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Vittorio MASELLI

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

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Pubblicazioni

2023 - Architecture, structural and tectonic significance of the Seagap fault (offshore Tanzania) in the framework of the East African Rift [Articolo su rivista]
Iacopini, D; Tavani, S; Pentagallo, S; Maselli, V; Dottore Stagna, M; Ebinger, C; Reynolds, D; van Vliet, A
abstract

The Southeastern portion of the East African Rift System reactivates Mesozoic transform faults marking the separation of Madagascar from Africa in the Western Indian Ocean. Earlier studies noted the reactivation of the Davie Fracture Zone in oceanic lithosphere as a seismically active extensional fault, and new 3D seismic reflection data and exploration wells provide unprecedented detail on the kinematics of the sub-parallel Seagap fault zone in continental/transitional crust landward of the ocean-continent transition. We reconstruct the evolution of the seismically active Seagap fault zone, a 400-km-long crustal structure affecting the Tanzania margin, from the late Eocene to the present day. The Seagap fault zone is represented by large-scale localized structures affecting the seafloor and displaying growth geometries across most of the Miocene sediments. The continuous tectonic activity evident by our seismic mapping, as well as 2D deep seismic data from literature, suggests that from the Middle-Late Jurassic until 125 Ma, the Seagap fault acted as a regional structure parallel to, and coeval with, the dextral Davie Fracture Zone. The Seagap fault then remained active after the cessation of both seafloor spreading in the Somali basin and strike-slip activity on the Davie Fracture Zone, till nowaday. Its architecture is structurally expressed through the sequence of releasing and restraining bends dating back at least to the early Neogene. Seismic sections and horizon maps indicate that those restraining bends are generated by strike-slip reactivation of Cretaceous structures till the Miocene. Finally based on the interpretation of edge-enhanced reflection seismic surfaces and seafloor data, we shows that, by the late Neogene, the Seagap fault zone switched to normal fault behaviour. We discuss the Seagap fault's geological and kinematic significance through time and its current role within the microplate system in the framework of the East African rift, as well as implications for the evolution and re-activation of structures along sheared margins. The newly integrated datasets reveal the polyphase deformation of this margin, highlighting its complex evolution and the implications for depositional fairways and structural trap and seal changes through time, as well as potential hazards.

2023 - Large-scale submarine landslide drives long-lasting regime shift in slope sediment deposition [Articolo su rivista]
Dottore Stagna, M; Maselli, V; van Vliet, A
abstract

Submarine landslides and associated mass-transport deposits (MTDs) modify the physiography of continental margins and influence the evolution of submarine sediment routing systems. Previous studies highlighted the control of landslides and MTDs on subsequent sedimentary processes and deposits at spatial scales ranging from tens of centimeters to few kilometers, leaving a knowledge gap on how and for how long large-scale submarine landslides (i.e., headscarps wider than 50–100 km) may affect the stratigraphic evolution of continental margins. To fill this gap, we used three-dimensional seismic reflection data tied to an exploration well to investigate the impact of one of the largest submarine landslides discovered on Earth, the Mafia mega-slide (Mms) offshore Tanzania, on slope sediment deposition. Seismic data interpretation indicates that turbidite lobes/lobe complexes and coalescent mixed turbidite-contourite systems formed the pre-Mms stratigraphy between 38 and ca. 21 Ma (age of the Mms), whereas coarser-grained sheet turbidites and debrites accumulated after the Mms for ∼15 m.y., primarily on the topographic lows generated by the emplacement of the landslide. We interpret this drastic and long-lasting regime shift in sediment deposition to be driven by the increase in seafloor gradient and the capture and focus of feeding systems within the broad failed area. We propose that the extensive evacuation zones associated with such giant landslides can generate major “conveyor belts”, trapping land-derived material or sediments transported by along-slope processes such as bottom currents. During the progressive healing of the landslide escarpments, which may last for several million years, sand-prone facies are deposited primarily in the upper slope, filling up the accommodation space generated by the landslide, while deeper-water environments likely remain sediment starved or experience accumulation of finer-grained deposits. Our study provides new insights into the long-term response of slope depositional systems to large-scale submarine landslides, with implications for the transfer of coarse-grained sediments that can be applied to continental margins worldwide.

2023 - Oceanographic exchanges between the Southern and Northern Atlantic during the Cenozoic inferred from mixed contourite-turbidite systems in the Brazilian Equatorial Margin [Articolo su rivista]
Alves, Dpv; Maselli, V; Iacopini, D; Viana, Ar; Jovane, L
abstract

The Equatorial Atlantic Ocean is a key region to study the oceanographic and climatic changes that occurred during the Cenozoic. Using of 2D and 3D seismic reflection data and boreholes from the Ceará Basin in the Brazilian Equatorial Margin, this work reconstructs how deep-water oceanographic currents in the Equatorial Atlantic Ocean changed during the Cenozoic by investigating the evolution of contourite depositional systems (CDS) and mixed contourite-turbidite system (mCTS). Seismic data interpretation indicates a southward-flowing proto-North Brazil Current (Proto-NBC) was already established in the Eocene and inverted direction in the late Miocene. During most of the Cenozoic, the Ceará Basin went through an alternation of CDS and mCTS, which evolved in response to different sea level and oceanographic regimes. We propose a six-phase evolutionary model for the Brazilian Equatorial Margin to summarize such changes: (1) Paleocene and early Eocene, formation of the CDS under the influence of a southeast-flowing, low intensity, proto-NBC; (2) early Oligocene, still dominance of southeast-flowing currents and further development of the CDS; (3) late Oligocene, initial deposition the m-CTS with prevalence of down-slope processes in proximal regions and bottom-current (still southeast-flowing) reworking in distal regions; (4) early Miocene, the previous late Oligocene conditions are sustained until the (5) middle Miocene, when the proto-NBC becomes weaker and start to invert its direction from southeast to northwest; finally, from the late Miocene (6), the onset of the northwest flow of NBC is established and the mCTS further develops. By documenting the evolution of Cenozoic contourite and mixed contourite-turbidite systems in the Brazilian Equatorial Margin, our study contributes to the understanding of the Atlantic Meridional Overturning Circulation in the Equatorial Atlantic, providing a baseline for future investigations.

2022 - Deep-water sedimentation processes on a glaciated margin: The Foula Wedge trough mouth fan, West of Shetland [Articolo su rivista]
Caruso, S; Maselli, V; Rea, B; Spagnolo, M
abstract

Trough Mouth Fans (TMF) are sedimentary depocenters located at glaciated continental margins and consist predominantly of glacigenic debris flow deposits. The Foula wedge is a Pleistocene TMF accumulated offshore West of Shetland over the Northeast Atlantic margin. This study presents an analysis of a 3D seismic reflection dataset imaging the distal Foula wedge basin fan deposits between 1010 and 1100 m water depth, directly downslope from a gully system which was active untill the end of the last deglaciation. Results reveal, in unprecedented detail, the basal surface of this fan system and its internal complex architecture. Features typical of both debris flow deposits and turbidites are identified, including a basin channel network with linear and diverging erosional features forming distinctive terminal lobes, stacked and backstepping. The study links the seafloor morphology of the basin fan with its subsurface geomorphology, showing connection with the downslope gully system to the east. It presents evidence for a complex distal depositional system on glaciated margins, characterised by heterogeneous sediment delivery processes and deposits. A conceptual evolution model is proposed, with a glacigenic debris flow-dominated TMF at the LGM, subsequently influenced by meltwater discharges, with deposition occurring as a function of the shelf margin and slope paleo-morphology, slope substrate composition, interaction of downslope and along slope processes and ice-margin dynamics.

2022 - Micro(nano)plastics sources, fate, and effects: What we know after ten years of research [Articolo su rivista]
Allen, S; Allen, D; Karbalaei, S; Maselli, V; Walker, Tr
abstract

The last decade has been transformative for micro(nano)plastic (MnP) research with recent discoveries revealing the extent and magnitude of MnP pollution, even in the world's most remote places. Historically, while researchers recognized that most plastic pollution was derived from land-based sources, it was generally believed that microplastic particles (i.e., plastic fragments <5 mm) was only a marine pollution issue with effects largely impacting marine biota. However, over the last decade MnP research has progressed rapidly with recent discoveries of MnPs in freshwater, snow, ice, soil, terrestrial biota, air and even found in ocean spray. MnPs have now been found in every environmental compartment on earth, within tissues and gastrointestinal tracts of thousands of species, including humans, resulting in harmful effects. The last 10 years has also seen the development of new techniques for MnP analysis, and re-purposing of old technologies allowing us to determine the extent and magnitude of plastic pollution down to the nano size range (<1 µm). This short review summarizes what key milestones and major advances have been made in microplastic and nanoplastic research in the environment, including their sources, fate, and effects over the last decade.

