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Luigi BRUNO

Professore Associato
Dipartimento di Scienze Chimiche e Geologiche - Sede Dipartimento di Scienze Chimiche e Geologiche

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Pubblicazioni

2024 - Multi-source detrital contributions in the Po alluvial basin (northern Italy) since the Middle Pleistocene. Insights into sediment accumulation in intermediate sinks [Articolo su rivista]
Demurtas, L.; Fontana, D.; Lugli, S.; Bruno, L.
abstract

Integrated stratigraphic-compositional studies on alluvial successions provide a valuable tool to investigate the provenance of detritus in multi-source systems. The Po Plain is an intermediate sink of the Po-Adriatic source-to-sink system, fed by rivers draining two orogens. The Alps are characterized by extensive outcrops of plutonic-metamorphic and ultramafic rocks to the north-west and of Mesozoic carbonates to the east (Southern Alps). The Northern Apennines, to the south, are dominated by sedimentary successions. The Po River flows from the Western Alps to the Adriatic Sea, interacting with a dense network of transverse tributaries that drain the two orogens. Stratigraphic, sedimentological and compositional analyses of two 101 and 77.5 m-long cores, recovered from the Central Po Plain, reveal the stacking of three petrofacies, which reflects distinct provenance and configurations of the fluvial network. A South-Alpine sedimentary input between MIS 12 and MIS 10 is testified by petrofacies 1, characterized by carbonate- and volcanic-rich detritus from rocks exposed in the Southern Alps. A northward shift of the Po River of more than 30 km is marked by a quartz-feldspar and metamorphic-rich detritus (petrofacies 2), similar to modern Po River sands. This dramatic reorganization of the fluvial network likely occurred around MIS 9-MIS 8 and is possibly structurally controlled. A further northward shift of the Po River and the onset of Apennine sedimentation in the Late Holocene is revealed by petrofacies 3, rich in sedimentary lithics from the Apennine successions. The results of this study document how compositional analysis, if framed in a robust stratigraphic picture, may provide clues on the evolution of multi-source alluvial systems.Inferred palaeogeography of the central Po Plain, deduced from compositional variations of core sands, during: (a) MIS 12 and MIS 10 (petrofacies 1). (b) MIS 5-4 (petrofacies 2). (c) MIS 2 (petrofacies 2). (d) The early Holocene (petrofacies 2). (e) The late Holocene (petrofacies 3).image

2023 - Sedimentary facies characterization through CPTU profiles: An effective tool for subsurface investigation of modern alluvial and coastal plains [Articolo su rivista]
Campo, B.; Bruno, L.; Amorosi, A.
abstract

Cone penetration tests, a method that is typically used to determine the engineering properties of soils, can be used as an effective tool for refined subsurface stratigraphic investigations of alluvial and coastal plains, aside from the geographic location. High-resolution calibration of piezocone penetration tests (CPTU) with 20 sediment cores enabled the detailed characterization of alluvial, deltaic and coastal depositional systems of the Po Plain. Twelve cored facies associations, typical of alluvial and coastal plain environments, were characterized based on four distinct CPTU profiles: basic cone resistance (Qc), sleeve friction (Fs), water pore pressure (U) and friction ratio (FR). Sandy facies associations (fluvial/distributary channel, bay-head delta, transgressive barrier, delta-front/beach-ridge) typically have high (>4 MPa) Qc, low-to-negative U and low (<2%) FR. Muddy deposits (well-drained/poorly-drained floodplain, swamp, lagoon and prodelta) exhibit opposite trends. Heterolithic facies associations (crevasse-levee, offshore/delta-front transition) display characteristic seesaw profiles. Plotting of late Quaternary deposits onto the latest version of the cone penetration test typical soil behaviour chart (Robertson, 2010) enables the identification of distinctive facies associations reflecting distinctive grain size. CPTU interpretation leads to sedimentary facies recognition well beyond the simple lithological differentiation and, in particular, allows the refined characterization of clay-rich and silt-rich depositional units (swamp clays and peats, central-inner and outer lagoon, proximal/distal prodelta deposits) that exhibit only subtle differences in lithology. CPTU data can also serve for the accurate detection of key stratigraphic surfaces with potential engineering applications, such as the Pleistocene-Holocene boundary. This latter, a common feature of several alluvial and coastal plain successions, is commonly marked by an abrupt upward decrease of basic cone resistance and sleeve friction from Late Pleistocene, pedogenized, stiff strata to overlying Holocene, organic-rich, soft deposits. This study offers an updated CPTU-facies characterization method that could be suitable for subsurface investigations of modern alluvial and coastal plains worldwide.

2022 - A strontium isoscape of Italy for provenance studies [Articolo su rivista]
Lugli, F.; Cipriani, A.; Bruno, L.; Ronchetti, F.; Cavazzuti, C.; Benazzi, S.
abstract

We present a novel database of biological and geological 87Sr/86Sr values (n = 1920) from Italy, using literature data and newly analysed samples, for provenance purposes. We collected both bioavailable and non-bioavailable (i.e. rocks and bulk soils) data to attain a broader view of the Sr isotope variability of the Italian territory. These data were used to build isotope variability maps, namely isoscapes, through Kriging interpolations. We employed two different Kriging models, namely Ordinary Kriging and Universal Kriging, with a geolithological map of Italy categorized in isotope classes as external predictor. Model performances were evaluated through a 10-fold cross validation, yielding accurate 87Sr/86Sr predictions with root mean squared errors (RMSE) ranging between 0.0020 and 0.0024, dependent on the Kriging model and the sample class. Overall, the produced maps highlight a heterogeneous distribution of the 87Sr/86Sr across Italy, with the highest radiogenic values (>0.71) mainly localized in three areas, namely the Alps (Northern Italy), the Tuscany/Latium (Central Italy) and Calabria/Sicily (Southern Italy) magmatic/metamorphic terrains. The rest of the peninsula is characterized by values ranging between 0.707 and 0.710, mostly linked to sedimentary geological units of mixed nature. Finally, we took advantage of the case study of Fratta Polesine, to underscore the importance of choosing appropriate samples when building the local isoscape and of exploring different end-members when interpreting the local Sr isotope variability in mobility and provenance studies. Our user-friendly maps and database are freely accessible through the Geonode platform and will be updated over time to offer a state-of-the-art reference in mobility and provenance studies across the Italian landscape.

2022 - Evolution of the Po–Alpine River System during the Last 45 Ky Inferred from Stratigraphic and Compositional Evidence (Ostiglia, Northern Italy) [Articolo su rivista]
Demurtas, L.; Bruno, L.; Lugli, S.; Fontana, D.
abstract

The stratigraphic and compositional study of three sediment cores recovered close to the Po River near Ostiglia provides clues on changes in fluvial dynamics at the transition from the last glacial to the present interglacial. Upper Pleistocene units are dominated by sands with high content in volcanic lithics, denoting high sediment supply from the south-Alpine fluvio-glacial tributary system. The Early–Mid Holocene unit, peat-rich and barren in fluvial sands, results from low sediment supply and waterlogging, encompassing the maximum marine ingression. The Late Holocene unit, characterized by fluvial-channel sands with lower content in volcanics and relatively abundant metamorphic lithics, records the Po River sedimentation since the Late Bronze Age. Late Holocene sands show a lower content in siliciclastic lithic fragments (supplied mainly by Apennine tributaries) compared to modern Po River sands. This distinctive composition could reflect the diversion of Apennine sediments into a southern Po River branch during the Late Bronze Age and into an Apennine collector flowing south of Ostiglia during Roman times and the Middle Ages. The integrated stratigraphic-compositional methods used in this study permitted to reconstruct the major climate-related changes in sediment dispersal and may be potentially applied to other alluvial and coastal settings.

