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The contourite depositional system (CDS) along the southwestern Iberian Margin (SIM), within the Gulf of Cadiz and offshore areas of western Portugal bear the unmistakable signal of Mediterranean Outflow Water (MOW) exiting the Strait of Gibraltar. This locality records key information concerning the effects of tectonic activity on margin sedimentation, the effects of MOW dynamics on Atlantic circulation, and how these factors may have influenced global climate. Over the last four decades, numerous studies have been conducted on the late Miocene, Pliocene and Quaternary sedimentary stacking pattern of Neogene basins along the SIM for both academic and resources exploration purposes. However, understanding of the region rests primarily on basic seismic stratigraphy calibrated with limited data from only a few exploration wells. The Integrated Ocean Drilling Program (IODP) Expedition 339 recently drilled five sites in the Gulf of Cadiz and two sites on the western Iberian margin. The integration of core and borehole data with other geophysical databases leads us to propose a new stratigraphic framework. Interpretation of IODP Exp. 339 data along with that from industry sources and onshore outcrop analysis helps refine our understanding of the SIM's sedimentary evolution. We identify significant changes in sedimentation style and dominant sedimentary processes, coupled with widespread depositional hiatuses along the SIM within the Cadiz, Sanlucar, Doñana, Algarve and Alentejo basins. Following the 4.5 Ma cessation of a previous phase of tectonic activity related to the Miocene–Pliocene boundary, tectonics continued to influence margin development, downslope sediment transport and CDS evolution. Sedimentary features indicate tectonic pulses of about 0.8–0.9 Ma duration with a pronounced overprint of ~ 2–2.5 Ma cycles. These more protracted cycles relate to the westward rollback of subducted lithosphere at the convergent Africa-Eurasia plate boundary as its previous NW–SE compressional regime shifted to a WNW–ESE direction. Two major compressional events affecting to the Neogene basins at 3.2–3 Ma and 2–2.3 Ma help constrain the three main stages of CDS evolution. The stages include: 1) the initial-drift stage (5.33–3.2 Ma) with a weak MOW, 2) a transitional-drift stage (3.2–2 Ma) and 3) a growth-drift stage (2 Ma-present time) with enhanced MOW circulation into the Atlantic and associated contourite development due to greater bottom-current velocity. Two minor Pleistocene discontinuities at 0.7–0.9 Ma and 0.3–0.6 Ma record the effects of renewed tectonic activity on basin evolution, appearing most prominently in the Doñana basin. Several discontinuities bounding major and minor units appear on seismic profiles. Quaternary records offer the clearest example of this, with major units of about 0.8–0.9 Ma and sub-units of 0.4–0.5 Ma. Sedimentation is controlled by a combination of tectonics, sediment supply, sea-level and climate. This research identifies time scales of tectonic controls on deep-marine sedimentation, specifically over periods of 2.5–> 0.4 Ma. Shorter-term climatic (orbital) mechanisms control sedimentation at time scales of ≤ 0.4 Ma. The role of bottom water circulation and associated processes in shaping the seafloor and controlling the sedimentary stacking pattern on continental margins has to be seriously reconsidered in future multidisciplinary studies. This is not only because of the common occurrence of sandy contourite deposits in deep water setting and their economic interest for hydrocarbon exploration, but principally because they archive the heartbeat of the interior Earth and therefore have important sedimentary and paleoceanographic implications. [ABSTRACT FROM AUTHOR]

The Contourite Depositional Systems (CDS) in the Gulf of Cádiz and on the West Iberian margin preserve a unique archive of Mediterranean Outflow Water (MOW) variability over the past 5.3 Ma. These CDS have been recently drilled in several places during the IODP Expedition 339. These drill sites now offer a new window to the internal Pliocene and Quaternary architecture of the CDS. In this study, we use downhole and core Gamma Ray (GR) data acquired from 5 sites drilled in the CDS along the middle slope and 1 site drilled in the deeper setting of the lower slope, out of the MOW path. The GR data primarily tracks the clay content in the sediment and is the expression of sediment supply and, for sites drilled in the CDS, of the bottom current processes. Both appear astronomically controlled as shown by spectral analysis performed on the GR data. Results also reveal that the GR log patterns correlate well across the sites over the last 1.4 My. Several GR horizons corresponding to drops in GR values were identified, most of which fit with coarse-grained deposits observed in cores and interpreted as contourite beds. The GR horizons are interpreted as isochronous horizons, providing a regional scale chronostratigraphic framework for the CDS depositional records with an accuracy of ~ 20 ky. We further assess the spatial and temporal variability of the CDS hiatuses at the regional scale. [ABSTRACT FROM AUTHOR]