2022 - Seismic characterization and depositional significance of the Nahr Menashe deposits: Implications for the terminal phases of the Messinian salinity crisis in the north-east Levant Basin, offshore Lebanon [Articolo su rivista]
Kabir, Smm; Iacopini, D; Hartley, A; Maselli, V; Oppo, D
abstract

Over the last decade, there has been a resurgence of interest in the climatic and tectonic mechanisms that drove the Messinian salinity crisis (MSC) and the associated deposition of thick evaporites. The MSC represents an unprecedented palaeoceanographic change that led to a very short (ca. 640 kyr) ecological and environmental crisis. However, across the Levantine offshore basin, the sedimentological nature of the top evaporitic units and the mechanisms that controlled the transition from a hypersaline evaporitic unit to brackish deposits (final MSC stage 3) are still disputed. Here, we re-evaluate the deposits associated with the terminal phase of the MSC, named in offshore Lebanon as the Nahr Menashe Unit (NMU). We describe the NMU seismic facies, characterize and map its internal seismic stratigraphy and provide a new interpretation of its depositional environment, which persisted during the late Messinian and then evolved through a regional reflooding event. The base of the NMU overlies semicircular depressions, randomly distributed linear marks and surface collapse features, which are indicative of a period of intense evaporite dissolution. The NMU seismic facies observed from the slope to the deep part of the basin support the interpretation of a layered salt-evaporite-sand depositional system subject to complex reworking, dissolution, deposition and final erosion. A drainage network of valleys and complex tributary channels incising into the top NMU shows marked erosional characteristics, which indicate a dominant southwards sediment transfer following deposition of the NMU. The drainage network was subsequently infilled by layered sediments interpreted here to represent the post-MSC marine sediments. Our analysis adds important details regarding previous interpretations of the NMU as fluvial in origin. Specifically, the presence of subcircular, linear dissolution features coupled with mound-like features indicates that the NMU is composed dominantly of evaporites that were subject to dissolution prior to erosion associated with the drainage network. The NMU is interpreted to represent the deposition/redeposition of a mixed evaporite-siliciclastic succession in a shallow marine or lacustrine environment during the tilting of the offshore Lebanese basin.

2022 - Structural controls on slope evolution and sediment dispersal pathways along the northern Tanzania continental margin, western Indian Ocean [Articolo su rivista]
Dottore Stagna, M; Maselli, V; Grujic, D; Reynolds, P; Reynolds, D; Iacopini, D; Richards, B; Underhill, Jr; Kroon, D
abstract

In this study, we investigate the tectonic and stratigraphic evolution of the northern Tanzania margin (western Indian Ocean) to provide new insights on the structural drivers governing the formation of Zanzibar and Pemba islands. Using 2D seismic reflection profiles and exploration wells, we have reconstructed the evolution of the submarine drainage network throughout the last 30 Myr, from the Oligocene to recent times, providing a tape-recorder with which we determine the different tectonic events that led to the eventual subaerial exposure of the islands. In detail, we observe a decrease in the number of slope canyon-channel systems during the lower-middle Miocene offshore Pemba Island that we interpret to represent the initial uplift of the island: tectonic deformation of the seafloor impeded up-dip to down-dip sediment transfer, forcing the abandonment of canyon-channel systems. At the same time, submarine canyons were still active offshore Zanzibar Island, located ~35 km south of Pemba, indicating that its uplift occurred later, likely during the upper Miocene to lower Pliocene. The changes in seafloor topography and slope gradient promoted the formation of two newly discovered giant canyons that represent the main feeder systems to this sector of the western Indian Ocean since the Miocene. We propose a new conceptual model for the post-Oligocene evolution of the area, highlighting the main tectonic structures and their timing of formation. In this model, the onset of the anticlines of Pemba and Zanzibar islands resulted from tectonic inversion probably originated during the Oligocene-lower Miocene due to reactivation of Mesozoic-aged rift faults. This compressional phase is followed by the establishment of an extensional tectonic regime which promoted the subaerial exposure of the islands since the middle Miocene. Extensional faults, which dissect the post-Oligocene stratigraphy, create horsts and grabens on a variety of scales, such as Zanzibar and Pemba troughs. These grabens show comparative size and orientation to onshore rift basins, which may indicate a relation with the tectonics of the East African Rift System. Our results provide new insights on the evolution of one the least explored, though fascinating, continental margin settings worldwide that can support future source-to-sink investigations in the region.

2021 - A 1000-yr-old tsunami in the Indian Ocean points to greater risk for East Africa: REPLY [Articolo su rivista]
Maselli, V; Oppo, D; Moore, Al; Gusman, Ar; Mtelela, C; Iacopini, D; Taviani, M; Mjema, E; Mulaya, E; Che, M; Tomioka, Al; Mshiu, E; Ortiz, Jd
abstract

2021 - Active faulting controls bedform development on a deep-water fan [Articolo su rivista]
Maselli, V; Micallef, A; Normandeau, A; Oppo, D; Iacopini, D; Green, A; Ge, Z
abstract

Tectonically controlled topography influences deep-water sedimentary systems. Using 3-D seismic reflection data from the Levant Basin, eastern Mediterranean Sea, we investigate the spatial and temporal evolution of bedforms on a deep-water fan cut by an active normal fault. In the footwall, the fan comprises cyclic steps and antidunes along its axial and external portions, respectively, which we interpret to result from the spatial variation in flow velocity due to the loss of confinement at the canyon mouth. Conversely, in the hanging wall, the seafloor is nearly featureless at seismic scale. Numerical modeling of turbidity currents shows that the fault triggers a hydraulic jump that suppresses the flow velocity downstream, which thus explains the lack of visible bedforms basinward. This study shows that the topography generated by active normal faulting controls the downslope evolution of turbidity currents and the associated bedforms and that seafloor geomorphology can be used to evince syn-tectonic deposition.

2021 - Different types of gravity-driven flow deposits and associated bedforms in the Upper Bengal Fan, offshore Myanmar [Articolo su rivista]
Lu, Y; Shi, B; Maselli, V; Luan, X; X, Xu; Shao, D; Fan, G; Wang, H; Ding, L
abstract

This study uses 3D reflection seismic data to investigate how sediment gravity flows contribute to the evolution of the lower continental slope of the Myanmar margin that is part of the Bengal Fan, the largest deep-water fan system in the world. Seafloor and subseafloor data show large sediment wave fields that developed on both flanks of an extensive submarine canyon. The sediment waves exhibit asymmetric stoss and lee sides, wave lengths and heights of 850–3000 m and 25–70 m, respectively, and an upslope direction of migration. Seismic data reveals the presence of multiple fields of vertically stacked sediment waves, interbedded with units characterised by a chaotic seismic facies that accumulate mainly in the troughs of the sediment waves and can be tracked laterally to the adjacent canyons. According to their seismic facies, geometry, and internal architecture these chaotic units are interpreted as debrites. Seismic attributes extracted from different horizons indicate that the sediment waves are dominated by fine-grained sediment, while the debrites are probably associated with coarser-grained deposits. The debrites fill the troughs of the sediment waves, as well as the downstream portions of canyon thalweg, thus flattening the paleo-seafloor. The sediment waves are interpreted as cyclic steps formed by low-density turbidity currents flowing across the slope down to the basin floor, where the change in gradient favours the formation of hydraulic jumps and the transition from supercritical to subcritical flow conditions. A conceptual model for the sediment wave evolution was proposed for the study area, in the transitional environment on the lower slope, with low-density gravity flow deposits and high-density debris flow deposits alternatively accumulating on the major gravity flow conduits.

2021 - Geometrical Breakdown Approach to interpretation of depositional sequences [Articolo su rivista]
Aali, M; Richards, B; Nedimović, ; Mr, ; Maselli, V; Gibling, Mr
abstract

Seismic and sequence stratigraphic analyses are important methodologies for interpreting coastal and shallow-marine deposits. Though both methods are based on objective criteria, terminology for reflection/stratal stacking is widely linked to eustatic cycles, which does not adequately incorporate factors such as differential subsidence, sediment supply, and autogenic effects. To reduce reliance on model-driven interpretations, we developed a Geometrical Breakdown Approach (GBA) that facilitates interpretation of horizon-bound reflection packages by systematically identifying upward-downward and landward-seaward trajectories of clinoform inflection points and stratal terminations, respectively. This approach enables a rigorous characterization of stratal surfaces and depositional units. The results are captured in three-letter acronyms that provide an efficient way of recognizing repetitive stacking patterns through discriminating reflection packages objectively to the maximum level of resolution provided by the data. Comparison of GBA with selected sequence stratigraphic models that include three and four systems tracts and the accommodation succession approach shows that the GBA allows a greater level of detail to be extracted, identifying key surfaces with more precision and utilizing more effectively the fine-scale resolution provided by the input seismic data. We tested this approach using a synthetic analogue model and field data from the New Jersey margin. The results demonstrate that the geometric criteria constitute a reliable tool for identifying systems tracts and provide an objective and straightforward method for practitioners at all levels of experience.