2022 - Timing and mechanisms of sediment accumulation and pedogenesis: Insights from the Po Plain (northern Italy) [Articolo su rivista]
Bruno, L.; Campo, B.; Hajdas, I.; Hong, W.; Amorosi, A.
abstract

The relationships between pedogenetic processes and fluvial-coastal dynamics in the Po Plain have been reconstructed through sedimentological analysis and correlation of ca. 170 core data chronologically constrained by 376 radiocarbon dates. Vertically stacked, weakly developed paleosols within Upper Pleistocene and Holocene mud-prone strata testify to intermittent pedogenesis, periodically interrupted by overbank sedimentation. Individual paleosols are laterally traceable for tens of km and exhibit A-Bk-Bw, A-Bk or A-Bw profiles. Stratigraphically ordered 14C calibrated ages from A organo-mineral horizons testify to slow aggradation during 4–6 thousand years-long exposure periods. Burial ages, with an error of few centuries, are provided by plant debris at the top of A horizons. Millennial-scale climate oscillations and glacio-eustasy are the main drivers of the pedo-sedimentary evolution of the area during the last 50 kyr. Upper Pleistocene paleosols (P1-P3) developed in well-drained floodplain environments, during relatively warm periods. Paleosol burial occurred during colder phases. High-sediment-supply during the Last Glacial Maximum hindered pedogenesis and led to the accumulation of 3–10 m-thick overbank strata. Widespread soil development (paleosol PH) occurred at the end of Last Glacial Maximum, following the retreat of Alpine glaciers and the afforestation of Apennine drainage basins. At distal locations, paleosol PH was progressively buried under estuarine sediments during the Holocene phases of post-glacial sea-level rise. Beyond the area of marine influence, burial ages of paleosol PH change from a place to another without specific spatial trends and reflect upstream fluvial sedimentation dominated by avulsions and deposition of spatially restricted alluvial units. Holocene (H1−H2) paleosols show a poor correlation potential and laterally variable degree of maturity that reflect avulsive sedimentation patterns and crevassing. This paper provides insights on the timing and mechanisms of formation and burial of weakly-developed paleosols. The outcomes of this research are applicable to similar Quaternary alluvial systems, and may help interpreting ancient paleosol-bearing successions.

2021 - Deformation patterns of upper Quaternary strata and their relation to active tectonics, Po Basin, Italy [Articolo su rivista]
Amorosi, A.; Bruno, L.; Campo, B.; Costagli, B.; Hong, W.; Picotti, V.; Vaiani, S. C.
abstract

Despite increased application of subsurface datasets below the limits of seismic resolution, reconstructing near-surface deformation of shallow key stratigraphic markers beneath modern alluvial and coastal plains through sediment core analysis has received little attention. Highly resolved stratigraphy of Upper Pleistocene to Holocene (Marine Isotope Stage 5e to Marine Isotope Stage 1) alluvial, deltaic and coastal depositional systems across the southern Po Plain, down to 150 m depth, provides an unambiguous documentation on the deformation of previously flat-lying strata that goes back in time beyond the limits of morphological, historical and palaeoseismic records. Five prominent key horizons, accurately selected on the basis of their sedimentological characteristics and typified for their fossil content, were used as highly effective stratigraphic markers (M1 to M5) that can be tracked for tens of kilometres across the basin. A facies-controlled approach tied to a robust chronology (102 radiocarbon dates) reveals considerable deformation of laterally extensive nearshore (M1), continental (M2 and M3) and lagoon (M4 and M5) marker beds originally deposited in a horizontal position (M1, M4 and M5). The areas where antiformal geometries are best observed are remarkably coincident with the axes of buried ramp anticlines, across which new seismic images reveal substantially warped stratal geometries of Lower Pleistocene strata. The striking spatial coincidence of fold crests with the epicentres of historic and instrumental seismicity suggests that deformation of marker beds M1 to M5 might reflect, in part at least, syntectonically generated relief and, thus, active tectonism. Precise identification and lateral tracing of chronologically constrained stratigraphic markers in the 14C time window through combined sedimentological and palaeoecological data may delineate late Quaternary subsurface stratigraphic architecture at an unprecedented level of detail, outlining cryptic stratal geometries at the sub-seismic scale. This approach is highly reproducible in tectonically active Quaternary depositional systems and can help to assess patterns of active deformation in the subsurface of modern alluvial and coastal plains worldwide.

2021 - Millennial-scale shifts in microtidal ecosystems during the Holocene: dynamics and drivers of change from the Po Plain coastal record (NE Italy) [Articolo su rivista]
Rossi, V.; Barbieri, G.; Vaiani, S. C.; Cacciari, M.; Bruno, L.; Campo, B.; Marchesini, M.; Marvelli, S.; Amorosi, A.
abstract

Framed into a robust stratigraphic context, multivariate analyses on the Holocene palaeobiological record (pollen, benthic foraminifers, ostracods) of the Po coastal plain (NE Italy) allowed the investigation of microtidal ecosystems variability and driving parameters along a 35-km-long land–sea transect. Millennial-scale ecosystem shifts are documented by coeval changes in the meiofauna, reflecting variations in organic matter–water depth (shallow-marine environments) and degree of confinement-salinity (back-barrier settings). In-phase shifts of vegetation communities track unsteady water-table levels and river dynamics in freshwater palustrine areas. Five environmental–ecological stages followed one another crossing four tipping points that mark changes in relative sea level (RSL), climate and/or fluvial regime. At the culmination of Mediterranean RSL rise, after the 8200 event, remarkable growth of peatlands took place in the Po estuary, while low accumulation rates typified the shelf. At the transgressive–regressive turnaround (~7000 cal a bp), the estuary turned into a delta plain with tidally influenced interdistributary embayments. River flow regime oscillations after the Climate Optimum (post-5000 cal a bp) favoured isolation of the bays and the development of brackish wetlands surrounded by wooded peatlands. The youngest threshold (~800 cal a bp), which led to the establishment of the modern delta, reflects a major avulsion of the Po River.

2021 - Patterns of geochemical variability across weakly developed paleosol profiles and their role as regional stratigraphic markers (Upper Pleistocene, Po Plain) [Articolo su rivista]
Amorosi, A.; Bruno, L.; Campo, B.; Di Martino, A.; Sammartino, I.
abstract

Weakly developed paleosols from two distinct interfluve surfaces of Late Pleistocene age provide excellent keys to high-resolution stratigraphic correlation and may serve to trace large-scale genetic packages (systems tract equivalents) across the continental portion of the Po Basin. Twenty-four paleosol profiles from 17 sediment cores were identified and characterized for bulk-geochemical analysis. X-ray fluorescence data were used to trace the degree of weathering. Paleosols, 0.5–1.5 m thick, are pedogenically altered floodplain deposits, developed over time spans of a few thousand of years and mostly partitioned into A-Bk horizons. The most notable paleosol features are dark, organic-matter-rich and carbonate-free mineral surface horizons (A) that overlie bright calcic horizons (Bk) typified by the accumulation of secondary carbonates in the form of pedogenic nodules. Paleosol profiles exhibit a homogeneous geochemical signature that fingerprints a moderate degree of weathering, with little strike- and dip-oriented variability across the different study localities. Plots of Al-normalized calcification and base loss indices against depth reveal systematic increasing values from intensely altered A horizons to underlying Bk horizons. These trends reflect consistent patterns of Ca translocation from surface horizons deeper into the profile, with significant to almost complete Ca removal from A horizons through leaching and accumulation in Bk horizons. Selected trace element ratios (Ba/Sr, Rb/Sr), redox-sensitive trace elements and Zr contents display opposite, up-profile increasing trends that reflect Sr loss in A horizons, with selective Zr concentration in residual minerals. Vertical trends in element ratios are laterally extensive and consistent on a regional basis and represent key pedochemical/stratigraphic markers that can be traced over great distances (tens of kms) throughout the inland portion of the basin. Through quantitative assessment of the degree of weathering, geochemical profiling provides high potential for robust subsurface paleosol correlation that might not be captured by visual core descriptions alone.