We here discuss a detailed investigation of the dense water formation, evolution and spreading in the Aegean Sea during the year 1987, immediately prior to the onset of the Eastern Mediterranean Transient (EMT). We use hydrologic data collected during the LIA cruise; satellite images for SST (Sea Surface Temperature), and PROTHEUS data (a coupled ocean–atmosphere numeric model) along with theoretical streamtube models. These hydrological analyses are related to late Quaternary sedimentary drifts in the Cyclades Plateau and in the Myrtoon Basin. Our analysis shows that streamtube dynamics provide a novel model of dense water evolution and spreading in the Aegean Basin. Applying this model to dense water masses observed in winter and spring 1987 near Samothrace and over the Limnos-Lesbos Plateau, results in a geostrophic flow of this dense, cold water towards the Limnos-Sporades Channel, in the North Aegean Sea. There it mixes with dense water from the Limnos-Lesbos Plateau and finally both move geostrophically towards the Cyclades Plateau. These results indicate that most of the dense water observed near the Cyclades, formed initially about 3 months earlier at Samothrace and Limnos shelves. During its long pathway it partially mixed with adjacent water masses. Although our analysis concerns only one year of dense water analyses, these results are thought to reflect a more general and recurrent phenomenon in the Aegean basin. Indeed, high-resolution (Airgun 10 in.) seismic-reflection data from the Cyclades Plateau reveal the presence of late Quaternary sediment drifts. These observations are concordant with results from our theoretical model. This suggests a direct link between such a dense-water cascading and contourite dynamics. The continuation of sediment drifts into the deep basin floor (≈ 900 m deep) of the Myrtoon Basin, moreover, indicates a cascading character of such bottom currents at the flanks of the basin, a feature that set further investigations. [ABSTRACT FROM AUTHOR]

Bottom current deposits (contourites) form in association with modern-day or ancient oceanic gateways. A paucity of examples in the ancient record and the lack of consensus on diagnostic criteria for differentiating them from other deepwater deposits limit our understanding of how they may record past global oceanic circulation, tectonic events and gateway evolution. This work describes an exceptional example of Eocene to middle Miocene deep-marine deposits located both onshore and offshore deepwater environments around the island of Cyprus. Multidisciplinary approaches were used to discriminate contourite facies associations, propose a sedimentary model, and interpret the relations with regional tectonics and the evolution of the nearby Indian Gateway. Contourite deposits appear in late Eocene to middle Miocene intervals interstratified with pelagic/hemipelagic sediments, turbidites and mass-transport deposits (MTDs). These deepwater deposits developed along a slope basin located on the upper plate of an active margin, evolving from a wide basin formed during a period of tectonic quiescent into a series of shallowing-upward, segmented sub-basins affected by compressional stress. The present study proposes a sedimentary model in which two contourite depositional systems developed: first in the Eocene (dominated by finer-grained contourites), and then during the latest Oligocene to middle Miocene (dominated by coarser-grained contourites). Both systems were buried by extensive marl deposits and record the respective influence of deep (circulating NW) and intermediate (circulating SE) water masses. The long-term evolution of the contourites reflects tectonic events that enhanced subduction processes south of Cyprus as well as exchange between the Neotethys Ocean and the Indian and Atlantic Oceans —until the final closure of the Indian Gateway by the end of the middle Miocene, when a new circulation pattern was established with the formation of the Mediterranean Sea. The contourites described here represent bi-gradational sequences that normally form in association with contouritic drifts, sometimes having the asymmetric top-cut sequence characteristics of plastered drifts and contourite terraces. The coarser (sandy) contourites, formed from the latest Oligocene to middle Miocene, consist of three packages associated with compressive and flexural phases. They pertain to I) Chattian (late Oligocene); II) Aquitanian/Burdigalian (early Miocene) and III) Langhian (middle Miocene). Evidence of enhanced bottom current episodes occurs toward the top of these packages before they are buried by later dominant marl deposits. The sandy contourites thus formed during the compressive phases, whereas the predominately finer-grained units formed during later flexural phases. The intermittent turbidites and MTDs (developed during compressional phases in combination with pelagic/hemipelagic sediments) represent the sediment supply for the contourite deposits after their winnowing and / or reworking. Our research found that the diagnostic criteria for discriminating ancient bottom current deposits from other deepwater deposits are related primarily to variations in sedimentary processes, current behaviour and its velocity, sedimentation rates and paleoenvironmental conditions. This highlights the importance of primary sedimentary structures, microfacies and ichnological features in making determinations at the sedimentary facies scale. Due to their common occurrence, sedimentary thickness (30-40 m), potential porosity and permeability, sandy contourites can form deepwater reservoirs for energy geosciences. In summary, this work demonstrates the role of plate tectonics and oceanic gateways in driving the paleo-oceanic circulation that, in turn, controls sedimentary processes and shapes the morphology of oceanic basins and continental margins. It also allows for comparison with other present-day and ancient continental margin deposits. Future high-resolution approaches and analyses of other geological settings could help resolve the sedimentary architectures of similar deepwater systems in terms of episodic tectonic processes —involving compressive-flexural stress variations. They control the Earth's surface environment (sea-level, climate and oceanic circulation) over time by influencing sediment supply, packages of strata and types of contourite deposits. • Deepwater deposits along a slope basin located on the upper plate of an active margin. • Contourite systems developed in the Eocene and during the latest Oligocene to middle Miocene. • These contourites record the exchange between the Neotethys Ocean and the Indian and Atlantic Oceans. • The closure of the Indian Gateway conditioned a new global oceanic circulation pattern. • Plate tectonics and oceanic gateways are driving the paleo global oceanic circulation. [ABSTRACT FROM AUTHOR]