2021 - Leaky salt: Pipe trails record the history of cross‐evaporite fluid escape in the northern Levant Basin, Eastern Mediterranean [Articolo su rivista]
Oppo, D; Evans, S; Iacopini, D; Kabir, Smm; Maselli, V; Jackson, Cal
abstract

Despite salt being regarded as an extremely efficient, low‐permeability hydraulic seal, an increasing number of cross‐evaporite fluid escape features have been documented in salt‐bearing sedimentary basins. Because of this, it is clear that our understanding of how thick salt deposits impact fluid flow in sedimentary basins is incomplete. We here examine the causes and evolution of cross‐evaporite fluid escape in the northern Levant Basin, Eastern Mediterranean. High‐quality 3D seismic data offshore Lebanon image hundreds of supra‐salt fluid escape pipes distributed widely along the margin. The pipes consistently originate at the crest of prominent sub‐salt anticlines, where overlying salt is relatively thin. The fact the pipes crosscut the salt suggests that hydrofracturing occurred, permitting focused fluid flow. Sequential pipes from unique emission points are organized along trails that are several kilometres long, and which are progressively deformed due to basinward gravity gliding of salt and its overburden. Correlation of pipes in 12 trails suggests margin‐wide fluid escape started in the Late Pliocene/Early Pleistocene, coincident with a major phase of uplift of the Levant margin. We interpret that the consequent transfer of overpressure from the central basin area, in addition to gas exsolution from hydrocarbons already trapped in sub‐salt anticlines, triggered seal failure and cross‐evaporite fluid flow. We infer that other causes of fluid escape in the Eastern Mediterranean, such as subsurface pressure changes driven by sea‐level variations and salt deposition associated with the Messinian Salinity Crisis, played only a minor role in triggering cross‐evaporite fluid flow in the northern Levant Basin. Further phases of fluid escape are unique to each anticline and cannot be easily correlated across the margin. Therefore, despite a common initial cause, long‐term fluid escape proceeded according to structure‐specific characteristics, such as local dynamics of fluid migration and anticline geometry. Our work shows that the mechanisms triggering cross‐evaporite fluid flow in salt basins vary in time and space.

2021 - Local marine reservoir age (δr) reconstructed based on the tsunami deposit from Pangani bay (Tanzania) [Articolo su rivista]
Soulet, G; Maselli, V
abstract

Quantifying the local marine reservoir age (ΔR) and its change over time is critical for precise radiocarbon calibration of marine samples and for the study of the ocean carbon cycle. ΔR values are scarce for the African coast facing the Indian Ocean, and the few values available were obtained from pre-bomb shells collected during the 19th century. Here, the ΔR value for calibrated year 1110 ± 25 (1σ) CE was reconstructed from radiocarbon dating and Bayesian analysis of marine and terrestrial materials coexisting in a tsunami deposit discovered in Pangani Bay (Tanzania, western Indian Ocean coast). The reconstructed ΔR of –8 ± 40 (1σ, n = 3) is similar to pre-bomb regional estimates and provides new information to investigate regional ΔR change over time. The Bayesian analysis of the dated samples revises the age of the tsunami event found in Pangani Bay to 1064–1157 cal CE (95.4% confidence level) or 1110 ± 25 (1σ) cal CE, about one century younger compared to the previous estimate. Our results indicate that the new ΔR value and the proposed calibration approach can be used to refine existing chronologies in the region, with implications for paleo-environmental reconstructions and archaeological studies of Early Swahili societies.

2021 - Submarine landslides triggered by iceberg collision with the seafloor [Articolo su rivista]
Normandeau, A; Mackillop, K; Macquarrie, M; Richards, C; Bourgault, D; Campbell, Dc; Maselli, V; Philibert, G; Clarke, Jh
abstract

Iceberg discharge influences ocean circulation, affects climate and increases global sea level. Icebergs are also known to gouge the seafloor in water depths limited by their keel depth, thus representing a hazard to subsea infrastructure. Here, we provide evidence that icebergs can affect the seafloor at depths greater than their keel depth by triggering submarine landslides. Using repeat bathymetric surveys from multibeam echo sounders, we investigate the cause of a submarine landslide that occurred in Southwind Fjord, Baffin Island, between September 2018 and September 2019. This landslide is shown to be closely associated with recently formed iceberg pits at its headscarp carved by an iceberg that grounded and that capsized in the fjord in early September 2018. Geotechnical data from a nearby sediment core indicate that the vertical loading induced by the iceberg grounding and capsizing is sufficient to trigger the observed landslide. These results imply that icebergs originating from the Arctic, Greenland and Antarctica are hazards thousands of kilometres away from their original source and can affect continental slopes by triggering submarine landslides. This process represents an additional source of marine geohazards, especially if climate change leads to increased iceberg discharge.

2020 - A 1000-yr-old tsunami in the Indian Ocean points to greater risk for East Africa [Articolo su rivista]
Maselli, V; Oppo, D; Moore, Al; Gusman, Ar; Mtelela, C; Iacopini, D; Taviani, M; Mjema, E; Mulaya, E; Che, M; Tomioka, Al; Mshiu, E; Ortiz, Jd
abstract

The December 2004 Sumatra-Andaman tsunami prompted an unprecedented research effort to find ancient precursors and quantify the recurrence time of such a deadly natural disaster. This effort, however, has focused primarily along the northern and eastern Indian Ocean coastlines, in proximal areas hardest hit by the tsunami. No studies have been made to quantify the recurrence of tsunamis along the coastlines of the western Indian Ocean, leading to an underestimation of the tsunami risk in East Africa. Here, we document a 1000-yr- old sand layer hosting archaeological remains of an ancient coastal Swahili settlement in Tanzania. The sedimentary facies, grain-size distribution, and faunal assemblages indicate a tsunami wave as the most likely cause for the deposition of this sand layer. The tsunami in Tanzania is coeval with analogous deposits discovered at eastern Indian Ocean coastal sites. Numerical simulations of tsunami wave propagation indicate a megathrust earthquake generated by a large rupture of the Sumatra-Andaman subduction zone as the likely tsunami source. Our findings provide evidence that teletsunamis represent a serious threat to coastal societies along the western Indian Ocean, with implications for future tsunami hazard and risk assessments in East Africa.

2020 - Characterisation of submarine depression trails driven by upslope migrating cyclic steps: Insights from the Ceará Basin (Brazil) [Articolo su rivista]
Maestrelli, D; Maselli, V; Kneller, B; Chiarella, D; Scarselli, N; Vannucchi, P; Jovane, L; Iacopini, D
abstract

Circular to elliptical topographic depressions, isolated or organized in trails, have been observed on the modern seabed in different contexts and water depths. Such features have been alternatively interpreted as pockmarks generated by fluid flow, as sediment waves generated by turbidity currents, or as a combination of both processes. In the latter case, the dip of the slope has been hypothesized to control the formation of trails of downslope migrating pockmarks. In this study, we use high-quality 3D seismic data from the offshore Ceará Basin (Equatorial Brazil) to examine vertically stacked and upslope-migrating trails of depressions visible at the seabed and in the subsurface. Seismic reflection terminations and stratal architecture indicate that these features are formed by cyclic steps generated by turbidity currents, while internal amplitude anomalies point to the presence of fluid migration. Amplitude Versus Offset analysis (AVO) performed on partial stacks shows that the investigated anomalies do not represent hydrocarbon indicators. Previous studies have suggested that the accumulation of permeable and porous sediments in the troughs of vertically stacked cyclic steps may create vertical pathways for fluid migration, and we propose that this may have facilitated the upward migration of saline pore water due to fluid buoyancy. The results of this study highlight the importance of gravity-driven processes in shaping the morphology of the Ceará Basin slope and show how non-hydrocarbon fluids may interact with vertically stacked cyclic steps.

2020 - Impact of sea-level fluctuations on the sedimentation patterns of the SE African margin: implications for slope instability [Capitolo/Saggio]
Micallef, A; Georgiopoulou, A; Green, A; Maselli, V
abstract

The sheared-passive margin offshore Durban (South Africa) is characterized by a narrow continental shelf and steep slope hosting numerous submarine canyons. Supply of sediment to the margin is predominantly terrigenous, dominated by discharge from several short but fast-flowing rivers. International Ocean Discovery Program Expedition 361 provides a unique opportunity to investigate the role of sea-level fluctuations on the sedimentation patterns and slope instability along the South African margin. We analysed >300 sediment samples and downcore variations in P-wave, magnetic susceptibility, bioturbation intensity and bulk density from site U1474, as well as regional seismic reflection profiles to: (1) document an increase in sand input since the Mid-Pliocene; (2) associate this change to a drop in sea-level and extension of subaerial drainage systems towards the shelf-edge; (3) demonstrate that slope instability has played a key role in the evolution of the South Africa margin facing the Natal Valley. Furthermore, we highlight how the widespread occurrence of failure events reflects the tectonic control on the morphology of the shelf and slope, as well as bottom-current scour and instability of fan complexes. This information is important to improve hazard assessment in a populated coastal region with growing offshore hydrocarbon activities.