2021 - Tracing marine flooding surface equivalents across freshwater peats and other wetland deposits by integrated sedimentological and pollen data [Articolo su rivista]
Amorosi, A.; Bruno, L.; Cacciari, M.; Campo, B.; Rossi, V.
abstract

Large volumes of peatland deposits characterise the Holocene stratigraphy of the Po Plain. A combination of sedimentological and pollen-based paleoenvironmental analyses enables recognition and stratigraphic correlation of small-scale (2–5 m thick) packages of peat-bearing strata, stacked rhythmically in a retrogradational to progradational set and bounded by chronostratigraphically significant surfaces. Across these repetitive lithofacies successions, the proportion of facies-controlled palynomorphs is used as a diagnostic signature to characterise marine flooding surface equivalents (helophytes and hydrophytes) and shoaling-upward (terrestrialization) trends (trees and mesophilous herbs) that record systematic variations in groundwater table associated with increasing/decreasing accommodation. Paludification surfaces at the base of peats delineate the updip (freshwater) equivalents of brackish/marine flooding surfaces recognized at seaward locations atop peat layers (give-up transgressive surfaces). Peat beds exhibit maximum thickness in aggradational strata of the lowermost highstand systems tract, above the maximum flooding surface (MFS). An extrinsic control due to eustatic rise can be inferred for peat development in transgressive deposits: peats, in particular, reveal warmer climates at flooding surfaces (specifically around the MFS) that invariably coincide with rapid shifts to deeper depositional environments. Under highstand conditions, autogenic mechanisms affected base-level changes in the paralic swamps. At this stratigraphic level, peat-bearing strata primarily reflect subtle changes in accommodation due to distributary-channel avulsion, subsidence, and peat autocompaction. Detailed patterns of Holocene peat distribution on millennial timescales can help decipher multiple high-resolution accommodation cycles developed in the rock record on sub-seismic scales, resulting in an improved stratigraphic analysis and prediction of chronologically less constrained non-marine successions.

2021 - Trunk river and tributary interactions recorded in the Pleistocene–Holocene stratigraphy of the Po Plain (northern Italy) [Articolo su rivista]
Bruno, L.; Amorosi, A.; Lugli, S.; Sammartino, I.; Fontana, D.
abstract

Tributary rivers can contribute significantly to alluvial-plain construction by supplying large volumes of clastic material. Their relation to the main axial river strongly influences sediment deposition and preservation. The Po Plain is fed by the Po River and a dense network of transverse tributaries draining the nearby Alpine and Apennine chains. Stratigraphic, sedimentological, petrographic and geochemical analyses on 38 cores permitted detailed differentiation of Po and Apennine sedimentary units. Po River deposits are vertically stacked channel-belt sand bodies with high contents of quartz–feldspar and metamorphic rock fragments, combined with high chromium levels. These sand bodies, 20 to 30 km wide, are replaced southward by finer-grained deposits that represent the distal Apennine tributary-rivers system. Apennine sands, confined in narrow ribbons, show lower quartz–feldspar contents, abundant sedimentary lithics and lower chromium levels. In the last 870 kyr, the boundary between the Po and the Apennine sediment delivery systems shifted along a north–south axis in response to distinct controlling factors. A 20 km northward shift of the Po channel belt, possibly related to a tectonic event, is recorded across a regional unconformity dating to the Marine Isotope Stage 12/11 transition. High sediment supply rates during glacial-lowstand periods widened the Po channel belt southward towards the Apennine domain for a few kilometres. The Last Glacial Maximum channel-belt sand body, 30 km wide and 40 m thick, progressively narrowed northward after the glacial culmination. During the Holocene, channel patterns became avulsive and distributive. Narrow channel belts (<3 km) formed along the Po River branches, and abundant swamp and poorly drained-floodplain muds were preserved in interfluvial areas. Activation and deactivation of the Po branches resulted in sharp narrowing and widening of the area available for Apennine-rivers sedimentation. This work provides insights into tributary-trunk river relations which control grain-size distribution and compositional characters of subsurface deposits.

2020 - Basin-scale stratigraphic correlation of late Pleistocene-Holocene (MIS 5e-MIS 1) strata across the rapidly subsiding Po Basin (northern Italy) [Articolo su rivista]
Campo, B.; Bruno, L.; Amorosi, A.
abstract

Eight stratigraphic transects, 40–140 km long reveal, for the first time on a regional scale, a comprehensive picture of facies architecture of the highly preserved Late Pleistocene-Holocene sedimentary succession from the rapidly subsiding Po Basin. Facies analysis and pollen-based correlation, supported by radiocarbon, electron-spin resonance and optically stimulated luminescence dates, enabled the attribution of distinct stratigraphic intervals to Marine Isotope Stages (MIS) 6 to 1. Basin-scale facies changes appear to have been driven mostly by glacio-eustatic oscillations falling in the Milankovitch band (∼100 ky). The MIS 5e coastal wedge was tracked continuously beneath the modern shoreline, for over 110 km along strike. Along-dip (west-east) stratigraphic correlation over 140 km revealed the characteristic landward transition from shallow-marine and coastal facies to lagoonal, swamp, and floodplain deposits. The MIS 5d-MIS 2 stratigraphic succession, up to 95-m-thick, records the stepped, basinward shift of facies related to the post-MIS 5e sea-level fall. In particular, lagoon and swamp facies mark minor transgressions (Substages 5c and 5a), whereas thick floodplain deposits and laterally extensive (>40 km) fluvial channel-belts, up to 30 m thick, characterized the glacial periods (MIS 4 and MIS 2). The Holocene (MIS 1) coastal wedge shares many similarities in terms of facies architecture and geometry with its MIS 5e counterpart, though maximum landward marine incursion during the MIS 5e transgression was 10 km farther inland (36 km inland of modern shoreline). Organic-rich (freshwater swamp) environments developed > 100 km landwards of the present-day coastline. The MIS 5e-MIS 1 succession of the Po Basin displays an exceptional thickness, up to 130 m. Minimum values (∼20 m) are recorded close to the Apennine margin and above the buried actively growing anticlines. The spatial distribution and geometry of the MIS 5e-MIS 1 strata, as well as rapidly varying subsidence rates (from 0.2 to 1.0 mm/y) reflect the strong influence of the structural setting (location of major thrust fronts) over the creation/destruction of accommodation.

