carbonate case studies as highlights in the evolution of the Miocene of northern Apennines
[Relazione in Atti di Convegno]
Grillenzoni, Claudia; Conti, Stefano; Fontana, Daniela; Fioroni, Chiara
abstract
Different case studies of seep-carbonate outcrops in the Northern Apennines show that an accurate timing of precipitation, and the identification of processes of ascent of methane-rich fluids, are important points for understanding and estimating the complex interplay of tectonics and climate changes during the Miocene of the northern Apennines.
2012
- Seep-carbonates as indicators of global cooling events (Miocene, northern Apennines
[Articolo su rivista]
Grillenzoni, Claudia; Conti, Stefano; Fontana, Daniela; Turco, Elena
abstract
Recent studies in dating seep-carbonates suggest that their occurrence is controlled by climatic changes (TEICHERT et alii 2003). KIEL (2009) suggests that this correlation exists from the late Jurassic to Recent, and shows a statistically relevant correlations between the frequency of seep-carbonates in the past 150 Ma and low deep-water temperature and low sea- levels. In the Miocene of the northern Apennines, the abundance and the extent of the seep-carbonates from different tectonic-sedimentary settings, foredeep to satellite basins, provide a rare opportunity to study the tectonic and/or climatic controls on seepage (CONTI & FONTANA, 1999 A detailed stratigraphic and biostratigraphic study of carbonates and enclosing marls indicates that the stratigraphic horizon bearing seep-carbonates lies between the T. cf. T. quinqueloba AE (13.75 Ma) and the P. siakensis A1B (13.32 Ma) encompassing a time interval of about 400.000 years. Since the AE of T. cf. T. quinqueloba approximates the mid- Miocene global cooling event, we infer that the beginning of the seep-carbonate precipitation in the Vicchio Marls seems to be related to this climatic event (Fig. 2). We assume that the ascent and emission of methane-rich fluids may have been triggered by the pressure drop due to the eustatic fall associated with the Mi3b event, estimated in about 60 m (HILGEN et alii, 2009). A drop of the hydraulic pressure on the plumbing
2011
- Possible Relationships between Seep Carbonates and Gas Hydrates in the Miocene of the Northern Apennines
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela
abstract
In the Miocene of the northern Apennines, a widespread carbonate precipitation was induced by the expulsion of methane-rich fluids. Numerous outcrops of carbonate masses share sedimentological, textural and geochemical features with present-day gas hydrate-associated carbonates. We hypotesize the contribution of paleo-gas hydrate destabilization on the base of the heavy oxygen isotope signature, the presence of distinctive sedimentary features (breccias, pervasive non-systematic fractures, soft sediment deformation), the close association between seep-carbonates and sedimentary instability and the huge dimensions of seep-carbonates bearing brecciated structures.
2010
- A contribution to the reconstruction of Miocene seepage from authigenic carbonates of the northern Apennines (Italy)
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela; S., Mecozzi
abstract
Authigenic carbonates from outcrops of the northern Apennines consist of small and irregular lenses and exhibit numerous features indicative for cold-seep settings. Detailed petrographic, mineralogical and geochemical studies from two Miocene deposits are presented. The first carbonate outcrop named Fosso Riconi is located in the foredeep basin of the Apenninic chain whereas the second deposit represents a satellite basin called Sarsetta. The stable isotope data from specific carbonate minerals show a wide range of values well known from other paleoseeps of the Apennine Mountains. From all carbonates analyzed during this study the majority of seep carbonates are formed by low-Mg calcite and ankerite. Those minerals have δ13C values between -7 and -23‰ V-PDB suggesting variable amounts of carbonate derived from oxidized methane, from seawater (DIC), and from sedimentary organic matter. Dolomite samples have the lowest δ13C values (-30.8 to -39.0‰ V-PDB) indicating methane as the main carbon source.The results from this study indicate an evolutionary formation of the seeps and development of the authigenic carbonates, influenced by the activity of chemosynthetic organisms from which large lucinid clams are preserved. Bioirrigation of those clams controlled the sediment-water exchange, and is here considered as an explanation for the anomalous Mg content of the calcite. We hypothesize that seep-carbonates are formed during periods of active methane-rich seepage, whereas during periods of slow seepage carbonate formation was reduced. Despite different geological settings, the two examined deposits of Sarsetta and Fosso Riconi show similar features, suggesting that the pattern of fluid circulation at both seep sites played a major role in their carbonate formation.
2010
- Late Miocene seep-carbonates and fluid migration on top of the Montepetra intrabasinal high (Northern Apennines, Italy): Relations with synsedimentary folding
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela; Mecozzi, S.; Panieri, G.; Pini, G. A.
abstract
During the Miocene, hydrocarbon seep-carbonates located atop intrabasinal highs and associated with sediment instability, formed commonly at the deformation front of the Northern Apennine collisional orogen. The parallelism between the structural trend and the distribution of seep-carbonates suggests a close relationship between tectonics and gas/fluid emission.The “Montepetra intrabasinal high” was formed during the closure stage of the foredeep, being related to the synsedimentary growth of an anticline. Field geometry suggests that detachment folding was the leading mechanism of anticline growth and synsedimentary instability along the anticline flanks. Ten different bodies of seep-carbonates occur in the Tortonian-early Messinian sediments: nine in the hinge zone and one in the southern backlimb of the anticline. Foraminiferal study, geochemistry, facies investigation and the three-dimensional geometry of carbonate bodies with respect to the encasing terrigenous sediments indicate a protracted (late Tortonian-early Messinian) activity of fluid migration with re-mobilization and ascent of sediments from the core of the anticline, stabilization of chemosynthesis-related communities, and in-situ brecciation. Seepage atop the intrabasinal high was fed by different circuits: one related to the compaction-dewatering of shallow (Tortonian-early Messinian) sediments, and a deeper one related to the deformation of the anticline core and to the activity of detachment surfaces and of faults propagating through the sedimentary cover.
2009
- Cold-seep carbonates: fossil archives of changes in seepage activity and fluid. composition through the Miocene. In: Geoitalia 2009. Epitome, Vol. 3, 89. FIST.
[Relazione in Atti di Convegno]
Mecozzi, Silvia; Conti, Stefano; Fontana, Daniela
abstract
The precipitation of authigenic carbonates
2009
- Discriminating fluid sources in Miocene cold seep systems using REEs in authigenic carbonates
[Abstract in Rivista]
Mecozzi, S.; Bayon, G.; Rongemaille, E.; Conti, Stefano; Fontana, Daniela
abstract
Authigenic carbonates are a common feature in cold seep environments, where fluids enriched in methane and other hydrocarbon gases escape from the seafloor. Seep-carbonates have been reported worlwide both in modern and ancient sedimentary deposits. In the Northern Apennines (Italy), numerous outcrops of seep-carbonates are particularly well-preserved. Evidences from paleoecological, sedimentological, geochemical and isotopic (O and C stable isotopes) analyses cleary show that they were derived from the microbial oxidation of methane-rich fluids. REE patterns and abundances in fossil seep-carbonates may provide additional informations for better constraining the origin and the composition of the fluids from which they have precipitated.Here, we report REE data for a series of Miocene carbonate samples recovered from various geological settings in the Northern Apennines. Samples were leached with 5% HNO3, prior to analysis by SF-ICPMS using the Tm addition method [1]. Total REE concentrations (ΣREEN) in our studied carbonates are very similar to those reported for modern authigenic carbonates, suggesting negligible post-depositional diagenetic alteration. The shale-normalized REE patterns vary significantly amongst the different authigenic carbonate samples analysed in this study. These data indicate that they were formed from fluids having distinct REE signatures. These results, coupled with other geochemical, petrographic and mineralogical data, allow us to reconstruct the variation of fluid seepage activity in the Northern Appenines during the Miocene.
2009
- I vulcani di fango dell’Appennino modenese
[Capitolo/Saggio]
Conti, Stefano; Fontana, Daniela
abstract
I vulcani di fango rappresentano un importante fenomeno
2009
- Investigation of miocene cold seep sources using rare earth element in authigenic carbonates
[Relazione in Atti di Convegno]
Mecozzi, Silvia; G., Bayon; E., Rongemaille; Conti, Stefano; Fontana, Daniela
abstract
Seep-carbonates are described
2009
- Methane seepages recorded in benthic foraminifera from Miocene seep carbonates, Northern Apennines (Italy)
[Articolo su rivista]
Panieri, Giuliana; Camerlenghi, Angelo; Conti, Stefano; Pini, Gian Andrea; Cacho, Isabella
abstract
Benthic foraminifera from seep carbonates and from enclosing non-seep marls presentwithin Miocene formations in the Northern Apennines (Italy) were investigated as proxies ofmethane seepage in the marine environment. Negative δ13C values of benthic foraminiferafrom these seeps indicate unambiguously the local influence of CO2 produced by microbialanaerobic methane oxidation on the benthic ecosystem. Calcareous species living withinmethane seeps display δ13C values ranging from -9.04 to -25.74 ‰ PDB, whereas in thecoeval surrounding marls the same species display δ13C values from -1.54 to 0.62 ‰ PDB.Different species analysed (Cibicidoides kullenbergi, C. pachyderma, Siphonina rethiculata,Planulina wuellestorfi, Bolivina miocenica, Brizalina dilatata, Vulvulina pennatula, andACCEPTED MANUSCRIPTACCEPTED MANUSCRIPTACCEPTED MANUSCRIPT2Cibicides praecinctus) in different seep carbonates indicate that benthic foraminifera,independently of the taxa and of microhabitat preferences, have more negative δ13C valuesthan those found in the enclosing marls. Therefore each species represents a potential proxyfor past seafloor methane emissions. In addition to the calcareous species, the agglutinatedspecies Vulvulina pennatula displays -27.5 ‰ PDB in seep carbonates against -2.69 ‰ PDBin the enclosing marls. This suggests that the species utilized strongly 13C depleted carbonateparticles from authigenic carbonate precipitation during the mineralization of their tests.
2009
- Multiproxy approach to the stydy of Croce della Moggiona cold seep-carbonates (Northern Apennines)
[Relazione in Atti di Convegno]
Mecozzi, Silvia; Birgel, D.; Peckmann, J.; Conti, Stefano; Fontana, Daniela
abstract
Seep-carbonates are described in both the present day marine environments and in the sedimentary record of ancient basins. They are the result of microbially-mediated processes that occur on the seafloor where hydrocarbon-rich fluids are seeping. These carbonate bodies have received considerable attention in the international scientific community because they may provide a clue to investigate the origin and the composition of the fluids from which they have precipitated. In the Northern Apennine foredeep, seep-carbonates are concentrated in pelitic successions from different settings. Seep carbonates occur in large turbiditic bodies (Mt. Cervarola and Marnoso-arenacea Formations) and in slope hemipelagites (Vicchio and Verghereto Marls, and Ghioli di letto mudstones).In this study we present evidence for a long time of hydrocarbon seepage during the Middle Miocene in the form of newly discovered occurrences of carbonate bodies and concretions. About ninety authigenic carbonate bodies occur in the examined Fosso Riconi outcrop. Carbonates are irregularly scattered, both laterally and vertically, and have irregular shapes and geometries, varying from stratiform to amygdaloid, lenticular bodies and pinnacles. The thickness vary from 50 dm to 7-8 m, with lateral extension ranging from 1 to 3 m. Carbonate lithologies consist of marly limestones and calcareous marls. The lateral conctact with host sediments varies from sharp to transitional and interfingering. The marly limestone, calcareous marl lithologies are typically associated with abundant fossil remains, mainly consisting of thick recrystallized closed shells and moulds of lucinid and vesicomyid-like clams and rare and small gastropod shells. Lucinids and vesicomyids are infaunal ad semi-infaunal bivalves living in cold-seep areas and sustained by mutual symbiosis with sulphide-oxidizing bacteria. The authigenic carbonate mineralogy is dominated by low Mg-calcite, ankerite, and dolomite. Petrographic observations show complex facies relationships, as indicative of different stages in seep-carbonates growth. Stable isotope analyses of these nodules show depleted δ13C values which are consistent with the formation of carbonates in a cold-seep setting. Thus, the Fosso Riconi carbonates exhibit numerous characteristics (mineralogy, sedimentary fabrics, fossil assemblages) found at modern and ancient hydrocarbon seeps.The objectives of this contribution are to investigate the nature and source of the fluids associated with Fosso Riconi carbonate precipitation and to delineate an evolutionary model of the formation and development of these seep-carbonates.We suggest that examined seep-carbonates may be a consequence of episodes of varying fluid-venting rates.
2009
- Northern Apennines authigenic carbonates: tracers of changes in cold seep activity
[Relazione in Atti di Convegno]
Mecozzi, Silvia; Conti, Stefano; Fontana, Daniela
abstract
Seep- carbonates are described
2009
- Ostracod fauna of the miocene cold seeps (Apennines near Modena)
[Relazione in Atti di Convegno]
Russo, A.; Fonda, G.; Pugliese, N.; Conti, Stefano
abstract
Cold seeps are sites charaterized by
2009
- Proposal to establishing paleontological sites in the Emilia-Romagna region (N.Italy)
[Abstract in Rivista]
Ceregato, A.; Bosellini, Francesca; Conti, Stefano; Iaccarino, S.; Landini, W.; Monegatti, P.; Papazzoni, Cesare Andrea; Taviani, M.
abstract
Region Emilia-Romagna in Northern Italy hosts a variety of valuable paleontological sites of late Tertiary age that merit protection and management for public interest. Such an impressive marine invertebrate legacy is known since over three centuries and has been functional to a number of taxonomic, stratigraphic and paleoenvironmental studies. In addition, there are also many remarkable plant and vertebrate sites in need of protection and visibility. As a first step in this direction, we have selected four sites of relevant paleontological significance. They are from NW to SE: (1) Stirone River, (2) Monticino, (3) Montepetra, and (4) Mondaino, all easily accessible from local roads.(1) The Stirone River (Parma Province) cuts through a Miocene-Pleistocene sedimentary succession useful to correlate major geological and paleoclimatic events at regional and global scales. Its outstanding paleontological content has been already recognized long ago leading to the establishment of the Regional Fluvial Park in 1988. Highlights of this paleontological site exceedingly rich in marine molluscs, brachiopods, corals, calcareous algae, echinoids, bryozoans, foraminifera, etc., are a Pliocene-age chemoherm containing various lucinid clams and the Early Pleistocene “Cascatelle” Calcarenite. This paleo-site also provided important vertebrates, namely two Pliocene whales and a Pleistocene rhinoceros.(2) The Monticino Geopark, established near Brisighella (Ravenna Province), comprehends a large area along the left side of the Lamone River characterized by a spectacular Neogene succession. The dismissed Li Monti quarry that exposes upper Tortonian-lower Pliocene deposits, including a complete Messinian succession, represents the core of this Geopark. The highly remarkable paleontological content of this site refers to Tortonian-lower Messinian marine deep-water faunas, well-preserved fossil fishes within intra-evaporitic anoxic layers, late Turolian-age vertebrate remains encased in karst-infilling continental sediment dikes, brackish Lago-mare molluscs of the Colombacci Formation and early Pliocene deep-sea invertebrates of the Argille Azzurre Formation.(3) The village of Montepetra (Forlì-Cesena Province) is partially built over an impressive methanogenetic chemoherm with associated chaotic levels belonging to the Miocene-age “Lucina Limestone” informal stratigraphic unit. The main limestone body is enclosed in slope hemipelagites of the Miocene Marnoso-Arenacea foredeep succession and considered Tortonian in age. The “Lucina Limestone” of Montepetra gained international reputation as a remarkable example of deep-sea hydrocarbon seepage. Its paleontological content includes a diverse chemosynthetic macrofauna (solemyid, bathymodiolinid and lucinid bivalves; tubeworms) as well as gastropods, corals and other marine invertebrates.(4) The Miocene fossil fish fauna of Mondaino (Rimini province) was cited already in 1832 (“mummified bodies”) and later described by Luis Agassiz. This rich pre-evaporitic ichtyofauna is sourced from diatomaceous sediments (tripoli), at present clearly visible on the northern side of the Il Monte hill, near La Celletta as a consequence of the 1983 landslide. The fossil legacy contains a diverse benthic and epipelagic fauna with fish assemblages dominated by Myctophidae. Terrestrial fossils include rare insects and birds and abundant flora. This potential paleontological site is already served by a dedicated museum that preserves an important collection from the local tripoli.
2009
- Reconstruction of Miocene fluid seepage activity in the northern Apennines (Italy) using authigenic carbonates
[Relazione in Atti di Convegno]
Mecozzi, S.; Conti, Stefano; Fontana, Daniela
abstract
Miocene fluid flow...
2009
- Seep-carbonates at the top of a growing anticline: the “Montepetra structural high”, Late Miocene of Northern Apennines (Italy)
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela; Panieri, G.; PINI G., A; Mecozzi, S.
abstract
During the Miocene,
2008
- Authigenic seep-carbonates cementing coarse-grained deposits in a fan-delta depositional system (middle Miocene, Marnoso-arenacea Formation, central Italy)
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela; C. C., Lucente
abstract
Seep-carbonates (13C-depleted) are present at different levels within the Miocene terrigenous succession of Deruta (Marnoso-arenacea Formation, central Italy). They are associated with pebbly sandstones and conglomerates in a tectonically active fan-delta slope depositional system. Most of them are included in slide/slump horizons as scattered blocks. The occurrence of seep-carbonates is clear evidence of flow of methane-rich fluids pervading the sediments. Fluids, probably of biogenic origin, may have reached the sea-bottom through thrust faults and selectively infiltrated the more permeable coarse-grained horizons deposited along the slope. Different stages of fluid emissions are documented: slow flux stage, corresponding to the development of large carbonate bodies and dense chemosynthetic communities, and fast fluid flow associated with intense carbonate brecciation, pipes and veins. Large amounts of authigenic carbonates are reworked by slope failures triggered by tectonics and fluids reducing sediment strength; in situ cementation of slide blocks may also have occurred due to remobilization of methane-rich fluids by mass-wasting processes.
2008
- Fluid expulsion and typology of seep-carbonates in the northern Apennines.
[Relazione in Atti di Convegno]
Mecozzi, Silvia; Conti, Stefano; Fontana, Daniela
abstract
Miocene seep-carbonates have been reported from marine sedimentary successions of the northern Apennines in the form of huge isolated carbonate bodies (type 1) and numerous horizontally and vertically scattered marly-calcareous lenses (type 2) (Conti and Fontana, 2005 and references herein). They are recognized by their peculiar palaeoecological, sedimentological, compositional and isotopic features as products of the microbial oxidation of methane-rich fluids and represent an excellent example of carbonate bodies interpreted as the remains of ancient cold seeps. In the Apenninic chain, the abundance and the extent of the outcrops provide a rare opportunity to study the geometry, facies distribution and internal structures of fossil seep-carbonates. The main parameters which control the composition and development of a carbonate body are the methane pressure in interstitial sedimentary fluids, the flux discharge and rate in the venting zone, and the evolutionary path of the rising fluids (Roberts, 2001). Mineralogical, petrographic analyses, carbon and oxygen isotopic compositions of type 1 and 2 carbonate samples indicate that different mechanisms of hydrocarbon fluid expulsion and variations in the upward methane flux control carbonate types and mineralogy.Mineralogical analyses of type 1 carbonate samples indicate that dolomite and ankerite represent the dominant phases, while low-Mg calcite is the type 2 dominant carbonate phase. The carbon and oxygen isotopic compositions of the carbonates display very large ranges, from -10‰ to -55‰ V-PDB, and from -3‰ to 6‰ V-PDB, respectively. Seep-carbonate type 1 appear significantly depleted in δ13C (ranging from -30‰ to -55‰ V-PDB) while seep-carbonate type 2 are only moderately depleted (δ13C varying from -10‰ to -23‰ V-PDB). Petrographic observations show complex facies relationships, as indicative of different stages in seep-carbonates growth.Type 1 seep-carbonates could be related to constant and discrete fluid seepage conditions while type 2 could be explained by variations in the upward methane flux (increasing, decreasing flow rates). The intraformational and rarely extraformational polygenic breccias which are often observed in the basal portions of type 1 seep-carbonates could indicate phases of violent venting of gaseous-rich fluids. The explosive escaping of carbon-rich fluids interrupted the conditions of constant fluid seepage and caused brecciation of the carbonate body. Our presentation will report the result of a detailed field observation of the two types of seep-carbonates coupled with geochemical, petrographic and mineralogical studies.
2008
- Fluid flux and migration conditioning Miocene-seep carbonate precipitation in the northern Apennines.
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela; Mecozzi, S.
abstract
In the Miocene satellite and foredeep basins of the northern Apennines, numerous outcrops of carbonate bodies share specific palaeoecological, sedimentological, compositional and isotopic features with present-day seep-carbonates.These carbonates occur in large turbiditic bodies (Mt. Cervarola and Marnoso-arenacea Formations) and in slope hemipelagites (Vicchio and Verghereto Marls, and Ghioli di letto mudstones). Apennine hydrocarbon seep-carbonates form isolated, irregularly-shaped masses of limestones with distinctive fabrics, specialized fossil fauna (chemosymbiotic clams and mussels) and exibit typical 13C-depleted signatures indicative of methane influence during precipitation. Several characteristics allow two type of seep-carbonates to be distinguished in the field (type 1 and 2). The type 1 is composed of a horizontal repetition of decametric to heptometric carbonate bodies, lenses and pinnacles. The basal portions of these huge bodies are strongly brecciated, made up of intraformational and rarely extraformational polygenic breccias. The type 2 is made of numerous and small marly-calcareous lenses, irregular column-like bodies aligned along bedding strikes, or horizontally and vertically scattered and not related to a precise stratigraphic level. Many of them consist of several lenticular units vertically stacked and separated by thin pelitic levels, thus suggesting periodic growth. Carbon isotope measurements show that carbonates from type 1 and 2 are typically depleted in 13C but the amount of depletion seem to differ between them. Therefore type 1 seep-carbonates appear significantly depleted in δ13C (δ13C ranging from -30‰ to -55‰ relative to the PDB standard) while type 2 seep-carbonates are only moderately depleted (δ13C varying from -10‰ to -23‰ relative to the PDB standard). Concerning oxygen isotopic measurements type 1 seep-carbonates seem to be enriched in δ18O (δ18O ranging from 1‰ to 6‰ relative to the PDB standard) whereas type 2 seep-carbonates show a more scattered range (δ18O varying from -3.00‰ to 2‰ relative to the PDB standard). Our presentation will report the result of detailed field observation of the two types of seep-carbonates coupled with petrographic, mineralogical and geochemical studies. In particular we discuss the isotope geochemistry, the mineralogy, the geometry in context with the precipitation and recrystallisation processes of the carbonates, the origin of carbon rich fluids and with different mechanisms of seep-carbonate formation.
2008
- Geological Processes and products related to Miocene cold seeps
[Relazione in Atti di Convegno]
Mecozzi, S.; Artoni, A.; Conti, Stefano; Fontana, Daniela
abstract
Cold seeps are commonly associated with the presence of authigenic carbonates, due to interaction between hydrocarbons-rich fluids, geological processes (tectonics, sediment instability, chaotic bodies) and biological activity.In these environments hydrocarbon-rich fluid emissions support flourishing communities of mussel, clam bivalves, gastropods, tube worms and bacterial mats, which rely on chemosynthetic energy for their metabolism. The formation of authigenic carbonates at cold vents is closely related to the anaerobic oxidation of methane (AOM) which releases sulfide and bicarbonate into the pore water. Seep-carbonates have been reported worldwide both in modern and ancient sedimentary deposits. Fossil seep-carbonates provide unique archives of focused methane seepage in the geological record. by their geochemical, petrographic, mineralogical, isotopic and structural inventory. In the northern Apennines numerous outcrops of seep-carbonates are excellently exposed. In the Apenninic chain, the abundance and the extent of the outcrops provide a rare opportunity to study the geometry, facies distribution and internal structures of fossil hydrocarbon-derived carbonates. They were recognized as products of the microbial oxidation of methane-rich fluids on the basis of their megafaunal assemblages and geological, compositional and isotopic attributes Our investigations have been carried out by means of detailed field observations of the northern Apennine seep-carbonates coupled with geochemical, petrographic, mineralogical and isotopic studies.In particular, this multidisciplinary approach permits an assessment of the pathways and origin of the fluids from which carbonates have precipitated (marine seawater source, marine organic matter source, thermogenic and biogenic methane); the final aim is the creation of a model for fossil seep-carbonate formation and development. The case study of the Salsomaggiore Ridge has been reported. This Ridge, a thrust-related anticline forming inside the middle Miocene foredeep at the outermost front of the Apenninic orogenic wedge, revealed a patchy distribution of mound- to pod-shaped seep-carbonates which, in few cases, preserve the deeper fluids feeding system consisting in a randomly arranged web of cm- to dm-sized tube conduits. The seep-carbonate facies and morphotypes are highly variable; either or not associated to typical macrofauna, they both encrust and cement siliciclastic turbidites or they inter-finger with hemipelagic marls. Seep-carbonates appear also brecciated with mottled and vuggy fabrics; a chaotic body reworks the seep-carbonates and other intra-basinal clasts. Stack of mound-shaped and bivalves-rich seep-carbonates are mainly located on the northern limb of the anticline while cementing and inter-fingering carbonates predominate on the southern limb of the same anticline. Northern and southern limbs differ also in the isotopic signature of the seep-carbonates which, overall attributable to methane oxidation, present markedly negative δ13C and positive δ18O only on the northern anticline limb. The above variability and differences are attributed to two different seepage modes which correspond also to evolutionary steps of the Salsomaggiore Ridge: a slow seepage mode that allows deposition of carbonate crusts, pods, mounds and seep-related fauna; a fast seepage mode that produce brecciated fabrics and chaotic bodies. The latter mode is considered coeval to tectonic pulses that generated the Ridge. By this integrated methodology applied to other cropping out examples in the Northern Apennines, we aim to reconstruct the complex mechanism of methane-rich fluid venting through the geological record, in particular in the Miocene
2008
- Miocene seep-carbonates as indicators of fluid migration in northern Apennines (Italy).
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela; Mecozzi, S.; Panieri, G.
abstract
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2008
- Miocene seep-carbonates as indicators of style and intensity of fluid migration.