2020 - Impact of the East African Rift System on the routing of the deep‐water drainage network offshore Tanzania, western Indian Ocean [Articolo su rivista]
Maselli, V; Kroon, D; Iacopini, D; Wade, Bs; Pearson, Pn; de Haas, H
abstract

The East African Rift System (EARS) exerted a major influence on river drainage basins and regional climate of east Africa during the Cenozoic. Recent studies have highlighted an offshore branch of the EARS in the western Indian Ocean, where the Kerimbas Graben and the Davie Ridge represent its sea floor expression. To date, a clear picture of the impact and timing of this EARS offshore branch on the continental margin of the western Indian Ocean, and associated sediment dispersal pathways, is still missing. This study presents new evidence for four giant canyons along the northern portion of the Davie Ridge offshore Tanzania. Seismic and multibeam bathymetric data highlight that the southernmost three canyons are now inactive, supra‐elevated relative to the adjacent sea floor of the Kerimbas Graben and disconnected from the modern slope systems offshore the Rovuma and Rufiji River deltas. Regional correlation of dated seismic horizons, integrated with well data and sediment samples, proves that the tectonic activity driving the uplift of the Davie Ridge in this area has started during the middle‐upper Miocene and is still ongoing, as suggested by the presence of fault escarpments at the sea floor and by the location and magnitude of recent earthquakes. Our findings contribute to placing the Kerimbas Graben and the Davie Ridge offshore Tanzania in the regional geodynamic context of the western Indian Ocean and show how the tectonics of the offshore branch of the EARS modified the physiography of the margin, re‐routing the deep‐water drainage network since the middle Miocene. Future studies are needed to understand the influence of changing sea floor topography on the western Indian Ocean circulation and to evaluate the potential of the EARS offshore tectonics in generating tsunamigenic events.

2020 - Large-scale mass wasting in the western Indian Ocean constrains onset of East African rifting [Articolo su rivista]
Maselli, V; Iacopini, D; Ebinger, Cj; Tewari, S; de Haas, H; Wade, Bs; Pearson, Pn; Francis, M; van Vliet, A; Richards, B; Kroon, D
abstract

Faulting and earthquakes occur extensively along the flanks of the East African Rift System, including an offshore branch in the western Indian Ocean, resulting in remobilization of sediment in the form of landslides. To date, constraints on the occurrence of submarine landslides at margin scale are lacking, leaving unanswered a link between rifting and slope instability. Here, we show the first overview of landslide deposits in the post-Eocene stratigraphy of the Tanzania margin and we present the discovery of one of the biggest landslides on Earth: the Mafia mega-slide. The emplacement of multiple landslides, including the Mafia mega-slide, during the early-mid Miocene is coeval with cratonic rifting in Tanzania, indicating that plateau uplift and rifting in East Africa triggered large and potentially tsunamigenic landslides likely through earthquake activity and enhanced sediment supply. This study is a first step to evaluate the risk associated with submarine landslides in the region.

2020 - Latitudinal response of storm activity to abrupt climate change during the last 6,500 years [Articolo su rivista]
Yang, Y; Maselli, V; Normandeau, A; Piper, Dwj; Li, Mz; Campbell, Dc; Gregory, T; Gao, S
abstract

This study examines the influence of the strength of Atlantic Meridional Overturning Circulation (AMOC) on storminess at different latitudes in the North Atlantic, based on a new 6.5‐Kyr record of large storms from the Scotian Shelf (Eastern Canada) that provides the first >3.5‐ka record from middle latitudes. Comparison with a compilation of other paleostorm records shows that peaks in storminess are at times synchronous (4.5–2.5 and since 0.5 ka) between low and middle latitudes but in the intervening period (2.5–0.5 ka) were latitudinally asynchronous. Synchronous (asynchronous) behavior correlates with sustained increase (decrease) of AMOC. Regime shifts in storm activity between low and middle latitudes were more frequent since 2.5 ka, related to increased frequency of abrupt climate changes. These findings indicate a latitudinal response of storm activity due to abrupt climate change, which is critical to correctly assess future storm risks along the North Atlantic coastline.

2020 - Numerical Modeling of the Hydro-Morphodynamics of a Distributary Channel of the Po River Delta (Italy) during the Spring 2009 Flood Event [Articolo su rivista]
Nones, M; Maselli, V; Varrani, A
abstract

One-dimensional (1D) numerical models generally provide reliable results when applied to simulate river hydraulics and morphodynamics upstream of the tidal influence, given the predominantly unidirectional flow conditions. Such models, however, can also be used to reproduce river hydraulics across the fluvial to marine transition zone when specific conditions occur, as during high discharge events, and the results obtained via these simple modeling tools can provide indicative trends that may guide more structured and detailed modeling of a particularly critical area. In this study, the application of a 1D model setup with hydrologic engineering centers river analysis system (HEC-RAS) for simulating the hydro-morphodynamic conditions of a distributary channel of the Po River Delta (Italy) during a flooding event that occurred in Spring 2009 is presented. The channel bathymetry and the grainsize composition was taken from field measurements, while the dimension of the plume offshore the delta was derived from a MODIS image acquired at the peak of the flood. The comparison between the numerical outcomes and the field evidence shows the reliability of the proposed 1D modeling approach in representing the delta dynamics at a large scale, as well as in showing locations where more spatially detailed studies are needed. The code was also able to adequately reproduce the channel hydro-morphodynamics and the sediment data as derived from a core sample taken a few km offshore during the flooding event of April–May 2009. Through a sensitivity analysis, it is also proven that the dimension of the river plume can influence the evolution of the prodelta, while having a rather negligible effect inland, because of the major stresses induced by the high river discharge during the flood event.

2020 - Tidal modulation of river-flood deposits: How low can you go? [Articolo su rivista]
Maselli, V; Normandeau, A; Nones, M; Tesi, T; Langone, L; Trincardi, F; Bohacs, Km
abstract

Quantification of the interaction between river discharge and tides is vital to characterize fluvio-deltaic systems, to identify diagnostic elements of tidal signatures in the rock record, and to reconstruct paleogeographies. In modern systems, even microtides can significantly influence delta morphodynamics; yet, many fundamental processes, particularly in prodeltaic settings, remain elusive. Here, by combining a unique process-product data set acquired during a flood event of the Po River (Italy) with numerical modeling, we show that tidal signatures are recorded in the open-water prodelta zone of a microtidal system. Based on the analyses of box-cores collected before and after a flood off the main distributary channel, we interpreted storm beds, tide-modulated flood strata of alternating normal and inverse graded beds, and rapid bioturbation. Modeling of the river discharge indicates that, at the peak of the flood, the steepening of the water-surface profile forced by 0.15 m lowering of sea level during low tides generated an 8% increase in river flow velocity. The alternation of profile steepness and associated cyclicity in flow strength during consecutive tidal cycles controlled the sediment load of the plume and, consequently, led to the deposition of tidal-modulated strata. Formation of microtidal signals appears to be enhanced in fluvio-deltaic successions characterized by multiple distributaries and in basins where river floods are out of phase with storm-wave activity. Bioturbation of sediment, which can start during the waning stage of the flow, and erosion by storm waves hamper the preservation of tidal signals, unless rapid burial occurs. The recognition of tidal-modulated strata in river-dominated settings may facilitate the characterization of mudstone reservoirs and reconstruction of paleogeographic conditions during deposition.

2019 - Sea floor bedforms and their influence on slope accommodation [Articolo su rivista]
Maselli, V; Kneller, B; Taiwo, O; Iacopini, D
abstract

In deep-water settings, the accommodation for sediment transported by turbidity flows relates to the difference between the elevation of the depositional surface and its equilibrium profile. As a consequence, accommodation creation, or disruption, may depend from changes in the physiography of the receiving basin, or changes in the flow properties. In topographically complex slopes, such where salt-withdrawal intra-slope basins occur, three different types of accommodation have been recognized. Among other parameters, the ratio between flow thickness and depth of the intra-slope basin controls the partial, or full, ponding of the sediment in suspension, and consequently, the lithology distribution within the deposit. On a smaller spatial scale, the behavior of bottom-hugging sediment-laden flows can be affected by topographic variations of the sea floor associated with the presence of km-scale bedforms. In this work, we show that ponded lobes accumulate on the convex-up stoss side of pre-existing large-wavelength bedforms (length up to 103, and height up to 102), and that their lithology distribution depends on the flow characteristics respect to the bedform height. In detail, when partial ponding of turbidity currents occurs, flow stripping promotes the accumulation of the coarse-grained fractions on the stoss side of the bedform, while the fine-grained cloud over-spills the lee side, affecting deposition basinward. By introducing the concept of stoss-side accommodation, this work suggests a new mechanism for the formation of ponded coarse-grained facies in slope settings due to the trapping effect large-wavelength bedforms with convex-up stoss sides.