We use newly available, extensive two- and three-dimensional seismic datasets in the Vøring Plateau sector of the mid-Norwegan continental margin to investigate the architecture and evolution of Quaternary contourite drifts in the Norwegian Sea. The drifts typically comprise tens of cubic kilometres of sediment, often intercalated between lenses of glacigenic debris flows, and demonstrate migrating depositional centres along the upper and middle slope sectors of the mid-Norwegian margin through the last ~2.7 M.yr. By contrast, the contourite deposited in the southern Vøring Plateau area is anomalously large covering an area of ~17,000 km2 and comprising over 720 km3 of sediment. Correlation of internal drift surfaces with well-dated sediment cores shows that the massive, up to 280 m thick drift contains two major units that were deposited over the last two glacial-interglacial cycles, yielding extremely high sedimentation rates, comparable to those sourced directly from erosive meltwater-rich glaciers and fast-flowing ice streams. A revised evolutionary drift model provides an end-member example of how a combination of rapid glacially-derived sediment delivery and its subsequent transport and deposition by along-slope processes may exert considerable influence on continental margin morphology over geologically short timescales. • The Quaternary evolution of contouritic sedimentation on the mid6 Norwegian continental margin has been examined using extensive 3D and 2D seismic data. • Seven individual buried contourite drifts have been mapped on the Vøring Plateau sector of the Norwegian Sea. • Contourites reported here typically comprise tens of cubic kilometres of sediment and demonstrate migrating depositional centres along the upper and middle slope sectors of the mid-Norwegian margin through the last ~2.7 Ma. • By contrast, the contourite deposited during the last 250,000 years in the southern Vøring Plateau area is anomalously large, covering an area of ~17,000 km2 and comprising over 720 km3 15 of sediment. • A revised drift evolution developed here provides an end-member example of how a combination of rapid glacially-derived sediment delivery and its subsequent transport and deposition by along-slope processes may exert considerable influence on continental margin morphology even over geologically short timescales. • Due to its thickness, the large contourite drift on the southern Vøring Plateau contains an exceptionally high-resolution record of the Late Quaternary palaeoceanography and palaeoglaciology, and may constitute an excellent target for future scientific drilling. [ABSTRACT FROM AUTHOR]