2020 - Climate control on stacked paleosols in the Pleistocene of the Po Basin (northern Italy) [Articolo su rivista]
Bruno, L.; Marchi, M.; Bertolini, I.; Gottardi, G.; Amorosi, A.
abstract

Paleosols are recurrent features in alluvial successions and provide information about past sedimentary dynamics and climate change. Through sedimentological analysis on six sediment cores, the mud-dominated succession beneath the medieval ‘Two Towers’ of Bologna was investigated down to 100 m depth. A succession of weakly developed paleosols (Inceptisols) was identified. Four paleosols (P1, P2, P3 and PH) were radiocarbon-dated to 40–10 cal ka bp. Organic matter and CaCO3 determinations indicate low groundwater levels during soil development, which spanned periods < 5 ka. The development and burial of soils, which occurred synchronously in the Bologna region and in other sectors of the Po Plain, are interpreted to reflect climatic and eustatic variations. Climatic oscillations, at the scale of the Bond cycles, controlled soil development and burial during Marine Isotope Stage (MIS) 3 (P1 and P2). Rapid sea-level oscillations probably induced soil development at the MIS 3/2 transition (P3) and favored burial of PH after 10 ka bp. Weakly developed paleosols in alluvial successions can provide clues to millennial-scale climatic and environmental variations. In particular, the paleosol-bearing succession of the Po Plain represents an unprecedent record of environmental changes across the Late Pleistocene (MIS 3 and 2) in the Mediterranean region.

2020 - Factors controlling natural subsidence in the Po Plain [Altro]
Bruno, Luigi; Campo, Bruno; Costagli, Bianca; Stouthamer, Esther; Teatini, Pietro; Zoccarato, Claudia; Amorosi, Alessandro
abstract

2020 - Linking Holocene vegetation dynamics, palaeoclimate variability and depositional patterns in coastal successions: Insights from the Po Delta plain of northern Italy [Articolo su rivista]
Cacciari, M.; Amorosi, A.; Marchesini, M.; Kaniewski, D.; Bruno, L.; Campo, B.; Rossi, V.
abstract

Mediterranean deltaic-coastal plains represent relatively underexplored depositional archives that record the Holocene response of vegetation and depositional systems to high-frequency climate changes. In this study, we examine a 25 m-thick succession of Holocene age (core EM2) recovered in the innermost portion of the Po delta plain of northern Italy, applying an integrated palyno-stratigraphic approach. The existence of a paludal, freshwater setting inland of the line of maximum marine transgression favoured a low degree of pollen transportation. Application of cluster analysis to this palynological record leads to the identification of pollen-derived biomes and seven (auto)ecological groups of taxa that discriminate environmental signal (depositional facies) and regional climate conditions within a well-dated coastal record. Percentage variations of hygrophytes, aquatics and pasture-meadow herbs reveal local environmental dynamics, enabling the detailed facies characterisation of the cored succession, especially in terms of water table conditions. Framed into a chronologically constrained, high-resolution facies context, the proportion of montane taxa (climate degradation indicator) relative to Mediterranean taxa and Quercus + other deciduous trees (climate optimum indicators) highlight a vegetation-climate variability in the plain that fits with Bond events, especially for the early-mid Holocene (i.e., Preboreal and Boreal Oscillation, 8.2 ka event), supporting a strong Mediterranean–North Atlantic climate connection. For the first time, pollen from a continental succession of the Adriatic area clearly depicts the effects of the 8.2 ka cooling event on vegetation patterns (progressive degradation in high altitude communities) and depositional dynamics (increased fluvial activity), assessing the major role played by climate changes in shaping coastal landscapes in addition to glacio-eustatic variations.

2020 - Tracing clinothem geometry and sediment pathways in the prograding Holocene Po Delta system through integrated core stratigraphy [Articolo su rivista]
Amorosi, A.; Bruno, L.; Campo, B.; Costagli, B.; Dinelli, E.; Hong, W.; Sammartino, I.; Vaiani, S. C.
abstract

Though clinothem geometry represents a key control on fluid flow in reservoir modelling, tracing clinothem boundaries accurately is commonly limited by the lack of sufficiently precise outcrop or subsurface data. This study shows that in basin systems with strongly heterogeneous compositional signatures, the combination of bulk-sediment geochemistry and benthic foraminiferal distribution can help identify clinothem architecture and generate realistic models of 3D deltaic upbuilding and evolution. Middle-late Holocene deposits in the Po Delta area form an aggradational to progradational parasequence set that reveals the complex interaction of W–E Po Delta progradation, S-directed longshore currents (from Alpine rivers) and Apennines rivers supply. Unique catchment lithologies (ophiolite rocks and dolostones) were used to delineate basin-wide geochemical markers of sediment provenance (Cr and Mg) and to assess distinctive detrital signatures. The geochemical characterization of cored intervals across different components of the sediment routing system enabled a direct linkage between clinothem growth, transport pathways and provenance mixing to be established. On the other hand, abrupt microfaunal variations at clinothem boundaries were observed to reflect the palaeoenvironmental response to sharp changes in sediment flux and fluvial influence. This study documents the ability of an integrated geochemical and palaeoecological approach to delineate three distinct sources (Po, Alps and Apennines) that contributed to coastal progradation and to outline the otherwise lithologically cryptic geometries of clinothems that using conventional sedimentological methods it would be virtually impossible to restore.

2019 - From geological and historical data to the geotechnical model of the Two Towers in Bologna (Italy) [Relazione in Atti di Convegno]
Marchi, Michela; Bertolini, Ilaria; Gottardi, Guido; Amorosi, Alessandro; Bruno, Luigi
abstract

This paper outlines the multidisciplinary approach developed for the definition of the geotechnical model of the foundations of Asinelli and Garisenda towers in Bologna. Historical information and previous site investigations were collected and analysed. Then a new geotechnical investigation was carried out in 2016, which enabled accurate identification of the soil-foundation systems of both towers. In addition, the geotechnical soil properties were investigated taking into account the geological setting of the area. The latter, enabled the recognition of prominent stratigraphic markers within the ~100 m thick alluvial succession beneath the Two Towers foundations, thus providing a new key to soil mechanical properties. This study enabled the identification of the significant features of foundation structures and subsurface stratigraphy, characters of authenticity of the Two Towers which should be carefully preserved in any future conservation strategy of these valuable monuments

2019 - How Close is Geological Thought to Reality? The Concept of Time as Revealed by the Sequence Stratigraphy of the Late Quaternary Record [Capitolo/Saggio]
Amorosi, Alessandro; Bohacs, Kevin M.; Bruno, Luigi; Campo, Bruno; Drexler, Tina M.
abstract

2019 - Peat layer accumulation and post-burial deformation during the mid-late Holocene in the Po coastal plain (Northern Italy) [Articolo su rivista]
Bruno, L.; Campo, B.; Di Martino, A.; Hong, W.; Amorosi, A.
abstract

Peat horizons are characteristic features of delta plains worldwide. In this study, we tested the use of peat-based correlations to assess the deformation of Holocene strata in the Po coastal plain (Northern Italy). The Holocene stratigraphy, about 30 km inland from the modern coastline consists of a peat-bearing, estuarine and deltaic succession, up to 23 m thick. Through the analysis of 31 core data and 100 piezocone penetration tests, we identified and mapped three 10–40 cm-thick peat layers (T1–T3) dated to 6.6–5.8, 5.5–5.0 and 3.3–2.7 cal kyr BP respectively. These peat horizons were found to be suitable stratigraphic markers within the Holocene succession over an area of about 200 km2. The mid-late Holocene palaeogeography, reconstructed through high-resolution peat correlation, supported by 72 radiocarbon dates, highlights a typical upper delta plain environment, with ribbon-shaped distributary channels and swamp interdistributary areas. Peat layers are inclined towards E-NE with gradients that increase downsection from ~0.016% (T3) to 0.021% (T1). The gradient of the oldest peat horizon is one order of magnitude larger than the slope of the modern delta plain (~0.0025%). We infer that peat horizons accumulated during periods of low sediment supply mainly controlled by autogenic processes and were deformed after deposition. Differential compaction of underlying sedimentary strata and recent tectonic activity of the buried Apenninic thrust systems are the most likely drivers of strata deformation. Based on isochore maps, we document that higher sedimentation rates in topographically depressed areas compensated, in part at least, the ongoing deformation, keeping unaltered the topographic gradient and the depositional environment. This study demonstrates that peat-based correlation and mapping can shed lights on the mechanisms of strata accumulation and deformation in deltaic settings, constituting a robust basis for reconstructing delta evolution.