2018 - Bottom currents, submarine mass failures and halokinesis at the toe of the Sigsbee Escarpment (Gulf of Mexico): Contrasting regimes during lowstand and highstand conditions? [Articolo su rivista]
Maselli, V; Kneller, B
abstract

In this study we explore the role of sediment supply, halokinesis and deep ocean circulation in promoting margin instability. The analysis was carried out on multibeam and high-resolution seismic data that allowed the imaging of mass failure deposits and current-driven depositional features along a portion of the lower continental slope and upper continental rise of the Sigsbee Escarpment (Gulf of Mexico). Different styles of deposition have been recognised during sea level lowstand (LST) and highstand (HST) conditions, due to alternating bottom current activity and salt tectonics. Lowstands are characterized by a reduced intensity of the Loop Current, as underlined by the lack of current-driven erosional features. On the contrary, highstands show a strengthened Loop Current that generates a fast bottom current circulation, as suggested by the presence of extensive furrow fields on the modern sea floor and on the Marine Isotope Stage 5e palaeo-sea floor horizon. Increased sediment load combined with changes in the intensity of deep water circulation are also responsible for the instability of the Sigsbee Escarpment, triggering mass failure phenomena with distinct morphology, size, location and timing of emplacement. Type 1 mass transport complexes (MTCs) form on the upper continental rise during sea level fall, and are genetically linked to the growth of deep water sediment drifts. Type 2 MTCs develop during sea level lowstands and originate along the slope of the Sigsbee Escarpment, triggered by oversteepening generated by halokinesis. Type 3 MTCs form during sea level rise to highstand conditions and mostly consist of debris flow deposits, generated in the lower portions of the Sigsbee Escarpment and then accumulated in the upper continental rise.

2018 - Deltaic and Coastal Sediments as Recorders of Mediterranean Regional Climate and Human Impact Over the Past Three Millennia [Articolo su rivista]
Jalali, B; Sicre, Ma; Klein, V; Schmidt, S; Maselli, V; Lirer, F; Bassetti, Ms; Toucanne, S; Jorry, Sj; Insinga, Dd; Petrosino, P; Châles, F
abstract

Deltaic and shallow marine sediments represent unique natural archives to study the evolution of surface coastal ocean water properties as compared to environmental changes in adjacent continents. Sea surface temperatures (SSTs) and higher plant biomarker records were generated from the Rhone and Var River deltaic sediments (NW Mediterranean Sea), and three sites in the South Adriatic Sea (Central/Eastern Mediterranean Sea), spanning all or part of the past three millennia. Because of the high sediment accumulation rates at all core sites, we were able to produce time series at decadal time scale. SSTs in the Gulf of Lion and the convection area of the South Adriatic Sea indicate similar cold mean values (around 17 °C) and pronounced cold spells, reflecting strong wind‐driven surface water heat loss. However, they differ in the rate of postindustrial warming, which is steeper in the Gulf of Lion. The three Adriatic Sea SST records are notably different reflecting different hydrological influence from nearshore to open sea sites. The compositional features of higher plant n‐alkanes in the Rhone and Var delta sediments and inferred vegetation types show differences consistent with the latitudinal extension of the drainage basins of both river streams. In the Adriatic Sea, both coastal and open sea sediments indicate enhanced land‐derived material over the past 500 years, which is not seen in the NW Mediterranean record. We suggest that increased erosion as the result of changes in land use practices is the most likely cause for this trend.

2018 - River morphodynamic evolution under dam-induced backwater: An example from the po river (Italy) [Articolo su rivista]
Maselli, Vittorio; Pellegrini, Claudio; Del Bianco, Fabrizio; Mercorella, Alessandra; Nones, Michael; Crose, Luca; Guerrero, Massimo; Nittrouer, Jeffrey A.
abstract

River systems evolve in response to the construction of dams and artificial reservoirs, offering the possibility to investigate the short-term effects of base level oscillations on fluvial architecture. A major effort has been dedicated to the understanding of river response downstream of large dams, where deep channel incisions occur in response to the removal of sediment that is sequestered in the upstream reservoir. Integrating field observations and numerical-modeling results, this work quantifies the sedimentary and morphological changes of the Po River (Italy) upstream of the Isola Serafini dam to investigate the impact of dam-induced backwater on river morphodynamics. The construction of a reservoir generates a new base level that forces an upstream shift of alluvial lithofacies and a change in the planform geometry of the river. The lateral migration rate of the channel is up to 45 m/yr upstream of the influence of backwater flow and ca. 10 m/yr at the transition from normal to backwater flow conditions (30 km from the dam). Within this reach, a reduction of the bed shear stress promotes deposition of coarse-grained sediment and the emergence of the gravel–sand transition of the river. The lateral migration of the channel continuously decreases over time, and rates, 5 m/yr can be observed in the reservoir backwater zone. This trend is accompanied by the drowning of channel bars, the reduction of river competence, and an increase in bedform spacing. Oscillatory backwater and drawdown surface water profiles can be observed closer to the dam, which are associated with varying low-discharge and high-discharge events, respectively. While low-flow conditions, persisting for much of the year, allow the deposition of fine-grained sediment, high-discharge events promote not only the resuspension and transport of fine material but also the progressive erosion of channel bars and the overall deepening of the thalweg. This study provides a clear picture of the river evolution in response to the construction of a hydropower dam that may be of help in predicting how other fluvial systems will respond to future human interventions. Moreover, the result of how changes in base level and oscillations in water surface profile (backwater and drawdown) control river hydro-morphodynamics and sediment transport may provide new insights when reconstructing ancient fluvial and deltaic sequences.

2018 - The Late Pleistocene Po River lowstand wedge in the Adriatic Sea: Controls on architecture variability and sediment partitioning [Articolo su rivista]
Pellegrini, C; Asioli, A; Bohacs, Km; Drexler, Tm; Feldman, Hr; Sweet, Ml; Maselli, V; Rovere, M; Gamberi, F; Dalla Valle, G; Trincardi, F
abstract

Although facies and stratal geometries of continental margin successions can be defined in detail based on subsurface and outcrop studies, most studies lack the high-resolution age control needed to constrain the time scale of formation of such successions and infer their external forcing mechanisms. Our work on the Po River Lowstand Wedge (PRLW) indicates that deposition rates are surprisingly high with the entire 350-m-thick succession being deposited in less than 17,000 years, and with individual clinothems recording time periods ranging from 400 to 4700 years. The PRLW preserves a high-resolution record of stacked, deltaic shelf-edge clinothems deposited during the Last Glacial Maximum (31.8–14.4 ky BP) in the Adriatic basin (Mediterranean Sea). We investigated clinothem internal geometry, stacking patterns, and facies distributions to infer the main controls on their growth by integrating seismic reflection data with seismic facies attributes and paleoenvironmental proxies. The stratigraphic framework of the shelf-edge clinothems was then related to major paleoenvironmental shifts during the last glacial cycle and driven by eustatic and climatic changes. Within the PRLW, we recognized three distinctive types of 100's-m-high shelf-edge clinothems, type A, type B and type C, each with diagnostic topset geometries, shelf-edge trajectories, and associated distal basin-fill deposits. These elemental clinothem types stack into two Clinothem Sets. Clinothem Set 1, with essentially flat to slightly descending shelf-edge trajectory, is composed of stacked types A and B clinothems, and records the direct influence of river flux leading to dysoxic conditions on the bottom of the basin. In particular, clinothem accumulation rates were as much as 200 km3/ky in some of the type B clinothems. Clinothem Set 2, showing ascending shelf-edge trajectory, records an aggradational stacking coupled with a retreat of the river-entry points with benthic fauna assemblages that reflect the influence of peaks in freshwater discharge. Whereas Clinothem Set 1 developed under perturbations of river supply linked to the multi-scale waxing and waning of glaciers during an interval dominated by eustatic fall, Clinothem Set 2 reflects the main thawing of glaciers concomitant to the first phase of the eustatic rise. From a sequence stratigraphic perspective, Clinothem Set 1 is interpreted as staked high-frequency sequences, while Clinothem Set 2 represents a stack of high-frequency parasequences. The high-resolution age control from boreholes and seismic data enabled us to relate stratal character to independently constrained environmental proxies: this revealed how the evolution of a shelf-edge system intricately convolves the influences of both global (eustacy) and regional (climate-driven supply fluctuations) controls, both at sub-Milankovitch scales. Finally, the thickness, geometry, and stacking patterns of the centennial to millennial clinothems of the PRLW vary in systematic ways resulting in geometries that closely resemble those of ancient shelf-edge systems, and offering the PRLW as a sub-modern analogue. Our observations also reinforce the focus of the classic sequence-stratigraphic approach on analyzing surfaces and their geometric relations and not on time duration or formation mechanisms.