Rodrigues et al. (2022) have proposed a new classification for mixed turbidite-contourite depositional systems based on their notion that there is only one type of tubidite and that there is only one type of contourite in deep-marine systems. However, there are at least 36 turbidite types and 4 contourite types in the published literature. Furthermore, they have used the term "bottom current" to represent a single unique current, which flows along-slope. Nevertheless, there are 4 major types of bottom currents (thermohaline contour currents, tidal currents, baroclinic currents, and wind-driven currents). With the exception of contour currents, the other three currents do not and cannot flow along-slope. The problem here is that the authors have failed to provide a clear and precise definition of the terms "turbidite", "contourite", and "bottom current" Consequently, their classification has added a new layer of confusion to an already muddled domain of turbidite-contourite research. Importantly, their review article suffers from failing to cite pioneering and seminal works on turbidites (e.g., Kuenen, 1957; Bouma, 1962; Bagnold, 1962,; Middleton, 1967; Sanders, 1965; among others) and on contourites (e.g., Hollister, 1967). In seeking clarity, the purpose of this discussion is to identify specific issues with 14 questions under the following topics: (1) the turbidite problem, (2) the contourite problem, (3) the bottom-current problem, and (4) the seismic geometry vs. process sedimentology problem. Hopefully, the authors would respond with necessary definitions, empirical data, and references. [ABSTRACT FROM AUTHOR]

Endurance Basin is an elongate broadly WNW–ESE trending basin located on the northern margin of the Scotia Sea, adjacent to the southern margin of the South Georgia micro-continent. Bathymetric and TOPAS sub-bottom profile data acquired in 2010 by the British research ship RRS James Clark Ross map this basin and its sedimentology for the first time. Endurance Basin contains a number of sub-basins and a substantial glaciogenic fan. The northern margin of Endurance Basin is formed by a series of steep slopes and intervening troughs. These are interpreted as a left-stepping en echelon array of oblique, strike–slip faults whilst the sub-basins are separated by compressional dip–slip faults. It appears that South Georgia is moving NW with respect to the basin. We interpret five seismic facies from TOPAS data, which are associated with distinct sedimentologies. The most striking units in the basin fill are: substantial contourite drifts located in the NW of the basin and on its southern margin; and two distinct mass transport deposits that pond in the centre of the basin. Combined with the known regional oceanographic setting, the contourites provide evidence of broadly eastward flowing bottom currents, entering the basin from at least two locations. Although landslide scars are present on the steep northern basin margin, the imaged mass transport deposits are interpreted to have been sourced from the glaciogenic fan, located in the SE of the basin, and from a contourite unit located on the basin's southern margin. Sediments from these events are transported at least 40 km. The contourite drift sequence is at least 100 m thick in the west of the basin and may contain a palaeoenvironmental archive of Antarctic Circumpolar Current (ACC) flow and the climate of South Georgia extending to the Pliocene. Such an archive would allow the reconstruction of ACC flow through the Pleistocene glaciations and provide a means of linking ocean circulation and climate records in the sub-Antarctic Polar Front region. [ABSTRACT FROM AUTHOR]

The Albian-Cenomanian breakup sequence (BS) offshore Northwest Iberia is mapped, described and characterised for the first time in terms of its seismic and depositional facies. The interpreted dataset comprises a large grid of regional (2D) seismic-reflection profiles, complemented by Industry and ODP/DSDP borehole data. Within the BS are observed distinct seismic facies that reflect the presence of: (a) black shales and fine-grained turbidites, (b) mass-transport deposits (MTDs) and coarse-grained turbidites, and (c) contourite drifts. Borehole data show that these depositional systems developed as mixed carbonate-siliciclastic sediments proximally, and as organic-carbon-rich mudstones (black shales) distally on the Northwest Iberia margin. MTDs and turbidites tend to occur on the continental slope, frequently in association with large-scale olistostromes. Distally, these change into interbedded fine-grained turbidites and black shales showing widespread evidence of deep-water current activity towards the top of the BS. Current activity is expressed by intra-BS erosional surfaces and sediment drifts. The results in this paper are important as they demonstrate that contourite drifts are ubiquitous features in the study area after Aptian-Albian lithospheric breakup. Therefore, we interpret the recognition of contourite drifts in Northwest Iberia as having significant palaeogeographic implications. Contourite drifts materialise the onset of important deep-water circulation marking the establishment of oceanic gateways between two fully separated continental margins. As a corollary, we postulate the generation of deep-water geostrophic currents to have had significant impact on North Atlantic climate and ocean circulation during the Albian-Cenomanian, with the record of such impacts being preserved in the contourite drifts analysed in this work. [ABSTRACT FROM AUTHOR]