[Relazione in Atti di Convegno]
Mecozzi, S.; Conti, Stefano; Fontana, Daniela
abstract
Ancient hydrocarbon Miocene seep-carbonates of Miocene age have been reported from marine sedimentary successions of the northern Apennines. They are recognized by their peculiar palaeoecological, sedimentological, compositional and isotopic features as products of the microbial oxidation of methane-rich fluids and represent an excellent on-land example of carbonate bodies interpreted as the remains of ancient cold seeps. These seep-carbonates occur from internal tectonic zones (Piedmont Terziary basins, epi-Ligurian and minor basins) to external zones of the foredeep. In the Miocene foredeep, they occur crop out in large turbiditic bodies (Mt. Cervarola and Marnoso-arenacea Formations) and in slope hemipelagites (Vicchio and Verghereto Marls, and Ghioli di letto mudstones). Dominant rock types are calcilutitic/marly limestones, calcareous marls and calcarenites. Enclosing sediments are hemipelagic/turbiditic mudstones, muddy sandstones and marlstones. In the Apenninic chain, the abundance and the extent of the outcrops provide a rare opportunity to study the geometry, facies distribution and internal structures of fossil methane-derived carbonates.On the basis of morphological and stratigraphic features two main types of seep-carbonates were distinguished in the field (type 1 and 2).The type 1 is composed of a horizontal repetition of decametric to heptometric carbonate bodies, lenses and pinnacles. They have a thickness of 5 - 30 m and an extension that ranges from 10 m to 100 m. The basal portions of these huge bodies are strongly brecciated, made up of intraformational polygenic breccias and rarely extraformational. The Sasso Streghe (Modena Apennines) and Monte Petra (Romagna Apennines) carbonate outcrops are excellent examples of this type of seep-carbonates. The type 2 is made of numerous marly-calcareous lenses, irregular column-like bodies with a dimension ranging from some decimetres to 3 – 4 m and a thickness of 20- 30 cm to 3 m. Carbonate bodies are aligned along bedding strikes, or horizontally and vertically scattered and not related to a precise stratigraphic level. The Vicchio outcrops (Tuscan Apennines) are representative of this second type of carbonates. Mineralogical analyses of type 1 carbonate samples indicate that dolomite and ankerite represent the most dominant phases while Low-Mg calcite represents type 2 dominant carbonate phase. The carbon and oxygen isotopic compositions of the carbonates display very large ranges, from -10‰ to -55‰ Vienna PeeDee Belemnite (V-PDB) and from -3‰ to 6‰ V-PDB, respectively. Seep-carbonates type 1 appear significantly depleted in δ13C (ranging from -30‰ to -55‰ V-PDB) while seep-carbonates type 2 are only moderately depleted (δ13C varying from -10‰ to -23‰ V-PDB). Petrographic observations show complex facies relationships, as indicative of different stages in seep-carbonates growth.Our presentation will report the result of a detailed field observation of the two types of seep-carbonates coupled with geochemical, petrographic and mineralogical studies. In particular we discuss distinctive characters, geometry, isotope geochemistry and mineralogy, in context relationship with precipitation and recrystallisation processes of the carbonates, the origin of carbon rich fluids, and with different mechanisms of seep-carbonate formation.
2008
- Sedimentary filling of a wedge-top basin and realationship with the foredeep (Middle Miocene Marnoso-arenacea Formation, northern Apennines.
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela; C. C., Lucente
abstract
The Middle Miocene Marnoso-arenacea Formation (?Langhian to Serravallian in age), at Deruta in the northern Apennines of Italy, rests unconformably on an orogenic wedge adjacent to the Adriatic foredeep. Based on a detailed facies analysis, the succession reveals two genetically related depositional systems, representing a more lower distal delta-fed sand-rich system and an upper more proximal fan-delta slope system. Petrographic data confirm the genetic relationship between the two depositional systems, with the fan-delta slope feeding the basinward sand-rich system. The Deruta depositional setting shows a multi-step sedimentary evolution controlled by tectonically induced relative sea-level changes. The first stage, corresponding to a sea-level rise, promoted deposition in a wedge-top basin of pebbly sand and sand lobes (delta-fed). The second stage, characterized by intense tectonic activity (uplift) and sea-level fall, promoted accumulation of a prograding fan-delta slope replacing the sand-rich lobes. This phase was dominated by mass failures and methanogenic cold seepages. During these stages, the wedge-top basin was isolated from the adjacent foredeep. Only during the third stage was a connection was established, with the development of a deep-sea fan in the foredeep, fed by a deltaic depositional system.
2008
- Sedimentary filling of a wedge-top basin and relationship with the foredeep (Middle Miocene Marnoso-arenacea Formation, northern Apennines)
[Articolo su rivista]
Conti, S.; Fontana, D.; Lucente, C. C.
abstract
The Middle Miocene Marnoso-arenacea Formation at Deruta in the northern Apennines of Italy rests unconformably on an orogenic wedge adjacent to the Adriatic foredeep. Based on a detailed facies analysis, the succession reveals two genetically related depositional systems: a distal delta-fed sand-rich system and a more proximal fan-delta slope system. Petrographic data confirm the genetic relationship between the two depositional systems, with the fan-delta slope feeding the basinward sand-rich system. The Deruta depositional setting shows a multi-step sedimentary evolution controlled by tectonically induced relative sea-level changes. The first stage, corresponding to a sea-level rise, promoted deposition in a wedge-top basin of pebbly sand and sand lobes (delta-fed). The second stage, characterized by intense tectonic activity (uplift) and sea-level fall, promoted accumulation of a prograding fan-delta slope replacing the sand-rich lobes. This phase was dominated by mass failures and methanogenic cold seepages. During these two stages, the wedge-top basin was isolated from the adjacent foredeep. Only during the third stage was a connection established, with the development of a deep-sea fan in the foredeep, fed by a deltaic depositional system. © Springer-Verlag 2008.
2007
- Fluid seepage in mud volcanoes of the northern Apennines: An integrated geophysical and geological study.
[Articolo su rivista]
F., Accaino; A., Bratus; Conti, Stefano; Fontana, Daniela; U., Tinivella
abstract
An integrated geophysical and geological study of small mud volcanoes occurring along the external compressive margin of the chain in the northern Apennines has beenwas carried out in order to investigate the fluid pathways and the mud reservoir. Results obtained by tomographic inversion of first arrivals of 3D seismic data, and models obtained by 2D geo-electrical data, have permittedmade it possible to determine the geometry of the buried shallow structures, and the details of the fluid seepage until down to 50 m below the mud volcano surface.A mud chamber has beenwas identified at a depth of 25 meters. This shallow reservoir could represent the last phase of mud accumulation before the final emission.The comparison Comparison with other mud volcanoes of the northern Apennines suggests a close relationship between extruded materials and substratum typology
2007
- I vulcani di fango dell'Appennino modenese: fenomeni attuali e fossili
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela
abstract
-
2007
- Integrated geophysical investigation of a mud-volcano in the Northern Apennines.
[Relazione in Atti di Convegno]
Bratus, A; Accaino, F; Tinivella, U; Conti, Stefano; Fontana, Daniela
abstract
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2007
- Le Salse di Nirano
[Software]
Castaldini, Doriano; Conti, Stefano; Conventi, M.; Dallai, Daniele; DEL PRETE, Carlo; Fazzini, M.; Fontana, Daniela; Gorgoni, Carlo; Ghinoi, A.; Russo, Antonio; Sala, Luigi; Serventi, Paolo; Verri, D.; Barbieri, Massimo
abstract
Questo CD-Rom, organizzato in appositi capitoli contrassegnati da colori differenti, riunisce i diversi aspetti della Riserva Naturale delle Salse di Nirano in cinque unità tematiche, alle quali è possibile accedere attraverso il menu di navigazione o attraverso un'apposita pagina introduttiva.Il primo capitolo s'intitola HOME e contiene, oltre alla pagina iniziale, i paragrafi relativi alla guida al CD-Rom, agli autori e alla mappa del sito.Il secondo, chiamato RISERVA, ha come oggetto la Riserva Naturale delle Salse di Nirano, descritta sotto il profilo storico-istituzionale, negli aspetti legati alle strutture di accoglienza e dei servizi offerti, oltre a fornire le informazioni sul regolamento di fruizione dell'area e sulle pubblicazioni inerenti le Salse di Nirano .Il terzo, ASPETTI SCIENTIFICI, raggruppa appunto gli aspetti più prettamente scientifici della riserva naturale delle Salse di Nirano, e contiene i "paragrafi" relativi alla geologia, al clima, alla geomorfologia, ai fossili, alla flora e vegetazione ed alla fauna.Il quarto capitolo, ASPETTI TURISTICI, fornisce una serie di utili informazioni turistiche ed allega una lista di interessanti attrazioni nei dintorni di Nirano; esso contiene inoltre un paragrafo dedicato alla Carta Geoturistica della Riserva.Il quinto capitolo, GALLERIA MULTIMEDIALE, contiene una ricca raccolta d'immagini delle Salse di Nirano, di suoni registrati all'interno della Riserva e di filmati delle salse; di particolare rilievo il volo virtuale sulla Riserva, un modo tutto nuovo di osservare il territorio di Nirano. La galleria multimediale presenta inoltre una significativa bibliografia scientifica sul fenomeno generale delle Salse e sui vari aspetti della riserva di Nirano, un'apposita sitografia (una raccolta di siti web) assieme ad una galleria studi in cui si possono scaricare i pdf di pubblicazioni scientifiche che permetteranno al lettore particolarmente interessato di approfondire i singoli aspetti sulle salse di Nirano.
2007
- Seep-carbonates and fluid expulsion processes in the Miocene of the northern Apennines.
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela; Mecozzi, Silvia
abstract
In the Miocene satellite and foredeep basins of the northern Apennines numerous carbonate bodies were identified by specific palaeoecological, sedimentological, compositional and isotopic features as products of the microbial oxidation of methane-rich fluids (Conti and Fontana, 1999a, 2002 and references herein).These methane-derived carbonates occur in large turbiditic bodies (Mt. Cervarola and Marnoso-arenacea Formations) and in slope hemipelagites (Vicchio and Verghereto Marls, and Ghioli di letto mudstones). Dominant rock types are calcilutitic limestones, marly limestones, calcareous marls and calcarenites. Carbonates exhibit typical 13C-depleted signatures indicative of methane oxidation On the basis of morphological and stratigraphic features two main types of seep-carbonates were distinguished in the field (Type 1 and 2 Conti and Fontana,1999a).The first type (Type 1) is composed of a horizontal repetition of decametric to heptometric carbonate bodies, lenses and pinnacles. They have a thickness of 5 - 30 m and an extension that ranges from 10 m to 100 m. The lateral contacts with marls and arenitic mudstones (host sediments) vary from sharp to transitional. The basal portions of these huge bodies are typically strongly brecciated, made up of intraformational polygenic breccias and rarely extraformational. The Sasso Streghe (Modena Apennines) and Monte Petra (Romagna Apennines) carbonate outrops are excellent examples of this type of methane-derived carbonates.The second type (Type 2) consist of numerous marly-calcareous lenses, irregular column-like bodies with a dimension that ranges from some decimetres to 3 – 4 m and a thickness of 20- 30 cm to 3 m. Carbonate Type 2 bodies can be aligned along bedding strikes or horizontally and vertically scattered and not related to a precise stratigraphic level. Many of them consist of several lenticular units vertically stacked and separated by thin pelitic levels, thus suggesting periodic growth. The Vicchio outcrops is clearly representative of this second type of carbonates.Carbon isotope measurements show that carbonates from Type 1 and 2 are tipically depleted in 13C but the amount of depletion seem to differ between them. Therefore seep-carbonates Type 1 appear significantly depleted in δ13C (up to …) while seep-carbonates Type 2 are only moderately depleted (…). Our presentation will draw attention to the distinctive characters of the two types of chemoherms, In particular we discuss geometry, isotope geochemistry and brecciation, in context with the composition and origin of carbon rich fluids, the flux discharge and rate, and with the mechanisms of expulsion (diffused or focused).
2007
- Seep-carbonates in a thrust-related anticline at the leading edge of an orogenic wedge: The case of the middle-late Miocene Salsomaggiore Ridge (Northern Apennines, Italy)
[Articolo su rivista]
Conti, Stefano; Artoni, A. PIOLA G.
abstract
Seep-carbonates are important indicators of seafloor submarine fluid expulsion and dewatering of sediments along convergent margins and accretionary prisms. In the Northern Apennine compressional wedge, seep-carbonates usually occur in pelitic successions from different settings of the middle -late Miocene foreland basin system. In Serravallian foredeep deposits of the Salsomaggiore area, seep-carbonates cemented and/or encrusted coarse-grained sandstones and conglomerates. Fluid expulsion, strictly related to variable intensities in tectonic stresses, generated seep-carbonate facies and sediment instabilities, depending on the position of the fluid-pathway feeders within the Salsomaggiore Ridge, a middle-late Miocene intra-basinal high, at the leading edge of the Apenninic orogenic wedge. This site provides a unique opportunity for analyzing depositional characters, and the three-dimensional distribution and evolution of a seepage system in a thrust-related anticline. The resulting evolutionary model shares common features with recent ridges in other accretionary wedges. In this model a strict relationship between tectonics, seepage and sediment instability during a major orogenytectonic phase is outlined. Because of the concentration of seep-carbonates during the late Serravallian global high-frequency climatic changes, or Miller events, these type of deposits assume a fundamental role to aid in understanding the feed-back between tectonic and climatic processes in convergent margins.
2007
- Tectonic and climatic controls on deposition of seep-carbonates in the middle-late Miocene Salsomaggiore Ridge (Northern Apennines, Italy).
[Relazione in Atti di Convegno]
Artoni, A; Conti, Stefano; Piola, G; Turco, E. IACCARINO S.
abstract
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2007
- The Montandone Melange in the Northern Apennines: evidente of mud diapirism.
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, D. LUCENTE C. C.
abstract
The Montardone melange (MM) is a chaotic unit consisting of polygenic breccias in a shale matrix (olistostrome texture) outcropping in the core of the E-W trending Montebaranzone syncline in the northern Apennines. The MM occurs mainly at the top of the Termina Formation, a Serravallian-Tortonian unit belonging to the Epiligurian succession; minor, lens-shaped bodies of MM occur at lower stratigraphic positions. The Termina Formation consists mainly of marlstones and includes lens-shaped sandstones and bodies of authigenic seep-carbonates (13C-depleted). Reworked blocks and slabs of the Termina marls are found within the MM.The succession is interpreted here as the filling of a tectonically active slope basin characterized by topographic constrains (lateral confinement) as testified by pinch-out, onlapping, and lateral facies changes to sandstone lobes.The main body of the MM covers the entire syncline with strong lateral thickness changes, making it possible to distinguish two different sectors of the syncline. In the eastern sector the MM achieves the maximum thickness of more than 200 meters. In the western sector it reduces to 40 meters, becoming progressively thinner westwards. In the eastern sector the MM shows a vertical contact with the hosting Termina marls. Bodies of authigenic carbonates occurs close to the contact within the hosting marls, and at the base of the melange. These carbonates, located in the southern flank of the Montebaranzone syncline, have systematic polygenic breccias at the base, with the same composition as the MM. Seep-carbonates occurring in the northern flank do not have these basal polygenic breccias. Previous interpretations suggested a gravity-driven emplacement for the MM, recognized as a large olistostrome. We propose here an alternative hypothesis interpreting the main body of the MM as a mud diapir on the basis of the following evidence: 1) distribution and geometry of the melange; 2) the vertical, abrupt contact with the hosting marls; and 3) the occurrence of basal polygenic breccias characterizing the seepage-carbonates close to the main diapiric body, along the southern flank of the syncline.Most likely, the surface expression was a mud volcano or a mud ridge affected by diffuse slope-instability with the emplacement of coalescent debris flows (olistostromes) also involving blocks of authigenic carbonates. Alternatively, the minor lens-like bodies of MM at different stratigraphic levels could be explained as sill-like intrusions of diapiric material. Mud diapirism and the formation of a mud volcano/mud ridge are attributed here to tectonic loading by overthrusting and the generation of a large amount of methane-rich fluid in the source rocks, i.e. a large older olistostromal body. The occurrence of methane-rich fluids, testified by authigenic carbonates, contributed to generate overpressured shales ascending along sin-sedimentary faults.
2006
- Authigenic seep-carbonates cementing coarse-grained deposits in a fan-delta depositional system (middle Miocene, Marnoso-arenacea Formation, central Italy).
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela; Gubertini, ; A., Lucente; Cc,
abstract
Outer shelf cracks and elongated gas blow out features have been first discovered along a 40 km long section of the U.S. Atlantic margin. Her, individual cracks are several km long, 1km wide and up to 50 m deep (Driscoll et al., 2000, Hill et al., 2004). The cracks and depressions seem to be caused by "gas blow outs" related to the release of shallow trapped gas. The precise age of the blowouts and the origin of the gas remains unknown, but post-LGM formation of the blowout features suggest that ocean warming triggered methane hydrate dissociation processes.The fact, that the gas hydrate outcrop zones of the largest gas hydrate provinces in Europe are on the Norwegian-Barents-Svalbard (NBS) margin makes the U.S. Atlantic margin - Norwegian Atlantic margin reaction of potential gas hydrates fields to post- Last Glacial Maximum (LGM) climate conditions particularly important for studies of submarine slope failures, i.e. geohazards. The NBS margin is not only an important gas hydrate province but also an area where numerous seeps are documented, and we thus know that there is gas migration in the sediments. In particular the area, where the theoretical outcrop zone of the base of the gas hydrate stability zone (BGHS) and the geophysical evidence as a bottom simulating reflector (BSR) lies, we observe outer shelf cracking, gas blow outs, shallow faulting and fluid escape features such as pockmarks in sediments. Our presentation will draw attention (1) to a system of cracks associated with high pockmark density "gas blowout" features along the northern extension of the giant and retrogressive Storegga slide on the Mid-Norwegian Margin and (2) to a system of potential large blowout features and shallow faults influencing slope failures on the W-Svalbard margin. On the Mid-Norwegian margin a 50 km long and up to 3 km wide zone of approx. 10 m deep depressions occur. They line up with the northern edge of the Storegga headwall elongating in N-S direction. Within the uncertainty of the BGHS modelling the approx. 50 ms TWT cracking zone corresponds well to the belt of the BGHS outcrops, where they intersect the upper continental slope. Radiocarbon age dating of the cracking reveals the same age on the main crack as the Storegga Slide event, but due to the 14C dating uncertainties it remains unknown whether the cracking predates, occurs at the same time, or postdates the Holocene giant submarine sliding event. The cracks are associated with fluid escape indicated by pockmarks typically 50-300 m in diameter and 1-5 m deep. On the W-Svalbard margin outer shelf post-LGM faulting and large depressions occur. The depressions have a diameter of 6 -10 km and a depth of up to 100 m but also smaller depressions (<20m) exist. The presented post-LGM formation of cracks, faults and gas blow out features along U.S. and Norwegian Atlantic margin outer shelf areas may be the result of a time dependent response of ocean clathrate reservoirs to climate change and therefore a "climate induced geohazard".
2006
- Fluid flow pathway and configuration of buried structures in mud volcanoes of the northern Apennines.
[Relazione in Atti di Convegno]
Accaino, F; Bratus, A; Conti, Stefano; Fontana, Daniela; Tinivella, U.
abstract
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2006
- Geophysical investigation of a mud-volcano in the Northern Apennines
[Relazione in Atti di Convegno]
Accaino, F.; Bratus, A.; Tinivella, U.; Conti, Stefano; Fontana, Daniela
abstract
In the frame of a cooperation between the Earth Science Department of the University of Modena and Reggio Emilia and the OGS
2006
- I carbonati connessi ad emissioni di fluidi ricchi in metano: i risultati di dieci anni di studi nell’Appennino settentrionale.
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela
abstract
Durante l’ultimo ventennio, l’emissioni di fluidi freddi è stata ampiamente documentata lungo i margini continentali attivi. L’espulsione dei fluidi nei prismi di accrezione è favorita dalle sovrapressioni interstiziali indotte dal carico tettonico e le velocità di emissione sono legate all’entità dei processi tettonici. Ai processi tettonici si possono sovrapporre processi climatici, ed entrambi possono contribuire a fenomeni d’instabilità sedimentaria. L’emissione di fluidi freddi è evidenziata da vari indicatori quali: - depositi di carbonati autigeni, - fuoriuscita d’idrocarburi liquidi e gassosi, - vulcani di fango e strutture legate a processi diapirici, - presenza di depositi ricchi in clatrati, - deformazioni sinsedimentarie, - presenza di peculiari comunità bentoniche chemiosintetiche. Il riconoscimento di questi caratteri è importante per identificare i processi ed i meccanismi che controllano l’espulsione dei fluidi nei margini continentali.I depositi fossili, quali quelli presenti nell’Appennino settentrionale, sono importanti perché forniscono una documentazione temporale dei processi di espulsione dei fluidi: evidenziano la struttura e l’evoluzione del sistema di circolazione dei fluidi e soprattutto i rapporti tra tettonica e sedimentazione. I depositi fossili sono riconoscibili per la presenza di: - carbonati autigeni impoveriti dell’isotopo 13C, - peculiari comunità chemiosintetiche, - strutture sedimentarie legate a processi diapirici. In quest’ultimo decennio abbiamo esaminato i carbonati legati alle emissioni di fluidi ricchi in metano in numerosi affioramenti del Miocene medio-superiore dell’Appennno Settentrionale. Questi depositi si trovano in vari contesti geotettonici della catena appenninica: nelle zone più interne si concentrano nei bacini satelliti epiliguri, (Marne del Termina del Serravalliano superiore-Tortoniano inferiore) mentre in quelle più esterne dell’avanfossa sono presenti generalmente nella parte prospiciente il fronte deformativo. In particolare, nell’avanfossa sono concentrati in due distinte posizioni: - in intervalli pelitici legati ad alti intrabacinali intercalati nella successione langhiano-serravalliana delle Formazioni del M. Cervarola e della Marnoso-arenacea, - in emipelagiti di scarpata di età compresa tra il Serravalliano ed il Messiniano inferiore (Marne di Vicchio, Marne di Verghereto e marne di letto) che delimitano al tetto le sopra citate formazioni. In quest’ultima situazione, i carbonati autigeni sono situati poco al di sotto del contatto tettonico con le unità Liguri.I carbonati sono irregolarmente distribuiti nel sedimento in senso sia orizzontale che verticale; pur non essendo degli indicatori stratigrafici, si concentrano solo in particolari momenti della successione stratigrafica miocenica. Morfologia e litologia dei corpi cartonatici sono varie, come pure le facies presenti, caratterizzate da contatti complessi. I carbonati sono associati a sedimenti di prodelta, a facies di scarpata, e soprattutto a depositi torbiditici di piana bacinale.I carbonati sono prevalentemente inclusi in sedimenti pelitici, ma possono cementare o incrostare arenarie grossolane e conglomerati. Sono sia in posizione primaria che secondaria, per rimaneggiamenti intraformazionali.Al loro interno sono state riconosciute diverse facies, alcune ricorrenti e indicative di processi di tipo diapirico. Evidenze diapiriche sono rappresentate dalla mescolanza e rimaneggiamento di sedimenti e fossili di natura molto diversa, provenienti dalle rocce incassanti, dalle chemioerme stesse, e da sedimenti extraformazionali costituiti da olistostromi. Il regime e la tipologia delle emissioni dei fluidi varia, con evoluzioni da flussi concentrati a diffusi, da esplosivi a moderati e viceversa. Le emissioni lente e moderate sono responsabili della precipitazione di grandi spessori di carbonati autigeni, con sviluppo di facies micritiche riccamente fossilifer
2006
- Risalita di fluidi freddi ricchi in metano, carbonati autigeni ed instabilità sedimentaria nel Miocene medio-superiore dell’Appennino settentrionale.
[Monografia/Trattato scientifico]
Conti, Stefano; Fontana, Daniela; MARCHETTI DORI, S.
abstract
Negli ultimi decenni numerose ricerche hanno evidenziato che le risalite di fluidi sui fondali oceanici, sia calde che fredde, sono fenomeni globalmente estesi, con importanti implicazioni geologiche e biologiche. La risalita di fluidi è generalmente connessa con: a) precipitazione di minerali autigeni fra cui carbonati primari (calcite, aragonite e dolomite), solfuri e solfati; b) peculiari caratteristiche geochimiche dei sedimenti, delle rocce, dell’acqua e degli organismi; c) l’instaurarsi di relazioni simbiotiche fra comunità macrofaunali e microrganismi; d) la formazione di processi diapirici con caoticizzazione dei sedimenti incassanti; e) processi d’instabilità sedimentaria (frane sottomarine di varia tipologia).Verso la fine degli anni ‘70 lo studio dei fondali oceanici, con l’impulso prodotto dall’utilizzo di sottomarini, ha permesso la scoperta dell’esistenza di risalite di fluidi idrotermali arricchiti in solfuri (hot vents) caratterizzati dalla strutturazione di camini costituiti principalmente da solfuri e dalla presenza di una peculiare ed abbondante fauna chemiosintetica (Lonsdale, 1977).A partire dagli anni ‘80, il proseguire delle indagini sottomarine ha evidenziato l’esistenza di risalite localizzate di fluidi freddi ricchi in idrocarburi leggeri (cold seeps), diffusi praticamente in tutti i contesti geodinamici oceanici: nei margini attivi sono segnalati nel prisma di accrezione dell’Oregon (Ritger et al., 1987; Bohrmann et al., 1998), del Giappone (Sakai et al, 1992), del Makran (Von Rad et al, 1996), del Perù (Sample, 1996), di Barbados (Lance et al, 1998), delle Aleutine (Suess et al, 1999) e del Mediterraneo orientale (Aloisi et al, 2000), nel Mar Nero (Peckmann et al., 2001), nel mare marginale di Okhotsk (Esikov and Pashkina, 1990; Greinert, 1999), nel bacino di avanarco della Sonda (Wiedicke et al, 2002), nella scarpata continentale della Nuova Zelanda (Lewis & Marshall, 1996). Nei margini passivi sono frequenti nel Mare del Nord (Hovland et al., 1987), al largo della Danimarca (Jorgensen, 1992), alla base della scarpata a gradoni della Florida (Paull et al., 1995), nel Golfo del Messico (Roberts, 2001). Sono presenti infine nei margini trascorrenti-conservativi della California (Embley et al, 1990; Stakes et al, 1999).Come già osservato per gli hot vents, i cold seeps sono caratterizzati dalla presenza di una fauna bentonica rigogliosa, sostenuta su base chemiosintetica. Si formano comunità a bivalvi in endosimbiosi con batteri solfo-ossidanti, solfato-riducenti e metano-ossidanti (Van Dover, 2000). I batteri utilizzano energia chimica al posto della luce solare e trasformano composti inorganici in sostanze utilizzabili dai bivalvi; viceversa questi ultimi forniscono protezione ai batteri. In corrispondenza dei cold seeps si può realizzare la precipitazione di carbonati autigeni, che sono stati riconosciuti nel record geologico a partire almeno del Fanerozoico (Barbieri et al. 2001; Campbell et al, 2002, Campbell, 2006 e riferimenti bibliografici in essi contenuti). E’ ampiamente riconosciuto che i migliori indicatori di prodotti fossili di cold seeps sono: a) forte impoverimento in 13C dei carbonati, con conseguenti valori isotopici negativi del δ13C; b) associazioni di macrofauna particolare e oligotipica; c) biomarkers specifici (Campbell and Bottjer, 1993; Aharon et al, 1992; Aharon, 2000; Taviani, 2001; Peckmann et al, 2001, 2002; Campbell et al, 2002); d) peculiari strutture riconducibili a fenomeni diapirici.Interessanti esempi fossili di cold seeps sono rappresentati dal “calcare a Lucina” dell’Appennino settentrionale, oggetto della presente escursione. Questi carbonati, caratterizzati da una composizione isotopica negativa del carbonio e da una consistente presenza di fossili di bivalvi (principalmente lucinidi di grandi dimensioni), sono testimonianza di una lunga e complessa storia di risalita di fluidi arricchiti in metano perdurata dura
2006
- Seep-carbonates in intrabasinal highs of the inner foredeep: new insights from the middle Miocene Salsomaggiore Ridge (Northern Apennines, Italy).