2019 - Three-fold nature of coastal progradation during the Holocene eustatic highstand, Po Plain, Italy – close correspondence of stratal character with distribution patterns [Articolo su rivista]
Amorosi, A.; Barbieri, G.; Bruno, L.; Campo, B.; Drexler, T. M.; Hong, W.; Rossi, V.; Sammartino, I.; Scarponi, D.; Vaiani, S. C.; Bohacs, K. M.
abstract

Although general trends in transgressive to highstand sedimentary evolution of river-mouth coastlines are well-known, the details of the turnaround from retrogradational (typically estuarine) to aggradational–progradational (typically coastal/deltaic) stacking patterns are not fully resolved. This paper examines the middle to late Holocene eustatic highstand succession of the Po Delta: its stratigraphic architecture records a complex pattern of delta outbuilding and coastal progradation that followed eustatic stabilization, since around 7·7 cal kyr bp. Sedimentological, palaeoecological (benthic foraminifera, ostracods and molluscs) and compositional criteria were used to characterize depositional conditions and sediment-dispersal pathways within a radiocarbon-dated chronological framework. A three-stage progradation history was reconstructed. First, as soon as eustasy stabilized (7·7 to 7·0 cal kyr bp), rapid bay-head delta progradation (ca 5 m year−1), fed mostly by the Po River, took place in a mixed, freshwater and brackish estuarine environment. Second, a dominantly aggradational parasequence set of beach-barrier deposits in the lower highstand systems tract (7·0 to 2·0 cal kyr bp) records the development of a shallow, wave-dominated coastal system fed alongshore, with elongated, modestly crescent beaches (ca 2·5 m year−1). Third, in the last 2000 years, the development of faster accreting and more rapidly prograding (up to ca 15 m year−1) Po delta lobes occurred into 30 m deep waters (upper highstand systems tract). This study documents the close correspondence of sediment character with stratal distribution patterns within the highstand systems tract. Remarkable changes in sediment characteristics, palaeoenvironments and direction of sediment transport occur across a surface named the ‘A–P surface’. This surface demarcates a major shift from dominantly aggradational (lower highstand systems tract) to fully progradational (upper highstand systems tract) parasequence stacking. In the Po system, this surface also reflects evolution from a wave-dominated to river-dominated deltaic system. Identifying the A–P surface through detailed palaeoecological and compositional data can help guide interpretation of highstand systems tracts in the rock record, especially where facies assemblages and their characteristic geometries are difficult to discern from physical sedimentary structures alone.

2018 - A mid-late Holocene tidally-influenced drainage system revealed by integrated remote sensing, sedimentological and stratigraphic data [Articolo su rivista]
Giacomelli, Serena; Rossi, Veronica; Amorosi, Alessandro; Bruno, Luigi; Campo, Bruno; Ciampalini, Andrea; Civa, Andrea; Hong, Wan; Sgavetti, Maria; de Souza Filho, Carlos Roberto
abstract

Despite the growing employment of Remote Sensing (RS) techniques in paleoenvironmental studies, the stratigraphic interpretation of RS-derived paleodrainage traces is still an open issue, as their relation to subsurface is largely unexplored. Here we applied a multi-data analysis approach, including publicly available optical images from different satellites (Landsat, ASTER, Sentinel, Hyperion), LiDAR-derived Digital Terrain Model (DTM), soil reflectance spectra and facies core data, which succeeded in revealing a paleodrainage system buried beneath a 200-sq km wide wetland (the Mezzano Lowland-ML) of the Po coastal plain (northern Adriatic Sea, Italy). Data integration in a GIS environment allowed the 3D mapping of numerous and temporally persistent meandering traces. From distal to proximal locations, the RS-derived traces show a hierarchical organization, in terms of sinuosity and width, and form a dense and dendritic pattern typical of a tidally-influenced system. Surface and subsurface cross-investigation of two meandering traces through soil reflectance spectra and core stratigraphy reveal that these landforms represent the surface expression of buried channels that eroded the underlying lagoonal succession, with lateral transition to intertidal deposits. LiDAR-detected micro-morphologies related to paleomeanders evolution strongly influenced the spatial distribution of mid-late Holocene peat-bearing lithofacies (i.e., salt marsh and swamp), and hence soil moisture distribution, inducing the sharp radiance contrasts (traces) detected by satellite sensors on the surface. On-trace areas invariably lack peat deposits and record the top of 3–4 m-thick channel-fill sands, some 2–4 m below the ground level. In contrast, out-of-trace areas are characterized by organic-rich soils that cap a 2.5–3.5 m-thick succession of intertidal-supratidal peat deposits, accumulated in depressed areas lateral to the channel-levee complex. We conclude that in the early stage of Po Delta construction, between ca. 6000–2500 cal yr BP, two distinct tidal-influenced drainage networks fed the Mezzano Lowland lagoon under a predominantly autogenic control. These findings indicate the suitability of a low-cost RS-stratigraphic approach to improve the reconstruction of past paleogeographic scenarios buried beneath deltaic lowlands, shedding new light on the evolution trends of coastal landforms, environments and sedimentary patterns under highstand conditions.

2018 - Decoupled geomorphic and sedimentary response of Po River and its Alpine tributaries during the last glacial/post-glacial episode [Articolo su rivista]
Bruno, L.; Piccin, A.; Sammartino, I.; Amorosi, A.
abstract

The complex geomorphic and sedimentary evolution of the central Po Plain (northern Italy) during the last 30 ky was reconstructed through the integration of stratigraphic, geomorphological, geochemical and radiocarbon data. A key element of the Late Pleistocene stratigraphy is a 20 km-wide channel-belt sand body, with its top at a depth of ~13 m, fed by the Po River. Whereas the southern boundary of the Po fluvial channel belt coincides with a sharp lithological contact with floodplain muds, its northern boundary is an erosional (sand-on-sand) surface that was traced tentatively in the subsurface with the aid of sediment provenance (Po versus Alpine) proxies and radiocarbon data. Stratigraphic and geomorphological features testify to a decoupled sedimentary and geomorphic response of the Alpine and Po River systems to climate change in the last 30 ky. Contemporaneous Po River incision and Alpine rivers aggradation occurred at the onset of the Last Glacial Maximum (LGM). In contrast, Po River aggradation and Alpine rivers entrenchment took place during early deglaciation. The Holocene stratigraphy records the overall aggradation and northward migration of the Po River, with the consequent erosion of distal Alpine LGM deposits and formation of a fluvial scarp parallel to the Po River course. Late Pleistocene and Holocene climate change influenced river dynamics controlling (i) the balance between sediment supply and water discharge, through glacier and vegetation dynamics, and (ii) the rate of sea-level fall/rise. Apennine, Alpine and Po river systems responded in distinct ways to climate forcing due to the influence of local factors. Lithology, drainage area and mean elevation of river catchments, as well as river and valley gradients, determined the type of sedimentary response (e.g., aggradation versus degradation). This study shows that a combined geomorphic and stratigraphic approach focusing on the geometric relations between exposed and buried features can provide valuable information about the evolution of a fluvial system and its controlling factors.