Seismic reflection profiles from the northwestern and central part of the Fram Strait show thick packages of drift type sediments mainly along the western Yermak Plateau flank, but also in the central, flat part of the Fram Strait. North of 80.5°N, a large-scale field of sediment waves along the Yermak Plateau rise separates a western, lower from an eastern, upper drift body. These drift bodies were deposited by bottom currents, most likely the northbound Yermak Branch of the West Spitsbergen Current, but we cannot rule out that the western drift body may also have been influenced by southbound bottom currents. A stratigraphic boundary is clearly visible within the drift bodies and even more pronounced within the sediment waves, separating a lower package of waves migrating upslope at low angle (∼5°) from an upper package with significantly increased wave crest migration (∼16.5°). This stratigraphic boundary could be tracked along the seismic network and corresponds to the lithostratigraphic boundary between units IA and IB at ODP Leg 151, Site 911 that was dated to 2.7 Ma. The increase in wave-crest migration angle indicates a shift towards higher sedimentation rates at 2.7 Ma, which corresponds to the intensification of the Northern Hemisphere glaciation with a major expansion of the Greenland, Scandinavian, northern Barents Sea and North American ice sheets. The subaerially exposed Barents shelf and the expansion of the northern Barents Sea ice sheet (as well as Svalbard) are likely sources for enhanced erosion and enhanced fluvial input along the pathway of the West Spitsbergen Current, resulting in higher sedimentation rates in the Fram Strait. [ABSTRACT FROM AUTHOR]

Rodriguez-Tovar (2022) has relied on vertical facies models (e.g., the Bouma Sequence) for distinguishing one facies (e.g., turbidites) from the others. However, he has failed to acknowledge inherent flaws in the Bouma Sequence. Furthermore, he has omitted key features such as internal hiatus from the original contourite model and erosional contact from the original hyperpycnite facies model. These units with internal hiatus or erosional contact cannot function as a predictive facies model. In deep-water research, one cannot selectively dismiss previous observations in order to promote one's skewed narrative, which is that turbidite-, contourite-, and hyperpycnite-facies models are functional. Available literature is antithetical to this narrative. Therefore, the purpose of this discussion is to identify 10 fundamental problems that undermine the basic tenet of the review article on ichnological analysis of deep-marine facies. [ABSTRACT FROM AUTHOR]

Contourites are sediments deposited or substantially reworked by the persistent action of bottom currents which are capable of forming a wide range of erosional and depositional features on the seafloor. The study of contourites is a multidisciplinary topic linking physical oceanography and marine geology. While near-bottom circulation is an important subject itself due to different dynamic aspects and climatic estimates of abyssal water transports, it becomes especially important for studies of lateral sedimentation. The precise direct data on bottom currents on the South American continental rise and adjacent abyssal plains remain extremely rare. Numerical modeling can appear helpful for filling the gaps in our knowledge on bottom circulation in the region. This work describes an approach for mapping erosion- and deposition-dominated areas based on the modeled circulation in the bottom layers. The model domain covers the regions with different seabed topography and velocities of bottom currents: the Vema Channel, the Santa Catarina Plateau, the Rio Grande Rise, and parts of the Argentine and Brazil basins. The high vertical resolution used in the model allowed us to study the near-bottom circulation in the deep ocean, while high horizontal resolution enabled modeling currents in narrow underwater passages such as the Vema Channel. The equations that encompass the bottom current velocities and data on surface sediment grain-size are well-known; in this study, we estimate the erosional-depositional potential of bottom currents using these equations. This approach allowed identification of the regions of dominant erosion (to the northeast of the northern exit from the Vema Channel), deposition (northern part of the Santa Catarina Plateau), and non-deposition under the influence of bottom currents. The results were validated by the analysis of echo-facies distribution in the study area and variations in the surface sediment grain-size. This study embraces the transition zone between the Argentine and Brazil basins, which is crucial for understanding the deep and bottom circulation in the western South Atlantic under modern conditions and in the geological past. The presented technique can improve our knowledge on how bottom currents shape the seafloor and control sediment distribution in the Southwest Atlantic. • Velocities of bottom currents were modeled in the Southwest Atlantic. • Sediment erosion and deposition areas were mapped based on the simulated velocities. • Sub-bottom profiling and grain-size data generally confirm the results of bottom current velocity modeling. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution swath-bathymetry data integrated with sub-bottom profiles and single-channel seismics reveal an 18km long, up to 1000m wide and 10–15m deep crack located approx. 4km upslope from a slide scar on the continental slope off northern Norway. This crack is formed by subsidence of the sea-floor sediments to a depth of 120m due to downslope movement of an ~80km2 large sediment slab that represents the final stage of retrogressive mass wasting in this area. From its morphological freshness, the crack this is inferred to have formed sometime during the last 13cal. ka BP. These findings add to our understanding of the origin of sea floor cracks on passive continental margins where explanations as slip of normal faults or gas expulsion from the dissociation of gas hydrates previously have been suggested for the formation of cracks in similar settings. [Copyright &y& Elsevier]