[Relazione in Atti di Convegno]
Artoni, Andrea; Conti, Stefano
abstract
Fluid seeps and dewatering of sediments are fundamental processes along the world’s continental margins. Seep-carbonates, recognized worldwide from Devonian to Pleistocene, associated with mud diapirism, sediment instability and specialized seep ecosystem are important indicators of seafloor fluid expulsion often related to gas-hydrates dissociation. In convergent margins and accretionary wedges fluids expulsion is very efficient because of the considerable reduction in pore space of sedimentary sequences due to tectonic compression. In the Northern Apennines orogenic wedge, seep-carbonates occur in different settings of the middle-late Miocene foreland basin system and they are generally found in pelitic successions. Instead, in the Salsomaggiore area (Northwestern Apennines) seep-carbonates outcrop at the top of Serravallian foredeep deposits and they cement and/or encrust coarse-grained sandstones and conglomerates, a case that rarely occurs. This site provides a unique opportunity for analyzing depositional characters, three-dimensional distribution and evolution of the seepage system at the leading edge of an orogenic wedge. Fluid expulsions, strictly related to variable intensities in tectonic stresses, generate seepage-carbonates facies and sediment instabilities depending on the position of the feeding fluid pathways within the Salsomaggiore Ridge, a middle-late Miocene intra-basinal high. These newly described seep-carbonates precise better the Miocene tectono-stratigraphic evolution of the Salsomaggiore area, a key area to unravel the history of Northern Apennine orogenic wedge, and they present an evolution from slow to fast seepage; the latter in connection with a major tectonic pulse. Then, the studied seep-carbonates are also climatically-controlled as they develop during late Serravallian global high-frequencies climatic changes, Miller events. Therefore, the detailed analysis of seep-carbonates assumes a fundamental role in order to understand the feed-back between tectonic and climatic processes in orogenic wedges, which often preserve these types of seep-related deposits.
2005
- Anatomy of seep-carbonates: ancient examples from the Miocene of the northern Apennines (Italy)
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela
abstract
Ancient hydrocarbon seep-carbonates of Miocene age have been reported from marine sedimentary successions of the northern Apennines in the form of irregularly shaped micritic masses containing abundant fossil remains of oligotypic assemblages. They are recognized by their peculiar biological, sedimentological and geochemical features, and represent an excellent on-land example of carbonate bodies interpreted as the remains of ancient cold seeps. In the Apenninic chain, the abundance and the extent of the outcrops provide a rare opportunity to study the geometry, facies distribution and internal structures of fossil methane-derived carbonates. The present study reports an integrated view of the sedimentology, mineral paragenesis and geochemistry of these seep-carbonates in two different tectono-sedimentary settings: foredeep and satellite basins. The main result of this study is the recognition of 17 facies in the investigated seep-carbonates. The detailed facies and microfacies analysis led to the identification of different structures, which occur in well-defined parts of the carbonate masses. The recurring and broadly similar stratigraphy and facies association from the two considered geological environments is diagnostic of the different stages of seep-carbonate formation and evolution.
2005
- Brecciated lithofacies in methane-derived carbonates in Middle-Late Miocene deposits (Northern Apennines, Italy).
[Relazione in Atti di Convegno]
Gubertini, A; Conti, Stefano; Fontana, Daniela
abstract
More than one hundread occurrences of methane-derived carbonate rocks cropping out in Middle-Late Miocene satellite and foredeep basins of the northern Apennines (pelitic intervals of the Mt. Cervarola and Marnoso-arenacea Formations and slope/closure hemipelagites) have been investigated. These authigenic carbonate blocks are interpreted as fossil equivalents of modern carbonate crusts, slabs or chimneys precipitated at cold seeps.We analyzed stratigraphical, compositional and geochemical aspects of brecciated lithofacies that characterize large portions of carbonate bodies, in order to reconstruct different phases of fluid venting and precipitation of authigenic phases.Apennine seep carbonates include two main types of brecciation: monogenic breccias, made up of micritic angular clasts cemented by sparry calcite or aragonite, and polygenic breccias, made up of extrabasinal and intrabasinal clasts chaotically floating in the authigenic micritic matrix.Detailed petrographic study, including UV fluorescence microscopy and cathodoluminoscope, show different typologies and distribution of mineral components, microfacies and microstructures.Mineral components of carbonates blocks are made of authigenic phases and detrital components. Authigenic minerals include micro- to cryptocrystalline micrite and sparry calcite, aragonite, pyrite, quartz and feldspars. Detrital components consist of siliciclastic, silt-sand sized terrigenous particles, fragmented macrofossils and planktonic foraminifera. Ultra-violet fluorescence microscopy shows the presence of several hydrocarbon inclusions in sparry calcite.Various microfacies are frequently intertwined and chaotically mixed. Biomicrite, pelmicrite, clotted micrite and hybrid arenites are the most common. Clotted micrite consists of dark-brown to black, cloudy aggregates rimmed by calcitic spar. Common microstructures are: veins, occluded by multiple generations of carbonate cements and/or sediment grains, corrosion surfaces, burrows, geopetal fabrics and cavities, and preferential orientation of clastic and bioclastic particles.All carbonate phases reveal strongly negative carbon isotope values (ranging from -56,25 ‰ to -10,72 ‰ vs PDB) and reflect different rate of methane oxidation, as well as variability of bacterial communities which induce carbonate precipitation. Oxygen isotope values range from -9,71 3 to +3,55 ‰ vs PDB; the positive values are concentrated in polygenic breccias.On the base of isotopic and thermometric data, the genesis of polygenic breccia can be probably related to gas hydrates dissociation. In present-day continental margins, this dissociation can trigger a widespread and intense sediment instability. The frequent association of polygenic breccias in methane-derived carbonates and chaotic deposits, could be a further evidence of gas-hydrate dissociation and fluid expulsion, and may represent the fossil activity of pseudodiapirs and/or mud volcanoes.
2005
- High resolution geophysical data in areas with evidences of fossil and active fluid seepage (Northern Apennines, Italy).
[Relazione in Atti di Convegno]
Accaino, F; Tinivella, U; DEL NEGRO, E; Bratus, A; Baradello, L; NIETO YABAR, D; Fontana, Daniela; Conti, Stefano
abstract
The University of Modena and Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS) collaborated to acquire two geophysical data set in two areas located near Sassuolo (Modena; Northen Appenines). The first area is characterized by fossil fluid expulsion structures forming in the Upper Miocene, while the second one is actually interested by expulsion of mud and free gas. We used seismic 3D surveys to reconstruct in detail the shallow structures in both areas. Ground Penetrating Radar (GPR) and geo-electrical survey are used only in the second area to better characterize the first meters. The fossil structures located in the first area (Sasso Strega) have a horizontal dimension of about 10 meters, and a vertical extension of few ten. To investigate the presence of these buried structures a 3D seismic acquisition was performed, in which additional shots are located across the investigated area by using the natural topography to have the same effect of a deep source. In this way, the structures are lightened directly from the bottom. The source was the mini-bang and the receivers are vertical geophones (10 Hz). The receiver inline and cross-line intervals were 5 m, while the source interval was equal to 5 m (for inline shots) and 10 m (for cross-line shots). After the processing of the data to increase the signal/noise ratio, the tomographic inversion of the first breaks was applied to determine the geometry and the compressional velocity of buried structures. In the second site (near Nirano), a 3D seismic acquisition was acquired using three component geophones. In this case, the source was a Vibroseis source, that generates both compressional and shear waves. So, the acquisition allowed us to obtain information about both compressional and shear velocity fields by using the inversion tomography of the first arrivals. Of course, the comparison between the two fields is an useful tool to investigate the fluid presence in the investigated area. In fact, it is well known that the compressional velocities are influenced by both matrix and fluid, while the shear velocities detect only the matrix change.In this site we also collected geoelectrical and GPR data to recostruct the shallow features of the subsoil. In particular the geoelectrical data are inverted using tomographic approach to obtain the resistivity and chargeability models.We present the preliminary results of the collected data in the two areas.
2005
- Looking for evidence of the past presence of gas hydrates in ancient sedimentary successions.
[Relazione in Atti di Convegno]
Clari, P; Cavagna, S; DELA PIERRE, F; Martire, L; Fontana, Daniela; Conti, Stefano
abstract
The present-day distribution of gas hydrates is world-wide, in permafrost of polar regions and along outer continental margins, and they are one of the more “hot” topics of modern geo-marine research. In fact, not only GH are considered by industry as a viable energy source for the future, but their possible involvement in margin stability and climate change attracts the interest of all researchers.In order to assess the real relevance of GH dissociation on both margin stability and climate changes, it could be useful to look into the sedimentary record for possible evidence both of mass wasting processes due to GH dissociation and of past, global peaks of GH dissociation. To do that, specific evidence of the occurrence of ephemeral products such as GH in ancient sedimentary sequences are needed. The presence of gas in sediments can leave “solid" evidence as authigenic carbonates generated by aerobic or anaerobic degradation of methane. “Cold seep carbonates” can be considered the specific proxy needed to identify sedimentary sequences flushed by CH4 rich fluids, bearing, however, in mind that not all the gas-charged fluids circulating in the sedimentary column originate from the dissociation of GH . Also the presence of brecciated structures, chaoticization of sediments by soft-sediment deformations and mud diapirism, have been considered as a convincing evidence of the past presence of GH as such features are widespread in the sediments hosting GH along present-day continental margins.Two possible lines of evidence can so be suggested to assess the past presence of GH in ancient sedimentary sequences:1)The presence of carbonate rocks resulting from diagenetic processes linked to biological degradation of gas previously trapped as GH. 2)The chaoticization of sediments generated by the large changes in pore fluid volumes due GH formation and dissociation. As a whole, lithological products of the dissociation of GH are , recently named clathrites. 3)Petrological, mineralogical and geochemical characteristics of clathrites are still imperfectly known as very few examples of present-day carbonate rocks precipitated within or in proximity to gas hydrate have been described. In ancient sediments, clathrites are concealed by other types of cold seep carbonate rocks that share with them an origin due to bacterial degradation of methane. The question is: how is possible to evaluate if that particular methane was caged in the gas hydrate structure before reaching the site where it was degraded by bacteria triggering carbonate precipitation? Methane-derived carbonate preserve the geochemical signatures of the interstitial fluids from which they are derived, registering not only the involvement of methane in their formation, but also, within certain limits, the oxygen isotopic signature of the water in which they formed. During hydrate formation, water molecules containing the 18O isotope are preferentially incorporated in the hydrate structure leaving the residual brines enriched in the light 16O isotope. The reverse happens during hydrate dissociation when an input of gas-driven,18O- enriched water, flushes the surrounding sediments. The carbonate phases resulting from the bacterial degradation of methane are so viable to register these changes in isotopic composition of pore-waters and to preserve it in the sedimentary record.However, as the oxygen isotopic composition of pore waters is influenced also by other factors unrelated to the presence of hydrates (evaporation, temperature, clay-dehydration) it is not correct at the moment to identify a clathrite only on the basis of its oxygen isotope composition. Only if the stratigraphic and structural setting of the carbonates are perfectly known and additional evidence as mineralogical composition, petrological features (as fluid inclusion) and chaotic structures of the enclosed sediments are present, the definition of a seep-carbonate as a clathrite can be proposed.
2005
- Seep-carbonates from the Oltrepo Pavese area (Northern Apennines, middle-late Miocene)
[Articolo su rivista]
Conti, Stefano; Panini, Filippo; A., Gubertini
abstract
Accurate isotopic and facies analyses have been carried out on a marly-calcareous lens cropping out in the Voghera Apennine which contains a particular macrofauna. The data collected show that these carbonates can be interpreted as sedimentary products related to the expulsion of methane-rich fluids and cold-vent processes, analogous to modern sea-floor seep-carbonates. The facies distribution and cyclicity are indicative of different stages in seep-carbonate growth and, presumably, of variations in fluid flow intensity. Field observations have demonstrated the primary position of the carbonate lens, which is located on top of a lenticular level of resedimented sandstones and arenaceous siltstones (Serravalle Sandstones), partially corresponding in facies and age to the Termina Formation deposits of the Emilia Apennines. Stratigraphic data confirm that in the epi-Ligurian Sequence of the Northern Apennines sedimentary and/or tectonic conditions prone to the precipitation of seep-carbonates occurred only during the sedimentation of the basal part of the Termina Fm. (late Serravallian-early Tortonian). The close links between tectonic, sedimentary instability and deposition of seep-carbonates suggest that chaotic deposits of the Termina Fm., such as sedimentary melanges or debris flow deposits, could be reinterpreted in the light of mud diapirism.
2004
- A multidisciplinary study of middle Miocene seep-carbonates from the northern Apennine foredeep (Italy)
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela; A., Gubertini; Sighinolfi, Giampaolo; F., Tateo; Fioroni, Chiara; Fregni, Paola
abstract
Several pelitic intervals are intercalated at various levels within the marly-arenaceous turbiditic successions of the middle Miocene northern Apennine foredeep. They range in thickness from 30 to 200 m, and represent sedimentation on top of ephemeral structural highs related to blind faults. Sediments are made up of hemipelagites and fine-grained turbidites, and include C-13-depleted carbonates, related to the rising of methane-rich fluids (hydrocarbon seep-carbonates). Large portions of pelitic intervals are involved in chaotic masses by soft sediment deformation (slumps, slides, intraformational breccias), revealing an intense sediment instability during middle Miocene. A stratigraphic, mineralogic and geochemical study was conducted on two of these pelitic intervals (Castagno d´Andrea, Mt Citerna) in order to reconstruct carbonate development, the composition of fluids, and to document the connections between fluid seepage and syndepositional tectonics. This multidisciplinary approach has allowed us to discriminate between the two examined pelitic intervals in terms of age, depositional rates and conditions, organic carbon and post-depositional processes. Seep-carbonates are characterized by chemosymbiotic fossil communities, autoclastic fractures and brecciation; carbonate bodies show complex facies relationships, as indicative of different stages in chemoherm growth. The compositional study evidences the peculiar chemistry of chemoherm carbonates (calcite low in Mg and Sr) compared with carbonates in associated enclosing pelites and with modern chemoherms, in general. The non-carbonate components within the chemoherms are enriched in detrital minerals and depleted in phyllosilicates with respect to the enclosing pelites. The mineralogical changes in the clay component within the brecciated unit of the Castagno d´Andrea chemoherms suggest authigenic precipitation of the Mg-rich phases. Isotopic analyses show the distinct carbon signature in the chemoherms from the two examined intervals (Castagno d´Andrea chemoherms more depleted, from - 15.8parts per thousand up to - 41.3parts per thousand PDB, than Mt Citema, from - 5.2parts per thousand up to - 16.7parts per thousand), and the transitional C-13-depletion trend observed moving from chemoherms to the enclosing pelites (moderately depleted) and Te (Bouma sequence) turbidites (in the range of marine carbonates). A slight but significant enrichment in delta(18)O (up to +1.4% PDB);is observed for all chemoherms when compared to values of carbonate phases present in enclosing pelites. Geochemical data indicate that the brecciated facies of seep-carbonates are related to an explosive release of gaseous fluids probably associated with the rise of deep hypersaline fluids.
2004
- Criteri e metodi di rilevamento delle rocce caotiche in aree campione: l'area tra Abbadia S. Salvatore e Piancastagnaio (Toscana meridionale). Carta Geologica alla scala 1:10000.
[Cartografia]
Bettelli, Giuseppe; Conti, Stefano; Fioroni, Chiara; Fregni, P; Gibellini, R; Panini, Filippo; Vannucchi, P.
abstract
Risorsa Elettronica
2004
- Criteri e metodi di rilevamento delle rocce caotiche in aree campione: l'area tra i Fiumi Sinello e Osento (Molise). Carta Geologica alla scala 1:10000.
[Cartografia]
Bettelli, Giuseppe; Conti, Stefano; Fioroni, Chiara; Fregni, P; Mondani, C; Panini, Filippo; Vannucchi, P.
abstract
Risorsa Elettronica
2004
- Deep-sea fluid expulsion and related products in the Miocene foredeep and satellite basins of the northern Apennines, Italy.
[Articolo su rivista]
Clari, P; Conti, Stefano; Fontana, Daniela; Taviani, M.
abstract
The last two decades have convincingly documented that both hot and cold fluid expulsion on the deep seafloor is a widespread, almost cosmopolitan phenomenon whose hydrological, geological and biological implications are multifold. Defluidization has been shown to be conducive to: (i) precipitating a variety of authigenic minerale, primarily carbonates (calcite, aragonite, dolomite), sulfides and sulphates; (ii) imposing distinct chemical signatures in sediments, rocks, biota and water; (iii) sustaining peculiar microbial consortia and macrofaunal communities. Beginning with the mid-80’s submarine investigations revealed the presence of localized deep-sea seeping of light hydrocabon-rich fluids (cold seeps) in many different geodynamic settings of the World’s oceans (e.g., Paull et al., 1984, 1992; Kulm et al., 1986; Aharon and Sen Gupta, 1994; Aharon, 2000; Bohrmann et al., 1998, 2002). As observed earlier at hydrotermal vent sites, modern loci of hydrocarbons-rich fluid seepage are characterized by a significantly high benthic biomass represented by microbial consortia and chemosynthetic macro-assemblages typically dominated by endosymbiont-bearing bivalves including clams (lucinaceans, Solemya, vesicomyids etc.), modiolid mussels (e.g., Bathymodiolus, Modiolus) as well as gastropods (e.g., Thalassonerita, Provanna), and tube worms (Pogonophora). These communities, in analogy with those found around hydrothermal vents, are basically sustained by a chemosynthetic food chain exploiting the bacterial oxidation of methane and/or hydrogen sulfide (Van Dover, 2000, with references therein.). Cold seepage may promote the formation of authigenic carbonates which can be recognized in the geological legacy of the Earth since the Phanerozoic and possibly earlier (Barbieri et al., 2001; Campbell et al., 2002).
2004
- Fluid expulsion imprints in sedimentary chaotic intervals of the northern Apennines; seep-carbonates from the Miocene foredeep and satellite basins.
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela; Gubertini, A.
abstract
Seep-carbonates are considered one of the most reliable indicators of fluid–expulsion processes along convergent margins.The majority of identified carbonate deposits containing fossil chemosynthetic assemblages (seep-carbonates) in the northern Apennines are concentrated in middle-late Miocene pelitic successions from two distint basin types: internal satellite Epiligurian basins, and external foredeep. The Epiligurian sediments consist of various depositional sequences; seep-carbonates are located in the middle-late Miocene outer shelf-slope deposits. In the foredeep, they occur in marly and clayey hemipelagites and fine-grained turbidites, located in slope-closure deposits (Langhian-early Messinian in age) passing laterally and capping huge arenaceous turbidites, or in slope deposits draping ephemeral topographic highs intercalated within the Langhian-early Serravallian basin plain turbidites (Mt Cervarola and Marnoso-arenacea Fms). In satellite basins, seep-carbonates occur in primary position and are associated with large debris flow deposits, whereas in the foredeep they are mainly hosted in thick pelitic intervals affected by an intense sediment instability such as slumps, intraformational breccias and extraformational slides.The great variability of the Apennine tectonic settings permitted different mechanisms of fluid expulsion: from diffuse discharge of pore fluids, related to mud diapir processes, to focussed or structurally aligned, fault-controlled pore fluid expulsion. Evidence of widespread discharge of fluids is commonly found in the chemoherms located in shallow-water deposits of the satellite basins and in foredeep slope pelites. Fault-controlled fluid expulsion characterizes venting within the thick pelitic intervals intercalated in the turbidite foredeep successions.These differences can be related to the degree of tectonic loading and rate of defluidization between the geometrically more elevated Epiligurian basins and the foredeep basins. Moreover, possible gas-hydrate contributions to fluid-expulsion processes are hypothesized in the foredeep, due to the more favorable conditions for gas hydrate dissociation in with respect to satellite basins
2004
- MAPPING OF CHAOTIC ROCKS IN ABRUZZO (CENTRAL APENNINES) COMPARISON WITH SELECTED EXAMPLES FROM NORTHERN APENNINES.
[Monografia/Trattato scientifico]
Bettelli, Giuseppe; Conti, Stefano; Panini, Filippo; Vannucchi, Paola
abstract
The mapping of chaotic rocks has led to the definition of principles, criteria and methods useful in their differentiation and characterization on the field. Basically field mapping has allowed the distinction of four types of chaotic rocks: 1) argillaceous or shaly-matrix sedimentary breccias; 2) in situ non-metamorphic tectonites or broken/dismembered formations (subdivided in monoformational and multiformational non- metamorphic tectonites); 3) gravity-displaced non-metamorphic tectonites or tectonites in secondary position; and 4) association of sedimentary breccias and tectonites. Specific examples of selected areas from different tectonic settings of the Apennines (southern Abruzzo, Oltrepo Pavese and southern Tuscany) are provided.
2003
- Carta Geologica alla scala 1:50.000 dell'area compresa tra Borgo Priolo e Ruino.
[Cartografia]
Bettelli, Giuseppe; Conti, Stefano; Fioroni, Chiara; Fregni, Paola; Mondani, C.; Panini, Filippo; Vannucchi, P.
abstract
-
2003
- Criteri e metodi di rilevamento delle rocce caotiche in aree campione: l’area tra i fiumi Sinello e Osento
[Cartografia]
Bettelli, Giuseppe; Conti, Stefano; Fioroni, Chiara; Fregni, Paola; C., Mondani; Panini, Filippo; P., Vannucchi
abstract
rilevamento geologico di arre campione, utili alla definizione di rocce caotiche
2003
- Diapiric mud breccias: modern and ancient examples (northern Apennines, Italy).
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela; Gubertini, A.
abstract
Composition and architecture of polygenic breccias actually extruded from the Modena-Reggio mud volcanoes have allowed insight into the genesis of similar chaotic deposits associated to ancient cold seep chemoherms in the northern Apennines. Both cold seeps and mud volcanoes result from rising and expulsion of variable amounts of hydrocarbon-rich fluids at the sea floor or in continental areas, and are the locus of abundant brecciated sediments. Subaerial mud volcanoes have a pattern of activity similar to submarine mud volcanoes: they present short eruptive periods with emission of chaotic breccias floating in a viscous mud, thus producing debris flows. Polygenic breccias extruded from their cones and craters show sedimentological features similar to monogenic and polygenic brecciated lithofacies observed in fossil methane-derived carbonates. These affinities suggest that autobrecciated structures and exotic sediments in fossil chemoherms are probably related to the offscraping and chaotic mixtures of sediments during the rapid fluid rise along diapiric conduits or fractures, following the same processes and mechanisms as in chaotic deposits associated with shale diapirs and mud volcanoes. Our data suggest a relationship between extruded sediments and substratum typology: mud breccias with polygenic clasts are associated with a geological substratum including sedimentary mélanges and olistostromes. It is possible that the block-in-matrix textures of these poorly consolidated chaotic deposits favour the offscraping of exotic sediments and also the upward migration of fluids.Similarities between the examined fossil seep carbonates and mud volcanoes include also: - the type of fluids which consist mainly of methane mixed with connate waters and clay mud, and their isotopic signatures strongly depleted in δ13C values (fluid origin can be both thermogenic and biogenic); - the presence of a population of active sulphate reducing bacteria (by comparison with modern seep carbonates); - the occurrence of chaotic deposits; - the existence of thick, fine-grained, plastic sediments in the enclosing sedimentary succession; - the control of tectonic activity, particularly compressional activity.The comparison between recent and fossil diapiric-related structures has been useful for constraining the nature of the fossil seepage pathway, understanding fluid expulsion processes and reconstructing models of chemoherm evolution. In particular, this investigation suggests that brecciated structures and exotic sediments in ancient chemoherms are due to the offscraping and chaotic mixtures of sediments during the rapid rise of methanogenic fluids along diapiric conduits or fractures, following similar processes and mechanisms as in chaotic deposits associated with mud volcanoes.Finally, the strictly association of seep carbonates, autobrecciation related structures and chaotic deposits is a more useful criterium than structural foliations as proposed by various authors (Orange et al., 1990; Orange and Brown, 1993) in order to distinguish diapiric mélanges from other type of chaotic deposits, because original features of sedimentary bodies are usually modified by later sedimentary or tectonic processes.
2003
- I carbonati autigeni di Cappella Monta (Miocene Medio -Sup., Appennino vogherese)
[Articolo su rivista]
Conti, Stefano; A., Gubertini; Panini, Filippo
abstract
Fin dalla seconda metà dell’800 (Taramelli, 1877; 1882; Sacco, 1891) e successivamente in Sacco (1929) erano state segnalate nella zona dell’Oltrepo pavese alcune località fossilifere con faune a grandi bivalvi (calcari a Lucina). Nell’Appennino settentrionale depositi carbonatici di questo tipo sono presenti in successioni di età Miocene medio-sup. affioranti in differenti contesti geotettonici (Ricci Lucchi & Vai, 1994; Conti & Fontana, 1998; 1999), dai bacini satelliti (Successione epiligure) all’avanfossa (peliti di scarpata e depositi torbiditici). Tali depositi sono stati recentemente interpretati, grazie ad analisi geochimiche, paleoecologiche e sedimentologiche, come carbonati autigeni (chemioerme), la cui precipitazione è legata all’espulsione di fluidi freddi ricchi in metano (cold seeps). Vengono qui presentati i risultati delle analisi sedimentologiche, composizionali e geochimiche dell’ammasso carbonatico di Cappella Montà, tra gli abitati di S. Antonino e Mondondone (Appennino vogherese) che mettono in luce la natura metanogenica di tali carbonati autigeni a grandi bivalvi. Il rilevamento di dettaglio ha permesso inoltre di evidenziare che tale ammasso carbonatico è in posizione primaria ed è situato al tetto di un orizzonte di areniti risedimentate e di siltiti arenacee probabilmente correlabile per facies ed età a depositi che nell’Apennino emiliano sono stati inclusi entro la Formazione del Termina. Tale caratteristica lo rende estremamente interessante per lo studio di peculiari litofacies, in quanto sono solo pochi, limitati all’avanfossa appenninica e quasi sempre in posizione secondaria (risedimentati), gli esempi di carbonati autigeni impostati su un substrato composto da litologie grossolane (arenaceo-conglomeratiche).