2018 - Palynological characterization of the Po delta succession (northern Italy): Holocene vegetation dynamics, stratigraphic patterns and palaeoclimate variability [Articolo su rivista]
Cacciari, Marco; Rossi, Veronica; Marchesini, Marco; Amorosi, Alessandro; Bruno, Luigi; Campo, Bruno
abstract

The 40 m-long core EM2, recovered in the innermost portion of Po delta plain, was sampled for palynological analysis, in order to link coastal-deltaic facies architecture to vegetation dynamics and Holocene climate variability. Pollen data refine facies characterization of the 25 m-thick Holocene succession: freshwater swamp clays alternating with overbank/channel sands document millennial to centennial-scale water table oscillations that invariably peak in correspondence of peaty layers. Pollen signature allows identification of the landward equivalent of the Maximum Flooding Surface atop the 7.6 ka-dated peaty interval and furnishes new insights on the relationship between coastal facies patterns and climate events.

2017 - Early Holocene transgressive palaeogeography in the Po coastal plain (northern Italy) [Articolo su rivista]
Bruno, Luigi; Bohacs, Kevin M.; Campo, Bruno; Drexler, Tina M.; Rossi, Veronica; Sammartino, Irene; Scarponi, Daniele; Hong, Wan; Amorosi, Alessandro
abstract

To understand the complex stratigraphic response of a coastal depositional system to rapid eustatic rise and sediment inputs, the evolution of the Adriatic coastline and Po River system, during the post-glacial (Holocene) transgression, was investigated. The landward migration and evolution of a wave-dominated estuary was mapped, based on an extensive data set comprising 14 boreholes, 28 core descriptions and 308 piezocone tests, chronologically constrained between 11·5 and 7·0 kyr bp by 137 radiocarbon dates. Palaeogeographic maps reveal temporal differences in retrogradational geometries and mechanisms that likely underpin shoreline retreat. The Po estuary initially developed within a shallowly incised valley and then spread onto the interfluves. Between 11·5 and 9·2 kyr bp the Po fluvial system became avulsive/distributive and wetlands developed in topographically depressed areas. The shoreline retreated at a mean rate of ca 10 m yearâ 1, between 9·2 kyr and 7·7 kyr bp, following a stepped trajectory at the centennial scale. After 7·7 kyr bp, bayhead deltas started to prograde and partially filled the estuary. The overall stratigraphic architecture is interpreted to reflect the sedimentary response of the coastal depositional system to the main pulses of early Holocene eustatic rise. The influence of antecedent topography, partly due to local subsidence, was dominant at the time of initial transgression. Basin morphology influenced sediment dispersal and partitioning. Sediment supplied by the Po River was trapped within the estuary, whereas coastal sand bodies at the estuary mouth were fed by alongshore currents and by reworking of older barriers. High-resolution age control that ties facies evolution to independently constrained eustasy provides direct data to test models of short-term coastal retreat under conditions of relative sea-level rise, and makes this case study a useful analogue for the interpretation of ancient marginal-marine, retrogradational systems where only stratal geometries are available.

2017 - Global sea-level control on local parasequence architecture from the Holocene record of the Po Plain, Italy [Articolo su rivista]
Amorosi, Alessandro; Bruno, Luigi; Campo, Bruno; Morelli, Agnese; Rossi, Veronica; Scarponi, Daniele; Hong, Wan; Bohacs Kevin, M.; Drexler Tina, M.
abstract

Holocene deposits exhibit distinct, predictable and chronologically constrained facies patterns that are quite useful as appropriate modern analogs for interpreting the ancient record. In this study, we examined the sedimentary response of the Po Plain coastal system to short-term (millennial-scale) relative fluctuations of sea level through high-resolution sequence-stratigraphic analysis of the Holocene succession.Meters-thick parasequences form the building blocks of stratigraphic architecture. Above the Younger Dryas paleosol, a prominent stratigraphic marker that demarcates the transgressive surface, Early Holocene parasequences (#s 1-3) record alternating periods of rapid flooding and gradual shoaling, and are stacked in a retrogradational pattern that mostly reflects stepped, post-glacial eustatic rise. Conversely, Middle to Late Holocene parasequences (#s 4-8) record a complex, pattern of coastal progradation and delta upbuilding that took place following sea-level stabilization at highstand, starting at about 7 cal ky BP. The prominent transgressive surface at the base of parasequence 1 correlates with the period of rapid, global sea-level rise at the onset of the Holocene (MWP-1B), whereas flooding surfaces associated with parasequences 2 and 3 apparently reflect minor Early Holocene eustatic jumps reported in the literature. Changes in shoreline trajectory, parasequence architecture and lithofacies distribution during the following eustatic highstand had, instead, an overwhelming autogenic component, mostly driven by river avulsions, delta lobe switching, local subsidence and sediment compaction. We document a ∼1000-year delayed response of the coastal depositional system to marine incursion, farther inland from the maximum landward position of the shoreline. A dramatic reduction in sediment flux due to fluvial avulsion resulted in marine inundation in back-barrier position, whereas coastal progradation was simultaneously taking place basinwards.We demonstrate that the landward equivalents of marine flooding surfaces (parasequence boundaries) may be defined by brackish and freshwater fossil assemblages, and traced for tens of kilometers into the non-marine realm. This makes millennial-scale parasequences, whether auto- or allogenic in origin, much more powerful than systems tracts for mapping detailed extents and volumes of sediment bodies.The Holocene parasequences of the Po coastal plain, with strong age control and a detailed understanding of sea-level variation, may provide insight into the driving mechanisms and predictability of successions characterized by similar depositional styles, but with poor age constraint, resulting in more robust interpretations of the ancient record.

2017 - Late Quaternary aggradation rates and stratigraphic architecture of the southern Po Plain, Italy [Articolo su rivista]
Bruno, Luigi; Amorosi, Alessandro; Severi, Paolo; Costagli, Bianca
abstract

The Po River Basin, where accumulation and preservation of thick sedimentary packages are enhanced by high rates of tectonic subsidence, represents an ideal site to assess the relations between vertical changes in stratigraphic architecture and sediment accumulation rates. Based on a large stratigraphic database, a markedly contrasting stratigraphy of Late Pleistocene and Holocene deposits is reconstructed from the subsurface of the modern alluvial and coastal plains. Laterally extensive fluvial channel bodies and related pedogenically modified muds of latest Pleistocene age are unconformably overlain by Holocene overbank fines, grading seaward into paralic and nearshore facies associations. In the interfluvial areas, a stiff paleosol, dating at about 12.5–10 cal ky BP, marks the Pleistocene–Holocene boundary. Across this paleosol, aggradation rates (ARs) from 16 radiocarbon-dated cores invariably show a sharp increase, from 0.1–0.9 mm year−1 to 0.9–2.9 mm year−1. Comparatively lower Pleistocene values are inferred to reflect fluvial activity under a low-accommodation (lowstand and early transgressive) regime, whereas higher ARs during the Holocene are related to increasing accommodation under late transgressive and highstand conditions. Holocene sediment accumulation patterns vary significantly from site to site, and do not exhibit common trends. Very high accumulation rates (20–60 mm year−1) are indicated by fluvial channel or progradational delta facies, suggesting that extremely variable spatial distribution of Holocene ARs was primarily controlled by autogenic processes, such as fluvial channel avulsion or delta lobe switching. Contrasting AR between uppermost Pleistocene and Holocene deposits also are reported from the interfluves of several coeval, alluvial-coastal plain systems worldwide, suggesting a key control by allogenic processes. Sediment accumulation curves from adjacent incised valley fills show, instead, variable shapes as a function of the complex mechanisms of valley formation and filling.