2017 - High resolution multibeam and hydrodynamic datasets of tidal channels and inlets of the Venice Lagoon [Articolo su rivista]
Madricardo, F; Foglini, F; Kruss, A; Ferrarin, C; Pizzeghello, N; Murri, C; Rossi, M; Bajo, M; Bellafiore, D; Campiani, E; Fogarin, S; Grande, V; Janowski, L; Keppel, E; Leidi, E; Lorenzetti, G; Maicu, F; Maselli, V; Mercorella, S; Montereale Gavazzi, G; Minuzzo, T; Pellegrini, C; Petrizzo, A; Prampolini, M; Remia, A; Rizzetto, F; Rovere, M; Sarretta, A; Sigovini, M; Sinapi, L; Umgiesser, G; Trincardi, F
abstract

Tidal channels are crucial for the functioning of wetlands, though their morphological properties, which are relevant for seafloor habitats and flow, have been understudied so far. Here, we release a dataset composed of Digital Terrain Models (DTMs) extracted from a total of 2,500 linear kilometres of high-resolution multibeam echosounder (MBES) data collected in 2013 covering the entire network of tidal channels and inlets of the Venice Lagoon, Italy. The dataset comprises also the backscatter (BS) data, which reflect the acoustic properties of the seafloor, and the tidal current fields simulated by means of a high-resolution three-dimensional unstructured hydrodynamic model. The DTMs and the current fields help define how morphological and benthic properties of tidal channels are affected by the action of currents. These data are of potential broad interest not only to geomorphologists, oceanographers and ecologists studying the morphology, hydrodynamics, sediment transport and benthic habitats of tidal environments, but also to coastal engineers and stakeholders for cost-effective monitoring and sustainable management of this peculiar shallow coastal system.

2017 - How to make a 350-m-thick lowstand systems tract in 17,000 years: The Late Pleistocene Po River (Italy) lowstand wedge [Articolo su rivista]
Pellegrini, C; Maselli, V; Gamberi, F; Asioli, A; Bohacs, Km; Drexler, Tm; Trincardi, F
abstract

The 350-m-thick succession of the Po River lowstand wedge (Italy) associated with the Last Glacial Maximum (deposited over ~17 k.y) contains stratal architecture at a physical scale commonly attributed to much longer time scales, with complex, systematically varying internal clinothem characteristics. This study investigated clinothem stacking patterns and controls through the integration of seismic reflection data with sediment attributes, micropaleontology, regional climate, eustacy, and high-resolution age control possible only in Quaternary sequences. Three clinothem types are differentiated based on topset geometry, shelf-edge and onlap-point trajectory, internal seismic facies, and interpreted bottomset deposits: type A has moderate topset aggradation, ascending shelf-edge trajectory, and mass-transport bottomset deposits; type B has eroded topset, descending shelf-edge trajectory, and bottomset distributary channel-lobe complexes; and type C has maximal topset aggradation, ascending shelf-edge trajectory, and concordant bottomsets. Type A and C clinothems exhibit reduced sediment bypass and delivery to the basin, whereas type B clinothems are associated with short intervals of increased sediment export from the shelf to deeper water. Clinothems individually span a range of 0.4–4.7 k.y., contemporaneous with significant eustatic and climate changes, but their stacking patterns resemble those found in ancient successions and ascribed to significantly longer durations, indicating that (1) the response time of ancient continental margin–scale systems to high-frequency variations in accommodation and sediment supply could be as short as centuries, (2) even millennial- to centennial-scale stratal units can record substantial influence of allogenic controls, and (3) sandy deposits can be compartmentalized even in a short-duration lowstand systems tract.

2017 - Large-scale response of the Eastern Mediterranean thermohaline circulation to African monsoon intensification during sapropel S1 formation [Articolo su rivista]
Tesi, T; Asioli, A; Minisini, D; Maselli, V; Dalla Valle, G; Gamberi, F; Langone, L; Cattaneo, A; Montagna, P; Trincardi, F
abstract

The formation of Eastern Mediterranean sapropels has periodically occurred during intensification of northern hemisphere monsoon precipitation over North Africa. However, the large-scale response of the Eastern Mediterranean thermohaline circulation during these monsoon-fuelled freshening episodes is poorly constrained. Here, we investigate the formation of the youngest sapropel (S1) along an across-slope transect in the Adriatic Sea. Foraminifera-based oxygen index, redox-sensitive elements and biogeochemical parameters reveal – for the first time – that the Adriatic S1 was synchronous with the deposition of south-eastern Mediterranean S1 beds. Proxies of paleo thermohaline currents indicate that the bottom-hugging North Adriatic Dense Water (NAdDW) suddenly decreased at the sapropel onset simultaneously with the maximum freshening of the Levantine Sea during the African Humid Period. We conclude that the lack of the “salty” Levantine Intermediate Water hampered the preconditioning of the northern Adriatic waters necessary for the NAdDW formation prior to the winter cooling. Consequently, a weak NAdDW limited in turn the Eastern Mediterranean Deep Water (EMDWAdriatic) formation with important consequences for the ventilation of the Ionian basin as well. Our results highlight the importance of the Adriatic for the deep water ventilation and the interdependence among the major eastern Mediterranean water masses whose destabilization exerted first-order control on S1 deposition.

2016 - Onshore to offshore anatomy of a late Quaternary source-to-sink system (Po Plain–Adriatic Sea, Italy) [Articolo su rivista]
Amorosi, A; Maselli, V; Trincardi, F
abstract

In understanding the evolution of siliciclastic systems, Late Quaternary analogs may enable reliable predictive models of facies-tract architecture. The Po Plain–Adriatic Sea system, where a wealth of research has been conducted during the last 20 years, represents one of the most intensively investigated late Quaternary successions. With the aid of a chronologically well-constrained stratigraphy, paleoenvironmental evolution is tracked for the first time from fluvial to deep-marine realms, over 1000 km in length. Vertical stacking trends (onshore) and stratal terminations (offshore) are the key observations that allow identification of surfaces with sequence-stratigraphic significance (systems tract boundaries) in the distinct segments of the system. Recurring motifs in stratigraphic architecture, showing tight coupling of sedimentary responses among source area, catchment basin, and coastal and marine depocenters, reveal a cyclicity driven by glacio-eustatic fluctuations in the Milankovitch band. Due to high rates of subsidence, middle Pleistocene forced regressive systems tracts are exceptionally expanded, and the MIS5e–MIS2 interval (Late Pleistocene) preserves a nearly continuous record of fourth-order (100 kyr) stepwise sea-level fall. The stratigraphic architecture of Last Glacial Maximum deposits highlights the genetic relations between channel–belt development, pedogenesis, and sediment delivery to the lowstand delta, through narrow incised-valley conduits. The Late glacial-Holocene succession records the last episode of sea-level rise and stabilization through well-developed patterns of shoreline transgression/regression (TST/HST) that can be readily traced updip, from offshore to onshore locations. Architectural styles across the whole system reflect a dominance of allogenic forcing in the TST, as opposed to a predominantly autogenic control on stratigraphic development in the HST. External drivers of facies architecture were also effective on millennial timescales: the Younger Dryas cold reversal, which marks the transgressive surface on land, records a short-lived episode of subaqueous progradation that is correlative onshore with widespread, immature paleosol development and small-sized channel–belt formation. Quantitative assessment of sediment budgets over different time intervals requires precise positioning of the key bounding surfaces. Based on this approach, we outline for the first time over the entire Po–Adriatic Basin an estimate of the sediment volumes stored in each systems tract.

2016 - Pliocene–Quaternary contourite depositional system along the south-western Adriatic margin: changes in sedimentary stacking pattern and associated bottom currents [Articolo su rivista]
Pellegrini, C; Maselli, V; Trincardi, F
abstract

The Pliocene–Quaternary history of the south-western Adriatic margin, represented by a complex contourite depositional system, records the palaeoceanography of the basin and the interactions between oceanographic processes and the uneven slope morphology that resulted from tectonic deformation. Three main stages can be recognized: (1) during the Pliocene, a giant sediment drift formed on the southern flank of the slope-transverse Gondola anticline that focused and accelerated the flow of slope-parallel bottom currents; (2) since the early to middle Pleistocene transition, a reorganization of bottom-current pathways led to a sharp change in the sedimentary architecture of the margin that became dominated by the growth of contourite deposits; (3) as of 350 ka, landward-migrating contourites on the outer shelf (less than 120 m water depth) reflect the presence of bottom currents also in shallow waters. This analysis of the sedimentary stacking pattern of the contourite depositional system that developed along the south-western Adriatic margin since the Pliocene enables disentangling the processes that controlled changes in bottom-current activity, demonstrating that bottom-current deposits constitute the bulk of depositional sequences at the Milankovitch timescale.