2003
- Methane-related carbonates in the Miocene Apennine foredeep (Italy). Sedimentological, mineralogical and geochemical considerations.
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela; Gubertini, A; Sighinolfi, Gp; Tateo, F.
abstract
Seep carbonate deposits with very negative δ13C values (chemoherms) are documented from various tectonic settings such as convergent plate boundaries, active transform and passive continental margins. In the middle Miocene foredeep basin of the northern Apennines, several pelitic intervals intercalated within turbidite sediments include carbonate bodies interpreted as chemoherms on the basis of isotopic data (δ13C as low as – 41.33 ‰ PDB) and paleontological evidences. These bodies are associated to features of intense sediment instability such as slumps, intraformational breccias and olistostromes. Sedimentological, mineralogical, chemical and isotopic studies where carried out on in-situ carbonate bodies from two of these pelitic intervals in order to reconstruct fluid sources and chemoherm genetical mechanisms and to document the connection between fluid seepage and syndepositional tectonics. Massive (micritic) carbonate authigenic phases of chemoherms consist of low Mg- and Sr-calcite and/or aragonite. Non stoichiometric dolomite and minor amounts of sulphur phases (sulphides and Ca sulphate) are concentrated in the brecciated lower portion of the bodies. Main carbonate phases from the muddy sediments which host the chemoherms consist of high Mg- and Sr-calcite with minor amounts of non-stoichiometric dolomite. The turbidite sediments (Te interval) differ from the pelites by containing significant amounts of stoichiometric (detrital) dolomite. Mineralogical analysis of the carbonate phases reveals that chemoherm bodies are richer in detrital quartz and in chlorite- smectite and lower in illite than the surrounding pelites. Differences are also observed in the distribution of some paleoenviromental indicator elements (Ni, Co, Cu, Zn), which indicate unstable oxidative conditions during or after chemoherm precipitation. Isotopic data (δ13C values as low as –20.31 ‰ PDB) of carbonates from pelites that surround the chemoherms indicate that the carbon is at least in part of biogenic origin and probably related to diffusion of CO2 and methane-rich fluids through the sea floor around the main vents where chemoherms grow. Mineralogical (enrichment in smectite and dolomite, Ca sulphate precipitation) and chemical (high chlorine content) features of some chemoherm bodies suggest that the aqueous fluids associated to the seeping gas were highly saline brines of problematic origin. Some features suggest genetical analogies between the chemoherm deposition in the Miocene foredeep basin and present sedimentary conditions where gas hydrates are generated. It is hypothesized that the pelitic intervals represent sedimentary episodes on top of ephemeral structural highs related to blind faults linked to the advancement of Northern Apennine deformational front. It is possible that the growth of structural highs was an effective mechanism for concentrating gas hydrates by gradually raising the base of their stability zone. Gas hydrates or similar fluids could have played an important role in triggering sediment instability and slumping along the margins of structural highs. The relation between methane seepage, sediment slumping and tectonics suggests a reinterpretation of many chaotic deposits and soft-sediment deformation features as a product of the episodic release of overpressured shallow methane accumulations in slope sediments.
2003
- Sediment instability triggered by gas hydrate dissociation: what can we learn from the fossil Northern Apennines ocean margin ?
[Relazione in Atti di Convegno]
Fontana, Daniela; Vannucchi, P.; Conti, Stefano
abstract
Gas migration and gas hydrates
2003
- The Modena-Reggio mud volcanoes (northern Italy): an actualistic model for the interpretation of Miocene authigenic carbonates related to fluid expulsion.
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela; Gubertini, A.; Bussi, P.
abstract
The paper examined physical, geochemical and geological features, and fluid expulsion processes of fossil seep carbonates and recent mud volcanoes in the northern Apennines. Chaotic brecciated deposits associated with short “eruptive” periods of the Modena-Reggio mud volcanoes (Regnano) are debris flows made of polygenic breccias floating in a viscous mud. These deposits show a number of analogies with monogenic and polygenic brecciated lithofacies of the Miocene methane derived authigenic carbonates of the northern Apennines. Similarities between the examined fossil seep carbonates and mud volcanoes include also the type of fluids which consist mainly of methane mixed with connate waters and clay mud, and their isotopic signatures strongly depleted in δ13C values. The comparison between recent and fossil diapiric-related structures has been useful for constraining the nature of the fossil seepage pathway, understanding fluid expulsion processes and reconstructing models of chemoherm evolution. In particular, this investigation suggests that brecciated structures and exotic clasts in ancient chemoherms are due to the offscraping and chaotic mixing of sediments during the rapid rise of methanogenic fluids along diapiric conduits or fractures, following similar processes and mechanisms as in chaotic deposits associated with mud volcanoes.
2002
- A pelitic interval enclosing primary chemoherms in the M. Cervarola Formation (Northern Apennines): evidence for synsedimentary tectonics during the Miocene.
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela
abstract
A decametric pelitic interval made up of marls and mudstones enclosing numerous carbonate bodies is present in the upper portion, Langhian in age, of the M. Cervarola Formation in the Bologna Apennines, between the Silla and Setta streams. A number of distinctive geometrical, sedimentological and compositional characteristics allow the carbonate bodies to be interpreted as authigenic carbonate buildups (primary chemoherms), related to methane venting. Chemoherms are always located in proximity of the tectonic contact separating the M. Cervarola Fm from the Sestola-Vidiciatico Unit. In this context, the expulsion of fluids was probably induced by tectonic compression and the chemoherms could be considered as syntectonic deposits related to structural highs. Syntectonics highs affected the early-middle Miocene sedimentation of foredeep turbidite units (M. Cervarola and Marnoso-arenacea formations) with pelitic turbidites overlapping structural reliefs, probably related with blind thrusts-fold drapes. Chemoherms within the pelitic intervals could be used as indicators of tectonic activity, as confirmed by the associated chaotic structures and slumps. These observations, and the comparison with the resedimented chemoherms occurring in other outrops of the M. Cervarola Fm. as well as in minor basins (Porretta-Suviana), are crucial to more accurate paleogeographic reconstructions of the middle Miocene foredeep.
2002
- Carta Geologico-Strutturale dell'Appennino Emiliano-romagnolo. -
[Cartografia]
CERRINA FERONI, A.; Ottria, G.; Martinelli, P.; Martelli, L.; Catanzariti, C.; con contributi di BETTELLI, G.; Panini, Filippo; Capitani, C.; Conti, Stefano; Vercesi, P. L.; Perotti, C.; Bernini, M.; Vescovi, P.; Lasagna, S.; Costa, E.; Frati, G.; Marroni, M.; Pandolfi, L.; Plesi, G.; Daniele, G.; Botti, F.; Palandri, S.; Ghiselli, F.; Poccianti, C.; Rosselli, S.
abstract
-
2002
- Carta geologico-strutturale del Montefeltro e dell'alta valle dei fiumi Savio e Tevere alla scala 1:100.000 (Appennino tosco-romagnolo e marchigiano)
[Cartografia]
Conti, Stefano
abstract
Carta Geologica dell'Appennino Tosco-romagnolo-marchigiano
2002
- Carta geologico-strutturale del Montefeltro e dell’alta valle dei fiumi Savio e Tevere.
[Cartografia]
Conti, Stefano
abstract
Abstract -Main stratigraphycal data and structural elements of a large area of the Apennine chain (Montefeltro and Tuscan-Romagna Apennines) are presented. The exposed deposits belong to the Ligurian, Tuscan, Umbro-Romagna and Marche-Adriatic Domains. The study has shown a complex structural evolution articulated in several deformative Neogene phases. Every tectonic phase is marked by the thrusting of an inner unit over an outer one and by the overriding of Ligurides on Tuscan and Umbro-Romagna-Adriatic units at the level of turbiditic closure facies and Argille Azzurre Fm (Lower Pliocene). In general the Ligurian thrust-sheet seal the overridings of the underlying thrust-units. A complex duplex formed, laterally bordered by transverse lines, where piggyback basins were filled both by the Epiligurian deposits and the terminal part of the closure facies units (Ghioli di letto and Argille Azzurre Fms) overriden by the Ligurian thrust-sheet.
2002
- Carta geologico-strutturale del Montefeltro e dell’alta valle dei fiumi Savio e Tevere.
[Relazione in Atti di Convegno]
Conti, Stefano
abstract
Main stratigraphycal data and structural elements of a large area of the Apennine chain (Montefeltro and Tuscan-Romagna Apennines) are presented. The exposed deposits belong to the Ligurian, Tuscan, Umbro-Romagna and Marche-Adriatic Domains. The study has shown a complex structural evolution articulated in several deformative Neogene phases. Every tectonic phase is marked by the thrusting of an inner unit over an outer one and by the overriding of Ligurides on Tuscan and Umbro-Romagna-Adriatic units at the level of turbiditic closure facies and Argille Azzurre Fm (Lower Pliocene). In general the Ligurian thrust-sheet seal the overridings of the underlying thrust-units. A complex duplex formed, laterally bordered by transverse lines, where piggyback basins were filled both by the Epiligurian deposits and the terminal part of the closure units (Ghioli di letto and Argille Azzurre Fm) overriden by the Ligurian thrust-sheet
2002
- Palaeogeographic implications and relations between tectonics and sedimentation in satellite basins (Northern Apennines): insights from Neogene Epiligurian arcs.
[Articolo su rivista]
Conti, Stefano
abstract
Starting from late Oligocene the migration of the Northern Apennine thrust belt was coupled with the counterclockwise rotation of the Corsica-Sardinia block, as shown by various palaeogeographic reconstructions. A further support to the palaeogeographic reconstructions comes from the tectonic transport direction registered by oroclinal bendings occurring in the Val Marecchia thrust sheet, cropping out between the Tuscan and Romagna-Marche Apennines. In the allochthonous sheet some antitaxial arcs are characterized by different directions of tectonic transport, reflecting a change of about 40 degrees (from N-S to NW-SE) in the direction of the Apennine deformational front during early Serravallian-early Tortonian. The timing of this change can be desumed both from the age of deposits underlying the allochthonus sheet and from arcuate Epiligurian deposits located on top of arcuate thrust faults.The unconformities separating the depositional sequences of these particular syntectonic deposits registered different Neogene tectonic events, related to the step-wise advancements of the Ligurian thrust sheet. These characteristics make them an excellent natural laboratory for gaining insight into arc-development processes and tectonic control on sequence boundaries in orogenic wedges. Following these data, a palaeogeographic reconstruction of the timing of the various stages of Neogene rotations of the Northern Apennine deformational front is proposed.
2002
- Sediment instability related to fluid venting in Miocene authigenic carbonate deposits of the northern Apennines (Italy)
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela
abstract
Chemosynthetic carbonates, identified by isotopic, paleoecological and sedimentological features, are concentrated in middle-late Miocene satellite and foredeep deposits of the northern Apennines. Chemoherms in the foredeep are hosted in thick pelitic intervals, probably deposited in intrabasinal structural highs, which are entirely or partly involved in large slumps, in many cases associated with extrabasinal slides. Sediment textures in carbonates and in the enclosing foredeep pelitic sediments indicate a link between hydrocarbon-fluid venting, sediment deformation and mobilization, and tectonics. The intensity and style of fluid release phases directly influenced chemoherm typology, and also determined overpressure conditions in low shear strength pelitic sediments, favouring sediment mobilization and influencing slope instability which widely affected the Apennine foredeep. Chemosynthetic carbonates are associated with sites of tectonically-fractured and compressed sediments in the Apennine foredeep-thrust belt system, thus indicanting a relation to the tectonic loading of the Apennine thrust-sheets which favoured fluid expulsion along forerunner faults. Possible gas hydrate contributions to fluid expulsion processes are discussed, based on sediment textures compared to modern vent areas. Finally, sediment instability may have facilitated large amount of fluid escape, thus stopping carbonate precipitation.
2002
- Strutture brecciate da emanazione di fluidi freddi: esempi attuali (Salsa di Regnano, RE) e fossili (chemioerme dell'Appennino Settentrionale di età miocenica).
[Relazione in Atti di Convegno]
Bussi, P.; Conti, Stefano; Fontana, Daniela; Gubertini, A.
abstract
I livelli di brecce associati all’attuale attività di un piccolo vulcano di fango nell’Appennino reggiano (Salsa di Regnano) presentano notevoli analogie con litofacies brecciate in carbonati autigeni fossili, di età miocenica medio-superiore, interpretati come il prodotto di associazioni biologiche chemiosintetiche (chemioerme) per risalita di fluidi freddi metanogenici sul fondo marino (cold seeps). La Salsa di Regnano, ritenuta uno dei più interessanti vulcanetti di fango dell’Appennino reggiano-modenese, è attualmente caratterizzata da emissione di fango molto liquido associato a bolle di idrocarburi gassosi, prevalentemente metano, e a tracce di petrolio ed acqua salata. La sua attività eiettiva ha portato alla costruzione di un cono principale di pochi metri d’altezza, con numerose bocche secondarie poste nell’area della salsa, e alla formazione di una colata che si estende verso la valle del Tresinaro, lunga circa un chilometro. La Salsa di Regnano è localizzata all’intersezione tra una importante faglia ad andamento antiappenninico (SO-NE) e faglie minori. In occasione di più intensa attività della salsa, generalmente in corrispondenza di attività sismica, assieme al fango marnoso-argilloso e ai normali prodotti di emissione, avviene la risalita di numerosi frammenti di roccia strappati ai sottostanti sedimenti attraversati. I clasti, generalmente spigolosi, hanno dimensioni variabili da pochi millimetri a diversi centimetri. Sono costituiti da varie litologie, tra cui le più frequenti sono arenarie, calcilutiti grigio-verdi, marne rosate e rocce ofiolitiche. La provenienza dei clasti è da successioni dei complessi Liguri e da depositi Epiliguri (Formazione di Ranzano e Montepiano). I clasti sono legati da una matrice marnoso-argillosa grigio-nocciola e costituiscono livelli di brecce poligeniche, intercalati alla pelite, di spessore fino a decimetrico ed estesi per numerosi metri a partire dalla bocca di emissione. La Salsa di Regnano costituisce una manifestazione “fredda” generata dalla risalita lungo fratture di fango trasportato da idrocarburi gassosi ed acqua vadosa in pressione, che in alcuni casi è in grado di strappare e trasportare clasti di dimensioni considerevoli: nel passato infatti sono stati segnalati anche blocchi di notevoli dimensioni (da decimetriche a metriche) trascinati dalle colate fino ad alcune decine o centinaia di metri di distanza dalla bocca di emissione.
2001
- Authigenic carbonates related to chemosynthetic activity in the Miocene foredeep deposits of the northern Apennines.
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela
abstract
Methane-derived chemosynthetic carbonates, identified by the peculiar isotopic signature and by paleoecological and sedimentological characters, are present in the middle-late Miocene foredeep deposits of the northern Apennines. They consist of authigenic carbonates and carbonate- cemented detrital sediments associated with chemosymbiotic taxa, and represent an excellent geological record of ancient hydrocarbon seepage processes on the sea floor related to the flourishmment of chemosynthetic communities. Chemoherms in the foredeep are hosted in thick pelitic intervals, deposited in structural highs, which are entirely or partly involved in large-sized slumps. Brecciated textures, as well as structures related to sediment instability processes, are commonly observed in carbonates. Brecciated limestones mark the sites where methane is episodically released explosively, frequently with the offscraping of exotic sediments during the rapid fluid rise along diapiric conduits or fractures. Widespread discharge of pore fluids lowers the shear strength of the sediments and triggers the movement of slumps or debris flows, which are frequently associated with chemoherms. Multiple phases of explosive breakage of micritic carbonates, diapirism, slumping, reworking processes as debris flows or local turbiditic events explain the chaoticization of many deposits associated with Miocene chemoherms of the northern Apennines. We suggest that the growing of structural highs was an effective mechanism for concentrating gas hydrates by gradually moving upward the base of their stability zone with subsequent decomposition, thus contributing to undermine the stability of slopes and inducing sediment deformation and failures.
2001
- Depositi caotici nella successione pliocenica del bacino di Radicofani (Toscana meridionale): relazioni con la tettonica estensionale
[Relazione in Atti di Convegno]
Bettelli, Giuseppe; Conti, Stefano; Panini, Filippo; P., Vannucchi
abstract
-
2001
- Gli intervalli pelitici della Formazione Marnoso-arenacea del Mugello (Miocene medio): relazioni fra tettonica, fluidi freddi e instabilità sedimentaria
[Articolo su rivista]
Conti, Stefano
abstract
Marine gas hydrates (clathrates) are ice-like solids composed predominantly of methane and water derived from methanogenic and thermogenic sources. Clathrates are readily destabilized by changes in pressure and /or temperature, which, in turn, are mainly due to tectonics, sea level change, sea-floor mass wasting and shallow geotherm raise (TREHU et al. 1999; KENNETT & FACKLER-ADAMS, 2000). During clathrate dissociation, the resultant methane and water become trapped by impermeable stratigraphic intervals (marlstones, mudstones and siltstones), producing overpressurization and associated low shear strength in pelitic sediments, making them highly susceptible to soft sediment deformations, and triggering slumps, slope failures and sediment gravity flows (sediment instability). Methane-based chemosynthetic communities and authigenic methane-related carbonates (chemoherms) are frequently associated with pelitic sediments bearing gas hydrates, confirming a relationship between carbonate formation and gas hydrate decomposition (PAULL et al. 1995; SUESS et al. 1999). These carbonates show peculiar brecciated structures, irregular vuggy fabrics and dense networks of non-systematic fractures, induced by a process similar to hydrofracturing of semi-consolidated sediment, due to ascending gas bubbles and the deposition of irregular gas hydrate layers (BOHRMANN et al. 1998). The occurrence of pelitic intervals enclosing chemoherms, and intraformational and extraformational slides within the middle Miocene foredeep turbidites (Marnoso-arenacea Formation) of the northern Apennines rises many questions about relationships between tectonics and sedimentation. In this paper, the classical gravitational hypothesis is integrated with a more complex syndepositional model. Pelitic intervals are probably linked to thrust activity; structural highs affected the middle Miocene sedimentation, with pelitic sediments overlapping structural reliefs, which could be related to blind thrusts. Thrust faults may have interrupted the gas hydrates stability zone, promoting hydrate destabilization, upward flow and entrapment of methane and water in impermeable pelitic sediments. Local inhomogeneity related to fractures contributed to seeping of fluids, random precipitation of authigenic carbonate, and chemosynthetic faunas. Development of fluid overpressures beneath pelitic structural reliefs may eventually undermine their stability causing deformation processes, sliding and slumping. Gas outburst is not only testified by chemoherm autobrecciated structures but also by the scraping off and mixing of the enclosing sediments (pelites and sandstones) during the rapid fluid rise along conduits or fractures (CONTI & FONTANA, 1999a, 1999b). Multiple phases of explosive breakage of micritic carbonates, slumping, sliding and reworking processes as debris flows or local turbiditic events are responsible of the chaoticization of wide portions of pelitic intervals. In this way, pelitic intervals with chemoherms reveal relationships between tectonics, cold seeps and sediment instability. In conclusion, pelitic intervals enclosing chemoherms are useful indicators of the advancing deformational front of the northern Apennines, thus heralding tectonic phases, as also demonstrated by the presence of extraformational slides of internal provenance (BERTI et al. 1994).
2001
- The Miocene chemosynthetic communities of the Northern Apennines and the mechanisms of fluid release from a convergent margin.
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela; Vannucchi, P.; Bettelli, Giuseppe; Panini, Filippo
abstract
The Miocene cold seep communities of the northern Apennines
2000
- Carta geologica dei calcari metanogenici dell'alto Mugello (F. Marnoso-arenacea, miocene medio).
[Cartografia]
Conti, Stefano
abstract
principali affioramenti dei calcari metano-derivati tra il Mugello ed il M. falterona
2000
- Cold vent processes in the Miocene Foredeep – thrust belt system of the Northern Apennines
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela; Vannucchi, P; Bettelli, Giuseppe; Panini, Filippo
abstract
Micritic limestones locally called "calcari a Lucina" packed with dense large bivalves and characterized by autoclastic breccias and fluid-flow conduits are present in middle-late Miocene sediments of the northern Apennines. After many years of geologic controversies, these limestones have been reinterpreted as cold vent deposits, thus becoming special indicators of clathrate dissociation and revealing important relationships between methane seepages, sediment instability, and tectonics.Chemoherms are found from internal tectonic zones (satellite Epiligurian basins) to external ones (foredeep turbidites) of the Apenninic chain. Dominant rock types are calcilutitic limestones, marly limestones and calcarenites; they are composed of authigenic micrite associated with minor neoformed pyrite, biogenic particles and siliciclastic detritus. Host sediments are mudstones, muddy sandstones and marlstones; characterised by low permeability but commonly fractured. In the foredeep chemoherms occur within thick pelitic intervals, deposited in structural highs, which are entirely or partly involved in slumps, frequently associated with extraformational slides. In this contest, chemoherms seem to be indicators of the advancing deformational front of the chain, thus heralding main tectonic phases. Otherwise, in the satellite basins, the distribution of chemoherms is not structurally controlled; a relationship between periods of sea level drops and clathrate destabilization processes in these relatively shallow successions should be taken into account.Two main types of chemoherms, respectively related to focussed and diffuse methane-rich flux venting, can be distinguished in the field. The first type consists of huge isolated lenticular carbonate to calcarenitic levels ranging in extension from 15 to 200 m and a maximum thickness up to 30 m. The second type of chemoherm consists of numerous horizontally and vertically scattered marly-calcareous and calcarenitic lenses with a diameter from decimetric to 5-7 m and a thickness from some dm to 3-5 m. Chemoherm autobrecciation marks the sites where ponded methane at shallow depth is episodically released explosively, as also testified by the offscraping of exotic sediments during the rapid fluid rise along diapiric conduits or fractures. As a whole, widespread discharge of pore fluids lowers sediment shear strength and permits the movement of slumps or debris flows, which are frequently associated with chemoherms.
2000
- Metodi e tecniche di rilevamento delle rocce caotiche appenniniche
[Relazione in Atti di Convegno]
Bettelli, Giuseppe; M., Bonacci; Conti, Stefano; Fregni, Paola; Fioroni, Chiara; R., Gibellini; C., Mondani; Panini, Filippo; P., Vannucchi
abstract
La ricerca si propone di definire i criteri di rilevamento (principi) ed i metodi pratici (tecniche) utilizzabili nella cartografia di rocce sedimentarie prive di una coerenza interna a causa dell’assenza di superfici di stratificazione lateralmente continue. Questo è stato possibile tramite l’esperienza maturata nel rilevamento di vasti settori dell’Appennino Settentrionale e attraverso lo studio di tre aree campione ubicate in differenti contesti geotettonici dell’Appennino (Toscana meridionale, Appennino vogherese e Abruzzo meridionale). Nello studio delle rocce caotiche deve essere tenuto distinto il problema che riguarda la genesi della loro struttura/tessitura da quello che riguarda la loro attuale giacitura. Devono essere individuati, pertanto, dei criteri utili a riconoscere in modo oggettivo i meccanismi responsabili della struttura/tessitura caotica, e dei criteri che permettano di ricavare le modalità con le quali la stessa roccia ha acquisito la sua attuale giacitura.Alla scala dell’affioramento i caratteri oggettivi che permettono di attribuire la genesi di una roccia caotica a meccanismi sedimentari o tettonici sono: l’associazione litologica, la tessitura e la struttura mesoscopica.Gli elementi diagnostici utili a riconoscere i meccanismi che hanno portato una roccia ad acquisire una giacitura caotica sono: l’estensione e lo spessore; la natura dei contatti; le relazioni con le rocce circostanti; il fatto che rappresenti un corpo che include altri corpi stratigraficamente incompatibili o che costituisca un corpo estraneo dal punto di vista stratigrafico; l’esistenza di stili strutturali contrastanti; la presenza di collocazioni stratigrafiche anomale; l’esistenza di caratteristiche paleoambientale incongruenti.L’insieme dei criteri e degli elementi diagnostici elencati permette di distinguere i seguenti tipi di rocce caotiche: brecce sedimentarie (depositi di debris e mud flow); tettoniti in situ o primarie; associazioni di tettoniti e brecce sedimentarie; tettoniti dislocate da meccanismi sedimentari o tettoniti secondarie.Le tecniche ed i criteri individuati hanno dimostrato una validità generale, applicabile nei vari domini geotettonici dell’Appennino, indipendentemente dall’entità delle deformazioni tettoniche. Essi rappresentano quindi uno strumento fondamentale non solo per migliorare la qualità della rappresentazione cartografica ma anche per ottenere informazioni di carattere stratigrafico e strutturale, indispensabili a descrivere la storia geologica di una regione caratterizzata dalla presenza di rocce sedimentarie stratigraficamente incoerenti.
2000
- Oroclinal bendings in allochthonous units: influence on Epiligurian sedimentation and implications for a palaeogeographic reconstruction of the Northern Apennines during the Neogene.
[Relazione in Atti di Convegno]
Conti, Stefano
abstract
Most fold-and-thrust belts show pronounced plan-view geometrical curves defined by lateral variations in structural trends. According to the transport direction, they can be subdivided in antitaxial curves (convex in the direction of the vergence) and syntaxial curves (concave in the direction of the vergence). Two types of bends are recognized: the first, non rotational arc, is a bend where the segments do not change strike during its development. The second, rotational arc or orocline, is a bend where the segments change strike during its development. In this way, the recognition of arcuate faults belonging to allochthonous thrust sheets, as oroclines, permits their formation to be linked to the thrusting phase of the allochthonous unit. At the same time the trasport direction of a bowed fault can be determined by: 1) the bisetrix of the chord connecting its terminal ends, 2) the strike of the tear faults bounding it, 3) the internal geometry of syntectonic deposits located atop the fault (piggy-back basins). In this context, the recognition of Neogene antitaxial oroclinal bendings in the Ligurian thrust sheet of the Northern Apennines, is of outstanding importance in understanding the relationships among thrusting direction, tectonic control on sequence boundaries and rotation of the Italian peninsula.Starting from late Oligocene the migration of the Northern Apennine thrust belt was coupled with the counterclockwise rotation of the Corsica-Sardinia block and of the northern Italian peninsula around a pivot north of Genoa. Following this opinion, various paleogeographic reconstructions indicated a NE-SW direction of the deformational front during late Oligocene, a N-S direction during early-middle Miocene and a NW-SE direction, similar to the recent position, during late Miocene-early Pliocene. Palinspastic restorations are essentially based on paleomagnetic measurements, absolute dating of the rotation of the Corsica-Sardinia block and distribution of sedimentary facies. A further support to the paleogeographic reconstructions comes from the tectonic transport direction registered by oroclinal bendings occurring in the Val Marecchia thrust sheet, cropping out between Tuscan and Romagna-Marche Apennines. In this allochthonous sheet some antitaxial arcs are characterized by different transport directions, reflecting a change of about 40 degrees in the direction of the Apennine deformational front during early Serravallian-early Tortonian. The timing of this change can be desumed both from the age of deposits underlying the allochthonous sheet and from arcuate Epiligurian deposits located on top of arcuate thrust faults.In a section view arcuate Epiligurian basins describe a wedge-shape geometry, with the maximum thickness localised in the back portion of the basin, which is confined by tear faults and couples of reverse faults or couples of frontal reverse faults and rear normal or vertical faults. These basins are filled by thick late Oligocene-early Pliocene deposits, that can be grouped in several depositional sequences. Each depositional sequence crops out always parallel to the arc curvature, with convex shape boundaries. Every younger sequence tends to occupy a more internal position within the arc, with a decreasing inclination of bedding planes up to a sub-horizontal attitude. The unconformities separating depositional sequences registered different Neogene tectonic events, related to step-wise advancements of the Ligurian thrust sheet. In conclusion, these peculiar syntectonic deposits are an excellent natural laboratory for gaining insight into arc-development processes and tectonic control on sequence boundaries in orogenic wedges. Following these data an accurate paleogeographic reconstruction of the timing of the various stages of Neogene rotations of the Northern Apennine deformational front is proposed.