2017 - Paleosols and associated channel-belt sand bodies from a continuously subsiding late quaternary system (Po basin, Italy): New insights into continental sequence stratigraphy [Articolo su rivista]
Amorosi, Alessandro; Bruno, Luigi; Cleveland David, M.; Morelli, Agnese; Hong, Wan
abstract

Previous sequence-stratigraphic work has emphasized the key role of paleosols and associated sand-dominated fluvial bodies as key features for interpreting alluvial architecture. The temporal resolution of the ancient record is, however, insufficient to fully explain the complex relationship between soil formation and the evolution of fluvial systems under changing sea-level and climate conditions. In this paper, we present a detailed record of paleosol-channel belt relationships reconstructed from the subsurface of a rapidly subsiding region (Po Plain, Italy) that spans almost all of the last glacial-interglacial cycle (~120 k.y.). The studied succession preserves a systematic bipartite zonation into a thick paleosol-bearing segment close to the basin margin and a sand-dominated interval, with vertically amalgamated channel belts, in an axial position. Individual paleosols are weakly developed and represent key stratigraphic markers that can be traced basinwide into adjacent, essentially contemporaneous, unconfined channel-belt deposits. Unlike conventional models of late Quaternary alluvial-coastal plain systems, no persistent incised valley was established in the Po system during the last glacial-interglacial cycle. Continuous accommodation was the key depositional control on alluvial stratigraphy during the prolonged (~90 k.y.) phase of late Pleistocene sea-level fall, which led to the deposition of a thick, dominantly aggradational alluvial succession. The development of shallowly incised, short-lived valley systems took place only at the transition to glacial stages associated with substantial sea-level drop (marine oxygen isotope stage [MIS] 3-2 transition, and possibly MIS 5-4 transition). This study shows that in rapidly subsiding settings with high rates of sedimentation, incised valley systems may be replaced by aggradationally stacked, essentially non-incised fluvial bodies. In these cases, overbank packages bounded by immature paleosols represent the most likely alternative to the highly weathered interfluve paleosol predicted by classic sequence-stratigraphic models. Fourth-order sequence boundaries and lower-rank erosional surfaces may be easily confused at the ~100 k.y. scale, and transgressive surfaces, defining the onset of retrogradation, may become the most readily identifiable sequence-stratigraphic surfaces.

2017 - Reconstructing Last Glacial Maximum and Younger Dryas paleolandscapes through subsurface paleosol stratigraphy: An example from the Po coastal plain, Italy [Articolo su rivista]
Morelli, Agnese; Bruno, Luigi; Cleveland, David M.; Drexler, Tina M.; Amorosi, Alessandro
abstract

Paleosols are commonly used to reconstruct ancient landscapes and past environmental conditions. Through identification and subsurface mapping of two pedogenically modified surfaces formed at the onset of the Last Glacial Maximum (LGM) and during the Younger Dryas (YD) cold event, respectively, and based on their lateral correlation with coeval channel-belt sand bodies, we assessed the geomorphic processes affecting the Po coastal plain during the Late Pleistocene (30–11.5 cal ky BP). The 3D-reconstruction of the LGM and YD paleosurfaces provides insight into the paleolandscapes that developed in the Po alluvial plain at the transitions between warm and cold climate periods. The LGM paleosol records a stratigraphic hiatus of approximately 5 kyr (29–24 cal ky BP), whereas the development of the YD paleosol was associated with a climatic episode of significantly shorter duration. Both paleosols, dissected by Apennine rivers flowing from the south, dip towards the north-east, where they are replaced by fluvial channel belts fed by the Po River. The LGM channel-belt sand body reflects the protracted lateral migration of the Po River at the onset of the glacial maximum. It is wider (> 24 km) and thicker (~ 15 m) of the fluvial sand body formed during the YD. The northern margin of LGM Po channel-belt deposits was not encountered in the study area. In contrast, a spatially restricted paleosol, identified in the north at the same elevation as the southern plateau, may represent local expression of the Alpine interfluve during the YD event. This study highlights how 3D-mapping of regionally extensive, weakly developed paleosols can be used to assess the geomorphic response of an alluvial system to rapid climate change.

2016 - Contrasting alluvial architecture of Late Pleistocene and Holocene deposits along a 120-km transect from the central Po Plain (northern Italy) [Articolo su rivista]
Campo, Bruno; Amorosi, Alessandro; Bruno, Luigi
abstract

High-resolution investigation of a ~ 120-km-long transect along the course of the modern Po River, northern Italy, revealed marked changes in alluvial architecture across the Pleistocene–Holocene boundary. Along the whole transect, a 20- to 30-m thick sheet-like succession of Late Pleistocene fluvial sands is invariably overlain by silt and clay deposits, with isolated fluvial bodies of Holocene age (< 9.4 cal ka BP). The Holocene succession displays consistent downstream changes in facies architecture: well-drained floodplain deposits are transitional at distal locations to increasingly organic, poorly drained floodplain to swamp facies associations. Thick paludal facies extend continuously up to 60 km landward of the Holocene maximum marine ingression, about 90 km from the modern shoreline. Based on 28 radiocarbon dates, the abrupt change in lithofacies and channel stacking pattern occurred at the transition from the last glacial period to the present interglacial, under conditions of rapid sea-level rise. The architectural change from amalgamated, Late Pleistocene sand bodies to overlying, mud-dominated Holocene units represent an example of chronologically well-constrained fluvial response to combined climate and relative sea-level change. The overall aggradational stacking pattern of individual channel-belt sand bodies indicates that high subsidence rates continuously created accommodation in the Po Basin, even during phases of falling sea level and lowstand.

2016 - Stratigraphic control on earthquake-induced liquefaction: A case study from the Central Po Plain (Italy) [Articolo su rivista]
Amorosi, A; Bruno, L.; Facciorusso, J.; Piccin, A.; Sammartino, I.
abstract

Studies on earthquake-induced liquefaction tied to high-resolution stratigraphic analysis have been rarely undertaken. We report the results of a multidisciplinary study from the Quistello–Moglia area, in the central Po Plain (northern Italy). In this region, combined stratigraphic, sedimentological, geotechnical, and geochemical data allowed assessment of liquefaction potential and identification of the primary source for liquefaction, following the second main shock (Mw ~ 6) of the 2012 Po Plain earthquake. Using Cone Penetration Test (CPT)-based simplified procedures for liquefaction hazard evaluation, we assessed the highest liquefaction potential of Holocene, fluvial-channel and related (crevasse/levee) fine sand-silt facies encased in thick, mud-prone floodplain and swamp successions. The liquefaction potential, and the intensity of the manifestations induced on the ground surface, decreased for the vertically-amalgamated, sheet-like Pleistocene sandy fluvial units encountered at depths greater than 13 m. Floodplain and swamp deposits were virtually non-liquefiable. In the Quistello area, the compositional characterization of sands that were liquefied and extruded during the 2012 earthquake reveals the diagnostic geochemical fingerprint of sediment carried by the Po River, as opposed to the Apennine composition of surficial sediments. These data rule out proximity of liquefied layers to the surface, and attest the buried, meandering Po River system at depths of ~ 7–10 m most likely representing the source for the liquefied sand that vented to the surface. Similarly, at Moglia, liquefied sands were likely sourced from loose and saturated, ribbon-shaped, fluvial sand bodies encased in mud, though at shallower (4–7 m) depths. Pronounced liquefaction phenomena in alluvial plain systems are commonly believed to be associated primarily with elongate topographic ridges following paleo-river courses. Here, we document that under favorable stratigraphic conditions liquefaction may also occur away from surficial channel–levee systems, in areas dominated superficially by overbank fines. Combining subsurface stratigraphic analysis with geotechnical data, thus, is critical to investigate liquefaction patterns and delineate liquefaction hazard zones.