Abstract: The Plio-Quaternary unidirectionally migrating channels (UMCs) and contourites in the northern slope of the South China Sea were investigated in this paper using seismic data. The UMCs include thalweg deposits (TDs) and laterally migrating deposits (LMDs), which result from the interaction between gravity flow and contour current. The LMDs migrating directions are northeast (NE) and west-southwest (WSW) and also display weak seismic reflection and obvious multi-stages. By contrast, the TDs show high seismic reflection and lateral aggradation. Giant elongated, confined, and slope sheeted drifts, as well as sediment waves are widespread in the northern slope of the South China Sea. Helicoidal contour currents can generate giant elongated and confined drifts associated with moats. By contrast, tabular contour currents can develop slope sheeted drifts with rare moats. NE-migrating channels, giant elongated drifts, and a number of sediment waves are exclusively formed at water depths of 200 m–1200 m. Drifts, sediment waves, and few WSW-migrating channels are developed at water depths of 1200 m–3000 m. The intermediate water contour current circulates clockwise, moving from Xisha Islands to Dongsha Islands and extending into the eastern part of Dongsha Islands because of the bathymetry. Deep water contour current may circulate counterclockwise and be transported northeastward through Dongsha Islands to Xisha Islands, bifurcating in the Xisha Islands because of topographical prominences. [Copyright &y& Elsevier]

New biostratigraphic, sedimentological and petrographic data and a thorough review of existing literature modify existing knowledge on the age, the sedimentology, the petrography and the palaeogeographic origin of the Gurnigel flysch from the Voirons massif (Haute Savoie, France). Planktonic foraminiferal biostratigraphy assigns the flysch to the upper Middle Eocene (zones P12 to P14) through to Lower Oligocene (zones P16 to P20) stages. This result contrasts with previous work, which assigned the unit to the Lower Palaeocene to upper Middle Eocene on the basis of calcareous nannofossil and dinoflagellate assemblages. The following findings suggest that the Voirons massif comprises several stacked flysch units that do not have exactly the same palaeogeographic origin: (i) the occurrence of flysch exposures in reverse stratigraphic order combined with the lack of evidence for bed overturning; (ii) the variability of palaeo-depositional settings inferred from different flysch outcrops of similar age; (iii) the differences in the heavy mineral content; and (iv) the anomalous superimposition of distal turbidites and/or basinal contourites (Saxel Marls) over proximal turbidites (Vouan Conglomerates). The young age of these kilometre-sized flysch slices precludes their hitherto postulated locus of deposition in the South-Penninic Ocean, and rather indicates a provenance from the Ultrahelvetic and/or North-Penninic (Valais) palaeogeographical domains. Finally, none of the nannofossil assemblages are contemporaneous with the observed planktonic foraminifera associations, suggesting that they have been reworked, dissolved, or just simply diluted and not found by earlier researchers. This study from the Voirons massif shows that planktonic foraminifera associations are a highly reliable biostratigraphic tool for obtaining accurate ages of flysch successions. [ABSTRACT FROM AUTHOR]