2000
- Primary chemoherms in the Mt. Cervarola Formation (Bologna Apennines): a tool in understanding the evolution of the Northern Apennines during the Miocene.
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela; Righetti, L.
abstract
In the upper portion of the Mt. Cervarola Formation in the Bologna Apennines, between the Silla and Setta streams, a decametric level made up of marls and mudstones intertongued with numerous carbonate bodies crops out. Based on preliminary biostratigraphic data, the age of these deposits is Langhian. A number of distinctive geometrical, sedimentological and compositional characteristcs allow the carbonate bodies to be interpreted as primary chemoherms, related to methane venting. They consist of micritic, marly calcareous to calcarenitic lenses, strongly brecciated and very rich in densely packed lucinid bivalves. The dimensions vary from a few decimeters to several meters and the thickness ranges from 20-30 cm to 4-5 m. Carbonate lenses are horizontally and vertically scattered and grade into the surrounding pelitic sediments with transitional lithologies in between. The methanogenic carbonates consist of authigenic micrite associated with neoformed pyrite; the micritic groundmass is commonly accompanied by abundant bioclastic debris and scarse fine-grained detritus. Brecciated structures are common, represented by monomictic and polymictic breccias, dense networks of non systematic carbonate-filled veins and fractures, and extensive vuggy fabrics. Other features, such as micritic doughnuts, nodular and cylindrical to encircling concretions and pipe-like structures, are interpreted as fluid-flow conduits. Chaotic structures are rare, consisting of small slumps involving marly and carbonate deposits.The recognition of primary chemoherms in the Mt. Cervarola Formation indicates that synsedimentary mobilization (cannibalism) was frequent not only in slope pelites but also in foredeep deposits. In fact, lucinid-bearing deposits occur in the Mt. Cervarola turbidites in various areas, such as Bobbio and Segavecchia, and in minor basin successions (Porretta, Suviana). They are not chemosynthetic and are reworked, consisting of lucinid clasts occurring at the base of resedimented arenite beds. A minor reworking is evident in the problematic Barigazzo outcrop, made up of limestone blocks with biogenic debris and disarticulated bivalve shells. Lucinid clasts and blocks come from different sources, such as the Mt. Cervarola primary chemoherms, intraformational argillaceous levels including chemoherms but no more preserved, and adjacent slope pelites (Vicchio Marls). The primary chemoherms in the Mt. Cervarola Fm from the Bologna Apennines are remarkably similar to the time-equivalent (Langhian) deposits of the inner Marnoso-arenacea Fm cropping out on the right side of the Sillaro line. In both cases chemosynthetic carbonates are enclosed in argillaceous lithofacies, probably draping over folds and thrust top. They may indicate interruption of normal turbidite deposition and could be used as indicators of tectonic activity, as confirmed by the associated chaotic structures and slumps. These observations are crucial to more accurate paleogeographic reconstructions of foredeep and minor basins (Porretta-Suviana) during the middle Miocene.Finally, the relationships among methane-derived authigenic carbonates, venting of methane rich fluids and tectonic activity are testified by the peculiar position of the Mt. Cervarola primary chemoherms. They are located in proximity of the tectonic contact separating the Mt. Cervarola Fm from the Sestola-Vidiciatico Unit, and are aligned along the overturned limb of an anticline. In this context, the expulsion of fluids was probably induced by tectonic compression and the chemoherms could be considered as syntectonic deposits. This has broad implications for constraining the age and the evolution of the structural setting.
1999
- 50 - Le discordanze e le forme calanchive nella successione neogenica - quaternaria, affiorante nella valle del Rio del Petrolio
[Capitolo/Saggio]
Conti, Stefano; Fioroni, Chiara; Gasperi, G.; Giusti, C.; Marchetti, M.
abstract
Gli affioramenti occupano la piccola valle del Rio del Petrolio
1999
- 64 - La Formazione di Contignaco, La Formazione di Pantano e la Formazione del Termina presso la stretta del Pescale: rapporti stratigrafici, orizzonte cineritico. Iterrazzi del Pescale.
[Capitolo/Saggio]
Conti, Stefano; Giusti, C.; Marchetti, M.; Panini, Filippo; Pellegrini, S.; Rossi, A.
abstract
L'alveo del Fiume Secchia
1999
- 77 - La chemioerma fossile nelle marne della Formazione del Termina. Il pinnacolo calcareo del Sasso delle Streghe
[Capitolo/Saggio]
Conti, Stefano
abstract
L'affioramento, dell'estemsione di
1999
- 78 - La chemioerma fossile nelle marne della Formazione del Termina a Poggio Andeotti
[Capitolo/Saggio]
Conti, Stefano
abstract
L'affioramento,
1999
- 80 - Gli affioramenti della Formazione del Termina presso Montebaranzone
[Capitolo/Saggio]
Conti, Stefano
abstract
Nei calanchi ubicati all'altezza
1999
- 82 - Le brecce poligeniche risedimentate della Formazione del Termina, al Castello di Montardone
[Capitolo/Saggio]
Conti, Stefano
abstract
In prossimità dei resti del castello di Montardone
1999
- 83- Gli affioramenti nel T. Fossa della Formazione di Pantano e le intercalazioni arenaceo pelitiche della Formazione del Termina
[Capitolo/Saggio]
Conti, Stefano
abstract
Lungo la strada che conduce da Rocca S. Maria
1999
- 84 - Gli strati risedimentati fossiliferi entro le Arenarie di Vallorsara (M. Modino), presso Ca' del Vento
[Capitolo/Saggio]
Conti, Stefano
abstract
L'affioramento situato a nord ovest di Castellara
1999
- Brecciated structures and fluid-flow conduits as indicators of methane-derived carbonates (northern Apennines, Italy).
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela
abstract
The recognition of fossil carbonates as products of microbial chemosynthesis associated with fluid and hydrocarbon venting at the sea floor (chemoherms) has been linked to two main indicators (Sakai et al., 1992; Terzi et al., 1994; Kelly et al., 1995; Corselli and Basso 1996): the marked depletion in carbon isotope composition of the authigenic carbonates and the low diversity/high abundance of benthic chemosymbiotic communities (densely packed mussels and clam bivalves, gastropods, tube worms). Nevertheless, not all methane-derived carbonates enclose remains of large chemosymbiotic taxa, making the recognition of unfossiliferous methanogenetic limestones in the field problematic. Recently, new studies (Cavagna et al., 1998; Conti and Fontana, 1998) have shown that other diagnostic criteria, such as geometric, sedimentologic and compositional characteristics, can be useful in the identification of fossil seep environments and associated carbonates. In particular, brecciated structures and fluid-flow conduits, which frequently occur in methane-related carbonates, are of outstanding importance in connecting fluid ventings, slumping of pelitic sediments and tectonics. Indeed, these structures could permit the reinterpretation of many chaotic deposits as due to diapiric processes.Carbonate deposits bearing fossil chemosynthetic assemblages are concentrated in middle-late Miocene of the northern Apennines and are found in various domains and basin types (Vai and Ricci Lucchi, 1994; Conti and Fontana, 1998): from internal tectonic zones (Epiligurian basins) to external ones (foredeep). Enclosing sediments are mudstones, muddy sandstones and marlstones; commonly they have low permeability but are severely fractured. They are present in syntectonic deposits, related to compression and thrusting of the Apennine chain. In the foredeep, chemoherms are moderately reworked and concentrated in slumped pelitic horizons, suggesting a close relationship between sediment instability and hydrocarbon-fluid venting. Field and petrographic examination of methane-derived carbonates permits different lithofacies to be recognized: light blue to dark grey micritic limestones, biomicritic marly limestones, light brown to grey calcareous marls, fine to coarse calcarenites, calcarenitic limestones and various types of calcareous breccias and fractured limestones.
1999
- Emanazioni di fluidi ed instabilità sedimentaria nell’avanfossa appenninica: l’esempio della F. Marnoso-arenacea
[Relazione in Atti di Convegno]
Conti, Stefano
abstract
Fin dalla seconda metà del secolo scorso sono stati riconosciuti nei terreni miocenici dell’Appennino settentrionale affioramenti di calcari e calcari marnosi contenenti una ricca macrofauna a bivalvi, noti col nome di “Calcari a Lucina”. Recentemente, grazie ad analisi geochimiche e paleoecologiche, tali calcari sono stati interpretati come chemioerme legate all’emanazione di fluidi freddi (cold seeps), dove la precipitazione autigena del carbonato è indotta dall’attività di batteri chemiosintetici (solforiduttori e metanossidanti), viventi in simbiosi con i bivalvi. Nell’Appennino settentrionale questi carbonati affiorano in differenti contesti geotettonici, dai bacini satellite (successione epiligure) all’avanfossa (peliti di scarpata e depositi torbiditici). Di particolare interesse sono i calcari metanogenici contenuti negli orizzonti pelitici della F. Marnoso-arenacea del Miocene medio, affioranti nell’Appennino tosco-romagnolo. Questi orizzonti sono composti da torbiditi prevalentemente siltoso-marnose in strati sottili, estesi lateralmente svariati chilometri e spiccanti rispetto al paesaggio circostante, tanto da essere assunti come marker litostratigrafici. Al loro interno contengono gigantesche frane sottomarine sia intraformazionali (megaslumps) che talvolta extraformazionali (di pertinenza ligure, subligure o toscana). Due di questi orizzonti sono stati rilevati in dettaglio (alla scala 1:10.000): uno di età langhiana (orizzonte di Podere Filetta-Castagno d’Andrea) viene segnalato per la prima volta, mentre l’altro (orizzonte di Fosso Rimaggio-Mondera) di età serravalliana, era in parte già conosciuto.Lo studio di dettaglio ha permesso di distinguere le torbiditi pelitiche in quattro litofacies: (a) siltiti e siltiti arenacee in strati sottili, (b) marne siltose e marne arenacee con rare e sottili intercalazioni arenacee, (c) areniti medio-grossolane in strati da sottili a medi alternate a peliti marnose, (d) areniti fini in strati sottili alternate a brecce argillose. Le prime due sono nettamente prevalenti sulle seconde. La successione verticale degli orizzonti si presenta così costituita: i primi 15-20 m sono sempre privi di chemioerme e possono non essere coinvolti in frane sottomarine; seguono 40-80 m caratterizzati da intercalazioni lentiformi di calcari metanogenici; la restante porzione è priva di carbonati ma è generalmente coinvolta, assieme alla precedente, in spettacolari megaslumps e può comprendere frane extraformazionali. I depositi carbonatici non solo sono concentrati alla base degli orizzonti pelitici, ma anche in gruppi separati lateralmente fra loro per circa 1-2 km. Essi possono essere distinti in due tipologie di affioramento: la prima caratterizzata da 3-4 lenti di grandi dimensioni (da decametriche ad ettometriche) e spessori (5-25 m), generalmente in posizione primaria (autoctona); la seconda è invece composta da lenti di dimensioni minori (da decimetriche a metriche) e di spessori esigui (30-300 cm), ripetute innumerevoli volte sia lateralmente che verticalmente, a composizione più marnosa della precedente, con passaggi più graduali al sedimento pelitico circostante e quasi sempre in posizione rimaneggiata (coinvolte nei megaslumps).Tutti i carbonati sono spesso ricchi di macrofossili disposti a nidi, con lucinidi nettamente predominanti rispetto ai mitilidi. Le chemioerme sono sempre caratterizzate da un intenso odore di zolfo e/o di idrogeno solforato, da litologie composte da calcari micritici, calcari marnosi e subordinate calcareniti, calcilutiti. Strutture caratteristiche sono i doughnuts e la brecciatura. I primi sono condotti circolari riempiti da calcite spatica, frammenti di gusci, piccoli inclusi pelitici e arenacei provenienti dal sedimento incassante, il tutto immerso in una matrice micritica. La brecciatura può essere composta sia da brecce calcaree monogeniche, sia da brecce poligeniche (composte da frammenti calcarei delle
1999
- Gli affioramenti della Formazione del Termina presso il Poggio di Montebaranzone
[Capitolo/Saggio]
Conti, Stefano
abstract
Lungo la strada che conduce ..
1999
- Gli affioramenti fossiliferi della Formazione del Termina, presso il Rio delle Bagole
[Capitolo/Saggio]
Conti, Stefano
abstract
lungo la strada provinciale ..
1999
- I Beni Geologici della Provincia di Modena
[Monografia/Trattato scientifico]
Bertacchini, Milena; Bettelli, Giuseppe; Bonazzi, U.; Capedri, S.; Capitani, M.; Castaldini, Doriano; Conti, Stefano; Corradini, D.; Fioroni, Chiara; Fontana, Daniela; Fregni, P.; Gasperi, G.; Giusti, C.; Lugli, Stefano; Marchetti, Mauro; Panini, Filippo; Panizza, M.; Pellegrini, M.; Piacente, S.; Rossi, A.; Soldati, Mauro; Tosatti, G.
abstract
Sono presentati, sotto forma di schede, i beni geologici (o geositi) censiti nella Provincia di Modena. Le schede sono state aggregate in cinque paragrafi: Beni geomorfologici, Fluidi sotterranei, Esposizioni di valore stratigrafico e strutture sedimentarie, Esposizioni di strutture tettoniche, Ofioliti. Si è cercato di privilegiare da un lato una guida scientifica alla geologia della Provincia e dall'altro di segnalare un alto numero di siti allo scopo di salvaguardare il più possibile l'ambiente modenese, caratterizzato, in molte sue parti, da un'intensa e continua antropizzazione.
1999
- Miocene chemoherms of the northern Apennines, Italy
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela
abstract
In the Miocene of the northern Apennines, methane-derived limestones from various geologic settings represent important examples of fossil chemoherms and provide a basis for more accurate interpretations of seepage systems. The systematic study of fossil chemoherms has allowed the definition of new field and compositional criteria for the recognition of these deposits, which were previously based almost exclusively on negative carbon isotope composition and peculiar chemosynthetic communities; this has constrained the relations between seepage and sedimentary and tectonic instability processes. We suggest that the peculiar brecciated structures associated with fossil chemoherms are related to diapirism or overpressured pelitic sediments due to fluid venting. Fluidization of sediments increases the instability of mudstones in which chemoherms are contained, thus favoring gravity slumping processes and the reworking of many chemoherms.
1999
- Problematiche relative all’analisi mesostrutturale di conglomerati neogenici provenienti da depositi dell’avanfossa, epiliguri e neoautoctoni (Appennino marchigiano-romagnolo).
[Articolo su rivista]
Capitani, M.; Conti, Stefano
abstract
A mesostructural analysis has been carried out on pebble-cobble surfaces belonging to various formations (Upper Tortonian-Early Pliocene) cropping out between the Savio, Marecchia and Foglia rivers (northern Apennines). The conglomerates occur at different structural levels: 1) in units belonging to the Umbro-Marche-Romagna Sequence, both underlying and overlying the allochthonous deposits of the Val marecchia thrust sheet, 2) in units belonging to the epi-Ligurian Sequence. The analysis of pitted and striated pebbles and cobbles, mesoscopic faults and fractures show evidences of three episodes of tectonic deformations. The first one, characterized by a NE-SW trending subhorizontal extension, is of Messinian age. This extensional episode could be related to the slowing in the outward migration rate of the Apennine deformational front during the late Tortonian-Messinian. The other episodes of deformations, of early Pliocene-Pleistocene age, are characterized by a main subhorizontal shortening direction trending NE-SW, the older one, and NW-SE, the younger one. The episode characterized by the NE-SW shortening direction is probably related to the main tectonic stress field acting in the Northern Apennines during the Neogene. The NW-SE shortening direction is more difficult to explain. It was detected in other sectors of the chain, where was linked to the tectonic activity of local trasverse structural elements. Indeed in the studied area there are transverse (transfer faults) structures that could be linked to this shortening direction. Another hypothesis is that the NW-SE shortening direction can be related to the sinistral transpressive stress field acting in the Northern Apennines during the Pleistocene.
1998
- Elementi di Scienze della Terra
[Traduzione di Libro]
Conti, Stefano
abstract
libro per la scuola media superiore
1998
- Recognition of primary and secondary Miocene lucinid deposits in the Apennine chain.
[Articolo su rivista]
Conti, Stefano; Fontana, Daniela
abstract
The examination of about eighty exposures of lucinid deposits of the Apennine chain based on new field analyses and previous data, and the compositional study of one hundred samples representative of the different geological settings in which lucinid assemblages are found, enable us to distinguish four types of deposits. Type 1 and type 2 are primary (autochthonous) deposits whereas type 3 and type 4 are secondary (allochthonous) deposits. Type 1 deposits consist of marly-calcareous and calcarenitic lenses or columnar bodies, jammed with articulated lucinid-like shells, usually belonging to oligotypic communities and grading into the surrounding pelitic sediments. Most of the samples are made of homogeneous micrites, biomiocrites and fossiliferous micrites, containing variable amounts of biogenic particles, chiefly planktonic foraminifera. Type 2 deposits are made up of lucinid shells, either isolated or associated with a more diverse fauna, in mudstones, marls, arenitic and calcareous marls. Type 3 deposits are constituted of carbonate olistoliths enclosed as blocks within chaotic horizons in turbiditic and hemipelagic formations of the Miocene foredeep. Type 4 deposits are represented by coquina debris, isolated articulated or disarticulated shells in resedimented arenites, calcarenites, carbonate breccias with biogenic debris. Samples of secondary deposits show a noticeable variety of lithologies and textures and are very heterogeneous even at the microscopic scale. The most common lithotypes include fine to medium grained arenites characterized by a loosely detrital fabric and by a pervasive micrite cement. Fossiliferous micrites and biomicrites with brecciated textures are common. The detrital framework show striking similarities to the composition of the host turbidites. Carbonate intraclasts and clasts deriving from lithotypes of the ligurian domain are present. Most of the type 1 and 3 deposits are strongly 13C depleted and are interpreted as chemosynthetic communities (chemoherms), with authigenic carbonate deposition related to methane-rich fluid venting. Type 1 deposits occur only in thick pelitic sediments belonging to the satellite (Termina Formation of the epiligurian sequence) and to the foredeep basins (Vicchio and Letto Marls). Type 2 deposits are instead related to normal marine conditions, whereas the type 4 could have their source from all the other types of deposits. Secondary lucinid deposits occur in a wide range of different tectonic setting, from backland to foreland, with a concentration in the middle Miocene foredeep. The secondary lucinid deposits of the foredeep turbidites evidenced several different grades of allochthony and multiple provenances. Lucinid deposits in the Marnoso-arenacea turbidites show evidence of a moderate reworking, probably from the enclosed pelitic horizons or from adjacent slope pelites. The source of the oldest chemoherms seems to be represented by the Vicchio Marls, whereas isolated shells and coquina debris in resedimented beds of the minor basins and Cervarola foredeep probably originate from satellite basins or from methane-derived biological communities located in fine-grained horizons no longer preserved. The peculiar brecciated structures observed in many lucinid chemoherms are probably the result of a number of superimposed processes, involving fluidization of sediments and reworking for gravity mass transport. Mud diapirism and/or injection, related to overpressuring of sediments due to methanogenic fluid venting, could account for the formation of the brecciated structures resembling those related to gravity flow processes. Fluidization of sediments may also represent an important mechanism able to increase the instability of pelitic marly sediments, thus favouring gravity slumping processes.
1997
- Analisi mesostrutturale di conglomerati neogenici provenienti da depositi dell’avanfossa, epiliguri e neoautoctoni (Appennino marchigiano-romagnolo): possibili implicazioni con le fasi deformative messiniano-plioceniche inferiori.
[Relazione in Atti di Convegno]
Capitan, i M; Conti, Stefano
abstract
Negli ultimi anni sono stati condotti vari studi finalizzati al miglioramento delle conoscenze relative all’assetto strutturale dell’Appennino Settentrionale: numerosi sono i lavori di sintesi alla scala macroscopica proponenti differenti modelli geodinamici, mentre quelli alla scala meso-microscopica sono generalmente riferiti ad aree geologicamente ristrette. Fra questi ultimi, diversi sono quelli che prendono in esame le tecniche di rilevamento e di analisi di strutture riconoscibili su ciottoli di conglomerati (improntature da presso-dissoluzione, strie, sliccoliti, stiloliti, mesofaglie). Utilizzando queste stesse tecniche si è deciso di studiare i depositi conglomeratici affioranti nelle valli dei fiumi Savio, Marecchia e Foglia, al confine tra le regioni Marche, Emilia Romagna, Toscana e Repubblica di San Marino, essenzialmente per due motivi. Il primo perchè a tutt’oggi sono stati pubblicati pochi lavori strutturali di dettaglio di quest’area, che peraltro prendono quasi esclusivamente in esame l’analisi cinematica e dinamica di sistemi di fratture (faglie e diaclasi). Il secondo perché in questo settore dell’Appennino Settentrionale affiorano, con rapporti di sovrapposizione tettonica, le principali unità che costituiscono la catena (unità umbro-marchigiano-romagnole, toscane esterne, subliguri, liguri ed epiliguri), caratterizzate, in alcuni casi, da depositi conglomeratici. Questi, distribuiti dal Tortoniano sup. fino al Pliocene inf., sono presenti perciò in differenti contesti strutturali (avanfossa, bacini satelliti epiliguri della coltre alloctona della Val Marecchia, bacini minori neoautoctoni di piggyback) e si rivelano quindi di particolare importanza, in quanto potenziali indicatori del campo degli stress agente durante le fasi tettoniche messiniano-plioceniche. Sono state misurate circa 1500 impronte da presso-dissoluzione e alcune decine di superficie striate in un totale di 21 affioramenti. Questi sono ubicati nelle Formazioni di Acquaviva (Tortoniano sup.-Messiniano inf.), Casa M. Sabatino (Messiniano sup.) appartenenti alla successione epiligure della Val Marecchia e in quelle a Colombacci (Messiniano sup., ma in 2 corpi conglomeratici di età differenti, uno alla base e l'altro al tetto della formazione) e di Perticara (Pliocene inf., Zona a G. puncticulata), appartenenti alla successione umbro-marchigiano-romagnola. Queste due ultime formazioni sono poi da distinguere l’una dall’altra in quanto occupano posizioni strutturalmente differenti: la prima è antecedente al sovrascorrimento della coltre della Val Marecchia, la seconda (neoautoctono) si è deposta sia durante che immediatamente dopo tale evento tettonico (databile alla parte alta del Pliocene inf.). I risultati ottenuti, nonostante una certa dispersione delle misure (legata probabilmente in parte a problemi di campionamento dei dati ed in parte alle modalità deformative, che forse non riflettono sempre l’ipotesi di omogeneità), permettono di riconoscere diversi episodi deformativi di natura sia compressiva che distensiva. Il più antico è l'episodio distensivo (a direzione antiappenninica e di età Messiniana), in quanto assente nei depositi pliocenici. Questo è probabilmente da mettere in relazione al rallentamento, susseguente alla fase tettonica tortoniana, della migrazione del fronte deformativo appenninico (perdurante per quasi tutto il Messiniano), che porta alla chiusura di una avanfossa con caratteristiche fliscioidi. Gli episodi compressivi sono stati registrati in tutte le formazioni conglomeratiche studiate, dove sono riconoscibili almeno 2 eventi deformativi caratterizzati da direzioni di raccorciamento suborizzontali a direzione antiappenninca, la più evidente, e appenninica, statisticamente meno frequente. Inoltre, alcuni affioramenti delle formazioni messiniane presentano (al posto della direzione di raccorciamento appenninica) raccorciamenti orientati E-O, ESE-OSO. Questi ultimi dat
1997
- Analysis of earthquake-induced surface effects in the Modena province: first approach in the area of Montese (Northern Apennines, Italy)
[Abstract in Atti di Convegno]
Panizza, M.; Bernagozzi, G.; Bertacchini, Milena; Berti, M.; Bettelli, Giuseppe; Bollettinari, G.; Castaldini, Doriano; Conti, Stefano; Cuzzani, M. G.; Elmi, C.; Gasperi, G.; Genevois, R.; Ghirotti, M.; Gibertini, M.; Panini, Filippo; Pellegrini, M.; Santangelo, R.; Simoni, A.; Tosatti, G.; Zucchi, M.
abstract
This paper describes the “I Lazzari di Maserno” landslide (Northern Apennines) which resumed its activity on 1st January 1996, following a 3.3 magnitude seismic shock that struck a vast sector of the north-western Apennines. The area is geologically characterised by clastic rock types belonging to Ligurian and epi-Ligurian Units. The landslide is ascribable to a slow, intermittent movement taking place along rotational and rotational-translational surfaces of rupture, accompanied by earth flows in the most superficial portion. During 1996 and in the following years several subsurface investigations and instrumental surveys were carried out; they allowed detailed knowledge of the geometrical, mechanical and kinematic characteristics of the landslide body to be obtained. In particular, the levels of soil subject to load decrease and the depth of the slip surfaces were identified and the mechanisms of rupture were reconstructed.
1997
- COLD-E-VENT. Hydrocarbon Seepage and Chemosynthesis in Tethyan Relic Basins: Products, Processes and Causes
[Relazione in Atti di Convegno]
Aharon, P; Conti, Stefano; Taviani, M; Vai, Gb
abstract
dedicated to Rodolfo Gelmini
1997
- Introduction to the field trip.