2015 - High-frequency depositional cycles within the late Quaternary alluvial succession of Reno River (Northern Italy) [Articolo su rivista]
Bruno, Luigi; Amorosi, Alessandro; Severi, Paolo; Bartolomei, Paolo
abstract

Palaeosol-based correlations within the Late Pleistocene- Holocene alluvial succession along the Reno River, in the southern Po Plain, enabled the identification of depositional cycles falling in the sub-Milankovitch band. Each cycle, composed of overbank and fluvial facies capped by poorly to weakly developed palaeosols, is correlatable upstream to a single fluvial terrace in the Reno River valley and to an individual channel belt close to the valley outlet. Four cycles, dated to about 15-10 (c1), 10-5.5 (c2), 5.5-1.5 (c3) and <1.5 (c4) cal ky BP, respectively, were identified within the Ravenna subsynthem (AES8), an unconformity-bounded unit of the Geological Map of Italy to scale 1:50,000, corresponding to the post-Last Glacial Maximum deposits. This unit, typically wedge-shaped in coastal areas, where it consists of retrogradational (coastal plain and estuarine) deposits overlain by progradational (deltaic) facies, at the basin margin is a mud-dominated alluvial succession deposited atop laterally extensive fluvial-channel complexes. The base of AES8, correlatable to the transgressive surface identified in the coastal area, is a palaeosol dated to about 18-15 ky BP. The bounding surfaces of the high-frequency cycles are diachronous along the Reno longitudinal profile, and not necessary associated to remarkable lithological contrasts, but can be detected even in mud-dominated successions. Climate change likely exerted a major control in triggering alternating phases of river aggradation and degradation, with an increasing contribution of anthropogenic factors since the middle-late Holocene. Based on the correlation of 34 core logs and 33 well descriptions, with the aid of 71 radiocarbon dates, this study highlights to what extent palaeosols can represent powerful stratigraphic tools to identify cyclic patterns in alluvial successions, even at the millennial time scale.

2015 - The value of pocket penetration tests for the high-resolution palaeosol stratigraphy of late Quaternary deposits [Articolo su rivista]
Amorosi, Alessandro; Bruno, Luigi; Campo, Bruno; Morelli, Agnese
abstract

Pocket penetrometer measurements, though commonly listed as accessory components of core descriptions, are almost totally ignored in shallow subsurface stratigraphic analysis. In this study, we prove that, if properly calibrated with core data, pocket penetration tests may serve as a quick and inexpensive tool to enhance high-resolution (palaeosol-based) stratigraphy of unconsolidated, late Quaternary non-marine deposits. A palaeosol sequence, made up of 12 vertically stacked, weakly developed palaeosols (Inceptisols) dated to the last 40ky cal BP, is reconstructed from the subsurface of the southern Po Plain. The individual palaeosols exhibit flat to slightly undulating geometries and several of them can be tracked over distances of tens of km. They show substantially higher compressive strength coefficients than all other fine-grained, alluvial (floodplain) facies, being typified by distinctive penetration resistance, in the range of 3.5-5kg/cm<sup>2</sup>. Along the palaeosol profiles, A and Bk horizons demonstrate consistent difference in relative compressive strengths, the highest values being almost invariably observed at the A/Bk boundary. Palaeosols are rarely described in conventional stratigraphic logs, and just a small proportion of them is likely to be identified by geologists with no specific sedimentological training. Through core-log calibration techniques, we document that vertical profiles of penetration resistance measured in the field can be used as an efficient method for palaeosol identification, and thus may represent a strategy for predicting stratigraphic architecture from limited core descriptions or poor-quality field logs. This technique allows to optimize the contribution of all available stratigraphic information, expanding significantly the coverage of well-described, one-dimensional core data.

2014 - Paleosol architecture of a late Quaternary basin–margin sequence and its implications for high-resolution, non-marine sequence stratigraphy [Articolo su rivista]
Amorosi, Alessandro; Bruno, Luigi; Rossi, Veronica; Severi, Paolo; Hajdas, Irka
abstract

Paleosol stratigraphy, a technique commonly applied in basin-margin settings to depict cyclic alluvial architecture on time scales of 10-100. ky, can be consistent with regional accommodation trends at even higher temporal resolution (1-10. ky), having strong implications for the sequence stratigraphy of late Quaternary, non-marine deposits. Three closely-spaced late Pleistocene paleosols (P1-P3), dating back approximately to 42-39, 35-31, and 29-26. cal. kyr BP, respectively, form prominent stratigraphic markers across a lithologically homogeneous interfluve succession in the subsurface of Bologna, close to the Apenninic foothills. These paleosols are weakly developed (Inceptisols) and can be tracked continuously for 6. km across the triangle-shaped interchannel zone between two gravel/sand-filled channel systems (Reno and Savena rivers). In particular, the thickest paleosol (P3) is a distinctive stiff horizon that can be traced into laterally extensive, erosional-based fluvial bodies. We infer the correlation between (P3) soil development (and channel downcutting) and the final stage of the stepwise Late Pleistocene sea-level fall that culminated at the marine isotope stage 3/2 transition around 29. cal. kyr BP (low accommodation systems tract). A fourth laterally extensive Inceptisol, encompassing the Pleistocene-Holocene boundary (PH), represents the major phase of soil development since the Last Glacial Maximum and is inferred to be related to channel entrenchment at the onset of the Younger Dryas. With the exception of the Iron Age-Roman paleosol, which reflects a predominantly anthropogenic control, the Holocene paleosols are laterally discontinuous and invariably more immature (Entisols) than their Pleistocene counterparts. This trend of decreasing paleosol development (and correlatability) upsection is interpreted to reflect increasing (transgressive-equivalent) accommodation during sea-level rise, thus confirming the possible extension of models used to interpret the ancient rock record to short-term depositional cycles.

2013 - Human-landscape interactions in the Bologna area (northern Italy) during the mid-late Holocene, with focus on the Roman period [Articolo su rivista]
Bruno, Luigi; Amorosi, Alessandro; R., Curina; P., Severi; R., Bitelli
abstract

Integrated sedimentological and archaeological investigations of mid-late Holocene deposits from the subsurface of Bologna elucidate the complex relationship among urban settlement, human society, geomorphology and climate change at the southern margin of the Po Plain. Above the Pleistocene-Holocene unconformity, the Holocene succession forms an intricate mosaic of alluvial deposits. Two palaeosols, spanning between about 8000-5000 cal. yr BP and 3200-1500 cal. yr BP, respectively, represent the most prominent stratigraphic markers across the study units. A huge amount of archaeological remains from the younger palaeosol enables the identification of an uninterrupted sequence of settlements from the Early Iron Age to the Late Roman period. The first permanent settlements of Iron Age took place in a topographically elevated region protected from flooding. The onset of paedogenesis during this period reflects the radical transformation of the environment by human settlements through widespread control of the river network and setting of regular patterns of irrigation channels. A period of exceptional climate stability characterized the expansion of the Roman Empire. This phase is testified by a wealth of exceptionally preserved archaeological material, including buildings, cemetery sites, streets and irrigation channels. Subsurface correlations of the Roman palaeosol enable detailed reconstruction of the Roman topography, with special focus on fluvial paths and communication routes. The decline of the Roman Empire, hit by a devastating epidemic and the barbarian invasions, was paralleled by a phase of climatic deterioration, resulting in the abandonment of rural lands and degradation of the river network, which ultimately favoured the burial of Roman settlement.

2012 - Subsurface stratigraphy and urban archaeology in the Bologna area [Abstract in Atti di Convegno]
A., Amorosi; Bruno, Luigi; R., Curina; P., Severi; V., Rossi
abstract