2016 - Role of the Mid-Adriatic deep in dense water interception and modification [Articolo su rivista]
Marini, M; Maselli, V; Campanelli, A; Foglini, F; Grilli, F
abstract

This study set out to gain insights into: i) the route of dense water (DW), which leaves a morphological signature including large-scale erosion, moats, and contourite sediment drifts, and ii) the physical and chemical modifications undergone by Northern Adriatic Dense Water (NAdDW) due to its entrapment in the Mid-Adriatic Deep (MAD) for one or more years, which leads to biogeochemical transformation into Mid-Adriatic Dense Water (MAdDW), a less dense and colder water mass with reduced oxygen content as a result of prolonged biological consumption. The paper provides an accurate description of how NAdDW, on its way to the Southern Adriatic basin, mixes with MAdDW on Palagruža Sill. Analysis of water column data (CTD) collected in spring 2005 and 2012 showed that part of the NAdDW flowing down the Western Adriatic shelf swerves left, splitting into a branch that fills the western MAD pit and another flowing along the 170 m contour towards the eastern pit and then south through Palagruža Sill. Due to the density difference, the recently formed NAdDW flows as a bottom-trapped current underneath the older MAdDW, lifting and pushing it over Palagruža Sill, thereby promoting water exchange among the MAD pits. The two water masses eventually mix as they flow over Palagruža Sill, in proportions that depend on NAdDW volume and the changes undergone by MAdDW, thus generating a new mixed bottom-flowing DW with a distinctive chemical signal. The bottom water pattern disclosed by CTD transects is consistent with seafloor and sub-seafloor morphologies detected on high-resolution seismic profiles, which show both erosion and deposition features along bottom water routes. Moreover, confinement of the mixed water within structural highs as it flows southward through Palagruža Sill promotes formation of shallow water contourites and giant sediment drifts, demonstrating a significant role for topography in the flow of all Adriatic DW.

2015 - Anatomy of a compound delta from the post-glacial transgressive record in the Adriatic Sea [Articolo su rivista]
Pellegrini, C; Maselli, V; Cattaneo, A; Piva, A; Ceregato, A; Trincardi, F
abstract

On the Mediterranean continental shelves the post-glacial transgressive succession is a complex picture composed of seaward progradations, related to sea level stillstands and/or increased sediment supply to the coasts, and minor flooding surfaces, associated with phases of enhanced rates of sea level rise. Among Late Pleistocene examples, major mid-shelf progradations have been related to the short-term climatic reversal of the Younger Dryas event, a period during which the combination of increased sediment supply from rivers and reduced rates of sea level rise promoted the formation of progradations up to tens-meter thick. While the documentation of coastal and subaqueous progradations recording the Younger Dryas interval is widely reported in literature, the model of compound progradation within transgressive deposits has not yet been proposed. Here we present the documentation of a deltaic system where both delta front sands and related fine-grained subaqueous progradations (prodeltaic to shallow marine) have been preserved. The Paleo Gargano Compound Delta (PGCD) formed offshore the modern Gargano Promontory (southern Adriatic Sea), and is composed of a coastal coarse-grained delta of reduced thickness and a muddy subaqueous clinoform, up to 30 m thick. The PGCD, probably the first worldwide documentation of a compound delta within the transgressive record, provides the opportunity to investigate the processes controlling the formation of a compound delta system during an overall sea level rise and the factors that allowed its preservation. The finding of the PGCD provides the opportunity for a comparison with modern worldwide compound systems.

2015 - Biodetrital carbonates on the Adriatic continental shelf imprinted by oxidation of seeping hydrocarbons [Articolo su rivista]
Taviani, M; Franchi, F; Angeletti, L; Correggiari, A; López-Correa, M; Maselli, V; Mazzoli, C; Peckmann, J
abstract

The gas-productive Bonaccia area located at ca. 80–90 m below sea level offshore Ancona (Central Adriatic Sea) is site of hydrocarbon-derived carbonate production. The carbonates include large dm-sized slabs (bryozoan limestone), smaller concretionary aggregates, mudstones and pipes. The mudstones and botryoidal aragonite cements within limestones show δ13C values as low as −47.8‰ VPDB, consistent with seepage of isotopically light hydrocarbons (e.g. methane). These hydrocarbon-derived carbonates commonly incorporate abundant shell remains, deriving from the prevalently coarse bioclastic-rich muddy deposits from post-glacial transgressive units. It is, therefore, hypothesized that hydrocarbon-rich fluids permeated the post-glacial sediments, resulting in seafloor seeps that were inhabited by chemosymbiotic lucinid bivalves and burrowing callianassid shrimps; fossils and traces of which have been found in the Bonaccia carbonates. Microbial oxidation of the reduced compounds contained in the seep fluids led to a locally patchy carbonate cementation of the sediments at the seep sites. The pipes are interpreted as decapod burrows that subsequently served as conduits for hydrocarbon leakage. Seepage is probably still active at present as testified by gas production at the study site. Interestingly, seep carbonates exhumed by erosion served as hard substrate for fouling benthos (i.e., bryozoans, oysters and red algae) in the Holocene. The main products of the processes at the Bonaccia study site are composite bryozoan-dominated limestones, whose multi-step and complex history was unfold thank to radiocarbon dating of key components and precise stratigraphic control. The Bonaccia case-study can serve as a model for the interpretation of ancient analogs, such as bryozoan dominated limestones and mudstones of Paleozoic to Mesozoic age, which are not uncommon in the geological record. It further calls for caution in assuming that the presence of dominant macrobenthic fossil in old hydrocarbon-derived limestones implies its ecological connection to active seepage.

2014 - Bathymetry of the Adriatic Sea: The legacy of the last eustatic cycle and the impact of modern sediment dispersal [Articolo su rivista]
Trincardi, F; Campiani, E; Correggiari, A; Foglini, F; Maselli, V; Remia, A
abstract

The Istituto di Scienze Marine (ISMAR-CNR) has conducted several research projects on the Italian side of the Adriatic Sea over more than 15 years, collecting bathymetric, geophysical and sediment core data to perform multidisciplinary studies of modern sediment dynamics and of past environmental changes during the last eustatic cycle. A crucial step in this direction was the construction of a detailed bathymetry, a time-consuming task due to the extensive shallow water portion of the basin. Given the setting of the Adriatic Sea and the long-lasting research effort, the bathymetric map is necessarily based on heterogeneous data with uneven spatial distribution of Single-Beam echo-soundings. The main objective of this work is to illustrate the methodology applied to compile the bathymetric map of the west side of the Adriatic Sea at basin scale (1:750,000) and to describe the main morphological units that characterise the seafloor and reflect its main geological features. This bathymetry can also be used in oceanographic modelling both at regional and local scale, focussing on the interaction between bottom currents and seafloor morphology.

2014 - Delta growth and river valleys: the influence of climate and sea level changes on the South Adriatic shelf (Mediterranean Sea) [Articolo su rivista]
Maselli, V; Trincardi, F; Asioli, A; Ceregato, A; Rizzetto, F; Taviani, M
abstract

Incised valleys across continental margins represent the response of fluvial systems to changes in their equilibrium dynamics, mainly driven by base level fall forced by glacial–eustatic cycles. The Manfredonia Incised Valley formed during the last glacial sea level lowstand, when most of the southern Adriatic shelf was sub-aerially exposed but the outer shelf remained under water. The pronounced upstream deepening of the valley is ascribed to river incision of the MIS5e highstand coastal prism and related subaqueous clinoform under the influence of MIS5-4 sea level fluctuations, while the downstream shallowing and narrowing mainly reflects the impact of increased rates of sea level fall at the MIS3-2 transition on a flatter mid-outer shelf. Until 15 ka BP, the valley fed an asymmetric delta confined to the mid-outer shelf, testifying that continental and deep marine systems remained disconnected during the lowstand. Sea level rise reached the inner shelf during the Early Holocene, drowning the valley and leading to the formation of a sheltered embayment confined toward the land: at this time part of the incision remained underfilled with a marked bathymetric expression. This mini-basin was rapidly filled by sandy bayhead deltas, prograding from both the northern and southern sides of the valley. In this environment, protected by marine reworking and where sediment dispersal was less effective, the accommodation space was reduced and autogenic processes forced the formation of multiple and coalescing delta lobes. Bayhead delta progradations occurred in few centuries, between 8 and 7.2 ka cal BP, confirming the recent hypothesis that in this area the valley was filled during the formation of sapropel S1. This proximal valley fill, representing the very shallow-water equivalent of the cm-thick sapropel layers accumulated offshore in the deeper southern Adriatic basin, is of key importance in following the signature of the sapropel in a facies-tract ideally from the shoreline to the abyss.