[Relazione in Atti di Convegno]
Conti, Stefano; Taviani, M; Vai, Gb
abstract
COLD-E-VENTGuide bookletS. CONTI, M. TAVIANI, G.B. VAIThe trips run entirely through the external part of the Northern Apennines. This part of the Northern Apennines is a NW to SE trending, NE verging thrust belt, mainly composed of Neogene to quaternary silicoclastic rocks, and having been involved in discrete, Serravallian to Middle Pleistocene deformational phases. A simplified account on Northern Apennines stratigraphy and tectonics including structural map and cross sections is attached (VAI, 1989).This booklet contains the basic informations concerning stops and transfers, and is supplemented by the following list of documents and papers.- A3 Location map and road plan of the Romagna Apennines trip (scale 1:200.000)- A3 Location map and road plan of the Modena Apennines Trip (scale 1:200.000)- A3 Northern Apennines simplified structural map and conceptual sections.- A3 Stratigraphic correlation chart of the Northern Apennines, plus A4 detail of the Romagna- Adriatic Apennines (VAI, 1992)- double A3 Geological map of the Modenese Apennine and surrounding areas (colour) (UNIVERSITY OF MODENA, GEOLOGICAL INSTITUTE, 1989)- A3 Geological map of the Romagna Apennines (colour) (LANDUZZI, 1990)- A3 Geological map of the Romagna Apennines (CAPOZZI et al., 1992)- A3 Balanced cross sections of the Romagna Apennines (LANDUZZI & CAPOZZI, 1992)G.B. VAI (1989) - A field trip guide to the Romagna Apennine geology. Boll. Soc. Pal. It., 28, 343-368.S. CONTI (1993) - Carta Geologica dell’alta Val Marecchia (Appennino tosco-marchigiano). S.EL.CA., Firenze.C. TERZI (1993) - The “Calcari a Lucina” (Lucina Limestones) of the Tuscan-Romagna Apennines as indicators of Miocene cold seep activity (northern Apennines, Italy). Giorn. Geol.,55(2), 71-81.BERTI M., CUZZANI M.G., LANDUZZI A., TAVIANI M., AHARON P. & VAI G.B. (1994) - Hydrocarbo-derived imprints in olistostromes of the Early Serravallian Marnoso-arenacea Formation, Romagna Apennines (Northern Italy). Geo-Marine Letters 14, 192-200.S. CONTI & R. GELMINI (1994) - Miocene-Pliocene tectonic phases and migration of foredeep-thrust belt system in Northern Apennines. Mem. Soc. Geol. It., 48(1)(1992), 261-274, figs.1-9, 1 pl., Roma.S. CONTI, R. GELMINI & L. PONZANA (1994) - Osservazioni preliminari sui calcari a Lucine dell'Appennino Settentrionale. Atti Soc. Nat. e Mat. di Modena, 124 (1993), 35-56, figg. 1-6, Modena.F. RICCI LUCCHI & G.B. VAI (1994) - A stratigraphic and tectonofacies frameworkof the "calcari a Lucina" in the Apennine Chain, Italy. Geo-Marine Letters, 14, 210-218.M. TAVIANI (1994) - The calcari a Lucina macrofauna reconsidered:Deep-sea faunal oases from Miocene-age cold vents in the Romagna Apennine, Italy. Geo-Marine Letters, 14, 185-191.C. TERZI, P. AHARON, F. RICCI LUCCHI & G.B. VAI (1994) - Petrography and stable isotope aspects of cold-vent activity imprinted on Miocene-age "calcari a Lucina" from Tuscan and Romagna Apennines, Italy. Geo-Marine Letters, 14, 177-184.S. CONTI, R. GELMINI, G. PONZANA & G.P. SIGHINOLFI (1996) - "Il Calcare a Lucina pomum”della Successione Epiligure dell’Appennino modenese: stratigrafia, sedimentologia e dati geochimici. Accad. Naz. Sci. Lett. Arti di Modena, Collana di Studi 15(1996) - Miscellanea Geologica, 105-139.S. CONTI (1997) - Synthetic review and geological framework of the main lucinid deposits (Italy). (this booklet)FIELD TRIP IN THE ROMAGNA APENNINESJune 24-25, 1997Leaders: A. Landuzzi, F. Ricci Lucchi, M. Taviani, G.B. Vai, P. Aharon, S. Conti.Transfer from Capaccio Centre near S. Sofia to le Caselle near M. Marino, either anticlockwise through Ridracoli Lake (drinking water reservoir of about 35 millions cubic meters) or clockwise through Poggio alla Lastra, depending on the state of unpaved road. Overview of the Alta Romagna Marnoso-arenacea (late Langhian-Serravallian) (see cross section Romagna in the attached A3 balanced cross sections sheet).STOP 1LE CASELLE OLISTOSTROME
1997
- Lucinid deposits from different geological settings of the northern Apennines.
[Relazione in Atti di Convegno]
Conti, Stefano; Fontana, Daniela
abstract
Sixty exposures of lucinid deposits ("calcari a Lucina" of the literature) in different depositional and tectonic settings of the northern Apeninnes, from backland (satellite and minor basins) to foredeep (turbidites and closure deposits) and foreland (Sicily), were studied and, in many cases, reinterpreted in the field. Field and compositional data show that lucinid deposits include not only peculiar carbonate blocks, but a variety of lithologies and fossil assemblages: micritic limestones, marly limestones, mudstones, marls and arenitic marls, fine to coarse-grained arenites, fine to coarse-grained calcarenites, carbonate monomictic and polymictic breccias and microconglomerates. The fossil content is not only adscribable to the genus Lucina, but more generally to lucinids or other bivalves. Lithological and compositional characters are mainly controlled by the depositional and tectonic setting. Lucinid deposits from satellite basins and foredeep slope sediments show evidences of primary deposition while those included in foredeep turbidite deposits are clearly reworked. In some cases only isolated shells are reworked. Primary lucinid deposits occur as: - type 1) marly-calcareous and calcarenitic lenses or column-like bodies, crowded with articulated specimens usually representing the dominant fauna of an oligotypic community; these lenses are often clustered but not related to a precise stratigraphic level and they gradually pass to the host sediments (marly mudstones); - type 2) isolated specimens or associated with a dense high diversity fauna in mudstones, marls, arenitic and calcareous marls. Secondary lucinid deposits occur as: - type 3) carbonate olistoliths crowded with articulated or disarticulated specimens associated with an oligotypic fauna; they are usually enclosed within chaotic horizons made up of intraformational slumps, ligurian-subligurian olistostromes, ligurian-epiligurian olistoliths, resedimented arenitic beds and polymictic breccias, intercalated in turbiditic formations; - type 4) coquina debris, isolated articulated or disarticulated shells, (in few cases associated with abundant fauna from shelf areas) in resedimented arenites, calcarenites, carbonate breccias with biogenic debris (debrites). Most of the type-1 and type-3 deposits are strongly 13C depleted, and are interpreted as chemosynthetic communities (pseudobioherms) with authigenic carbonate deposition related to methane-rich fluid vents.Petrographic data show that the composition of the siliciclastic fraction present in lucinid deposits is consistent with the composition of the host deposits. Lucinid deposits included in the foredeep turbidites of the Marnoso-arenacea and Cervarola Formations display a wide variety of textures and lithologies. Most of the samples are characterized by a sort of "chaotic" texture with an abundant terrigenous fraction associated with micritic intraclasts and planctonic foraminifera. The interstitial fraction is made of micrite, but microspatic to spatitic calcite cements and patchy poikilotopic calcite are also present. The composition of the terrigenous fraction shows a great similarity with the composition of the including turbidites, thus indicating only an intrabasinal reworking of lucinid deposits. In primary, non reworked lucinid deposits of the epiligurian (Termina Formation) and slope sediments (Vicchio and Letto Marls) the terrigenous fraction is absent or very scarse and fine-grained. Samples show more homogeneous textures and lithologies, mainly represented by micritic to biomicritic limestones; planctonic foraminifera are abundant. Detrital carbonate clasts of ligurian affinity are sometimes present in epiligurian lucinid outcrops.According to this study, primary pseudobioherms occur only in epiligurian and foredeep closure pelitic sediments, rich in organic matter. Lucinid deposits in the Marnoso-arenacea and Cervarola foredeep turbidites show evidence of a moderate reworking probably from adjacen
1997
- References of the italian lucinid deposits.
[Relazione in Atti di Convegno]
Conti, Stefano
abstract
REFERENCES OF THE ITALIAN LUCINID DEPOSITSS. CONTI##Dipartimento di Scienze della Terra, Università di Modena, Largo S. Eufemia 19, 41100 Modena (sconti@unimo.it)AHARON P. & SEN GUPTA B.K. (1994) - Bathymetric reconstructions of the Miocene age "calcari a Lucina" (Northern Apennines, Italy) from oxigen isotopes and benthic foraminifera. Geo-Marine Letters, 14, 219-230.AMADESI E. (1967) - Considerazioni generali sulla stratigrafia e l'evoluzione geologica dell'Appennino Settentrionale fra l'Abetone e Castiglione dei Pepoli. Giorn. Geol., 34(2) (1966), 1-34.ANELLI M. (1913) - I terreni miocenici tra il Parma ed il Baganza (Prov. di Parma). Boll. Soc. Geol. It., 32, 195-272.ANELLI M. (1915) - Cenni geologici sui dintorni di Traversetolo e di Lesignano Bagni (Prov. di Parma). Boll. Soc. Geol. It., 34, 79-136. ANELLI M. (1927) - Cenni tettonici sulla regione collinosa interposta tra lo Stirone ed il Taro (Prov. di Parma). Boll. R. Uff. Geol. d'It., 52(7), 1-56.ANELLI M. (1935) - Cenni geologici sulla regione collinosa fra il F. Secchia e il T. Tiepido (Prov. di Modena). Agip, Roma, 1-75 (1933).ANGELI A. & VEGGIANI A. (1964) - Note su un rilevamento geologico tra Sarsina e Mercato Saraceno. Quad. Studi Rom., 1, 5-14.AUDENINO L. (1902) - Terreni terziari e quaternari dei dintorni di Chieri. Boll. Soc. Geol. It., 21, 78-92.BALDACCI L. (1886) - Descrizione geologica dell'isola di Sicilia. Mem. descr. carta Geol. d'It., 1, 1-403.BELLARDI L. (1872-90) - I molluschi dei terreni terziari del Piemonte e della Liguria. Mem. R. Acc. Sc.Torino, vv. 1-6, 27, 29, 34, 37, 38, 40.BELLINI R. (1905) - Le varie facies del Miocene medio nelle colline di Torino. Boll. Soc. Geol. It., 24, 607-653.BELLINZONA G., BONI A., BRAGA G., & MARCHETTI G. (1971) - Note illustrative della Carta Geologica alla scala 1:100.000. Foglio 71 Voghera. Serv. Geol. d'It., 1-121.BENEO E. con appendice paleontologica di PARONA C.F (1936) - La formazione miocenica e la tettonica della valle Roveto (alta Valle del Liri). Boll. R. Uff. Geol. d'It., 41, 1-15.BERTI M., CUZZANI M.G., LANDUZZI A., TAVIANI M., AHARON P. & VAI G.B. (1994) - Hydrocarbon-derived imprints in olistostromes of the Early Serravallian Marnoso-arenacea Formation, Romagna Apennines (Northern Italy). Geo-Marine Letters, 14, 192-200.BIANCONI G. (1867) - Sur les Apennins de la Porretta. Boll. Soc. Geol. Fr., 24, 482-484.BIANCONI G. (1877) - Considerazioni intorno alla Formazione miocenica dell'Appennino. Mem. Ac. Sc. Ist. Bol., ser. 3, 8(3), 175-192.BOMBICCI L. (1882) - Le formazioni geologiche del territorio bolognese. In: L'Appennino bolognese. CAI (1881), 1-73.BONARELLI G. (1899) - Alcune formazioni terziarie fossilifere dell'Umbria. Boll. Soc. Geol. It., 18, 484-490.BONARELLI G. (1901) - Miscellanea di note geologiche e paleontologiche per l'anno 1900. Boll. Soc. Geol. It., 20, 215-232.BONARELLI G. (1902) - Miscellanea di note geologiche e paleontologiche per l'anno 1901. Boll. Soc. Geol. It., 21, 544-570.BONARELLI G. (1903) - Miscellanea di note geologiche e paleontologiche per l'anno 1902. Boll. Soc. Geol. It., 22, 429-445.BONI A. (1967) - Note illustrative della Carta Geologica alla scala 1:100.000. Foglio 59 Pavia. Serv. Geol. d'It., 1-68.BONI A., BRAGA G. & MARCHETTI G. (1963) - Segnalazione di calcari marnosi a Lucine a tetto del "Macigno" di Bobbio (Appennino Settentrionale). Boll. Soc. Geol. It., 82(3), 203-233.BONSIGNORE G., BORTOLAMI GC., ELTER G., MONTRASIO A., PETRUCCI F., RAGNI U., SACCHI R., STURANI C. & ZANELLA E. (1969) - Note illustrative della Carta Geologica alla scala 1:100.000. Fogli 56 e 57 Torino-Vercelli. Serv. Geol. d'It., 1-96.BRUNI P. (1973) - Considerazioni tettoniche e paleogeografiche sulla serie dell'Appennino bolognese tra le valli dell'Idice e del Santerno. Mem. Soc. Geol. It., 12(2), 157-185.CAFICI I. (1880) - Sulla determinazione cronologica del calcare a selce piromaca e del calcare compatto e marnoso (forte e franco) ad
1997
- Synthetic Review and geological framework of the main lucinid deposits (Italy).
[Relazione in Atti di Convegno]
Conti, Stefano
abstract
SYNTHETIC REVIEW AND GEOLOGICAL FRAMEWORK OF THE MAIN LUCINID DEPOSITS (ITALY)S. CONTI##Dipartimento di Scienze della Terra, Università di Modena, Largo S. Eufemia 19, 41100 Modena (sconti@unimo.it)INTRODUCTIONThe main italian lucinid deposits, as reported from the geological literature, have been studied and, in many cases, reinterpreted in the field. The results are summarized in the following list. The outcrop localities have been differentiated on the base of various elements: 1) tectonofacies, 2) geographic position, 3) stratigraphy, 4) sedimentology, 5) faunal assemblage, 6) evidences of reworking.Key: In the following format type are indicated the outcrops, sometimes as reported from the literature, found by the author in the field. In many cases the same locality was reported under different names.The term "Lithology" refers to lucinid deposits, whereas "stratigraphy" refers to the sediments embedding lucinid deposits or isolated lucinid valves. "Bibliography" does not include all the papers reported in the “References of the italian lucinid deposits”.PIEDMONT BASINS(TORINO, MONFERRATO, LANGHE HILLS AND PAVIA FOOTHILLS) MARMORITO AND “LUCINA LIMESTONES”Location- Marmorito di Passorano (Cascina Galè, Cascina Fabiasco).Lithology- cream to light brown marly limestones blocks packed with lucinid remains (both articulated and disarticulated shells).Fossil assemblage- planktonic and subordinate benthic foraminifers, echinoid spines, serpulid tubes, gastropods, bivalvs (Anodontia dicomani), solitary and colonial corals, ostracods, bryozoans, fish remains, scaphopods.Stratigraphy- Marmorito and “Lucina Limestones” (late Tortonian?).Reference map- CTR 157090 Cocconato.Geological notes- the original geological framework is lost for poor exposure, lucinids probably enclosed in mudstones; methane-derived autigenic carbonates. POSITION: secondary. ENVIRONMENT: ?Bibliography- CLARI et al. (1988), CLARI et al. (1994), CLARI & MARTIRE (1995).S. AGATA FOSSIL MARLS 1)Portalbera (Pavia oltrepo’). Lithology- marly-calcareous blocks.Fossil assemblage- Lucina globulosa.Stratigraphy- S. Cipriano Po Formation (late Tortonian-early Messinian ?), correlable to the epiligurian deposits?.Reference map- Geological Sheet 59 Pavia.Geological notes- geological framework not known because of the poor exposure. POSITION: Primary? ENVIRONMENT: ?Bibliography- TARAMELLI (1882), SACCO (1891, 1929), PATRINI (1916), BONI (1967).2) Serravalle Scrivia = Carezzano near Fontana (Pavia area), 3) Monticello d'Alba (Roero), 4) Villa Majolo NW of Chieri (Monferrato hill). Fossil assemblage- hundred of species (see bibliography).Stratigraphy- S. Agata Fossil Marls (Tortonian).Reference map- Geological Sheet 70 Alessandria and Geological Sheet 56 Torino.Geological notes- Lucinids as not abundant specimens associated with a numerous high diversity fauna.POSITION: Primary. ENVIRONMENT: outer shelfBibliography- MAYER (1877), SACCO (1899), AUDENINO (1902), NELLI (1903), CAVALLO & REPETTO (1992).SERRAVALLE SANDSTONESRivanazzano e Cappella Montà (Moma), Nazzano hills between S. Antonino and Madonna del Monte (Pavia foothills). Lithology- marly calcareous bodies packed with big lucinids.Fossil assemblage- Lucina doderleini, Amussium denudatum.Stratigraphy- at the top of the Serravalle Sandstones (late Serravallian).Reference map- Geological Sheet 71 Voghera.Geological notes- Lucinid bodies enclosed in mudstones. The faunal association is characterised by low diversity and abundant fauna.POSITION: primary. ENVIRONMENT: inner, outer shelf. Bibliography- TARAMELLI (1882), SACCO (1891,1929), BELLINZONA et al. (1971), DESIO (1973).BALDISSERO FORMATIONBetween Pino Torinese and Pecetto north of Chieri, Superga, Baldissero, Sciolze, Cornaro, Albugnano, Bersano, S. Pietro delle Langhe, La-Moja di Montaldo Torinese, S. Defendente (Tagliolo), S. Mauro Torinese.Lithology- arenaceous calcarenites with red calcareous algae and big isolat
1996
- "Il Calcare a Lucina pomum”della Successione Epiligure dell’Appennino modenese: stratigrafia, sedimentologia e dati geochimici.
[Articolo su rivista]
Conti, Stefano; Gelmini, R.; Ponzana, G.; Sighinolfi, G. P.
abstract
In this paper "Lucina limestones", outcropping in the Modena area, where for the first time were found, are investigated from a stratigraphical, sedimentological and geochemical viewpoint. The data collected allow these deposits to be ascribed to the Termina Formation of the Epiligurian Sequence and to be dated at the top of the Upper Serravallian. Different outcrop types are recognized: 1) marly-calcareous lenses with lucinids, 2) marly-calcareous and calcarenitic hectometric levels with lucinids, 3) marly-calcareous breccias with lucinids. The first two outcrop types clearly show show evidence of a primary deposition and gradually pass to surrounding pelitic marls, whereas the third one is resedimented. The sedimentological and stratigraphical results obtained from this research permit to differentiate the numerous "Lucina deposits" reported in literature. Geochemical and taphonomic analyses confirm the stratigraphical and sedimentological data and lead to interpret the lucinid assemblages of the Modena territory deposits as chemosynthetic communities related to hydrocarbon sources. A methanogenic hypothesis, different from those commonly reported in literature, is here proposed which considers lucinid chemoherm as derived from local bacterical oxidation of marly-pelitic sediments
1996
- Conclusioni. In: R. Gelmini “Le fasi tettoniche: tipologie e loro propagazione spazio-temporale”.
[Articolo su rivista]
Conti, Stefano
abstract
In una recente nota (GELMINI, 1991) richiamavo l'attenzione sul fatto che l'uso del termine "fase tettonica" ha subito una qual sorta di inflazione; esso viene spesso usato sia per indicare l'insieme dei fenomeni tettonici "omogenei" a scala regionale, sia per singoli eventi, talvolta a carattere molto locale, tanto da ingenerare una notevole confusione nella comprensione dei fatti descritti, della loro valenza e della loro corretta reciproca collocazione spazio-temporale.Al fine di chiarire il concetto di fase tettonica mi sembra opportuno richiamare alcuni concetti generali
1996
- La tettonica trasversale dell’Appennino Settentrionale: il caso della Val Marecchia.
[Articolo su rivista]
Conti, Stefano; Gelmini, R.
abstract
Structural, geological, sedimentological and geophysical data support the existence of transversal tectonics in the Val Marecchia area. Such tectonics is related to the migration of the deformational front and is expressed by dynamic and mobile activity. Until the Tortonian phase, the migration of the foredeep-thrust belt front regularly occurred involving turbiditic closure pelites and transversely delimiting them by the tectonic lineament Arezzo-Badia Tedalda. Afterwards, the counter-clockwise rotation of the Italian peninsula leads, since Lower Messinian, to the formation of tectonic arcs. Among these arcs, the Romagnan and Adriatic ones come to separate in correspondence with the Val Marecchia tectonic lineament via the formation of a depressed area bending inside of the Apenninic chain. Transversal tectonics is then related to different rates of migration of the deformational front, which in turn is probably linked to discontinuities and /or heterogeneities of the underlying basement.
1996
- Tectonic vs gravitational processes affecting Ligurian and Epiligurian units in the Marecchia valley (Northern Apennines)
[Articolo su rivista]
Conti, Stefano; Tosatti, Giovanni
abstract
Thrusts of the Northern Apennine tectonic units are currently referred to horizontal compression, even if some authors still attribute the emplacement of the Ligurian and Epiligurian units to gravitational mechanisms. This research aims to contribute to the distinction between tectonic and gravitational processes, by means of structural, sedimentological-stratigraphic and geotechnical investigations on some Ligurian and Epiligurian formations of the Val Marecchia thrust sheet (central Italy). The identification of syntectonic Epiligurian basins describing antitaxial arcs and of structures related to Neogene brittle tectonics in the Ligurian units, shows that the emplacement of the Val Marecchia thrust sheet was probably due to compressive tectonics. This assumption is furthermore corroborated by geotechnical tests. Gravitational processes are limited to episodic submarine landslides, during the Neogene stages of advancement of the deformation front, and to recent subaerial active and dormant mass movements linked to superficial erosion and softening processes.
1995
- Brecce poligeniche a matrice argillosa alla base della Successione Epiligure della coltre della Val Marecchia (Appennino tosco-marchigiano): implicazioni tettoniche.
[Articolo su rivista]
Bettelli, Giuseppe; Conti, Stefano; Panini, Filippo
abstract
Middle Eocene-Upper Oligocene submarine debris flow deposits, unconformably overlying the highly deformed Ligurian allochthonous formations (Lower Cretaceous - Middle Eocene), exstensively outcrop on the Po Valley side of the Northern Apennines north-west of the "Sillaro tectonic line". These chaotic rocks show Ligurian provenances and represent the renewal of the sedimentation, in a deep water setting, on the Ligurian units previously deformed by the Ligurian tectonic phase (Middle Eocene). Due to the complex structure of the region and the widespread block-in-matrix fabric shown by the Ligurian formations at the outcrop scale, almost all of these debris flow deposits and the underlying Ligurian units were indistinctly reported in the geological literature as the "Chaotic Complex of the Northern Apennines". Accordingly, some authors hypothesized that this large complex was a stack of olistostromes and/or of "orogenic landslides". Only recently it has been recognized that the main body of the "Chaotic Complex" of the Northern Apennines is made up of broken formations or non-metamorphic tectonites. Furthermore, it has been realized that thick debris flow deposits unconformably overlie Ligurian tectonites and that these chaotic sedimentary rocks belong not to the Ligurids but to the overlying Middle Eocene - Upper Miocene epi-Ligurian Sequence.The same stratigraphic and structural framework occurs in the Val Marecchia allochthonous Ligurian sheet. In fact, at Sasso di Simone and adjoining areas polymictic shaly matrix-supported breccias outcrop in this allochthonous sheet at the base of the arenaceous and bio-calcarenitic San Marino Formation (Upper Burdigalian-Lower Langhian) of the epi-Ligurian Sequence and unconformably overlie the Val Marecchia varicoloured shales formation (Lower Cretaceous-Lower Eocene) belonging to the Ligurids.The Val Marecchia varicoloured shales formation outcropping in the studied area displays a wide range of structural styles: it looks as a large tectonic mélange, but as exotic blocks are lacking, it is here considered a dismembered formation or a unit made up of tectonites. The more evident mesoscopic structure of this unit is represented by a striking tectonic layering due to a great number of anastomosing ductile shear surfaces ranging from few meters to some hectometers. These shear surfaces split out the formation in a number of more or less large lozenge-shaped or lenticular bodies in which different deformation styles are apparent: rootless folds of different styles or isolated hinges of isoclinal folds, boudinage and pinch-and-swell are the more recurrent deformational structures affecting these bodies. The primary bedding within these bodies is rarely preserved, but where recognizable it parallelizes the main tectonic layering. The shales show a prominent primary fissility running parallel to the bedding in the coherent (i.e., bedded) units and a penetrative scaly cleavage in the incoherent ones. The wide spectrum of complex deformational structures shown by the Val Marecchia varicoloured shales formation is here ascribed to tectonic deformation (i.e., folding and shearing) of poorly lithified or unlithified sediments probably due to tectonic detachment of the originally overlying M. Morello Formation during the Ligurian tectonic phase (Middle Eocene). The penetrative scaly cleavage affecting the shales is here interpreted as deriving from a mechanism of frictional grain-boundary sliding involving the slipping of clay platelets past each other, acting on unconsolidated sediments at low effective stresses.The mesoscopic tectonic layering of the Val Marecchia varicoloured shales formation is unconformably sealed by the overlying polymictic breccias. Even if the absence of lenses and blocks of pelitic hemipelagic epi-Ligurian formations does not allow a correct definition of the age of these breccias, they can presumably be ascribed to a span o
1995
- Caratteristiche strutturali e geotecniche delle Argille Varicolori della Val Marecchia. Rapporti con i meccanismi di deformazione
[Articolo su rivista]
Conti, Stefano; Tosatti, Giovanni
abstract
Le Argille Varicolori della Val Marecchia sono caratterizzate da un'estrema complessità strutturale, presentando stili di deformazione sia duttile che fragile. Il primo è legato alla fase ligure, mentre il secondo è riconducibile in massima parte a fasi tettoniche successive, che hanno interessato anche la Successione Epiligure. Tali stili strutturali hanno permesso di meglio definire la dinamica dei fenomeni gravitativi che interessano sia il substrato argilloso che i sovrastanti litotipi competenti.
1995
- La geologia dell'alta Val Marecchia (Appennino tosco-marchigiano) - Note illustrative alla carta geologica 1:50.000.
[Articolo su rivista]
Conti, Stefano
abstract
A geological survey (1:10.000 scale) provided new data on the evolution of the Val Marecchia area. The deposits belong to Ligurian, Subligurian, epi-Ligurian and Umbro-Romagnan Domains outcrop in the mapped area; the lithostratigraphic units of the first three domains, included in Val Marecchia thrust-sheet, overthrust Umbro-Romagnan Domain (respectively Verghereto Marls, Ghioli di letto mudstones and Argille Azzurre) at the Lower-Upper Tortonian boundary, during Lower Messinian and at the end of Lower Pliocene (Globorotalia puncticulata Zone). The various units constituting Umbro-Romagnan Domain are also stacked by imbricated thrusts: every inner unit overrides the adjacent outer one and the age of thrusting is progressively younger towards NE, their formation being linked to the tectonic phases of the Northern Apennines. The structural pattern of Val Marecchia sheet is made up of imbricated slices, NE-verging and displaying an arcuate shape in a planar view. These imbrications are not only related to the emplacements of the thrust-sheet over the substratum tectonic Units but also to the Ligurian tectonic phase.New collected field data show the occurrence, inside the Ghioli di letto mudstones, of a wide belt characterized by resedimented deposits of Apenninic provenance (olistostromes and olistoliths of Ligurian and epi-Ligurian sources, turbiditic sandstones with Ligurian affinities), which were previously included in the Val Marecchia thrust-sheet. Furthermore piggyback basins filled by Ghioli di letto deposits have been recognized both in Umbro-Marchean-Romagnan Sequence and over Val Marecchia sheet. The presence of a fragile deformation style affecting the Val Marecchia thrust-sheet (arcuate thrusts, pop up structures, back thrusts, tear faults), led to envisage its emplacement as triggered by active tectonics, due to horizontal compressive pushes as in tapered sheets or in accretionary wedges. The emplacement of the Val Marecchia sheet occurs in a piggyback sequence of imbricated slices, filled not only by epi-Ligurian deposits, but also, exclusively at the thrust front and with a minor extension, by the terminal parts of the same deposits overriden by the thrust-sheet.Consequentely, a complex system composed of a duplex and a leading imbricate fan (in the substratum) arises. The role of transverse tectonics in Val Marecchia is strictly related to thrust-front activities: during every tectonic phase it acts in the outermost part of the thrust belt as a line dividing fronts with different degrees of advancement and it affects the sedimentation of those deposits that will be afterwards overthrust by Val Marecchia sheet.These elements have then been utilized to describe the structural evolution of the studied area during Miocene, according to the model of the migration of foredeep-thrust belt system, and to explain the tectonic relationships due to compressive horizontal forces. Collected data have also shown that gravitational episodes with an Apenninic provenance are of restricted importance and forerunners of Ligurian tectonic emplacements.
1995
- La tettonica trasversale dell'Appennino Settentrionale: il caso della Val Marecchia.
[Relazione in Atti di Convegno]
Conti, Stefano; Gelmini, R.
abstract
Numerosi autori già da lungo tempo hanno rilevato l'esistenza di linee tettoniche trasversali alla catena appenninica, che possono sia interessare il basamento, e quindi essere legate alla rotazione antioraria della penisola italiana, sia essere semplici svincoli cinematici di unità della copertura a differente entità di movimento. Le prime sono in genere separabili dalle seconde per essere evidenziabili in superficie non tanto come linee geometriche ma quanto come fasce caratterizzate da elementi riconducibili spesso solo indirettamente ad una tettonica trasversale. Una linea tettonica trasversale del primo tipo è messa in evidenza nell'area della Val Marecchia da numerosi elementi di natura geologico-strutturale, sedimentologica e geofisica (fig. 1). Fig. 1 - Carta strutturale dell'area studiata. 1) depositi alluvionali; 2) depositi del Pliocene medio; 3a) depositi del Pliocene inf., 3b) depo-siti del Messiniano sup.; 4a) Formazione Gessoso-solfi-fera (Messiniano medio) e Ghioli di letto (Tortoniano-Messiniano inf.), 4b) Mar-noso-arenacea Esterna (fa-cies prossimale) (Tortoni-ano) 4c) Marnoso-arenacea Esterna (facies distale), (Serravalliano sup.-Torto-niano), 4d) Schlier; 5a) Mar-ne di Verghereto (Serraval-liano inf.-Tortoniano inf.), 5b) Marnoso-arenacea Inter-na (Langhiano-Serravallia-no inf.); 6a) Marne di Vic-chio (Miocene inf.-medio), 6b) Arenarie del Falterona (Miocene inf.); 7) depositi epiliguri; 8a) Flysch eoce-nici liguri e Unità di Cane-tolo, 8b) complessi di base1) Dati geologici ricavati da foto aree, da satellite e da rilevamenti di campagna evidenziano faglie sia minori che maggiori a direzione NE-SW e con componente trascorrente in corrispondenza dell'allineamento Arezzo-Badia Tedalda-Valle del Conca (figg. 1, 2). Le faglie minori sono sia le rampe laterali dei thrusts di forma arcuata che caratterizzano la coltre della Val Marecchia sia tear faults che svincolano thrusts a differente componente di movimento. Quelle d'importanza maggiore delimitano verso est, ed in alcuni casi separano, i fronti degli accavallamenti della coltre sulle varie unità del substrato, che sono progressivamente più recenti verso NE (fig. 2), facendo intuire una loro origine profonda e che fungano da zone di svincolo per le diverse fasi di avanzamento dell'alloctono. 2) Variazioni ambientali e di facies fra i depositi situati ad ovest e ad est dell'allineamento Arezzo-Badia Tedalda-Valle del Conca (fig. 3). Fig. 2 - Carta gravimetrica dell'area dellla Val Marecchia i numeri fanno riferimento alla posizione del fronte dei thrusts durante il (1) Serravalliano inf; (2) Tortoniano inf.; (3) Messiniano inf.; (4) Pliocene inf.; (5) situazione attuale.Fig. 3- Differenze di facies fra le aree situate ad occidente ed oriente della "linea della Val Marecchia". PI= Pliocene inf., TSS= Tortoniano-Serravalliano sup.3) Sistema di faglie a direzione antiappenninica che, nella zona compresa fra S. Agata Feltria e Carpegna, disloca il sovrascorrimento della Marnoso-arenacea Esterna in facies distale. In tale zona questa unità si accavalla direttamente sui propri depositi di chiusura (Ghioli di letto) senza l'interposizione dei depositi in facies prossimale ("molasse grossolane", Arenarie di Urbania, ecc.) (fig. 1).4) Variazione di orientazione degli elementi strutturali presenti nelle varie unità tettoniche: ad occidente della linea della Val Marecchia essi hanno prevalentemente direzioni NW-SE, ad oriente tendono ad assumere una direzione più marcatamente N-S (fatto ancora più evidente in aree poste immediatamente ad oriente di fig. 1).5) Presenza di una fascia (di estensione variabile dalle poche centinaia di metri a circa un paio di chilometri, a seconda dell'entità della laminazione tettonica esercitata dalla coltre durante il suo avanzamento) in cui le direzioni di strato delle varie formazioni delle unità del substrato seguono un andamento antiappenninico (a partire dalle Marne di Vicchio
1995
- Sabbia
[Traduzione di Libro]
Conti, Stefano
abstract
Ogni geologo ha la sua roccia preferita, la mia è l'arenaria
1994
- Brecce poligeniche a matrice argillosa alla base della Successione epiligure della coltre della Val Marecchia (Appennino tosco-marchigiano).
[Articolo su rivista]
Bettelli, Giuseppe; Conti, Stefano; Panini, Filippo
abstract
-
1994
- Caratteristiche geologico-strutturali della Pietra di Bismantova e fenomeni franosi connessi (Appennino reggiano)
[Articolo su rivista]
Conti, Stefano; Tosatti, Giovanni
abstract
In questa nota viene preso in esame il caso della Pietra di Bismantova e, per confronto, quello del Monte Valestra (Appennino reggiano). In base alle caratteristiche morfologiche e strutturali della Pietra di Bismantova sono riconoscibili in pianta due aree distinte: una a forma tabulare e l'altra, più ridotta arealmente, di forma arcuata. La diversa evoluzione dei fenomeni franosi in queste due aree è strettamente legata alla differente natura del substrato, che nel caso della porzione tabulare è costituito da litotipi prevalentemente marnosi della Successione epiligure, mentre in quella arcuata, è rappresentato dalle Argille Varicolori, appartenenti ai Complessi liguri. L'analisi delle relazioni fra elementi strutturali e morfologici e caratteristiche geotecniche e mineralogiche ha permesso di riconoscere una tipologia complessa dei movimenti, soltanto in parte riconducibili a deformazioni gravitative profonde di versante. Sia nel caso della Pietra di Bismantova che del Monte Valestra gli elementi morfologici che più di ogni altro possono far pensare a cedimenti generalizzati del substrato sono ascrivibili piuttosto a sollecitazioni distensive lungo i margini esterni delle placche dovute alla maggiore deformabilità dei terreni d'appoggio.
1994
- Caratteristiche strutturali e geotecniche delle Argille varicolori della Val Marecchia e rapporti con i meccanismi di deformazione
[Abstract in Atti di Convegno]
Conti, Stefano; Tosatti, Giovanni
abstract
Le Argille varicolori della Val Marecchia (RN) presentano caratteristiche strutturali e geotecniche molto complesse a causa delle intense vicissitudini tettoniche alle quali sono andate soggette. L'articolo descrive queste caratteristiche mettendole in relazione con i meccanismi di deformazioni gravitative pregresse e in atto.
1994
- I Calcari a Lucine dell'Appennino Settentrionale quali indicatori paleogeografici e geodinamici.
[Relazione in Atti di Convegno]
Conti, Stefano; Gelmini, R.; Ponzana, L.
abstract
La presenza di "calcari a Lucine" nei terreni miocenici dell'Appennino Settentrionale era stata segnalata già nella seconda metà del secolo scorso anche se ad essa veniva dato erroneamente un valore stratigrafico. I "calcari a Lucine" affiorano infatti in tutti i piani miocenici ad esclusione dell'Aquitaniano e sono segnalati dalla Liguria (M. Colma di Rossiglione) fino a Deruta (SE di Perugia); altre segnalazioni provengono dalla Sicilia sia dalla catena magrebide che dall'avampaese ibleo. L’esame delle più note località a Lucine ha permesso di effettuare alcune considerazioni: 1) le Lucine non sono solo comprese all’interno di sedimenti calcarei, ma sono anche incluse in depositi pelitico-marnosi o addirittura arenacei risedimentati; 2) le Lucine possono essere isolate nel sedimento o più spesso riunite a nidi ed in associazione con abbondanti macrofaune (coralli, echinodermi, ostreidi, alghe calcaree, gasteropodi, briozoi, altri bivalvi), indi¬cative di un ambiente di piattaforma da interna ad esterna; 3) esistono affiora¬menti con Lucine in giacitura primaria ed altri con Lucine in giacitura secondaria. Affioramenti contenenti depositi a Lucine in giacitura primaria sono stati rinvenuti soltanto nella Successione Epili¬gure a differenti altezze stratigrafiche: nelle Formazioni di Bismantova e S. Marino (Burdigaliano sup.-Serravalliano inf.) e in quella del Termina (Serravalliano sup.-Messiniano inf.). Affioramenti contenenti depositi a Lucine in giacitura secondaria sono ubicati in differenti contesti geolo¬gici: a) entro formazioni fliscioidi dell’avan¬fossa (Arenarie di Monte Cervarola-Falterona, Marnoso-arenacea Interna ed Esterna); b) in formazioni sedimentatesi entro bacini minori ubicati alla sommità dei thrusts liguri (Arenarie di Por¬retta-Suviana); c) entro le peliti marnose che hanno chiuso la sedi¬mentazione fliscioide dell’avanfossa (Marne di Vicchio, Marne di Ver¬ghereto, Ghioli di Letto e depositi a queste correlabili). I depositi contenenti Lucine in giacitura se¬condaria sono a loro volta suddivisibili in base al mec¬canismo di messa in posto in: 1) brecce calcareo-marnose con Lucine a valve general¬mente aperte e frammentate (risedimentazione ad opera di debris flows ); 2) are¬narie risedi¬mentate contenenti im¬pronte di Lucine isolate, in¬cluse come clasti alla base degli strati gradati (risedimentazione ad opera di correnti di tor¬bida e fluidi¬zed flows ); 3) “blocchi” di calcari marnosi (olistoliti) con modelli interni e gusci di Lucine spesso di grandi dimensioni e spes¬sore, ora sparsi ora concentrati in nidi (da no¬tare che in questo caso le valve sono quasi sempre riunite). Inoltre i depositi a Lucine in giacitura secondaria sono generalmente as¬sociati a frane sottomarine sia intraformazionali (slump) che extra¬forma¬zionali (olisto¬stromi, olistoliti, de¬positi da debris flow ) di pertinenza ligure, subligure ed epiligure, o a strati torbiditici a provenienza appenninica e legati al disfacimento di depositi epiliguri di piattaforma (Formazione di S. Marino). Tali af¬fiora¬menti sono organizzati in veri e pro¬pri orizzonti che de¬notano episodi d'instabilità tettonica, databili al Serravalliano inf., al Tortoniano inf. e al passaggio Tortoniano-Messiniano e sono sia antici¬patori dei th¬rusts delle Liguridi sulle varie unità dell'avanfossa (depositi a Lucine nelle peliti di chiusura torbiditica), sia contemporanei (depositi a Lucine nell'avanfossa antistante all'avanzamento dei thrusts liguri e destinata a chiudersi a seguito dell'evento tettonico). Anche quando i depositi a Lucine in giacitura secondaria non sono associati ad elementi di sicura provenienza appenninica ten¬dono sempre ad essere situati al fronte dei sovrascorrimenti che hanno portato all'accavalla¬mento delle varie unità dell'avanfossa (Cervarola-Falterona, Marnoso-arenacea In¬terna, Mar¬noso-arenacea Esterna) e delle Unità Liguri
1994
- Miocene-Pliocene tectonic phases and migration of foredeep-thrust belt system in Northern Apennines.
[Articolo su rivista]
Conti, Stefano; Gelmini, R.
abstract
In this paper a space-time evolution of the Northern Apennines during the Miocene-Lower Pliocene is proposed, following the migration of the foredeep-thrust belt system towards the foreland. Every tectonic phase is marked by the thrusting of an inner unit over an outer one and by the overriding of Ligurides on Tertiary units at the level of closure facies. The peak of tectonic activity is preceded by a period of instability marked by the deposition of submarine slides and of minor turbiditic bodies showing Alpine and Apennine sources supplied by both Ligurian and flysch nappes. During each tectonic phase, except the Tortonian and Early Messinian phases, an outward foredeep migration took place. The emplacement of Ligurian units, driven by horizontal compression, occurred by imbricate slices involving closure pelites via the formation of piggyback basins. A complex duplex formed, laterally bordered by transverse lines, which, in their turn, affected closure facies during thrust advancement.
1994
- Osservazioni preliminari sui calcari a Lucine dell'Appennino Settentrionale.
[Articolo su rivista]
Conti, Stefano; Gelmini, R.; Ponzana, L.
abstract
La presenza di "calcari a Lucine" nei ter¬reni miocenici dell'Appennino Settentrionale era stata se¬gnalata già nella seconda metà del secolo scorso (PARETO, 1865; MANZONI, 1876; DE STEFANI, 1880, 1887a, 1900; MAZZETTI, 1874; PANTANELLI & MAZZETTI, 1877; COPPI, 1877; CAPELLINI, 1881a, 1881b; DEL PRATO, 1881; PANTANELLI & MALAGOLI, 1884; GIOLI, 1887; LOTTI, 1895) dando loro erroneamente un valore strati¬gra¬fico. I calcari a Lucine (d'ora in poi CaL) affiorano infatti in tutti i piani miocenici ad esclusione dell' Aquitaniano e sono se¬gnalati in tutto l'Appennino Settentrionale dalla Liguria (M. Colma di Rossiglione) (DE STEFANI, 1887b) fino a Deruta (SE di Perugia) (VERRI & DE ANGELI D'OSSAT, 1900); altre segnalazioni provengono dalla Sicilia sia nella catena magrebide che nell'avampaese ibleo (CAFICI, 1880; DI STEFANO, 1903). Inoltre, elemento che già i vecchi au¬tori avevano notato, il genere Lucina si presenta quasi sempre associato ad altri ma¬crofossili (coralli, echinodermi, ostriche, alghe calca¬ree, gasteropodi, briozoi, altri bivalvi) spesso indicativi di un ambiente di sedimentazione poco pro¬fondo (MONTANARO, 1939; PETRUCCI, 1960; MORONI, 1966; DAVOLI, 1982).Di recente TERZI (1992), facendo propria l'interpretazione del lavoro di CLARI et al. (1988) che analizzava CaL del Monferrato, ha riesaminato, soprattutto dal punto di vista geochimico, nume¬rosi affioramenti di CaL tra l'Appennino roma¬gnolo e quello bolognese, proponendo un ambiente di sedimentazione di mare profondo legato alla risalita di acque fredde ricche in metano (cold seep ) lungo faglie, similmente a quanto avviene nei prismi di accrezione in aree di attuale subduzione. Infatti in tali aree, e precisamente in corrispon¬denza dell'espulsione di fluidi "freddi" ricchi di metano, sono state segnalate delle comunità a bivalvi giganti e anellidi (SUESS et al., 1985; RITGER et al., 1987) confrontabili alle più note comunità a bivalvi giganti, crostacei, pogonofori e tiobatteri im¬po¬state lungo le dorsali oceaniche nei pressi di black smokers e hot springs . Ad ogni modo nelle comunità bentoniche legate alla fuoriuscita di fluidi sul fondo marino, non sono mai state segnalate specie del genere Lucina nè tantomeno gli altri macrofossili che sono presenti nella maggior parte degli affioramenti di CaL. Inoltre le specie del genere Lucina vivono attualmente a scarsa profondità, in¬fossate in sedimenti fangosi, pochi metri al di sotto della linea di bassa marea e prediligono spesso le acque calde intertropicali (ad es. Lucina pectinata, L. pensylvanica).Il problema riguardante l'originario ambiente di deposi¬zione delle Lucine è dunque ben lungi dall'essere risolto, in virtù anche del fatto che la maggior parte dei depositi citati in letteratura è in realtà risedimentata (Lucine isolate in strati torbiditici, olistoliti calcarei e brecce a Lucine associati a slump o a olistostromi li¬guri). I dati fi¬nora raccolti testimoniano la presenza di Lucine in posizione primaria nella sola Successione epi¬ligure e secondaria invece nei depositi dell'avanfossa (le Lucine sono spesso as¬sociate a slump, olistostromi di pertinenza ligure, brecce e torbiditi a prove¬nienza appenninica). Il fatto poi che l'età dei più antichi depositi di Lucine, la loro posi¬zione stratigrafica e associazione faunistica sia del tutto correlabile a quella delle Forma¬zioni di Bismantova-S. Marino (SIMONELLI, 1883, 1891; DEL BUE, 1900; TRABUCCO, 1900, 1906; SACCO, 1901; NELLI, 1907) e che a loro volta blocchi di questi depositi si trovino in¬clusi come olistoliti negli stessi terreni dell'a¬vanfossa in cui si trovano gli olistoliti a Lu¬cine (addirittura talvolta associati in affiora¬mento) (PIALLI, 1966; RICCI LUCCHI & PIALLI 1973; CONTI, 1993), ci sembra possa fornire interes¬santi elementi nella comprensione degli eventi geodinamici (fasi tettoniche, correla¬zione fra depo¬siti epiliguri e peliti di chiusura, ecc.) che hanno intere
1993
- Carta Geologica dell'alta Val Marecchia (Appennino tosco-marchigiano). S.EL.CA., Firenze
[Cartografia]
Conti, Stefano
abstract
S.EL.CA. Firenze
1993
- Caselle di Fanano
[Capitolo/Saggio]
Conti, Stefano; Tosatti, Giovanni
abstract
La frana che interesse l'abitato di Caselle di Fanano (MO) è classificabile come uno scivolamento di detrito. La causa del dissesto è individuata nello stato di saturazione del materiale detritico di versante che, in seguito a scossa sismica, è andato soggetto a liquefazione.
1993
- I calcari a Lucine dell'Appennino Settentrionale quali indicatori paleogeografici e geodinamici
[Monografia/Trattato scientifico]
Conti, Stefano; Gelmini, R.; Ponzana, L.
abstract
I CALCARI A LUCINE DELL'APPENNINO SETTENTRIONALE QUALI INDICATORI PALEOGEOGRAFICI E GEODINAMICIESCURSIONE La presenza di calcari a Lucine nei terreni miocenici dell'Appennino Settentrionale era stata segnalata già nella seconda metà del secolo scorso (PARETO, 1865; MANZONI, 1876; DE STEFANI, 1880; MAZZETTI, 1874; COPPI, 1877; CAPPELLINI, 1881; DEL PRATO, 1881; PANTANELLI & MALAGOLI, 1884; LOTTI, 1895) con lo scopo, rivelatosi poi erroneo, di dare loro un valore stratigrafico. Attualmente calcari a Lucine sono segnalati in tutto l'Appennino Settentrionale e precisamente dalla Liguria (M. Colma di Rossiglione) fino a Deruta (SE di Perugia); altre segnalazioni provengono dalla Sicilia sia nella catena magrebide che nell'avampaese ibleo. Inoltre, elemento che già i vecchi autori avevano notato, le Lucine si presentano quasi sempre associate ad altri macrofossili (coralli, echinodermi, ostriche, alghe calcaree, gasteropodi, bivalvi) spesso indicativi di un ambiente di sedimentazione poco profondo (PETRUCCI, 1960; MORONI, 1966).Di recente, nella sua documentata tesi di dottorato, la Terzi (1991) ha riesaminato, soprattutto dal punto di vista geochimico, numerosi affioramenti di calcari a Lucine tra l'Appennino romagnolo e quello bolognese, proponendo un ambiente di sedimentazione di mare profondo legato alla risalita di acque fredde ricche in metano (cold seeps) lungo faglie. Si venivano così a creare dei biota del tutto simili alle attuali comunità a bivalvi giganti, crostacei, pogonofori e tiobatteri impostate nei pressi dei blake smokers e delle hot springs delle dorsali oceaniche. Ad ogni modo la maggior parte delle specie attuali del genere Lucina vive a scarsa profondità, infossata in sedimenti fangosi, pochi metri al di sotto della linea di bassa marea.Il problema sull'ambiente di deposizione originario delle Lucine è dunque ben lungi dall'essere risolto, in virtù anche del fatto che la maggior parte dei depositi citati in letteratura sembra essere risedimentata (strati a Lucine associate a torbide, olistoliti calcarei a Lucine associati a slump o a olistostromi liguri) e quindi l'escursione non si propone di illustrare i risultati di una ricerca ormai portata a termine, ma di far conoscere i dati finora raccolti (oggetto di una prossima pubblicazione). Questi testimoniano la presenza di Lucine in posizione primaria nella sola Successione epiligure e secondaria invece nei depositi dell'avanfossa (le Lucine sono spesso associate a slump, olistostromi di pertinenza ligure, brecce e torbiditi a provenienza appenninica). Il fatto poi che l'età dei più antichi depositi di Lucine, la loro posizione stratigrafica e associazione faunistica sia del tutto correlabile a quella delle Formazioni di Bismantova-S. Marino e che a loro volta blocchi di questi depositi si trovino inclusi come olistoliti negli stessi terreni dell'avanfossa in cui si trovano gli olistoliti a Lucine (addirittura talvolta associati in affioramento), ci sembra possa fornire interessanti elementi nella comprensione degli eventi geodinamici (fasi tettoniche, correlazione fra depositi epiliguri e peliti di chiusura, ecc.) che hanno interessato l'Appennino Settentrionale nel Miocene.In base alle loro posizione di affioramento i "calcari" a Lucine che abbiamo finora esaminato (dati di campagna e di letteratura) si possono così raggruppare:IN GIACITURA PRIMARIA:1- lenti di calcari marnosi, marne debolmente calcaree intercalate nei terreni epiliguri. DATI DI CAMPAGNA- a) Montebaranzone, b) Rocca S. Maria, c) Salsetta (Appennino modenese); in: Marne del Termina (Tortoniano);- a) M. della Rocca, b) Ducentola, c) Carbonara (Appennino bolognese); in: Marne del Termina (Serravalliano sup.-Tortoniano (?)-Messiniano ?);DATI DI LETTERATURA- a) Montegibbio (Appennino modenese); in: Marne del Termina (Tortoniano);- a) Pantano, b) castello di Baiso (Appennino reggiano); Formazione di Bismantova, membro di Pantano (Langhiano sup.?-S
1993
- Landslides affecting tabular rocks in complex geological situations: the case of Sasso di Simone and Simoncello (Northern Apennines, Italy)
[Relazione in Atti di Convegno]
Conti, Stefano; Tosatti, Giovanni
abstract
In the Northern Apennines, the geological situations due to the superimposition of competent rocks on argillaceous and shaly clay substrata are particularly widespread and give rise to complex and prolonged mass movements. To these situations, the case of Sasso di Simone and Simoncello is ascribable. Due to the intense tectonic stresses which have accompanied the orogenesis of the Apennine chain, these competent tabular-shaped cliffs are affected by widespread fractures whose nature and distribution directly influence the evolution of the slope movements. The latter are not confined to the lithic rocks, but extend also to the clayey substratum, which is also highly tectonised, thus causing complex landslides, prevalently showing lateral spreading deformations, concentrated along the cliff margins. The main cause of the persistent slope instability is identified with the high erodibility and deformability of the clayey soils, of which a basic geotechnical classification is given.
1993
- Ospitale
[Capitolo/Saggio]
Conti, Stefano; Tosatti, Giovanni
abstract
Le numerose frane di estensione variabile che interessano l'abitato di Ospitale (Comune di Fanano) sono classificabili come scorrimenti rotazionali e traslativi di detrito. I movimenti di versante hanno interessato il capoluogo e altri centri minori della zona. Sono state costruite diverse briglie per la regimazione dei corsi d'acqua ed è stata completata una sistemazione forestale del pendio.
1993
- S. Andrea Pelago
[Capitolo/Saggio]
Conti, Stefano; Tosatti, Giovanni
abstract
L'abitato di S. Andrea Pelago (Comune di Pievepelago) è interessato da una colata di terra appartenente ad un più ampio movimento gravitativo complesso. Il movimento franoso interessa attualmente l'abitato di Casoni e solo marginalmente quello di S. Andrea Pelago. Fra le cause predisponenti il dissesto vanno annoverati i fenomeni di erosione fluviale al piede, le condizioni idrogeologiche sfavorevoli e le caratteristiche meccaniche scadenti dei materiali coinvolti.