2013 - Large-scale single incised valley from a small catchment basin on the western Adriatic margin (central Mediterranean Sea) [Articolo su rivista]
Maselli, V; Trincardi, F
abstract

The Manfredonia Incised Valley (MIV) is a huge erosional feature buried below the Apulian shelf, on the western side of the Adriatic margin. The incision extends more than 60 km eastward, from the Tavoliere Plain to the outer shelf, not reaching the shelf edge. High-resolution chirp sonar profiles allow reconstruction of the morphology of the incision and its correlation at regional scale. The MIV records a single episode of incision, induced by the last glacial–interglacial sea level fall that forced the rivers draining the Tavoliere Plain to advance basinward, reaching their maximum extent at the peak of the Last Glacial Maximum. The valley was filled during a relatively short interval of about 10,000 yr during the Late Pleistocene–Holocene sea level rise and almost leveled-off at the time of maximum marine ingression, possibly recording the short-term climatic fluctuations that occurred. The accommodation space generated by the lowstand incision was exploited during the following interval of sea level rise by very high rates of sediment supply that allowed the preservation of up to 45 m of valley fill. High-resolution chirp sonar profiles highlight stratal geometries that are consistent with a typical transgressive valley fill of an estuary environment, including bay-head deltas, central basin and distal barrier-island deposits, organized in a backstepping configuration. The highest complexity of the valley fill is reached in the shallowest and most proximal area, where a kilometric prograding wedge formed during a period dominated by riverine input, possibly connected to high precipitation rates. Based on the depth of the valley margins during this interval, the fill was likely isochronous with the formation of sapropel S1 in the Mediterranean region and may have recorded significant fluctuations within the hydrological cycle.

2013 - Man Made Deltas [Articolo su rivista]
Maselli, V; Trincardi, F
abstract

The review of geochronological and historical data documents that the largest southern European deltas formed almost synchronously during two short intervals of enhanced anthropic pressure on landscapes, respectively during the Roman Empire and the Little Ice Age. These growth phases, that occurred under contrasting climatic regimes, were both followed by generalized delta retreat, driven by two markedly different reasons: after the Romans, the fall of the population and new afforestation let soil erosion in river catchments return to natural background levels; since the industrial revolution, instead, flow regulation through river dams overkill a still increasing sediment production in catchment basins. In this second case, furthermore, the effect of a reduced sediment flux to the coasts is amplified by the sinking of modern deltas, due to land subsidence and sea level rise, that hampers delta outbuilding and increases the vulnerability of coastal zone to marine erosion and flooding.

2013 - The submerged paleolandscape of the Maltese Island: Morphology, evolution and relation to Quaternary environmental change [Articolo su rivista]
Micallef, A; Foglini, F; Le Bas, T; Angeletti, L; Maselli, V; Pasuto, A; Taviani, M
abstract

After the end of the Last Glacial Maximum, 450 km2 of former terrestrial and coastal landscape of the Maltese Islands was drowned by the ensuing sea level rise. In this study we use high resolution seafloor data (multibeam echosounder data, seismic reflection profiles, and Remotely Operated Vehicle imagery) and bottom samples to reconstruct ~ 300 km2 of this submerged Maltese paleolandscape. The observed paleolandscape is exceptionally well preserved and comprises former coastal landforms – (i) fault-related escarpments, (ii) paleoshore platforms and associated shorelines, (iii) paleoshoreline deposits, and (iv) mass movement deposits – and former terrestrial landforms – (v) river valleys, (vi) alluvial plains, (vii) karstified limestone plateaus, and (viii) sinkholes. These elements indicate that the paleolandscape has been primarily shaped by tectonic activity combined with fluvial, coastal, slope instability and karstic processes; these are the same processes the shaped the current terrestrial and coastal landscape. By correlating the identified landforms with the timing of known changes in sea level during the last glacial cycle, we infer that the alluvial plains and the shallowest limestone plateaus had up to 100 kyr to develop, whereas the paleoshoreline deposits are likely to have formed between 28 kyr and 14 kyr. The most prominent paleoshore platforms, shorelines and river valleys were generated between 60 kyr and 20 kyr. Fluvial erosion is likely to have been prevalent during periods of low sea level (Last Glacial Maximum and stadial conditions during MIS 3), whereas karst processes should have been more effective during warm and humid interstadial periods. Our results have implications for improving the characterization of past environments and climates, as well as providing a much needed background for prehistoric and geoarcheological research in the central Mediterranean region.

2012 - Drowned karst landscape offshore the Apulian Margin (Southern Adriatic Sea, Italy) [Articolo su rivista]
Taviani, M; Angeletti, L; Campiani, E; Ceregato, A; Foglini, F; Maselli, V; Morsilli, M; Parise, M; Trincardi, F
abstract

The south Adriatic shelf offshore of the redominently carbonate Apulian coast is characterized by a peculiar rough topography interpreted as relic karst formed at a time of lower sea level. The study area covers a surface of about 220 km2 , with depths ranging from 50 to 105 m. The most relevant and diagnostic features are circular depressions a few tens to 150 m in diameter and 0.50 to 20 m deep thought to be dolines at various stages of evolution. The major doline, Oyster Pit, has its top at about 50 m water depth and is 20 m deep. It is partly filled with sediments redeposited by episodic mass failure from the doline’s flank. Bedrock samples from the study area document that Plio-Pleistocene calcarenites, tentatively correlated with the Calcarenite di Gravina Fm, are a prime candidate for the carbonate rocks involved in the karstification, although the presence of other units, such as the Peschici or Maiolica Fms, is not excluded. The area containing this subaerial karst landscape was submerged about 12,500 years ago as a result of the postglacial transgression over the continental shelf.

2011 - High-frequency sea level and sediment supply fluctuations during Termination I: An integrated sequence-stratigraphy and modeling approach from the Adriatic Sea (Central Mediterranean) [Articolo su rivista]
Maselli, V; Hutton, Ew; Kettner, Aj; Syvitski, Jpm; Trincardi, F
abstract

After the end of the Last Glacial Maximum (LGM), Termination I recorded one of the fastest and highest amplitude eustatic oscillations of the Late Quaternary: in less then 15 kyr (between ca. 20 and 5.5 kyr cal. BP) sea level rose ~ 120 m, with at least two steps of increased rate of ice melting and eustatic rise, named Meltwater pulses 1A and 1B. The transgressive sedimentary succession deposited during this interval on several mid-latitude continental margins, among which the central Adriatic margin, includes three distinct units each deposited during a specific interval of the last sea level rise. In particular, the central Adriatic middle TST unit (mTST), composed of two prograding sedimentary wedges separated by an erosional surface, appears the most complex of the three TST units. The mTST unit formed during an interval of extreme climatic instability, including the Bölling-Allerød and the Younger Dryas–Holocene transition. Sequence stratigraphy analyses, integrated by core samples and 14C age estimates, indicate an enhanced sediment flux during the deposition of the mTST unit as a consequence of high-frequency climatic oscillations. Model simulations with Hydrotrend v3.0, a hydrological water balance and transport model, show high rates of sediment delivery within the interval between 13.8 and 11.5 kyr cal. BP as a consequence of increased rates of rainfall and partial melting of the Alpine glaciers. Reconstructions of the sediment architecture using 2D Sedflux 1.0C, a basin-fill model, reproduce the complexity of the internal architecture of the middle TST unit driven primarily by sea level. The internal unconformity within the mTST unit can best be explained by introducing a minor sea level fall during the Younger Dryas. This conclusion is supported by the presence of an extensive barrier–island–lagoon system at −75 m below present sea level, corresponding to the Younger Dryas time interval and representing the best evidence of paleo-shoreline for this interval.

2010 - Subsidence pattern in the central Adriatic and its influence on sediment architecture during the last 400 kyr [Articolo su rivista]
Maselli, V; Trincardi, F; Cattaneo, A; Ridente, D; Asioli, A
abstract

The western Adriatic margin (eastern Mediterranean), part of the Apennine foreland, is characterized by a differentiated tectonic setting, showing high subsidence rates (up to 1 mm/yr) in the northern area and tectonic uplift (on the order of 0.3–0.5 mm/yr) in the southern part corresponding with the so‐called Apulia swell. The central Adriatic marks the transition between these two areas. To calculate subsidence values, the stratigraphy of the central Adriatic has been investigated through the borehole PRAD1.2 (European project Profiles across Mediterranean Sedimentary Systems), the first continuous Quaternary marine record in the Adriatic basin (71.2 m long) reaching the top of Marine Isotope Stage 11 (MIS 11). Subsidence calculations were performed first by applying the backstripping procedure to PRAD1.2, in order to investigate the contribution of sediment load and tectonic driving forces to subsidence. Despite the large error bars, mostly caused by the uncertainties in paleowater depth reconstructions, the values obtained demonstrate that tectonics is the main driver for subsidence in this area. In order to better estimate the subsidence rates, an independent approach is introduced, based on the correlation of the present‐day burial depth of past shorelines deposited during the main glacial lowstands, from MIS 2 to MIS 10. The average subsidence rate of about 0.3 mm/yr appears greater than the average sediment supply rate (0.15 mm/yr), and this fact explains the overall backstepping of the 100 kyr regressive depositional sequences on the margin. The results obtained help to improve the understanding of the regional tectonics and can be used for quantitative reconstruction of Quaternary sea level changes in the Adriatic region. In general, the paper shows that even a short (71 m) borehole across a relatively short time span (340 kyr) can be useful for subsidence calculations, provided that a high‐resolution definition of its stratigraphy is available and a correlation can be drawn with the geomorphologic proxies such as paleoshoreline deposits.