1993
- Some cases of landslides affecting urban areas in the Marche (central Italy)
[Relazione in Atti di Convegno]
Conti, Stefano; Tosatti, Giovanni
abstract
The valley of the River Marecchia (Northern Apennines, central Italy) is characterised by the presence of competent fractured formations outcropping in isolated and dismembered slabs, overlying argillaceous soils with a prevalent plastic-ductile behaviour. This particular geological situation has favoured in the past the construction of castles, strongholds and villages since from their privileged strategic position they could better control the communications and movements at the bottom of the valley. Nevertheless, the superimposition of geological formations characterised by extremely different mechanical parameters has determined the activation of several mass-movements, which for many centuries have threatened the stability of these urban centres. Most of these landslides, which had previously been interpreted as surficial movements, have now been ascribed to deep-seated gravitational deformations, thanks mainly to new evidences deriving from detailed field and laboratory data. In fact, the presence of numerous geomorphological elements, such as sagging of the rigid slabs' central parts along structural discontinuities and bulging of the ductile substratum, lead toward this interpretation. In this paper the slabs of Pennabilli and San Leo are being considered, since on them two of the most important historical towns of the valley are placed. The situations studied correspond to two different kinds of slabs: Pennabilli belongs to a tabular-type slab, whilst San Leo is ascribable to an arcuate-type slab. Moreover, both cases differ not only for the structural elements but also for the characteristics of the substratum. The two slabs are interested by dense fracture network systems that control their dismemberment and the kinematics of the mass-movements, with different patterns of evolution according to the diversity of the structural elements and of the clayey substratum. In particular, the relationships between the mineralogical and geotechnical properties of the substratum, the structural characteristics and the evolution of the landslides have been investigated. On these sites, monitoring systems have also been installed and consolidation and upgrading works have been enterprised. Notwithstanding this, the interventions carried out so far have not solved the problems related to slope movements, that by now involve a large number of buildings, since they were not based on a correct and thorough interpretation of the instability causes.
1992
- Caratteristiche geologico-strutturali delle placche epiliguri della coltre della Val Marecchia e loro riflessi sulla franosità.
[Articolo su rivista]
Conti, Stefano
abstract
The epi-Ligurian Sequence of the Val Marecchia thrust sheet (Northern Apennines) crops out in several "slabs". Ligurian deposits, belonging to the Monte Morello tectonic Unit, are mostly composed by clayey and shaly "argille varicolori" (basal complex of the Monte Morello Formation). Four epi-Ligurian formations (Antognola, Bismantova, Termina and Monte Sabatino - Upper Oligocene to Lower Pliocene), separated by erosional surfaces, occur in the "slabs", which, on the base of structural data, can be subdivided in three groups: 1) "arcuate slabs", 2) "tabular slabs" and 3) small "slabs" slumped in Upper Tortonian sediments of the Ghioli di Letto Formation. The "arcuate slabs", occurring in frontal parts of the Val Marecchia thrust sheet, dip uphill and display vertical cliffs on the NE side facing the Adriatic Sea. The arcs, elongated to the direction of the Apenninic chain, are characterized by distinctive fracture sets: A) perpendicular to the curvature, B) fan-shaped and intersecting the previous one, C) parallel to the length of arc. Syntectonic sedimentary wedges were deposited in "arcuate slabs" from Tortonian to Lower Pliocene and sedimentation was strongly controlled by movement of arcuate thrust-system of the Val Marecchia sheet. The "tabular slabs", outcropping in internal parts of the Val Marecchia thrust sheet, show margins located nearly at the same altitude and are constituted only by a shelf carbonate unit (San Marino Formation). These "slabs" are characterized by subhorizontal stratification and dense network of fracture sets directed parallel to the margins. The position of two main "slabs" seems to be controlled by a transversal tectonic line running parallel to the course of the River Marecchia, 3-4 km east of it. Different structural patterns of "arcuate" and "tabular slabs" could be related to the influence of the "substratum" (Umbro-Marchean-Romagna Sequence) overthrusted by the Val Marecchia thrust sheet. The fracture system control the dismemberment of the two kinds of "slabs" and the evolution of the mass-movements. The latter affect both the clay substratum and the overlying rocks with different patterns of evolution according to structural elements.
1992
- DOMINIO EPILIGURE. INTERVALLO EOCENE MEDIO-TORTONIANO P.P.
[Capitolo/Saggio]
Conti, Stefano; Panini, Filippo
abstract
Sul versante padano dell' Appennino settentrionale affiora estesamente, in discordanza o apparentemente concordante (paraconcordanza) sulle varie unità liguri, una successione stratigrafica, che seppure variabile in termini di associazioni litologiche e di potenza, presenta caratteristiche comuni dal Monferrato alla valle del F. Foglia (Appennino marchigiano).Durante l'Eocene medio (Luteziano), subito dopo la fase tettonica ligure, la sedimentazione comincia su di un substrato fortemente deformato ed in ambiente marino piuttosto profondo, con depositi rappresentati da potenti accumuli di brecce poligeniche a matrice argillosa (melange sedimentari, olistostromi), da marne ed argille emipelagiche con strati torbiditici e da corpi arenacei risedimentati. I primi sono segnalati nell' Appennino reggiano ed in maggior misura nel settore modenese e bolognese fino alla val Sillaro; simili depositi affiorano poi anche a SE, nell' Appennino tosco- marchigiano (Sasso di Simone e Simoncello). Questi depositi, a lungo erroneamente accomunati ai terreni caotici di origine tettonica sottostanti, sono noti con varie denominazioni ( brecce argillose della Val Fossa-Baiso, di Costa dè Buoi, della Val Tiepido p.p.) e si differenziano per talune loro peculiari caratteristiche litologiche (varietà della matrice e dei clasti) ed in qualche caso contengono lembi, anche di dimensioni ettometriche, di unità appartenenti ai complessi di base liguri, interpretabili come frane di scivolamento in massa.Tutte le brecce poligeniche derivano da colate miste di fango e detrito e mostrano una tipica tessitura clastica rappresentata da una matrice pelitica (in qualche caso anche sabbiosa) e da clasti di varia natura litologica e taglia. Il materiale che costituisce questi depositi deriva quasi invariabilmente dalle unità liguri: nella maggioranza dei casi esse sono rappresentate dalle unità litostratigrafiche appartenenti ai cosiddetti "complessi di base", ma sono segnalate anche brecce poligeniche costituite da materiali provenienti dai flysch ad elmintoidi cretaceo-eocenici (Gruppo della Val di Sambro). I depositi pelitici eocenici, a luoghi presenti entro le brecce poligeniche sotto forma di clasti e/o livelli di sedimentazione "normale", sono rappresentati da argille e marne grigio-scure e rosate. Queste peliti costituiscono, assieme a potenti corpi arenacei risedimentati, la Formazione di Montepiano. Essa affiora in tutto l'Appennino emiliano, mentre è assente nell' area marchigiano romagnola (coltre della Val Marecchia); corpi arenacei risedimentati (Arenarie di Loiano) rappresentano la quasi totalità della formazione nelle parti più meridionali dell'Appennino emiliano. Le Arenarie di Loiano nell' area tipo (medie valli del Setta e del Savena) sembrano essere interamente comprese entro l' Eocene medio, ma altrove corpi arenacei ad esse correlabili potrebbero raggiungere, assieme ai depositi pelitici, anche l' Oligocene inferiore.Le peliti della Formazione di Montepiano sono spesso coinvolte in fenomeni di franamento sinsedimentario (slumping) e presentano intercalazioni di torbiditi pelitico-siltose od arenacee, o più raramente di siltiti brune. Sono in genere policrome, ma nella zona meridionale, in alcuni affioramenti sovrastanti le unità litostratigrafiche del Gruppo della Val di Sambro, prevalgono nettamente argille nerastre o grigio-verdi con intercalazioni arenacee e piccoli accumuli derivati da colate di fango e detrito (Argille di rio Giordano) che passano rapidamente, attraverso un progressivo aumento delle intercalazioni arenacee, alle sovrastanti Arenarie di Loiano. Queste sono costituite da torbiditi arenacee quarzoso-feldspatiche biancastre in strati molto spessi o massicci; più raramente, sia alla base che nella parte superiore del membro, compaiono torbiditi arenaceo-pelitiche con rapporto arenaria/pelite piuttosto variabile. Alle torbiditi arenacee si associano localmente (zone di
1992
- Dominio epiligure. Intervallo Tortoniano superiore-Pleistocene p.p.
[Capitolo/Saggio]
Amorosi, A.; Conti, Stefano; Pini, G. A.; Vai, G. B.
abstract
A partire dal Tortoniano superiore la deposizione epiligure si estende dalla fascia appenninica interna, centrata sulle aree del Bolognese-Modenese e del Marecchia, alla fascia esterna pedemontana, presente sia nel Riminese che nel Bolognese-Emiliano (ovviamente nella posizione palinspastica del tempo). Questo è il risultato dell'importante fase tettonica Toscana che porta le Liguridi in prossimità del bacino umbro-romagnolo. Dopo questa nuova fase tettonica la sedimentazione continua con caratteri sostanzialmente simili sia nella successione epiligure, sia in quella romagnolo-adriatica. Per quanto riguarda la successione epiligure sono state distinte tre aree leggermente differenti.Nell'area del Bolognese .............. V. VAINell'area del Marecchia la fase toscana è evidenziata da una lacuna e dalla ripresa della sedimentazione nel Tortoniano superiore-Messiniano inferiore con la deposizione della Formazione di Acquaviva. Essa è caratterizzata da spessi banchi di conglomerati a matrice arenacea con ciottoli calcarei (di provenienza ligure), passanti lateralmente e verso l'alto ad arenarie giallastre poco cementate, spesso a laminazione incrociata con inclusi pelitici e lenti di beach rocks a bivalvi e scafopodi. Nella parte inferiore vi possono essere intercalazioni di argille sabbiose, talore con lenti di lignite picea. La Formazione di Acquaviva passa verso l'alto e lateralmente per progressivo aumento della frazione argillosa alle Argille di Casa i Gessi (Messiniano inferiore).Si tratta di argille siltose grigie con frequenti livelli carboniosi e con sporadiche intercalazioni di sottili marne calcaree di colore grigio-chiaro. Le argille sono quasi sempre molto fossilifere contenendo abbondanti scafopodi, bivalvi e gasteropodi e ostracodi caratteristici del "Saheliano" preevaporitico. Al di sopra delle Argille di Casa i Gessi seguono i depositi evaporitici, che nella Val Marecchia sono caratterizzati da due facies differenti, talora anche sovrapposte. La prima, più frequente, è formata da gesso selenitico, con geminati a coda di rondine, affiorante in spessi banchi, alternati a sottili livelli di argille sabbiose bituminose; alla base può essere presente un livello a calcari dolomitici. La seconda è costituita da gesso biancastro microcristallino nodulare, con sottili intercalazioni di peliti bituminose scure e marne nocciola ricche di frustoli vegetali. La prima facies è indicativa di un ambiente leggermente più frondo, intertidale evaporitico, della seconda, denotante un ambiente sopratidale di sabkha (v. Cap. xx per l'interpretazione regionale).La successiva sequenza deposizionale, discordante sulla precedente ed affiorante solamente in Valle di Teva (parte orientale della coltre della Val Marecchia) è costituita dai sottili e sparuti affioramenti della Formazione di Casa Monte Sabatino (Messiniano superiore) e dalle peliti del Pliocene inferiore. La prima è costituita alla base da un conglomerato, talvolta ben cementato, con clasti prevalentemente calcarei e di provenienza ligure ed epiligure, passante verso l'alto e lateralmente ad arenarie gialle a laminazione incrociata a basso angolo contenenti livelli pelitici con inclusi calcarei mescolati a tritume conchigliare in maniera disordinata (depositi di tempesta). L'ambiente di sedimentazione (delta-conoide) è del tutto simile a quello in cui si sono depositati i conglomerati di Pietrarubbia della Formazione a Colombacci (Successione marchigiano-romagnola). La formazione è ricoperta da un sottile livello di peliti grigie del Pliocene inferiore (Zona a Sphaeroidinellopsis) con una microfauna di ambiente nettamente più profondo del precedente.Dopo una lacuna significativa la sedimentazione riprende, discordante sui terreni precedenti, nella parte alta del Pliocene inferiore (Zona a G. puncticulata), con depositi in prevalenza argillosi (Argille Azzurre) in cui si intercalano potenti corpi arenaceo-conglomeratici (Arena
1992
- Eventi tettonici e migrazione del sistema fronte deformativo-avanfossa nell'Appennino Settentrionale dal Miocene inferiore al Pliocene inferiore.
[Relazione in Atti di Convegno]
Conti, Stefano; Gelmini, R.
abstract
L'evoluzione stratigrafica e strutturale del versante padano dell'Appennino Settentrionale tra il Miocene inferiore ed il Pliocene inferiore è caratterizzata dalla migrazione verso l'esterno della catena dei bacini torbiditici (Flysch), del fronte deformativo compressivo e del conseguente ricoprimento da parte dei complessi liguri ed epiliguri. Nella "zona della Val Marecchia", procedendo da SW a NE si attraversano fasce subparallele a direzione appenninica di età sempre più giovane, separate tra loro da contatti di sovrapposizione tettonica e costituite da unità arenacee risedimentate chiuse da sedimenti marnoso-siltosi. La fascia più sud-occidentale è rappresentata dalle Arenarie del Cervarola-Falterona (Aquitaniano-Langhiano) e dalle Marne di Vicchio (Burdigaliano-Serravalliano), seguita da una seconda di Marnoso-arenacea (Langhiano-Serravalliano) e di "Marne di Verghereto" (Serravalliano-Tortoniano) e infine da quella più esterna di Marnoso-arenacea (Serravalliano-Tortoniano) e di marne dei "ghioli di letto" (Tortoniano-Messiniano inf.). Come si può dedurre dalla loro età le marne legate ai Flysch arenacei sono sia ad essi parzialmente eteropiche (depositi di scarpata a margine del bacino) sia di chiusura della sedimentazione torbiditica.L'evoluzione strutturale della catena è riconducibile, come d'altra parte già riconosciuto da molti autori, ad una tettonica a thrust vergenti a NE, che tendono a raccordarsi nei due livelli principali di scollamento rappresentati dalla Scaglia Toscana-Scaglia Cinerea e dalle più profonde evaporiti triassiche. L'età dei thrust è progressivamente più recente verso NE e la loro formazione è collegabile ad altrettanti eventi compressivi separati da più lunghi periodi di stasi.I rapporti fra tettonica e sedimentazione, anche se un notevole limite alla definizione cronologica degli eventi sopra descritti deriva dalla non precisa datazione dei litosomi risedimentati, possono essere così schematizzati:- il carico tettonico delle falde delimitate dai thrust determina una subsidenza (avanfossa) nella zona esterna a cui si associa ancora più all'esterno un sollevamento periferico (peripheral bulge );- nella zona subsidente s'incanalano le torbide arenacee mentre nelle zone marginali e più elevate si sedimentano marne che rappresentano in buona parte la componente pelitica delle torbide;- la sedimentazione torbiditica viene chiusa da quella marnosa quando l'avanfossa viene ad essere coinvolta nell'attivazione della compressione (fronte deformativo), che porterà alla diretta sovrapposizione delle Liguridi sui depositi marnosi. In alcuni casi l'instabilità del bacino è testimoniata dalla messa in posto di frane sottomarine sia formazionali che extraformazionali che precedono l'arrivo della coltre ligure;- all'esterno del sollevamento periferico, che inizialmente può essere di tipo flessurale, ma che si evolve come thrust nell'evento tettonico successivo, si sviluppa un'area subsidente che diventerà un ulteriore bacino torbiditico, quindi sfasato nello spazio e nel tempo rispetto al precedente, - nei bacini epiliguri gli eventi tettonici corrispondenti alla massima attivazione dei thrust sono registrati da discontinuità nelle sequenze sedimentarie, che possono essere rappresentate da brusche variazioni batimetriche e/o discordanze angolari con o senza emersione (lacune stratigrafiche).Sulla base dei dati raccolti, integrati da quelli bibliografici, sono riconoscibili diversi eventi tettonici compressivi, che vengono datati sulla base dell'età delle marne di chiusura dei bacini torbiditici:1) Evento burdigaliano - caratterizzato dalla sovrapposizione del Macigno del Chianti sulle Arenarie del Cervarola-Falterona (fronte della Falda Toscana AA.) e dalla discontinuità nell'epiligure tra le Formazioni di Antognola (Oligocene sup.-Burdigaliano inf.) e quelle soprastanti di Bismantova-S. Marino (Burdigaliano sup.-Langhiano inf.);2) Evento serravalliano -
1992
- Itinerario n°12. Dal Valdarno a San Marino.
[Capitolo/Saggio]
Bortolotti, V; Bruni, P; Conti, Stefano; Sani, F; Amorosi, A.
abstract
INFORMAZIONI GENERALI SULL'ITINERARIOL'itinerario consta di varie parti, che, affrontando temi differenti, possono essere percorse separatamente; il tempo di percorrenza di una singola parte varia dalla mezza all'intera giornata, mentre l'itinerario completo necessita di almeno 3-4 giorni per poter osservare con calma tutte le varie situazioni e le eventuali località d'interesse artistico-naturalistico.La prima parte.......La seconda parte scende dal Passo dei Mandrioli, in direzione di Bagno di Romagna, fino alla valle del F. Savio, per poi proseguire a destra per Verghereto. Dirigendosi verso Pieve S. Stefano, si entra nella terza parte.....La quarta parte scende dal Passo di Viamaggio lungo la statale n°258, e, dopo aver attraversato Badia Tedalda, entra nella valle del F. Marecchia. All'altezza di Ponte Messa si volta in direzione di Rocca Pratiffi, per poi salire fino a S. Agata Feltria; si scende quindi fino a Sarsina (valle F. Savio), per risalire verso Perticara ed infine ridiscendere nella valle del F. Marecchia (Novafeltria). Il percorso è tutto su strada asfaltata tranne un tratto di circa 3 km in prossimità di Rocca Pratiffi. Da Novafeltria si può passare direttamente all'ultima parte dell'itinerario saltando la quinta parte; questa, dopo aver attraversato Serra di Maiolo, percorre la Valle del F. Marecchia in direzione sud per salire verso Petrella Guidi e Perticara. Si entra quindi nella valle del T. Uso, dopo aver attraversato i paesi di Savignano di Rigo e Rontagnano, per ritornare in valle Marecchia all'altezza di Secchiano.La sesta ed ultima parte attraversa le rocche ed i castelli più caratteristici della Val Marecchia: si passa S. Leo e si scende, percorrendo una stradina sterrata, verso Legnanone e poi a Pietracuta. Successivamente l'itinerario si suddivide in due tappe: la prima sale fino a S. Marino, mentre la seconda raggiunge i borghi di Torriana e Montebello.
1991
- Le “placche” di San Leo e Pennabilli (Val Marecchia): rapporti fra gli elementi strutturali e le deformazioni gravitative profonde
[Relazione in Atti di Convegno]
Conti, Stefano; Tosatti, Giovanni
abstract
Sono state considerate le frane che interessano le placche competenti sulle quali sorgono San Leo e Pennabilli e i sottostanti terreni argillosi. Le placche studiate sono interessate da vari sistemi di fratturazione, causati in massima parte dagli intensi stress tettonici legati ai movimenti di traslazione della coltre della Val Marecchia. I sistemi di fratturazione controllano la scomposizione delle placche e l'evoluzione dei fenomeni franosi. Questi ultimi interessano sia il substrato argilloso che i sovrastanti litotipi rigidi, con modalità differenti nei due tipi di placche studiate. Il presente lavoro analizza i rapporti esistenti fra orientazione ed intensità degli elementi strutturali e distribuzione e frequenza dei movimenti gravitativi. Lo smembramento delle placche in entrambe le situazioni e la distribuzione dei fenomeni franosi lungo i margini delle stesse, pur avvenendo con meccanismi evolutivi diversi, sono riconducibili a deformazioni gravitative profonde di versante, come testimoniato dai numerosi elementi morfologici presenti.
1990
- Geologia dell'Appennino marchigiano-romagnolo tra le valli del Savio e del Foglia (Note illustrative alla carta geologica a scala 1:50.000).
[Articolo su rivista]
Conti, Stefano; con un contributo di FREGNI, P.
abstract
This paper takes into account the relationships between "autochthonous" deposits of the Umbro-Marchean-Romagna sequence and allochthonous ones of the Val Marecchia sheet. New structural data, regarding both Epiligurian and Early Pliocene deposits, show strong evidences of the existence of synsedimentary tectonics. Six depositional sequences, separated by erosional surfaces, have been recognized inside Epiligurian deposits and they were controlled by different tectonic phases. During these phases the movement of the Val Marecchia sheet took place by thrust faults set in imbricated slices along one or more surfaces: Apenninic compressional regime (from SW to NE) caused this pattern and modelled "autochthonous" sequence in folds and slices overthrusted to NE.A deep structural depression, transversal to the Apenninic chain, probably related to wrench-fault tectonics (Grosseto-Marecchia line) occurred since Tortonian and controlled the sedimentation of the Umbro-Marchean-Romagna sequence until Early Pliocene (Globorotalia puncticulata Zone).A palaeogeographic reconstruction of this area during Middle Miocene-Early Pliocene is proposed; Apenninic compressional regime played two different roles in the construction of the structural elements of the Val Marecchia area. Structural "autochthonous" highs became evident since Middle-Late Miocene and controlled rate and dynamics of the "substratum" of the Val Marecchia sheet. On the other hand over the allochthonous sheet small sedimentary basins (piggyback and overstep basins) were formed during Middle Miocene to Early Pliocene and their stratigraphic wedging and unconformities were controlled by continuous movement of the Val Marecchia sheet.
1990
- Upper Ordovician Bryozoa from Sardinia.
[Articolo su rivista]
Conti, Stefano
abstract
This paper presents the taxonomical descriptions of Upper Caradocian to Ashgillian bryozoans recovered from different localities from SW Sardinia and from one locality (Mulargia lake) from SE Sardinia. The investigated fauna belongs to 4 bryozoan orders: the Trepostomata, the Cystoporata, the Cryptostomata and the extant order Tubuliporata. These orders are represented by 39 species belonging to 28 genera. Twenty species and one cryptostome genus (Stereodictya) are new. The Trepostomata are the main constituents of the fauna; nevertheless in some localities (Mulargia lake, Portixeddu cove) the Cryptostomata become prevalent. The following new trepostome species are described: Batostoma phragmorarum, Bythopora crenulata, Dekayia minima, Dianulites cupuliformis, Diplotrypa sardoa, Eridotrypa constans, Eridotrypa obliqua, Hallopora cystoidalis, Hemiphragma curvilineum, Hemiphragma subtile, Panderpora gemmata, Panderpora moniliformis and Stigmatella sinuosa. The following new cystoporate species are described: Ceramoporella discoidalis, Crassaluna cystata and Papillalunaria magnum. The following new cryptostome species are described: Graptodictya vinassae, Nematopora hispida, Stereodictya crassum and Ulricostylus radiatus. Sardinian fauna shows similarities with both fauna of the Carnic Alps and southern France (Montaigne Noire), but this comparison needs further study. In SW Sardinia, the lithostratigraphic unit c (Upper Caradoc-Lower Ashgill) is dominated, in order of abundance, by Hallopora elegantula, Chasmatopora corniculata, Graptodictya meneghinii, Anaphragma meneghinii, Ceramopora discoidalis, Anaphragma regulare and Trematopora sardoa. Whereas in SE Sardinia the same unit is dominated by Chasmatopora corniculata, Graptodictya meneghinii, Hallopora elegantula, Ulricostylus radiatus and Dekayia minima. An important environmental change is shown by the bryozoan fauna, at the base of the unit e (Middle Ashgill), because of the dominance of large dome-like zoaria, belonging to Papillalunaria magnum, Prasopora fistuliporoides, Diplotrypa sardoa and Dianulites cupuliformis; abundant but subordinate are encrusting forms as Ceramophylla sp. and ramose bryozoans Nematopora hispida and Hallopora elegantula.
1989
- L'età della messa in posto della coltre della Val Marecchia. Implicazioni paleogeografiche e strutturali.
[Articolo su rivista]
Conti, Stefano; Fregni, P.; Gelmini, R.
abstract
-----
1988
- Bimineralic (calcareous and phosphatic) skeleton in Late Ordovician Bryozoa from Sardinia: Geological implications.
[Articolo su rivista]
Conti, Stefano; Serpagli, E.
abstract
The study of Palaeozoic Bryozoa from the Upper Ordovician of Sardinia was carried out by integrating the traditional thin section description with the SEM observation of single zooecia or zoarial remnants, isolated by acid acetic technique. This technique was made possible by the presence of a bimineralic (calcareous and phosphatic) skeleton,which is interpreted as the result of the mineralization of the membranous part of the cryptocyst originally very rich in phosphorus. The frequent records of phosphatic bodies in Bryozoa lead us to hypothesize the possibility that some Bryozoa secrete,at least in the Palaeozoic, a phosphatic skeleton in response to particular environmental conditions. The deposition of calcium phosphate occurred in the zooecial cavity owing to the change in chemical conditions between the regeneration and degeneration phases.
1988
- Biomineralizzazione e fosfato di calcio: considerazioni geologico-paleontologiche.
[Articolo su rivista]
Conti, Stefano
abstract
At the onset of hard-part mineralization, during the Precambrian-Cam¬brian transition, most of the organisms formed phosphatic skele¬tons. This event was probably related to a global phosphogenic episode re¬sulted from a prolonged period of anoxia during which high-phosphorus waters were formed in the deep ocean. At the end of the Proterozoic a phase of continental drift produced and in¬creased the rate of oceanic overturn and waters rich of phosphorus were upwelled to continental shelfs. High-phosphorus contents and the formation of extensive shal¬low epicontinental seas, which were available for colonization, caused the change from soft bodied to shelly faunas and the Cambrian radia¬tion event. The present status of knowledge regarding fossil records of the Precambrian-Cambrian transition is rewieved and a trend in the de¬position of hard parts is proposed.
1988
- Carta Geologica dell'area compresa tra i fiumi Savio e Foglia (Appennino romagnolo-marchigiano).
[Cartografia]
Conti, Stefano
abstract
S.EL.CA., Firenze
1987
- Functional morphology of the cap-like apparatus in autozooids of a Paleozoic trepostome bryozoan
[Articolo su rivista]
Conti, Stefano; Serpagli, E.
abstract
Functional morphology in Ordovician bryozoa
1987
- L'età della messa in posto della coltre della Val Marecchia. Implicazioni paleogeografiche e strutturali.
[Relazione in Atti di Convegno]
Conti, Stefano; Fregni, P.; Gelmini, R.
abstract
---
1986
- Studio geologico della geotraversa Grosseto-Val Marecchia tra le valli del Savio e del Foglia (Appennino romagnolo-marchigiano).
[Monografia/Trattato scientifico]
Conti, Stefano
abstract
Tesi di Dottorato, Biblioteca Nazionale di Firenze
1984
- A new interpretation of the anthozoan Septodaeum Bischoff, 1978 as a bryozoan.
[Articolo su rivista]
Conti, Stefano
abstract
----
1983
- Un esempio di fossilizzazione eccezionale in alcuni Briozoi dell'Ordoviciano della Sardegna
[Articolo su rivista]
Conti, Stefano
abstract
viene descritto per la prima volta la fossilizzazione di un polipide in uno zoecio
1982
- A new morphological structure in some Ordovician bryozoans from Sardinia
[Relazione in Atti di Convegno]
Serpagli, Enrico; Conti, Stefano
abstract
Ordovician Bryozoa from Sardinian°280Paleont. Contr. Univ. Oslo