Abstract: New high-resolution seismic and swath bathymetry data reveal the detailed structure of nine mud volcanoes and two large fields of pockmarks at water depths of 400–1100m in the western Alborán Sea. These features are related to episodes of focused fluid flow through Pliocene-Quaternary contourite deposits of the Ceuta Drift. We describe nine mud volcano systems, composed of two key structural elements: (i) extrusive edifices comprising cones, bicones and low-dip mudflows interfingering with adjacent drift sediments and (ii) intrusive feeder complexes comprising pipes and unstratified downward-tapering cones underlying the extrusive edifices. The mud volcano systems are grouped into four types: I: Complex edifices; II: Stacked single edifices; III: Single edifices fed by buried bicones and IV: Single edifices. All except the last record episodic extrusive activity since the Pliocene, the timing of which is constrained by correlation between the main mud extrusion episodes and dated unconformities within the Ceuta Drift. Complex mud volcanoes composed of twin to multiple seabed cones are the longest-lived systems, with at least six extrusive episodes since the mid-Pliocene; most of the mud volcanoes appear to have been reactivated in the mid-Pleistocene (~0.9Ma, MPR discontinuity) and all at MIS12 (0.4Ma). While the onset of focused fluid flow was triggered by mid-Pliocene tectonically-driven diapirism of Lower Miocene shales that form the rooting zone of the mud volcanoes, we suggest that some of the Pleistocene phases of mud extrusion might be related to erosion of the contourite drift during major sea-level falls. In addition to vertical focused fluid flow, we propose that leakages from the mud volcano feeder complexes into high-permeability contourite sediments may cause lateral fluid migration and form gas accumulations. Lateral fluid flow in the near surface sediments could be responsible of forming subsurface reservoirs and consequently, random pockmarks by fluidification and/or liquefaction of the non-consolidated shallow sediments. Stacked buried paleo-pockmarks indicate that this mechanism has been persistent along recent times, at least after the mid-Pleistocene. [Copyright &y& Elsevier]

Abstract: The recognition of contourite and turbidite deposits in deep-marine sequences can be challenging, as deposits may show similar sedimentary characteristics. In Flemish Pass, a small, 1100m deep, perched basin along the southeast Canadian continental margin, both types of deposits occur. Late Quaternary sediments include thin sand layers interbedded with hemipelagic muds. The distribution, age, sedimentary structures and petrology of these sands were used to distinguish between turbidite and contourite deposits, which were then characterized by detailed grain size distribution for understanding the conditions leading to deposition of each type. Seven sediment facies each with a distinctive grain size distribution were recognized. They are 1—transported contourites, 2—winnowed beds, 3—possible jökulhlaup deposits, 4—sandy turbidites, 5—muddy turbidites, 6—hemipelagic sediment and 7—turbidites from well-sorted materials. Sand packets comprised of several stacked turbidite sand beds, some with erosive contacts, were correlated from the margin to the basin floor, showing clear distal fining, and creating a small lobe. The temporal distribution of the sand beds indicates that most turbidites and contourites were deposited at stadial to interstadial transitions. This linkage may be related to variations in the oceanic circulation in Flemish Pass, which winnowed turbidites and may have triggered turbidity currents by moving sands into canyon heads. [Copyright &y& Elsevier]

Abstract: Thermohaline ocean currents with near-bed velocities of a few tens of cms−1 have the ability to transport and sort sand, which is often deposited in thin sheets referred to as ‘contourite’ sand sheets. We examine a small sandy contourite sheet located in 800–1000m water depth on the west Shetland slope in the Faroe–Shetland Channel. We describe the sedimentology of the contourite, and the relationship between sediment transport processes and contourite distribution through the last deglaciation and Holocene, based on a set of 17 short cores. Four sedimentological units ranging from very poorly sorted mud at the base (unit 1) to moderately sorted, slightly muddy, fine sand at the top (unit 4) are recognised. Ice-rafted detritus (IRD) occurs in the lower three units, but is absent in unit 4. The upper two units, 3 and 4, make up the contourite sand sheet. Analysis of the sand fraction of units 3 and 4 shows that the mean sand grain size is remarkably constant at around 3ϕ throughout, except in some unit 3 samples with unusually high IRD content, where the mean can be coarser. IRD content correlates strongly with mean grain size, sorting and skewness throughout unit 3 even when the IRD content is small, showing that IRD input is one of the key processes controlling the sedimentology of unit 3. We conclude that the muddy sand contourites form by incomplete winnowing of the underlying glaciomarine sediments. The mud component is transported with the sand from the same source, either as small particles attached to sand grains or as sand-sized mud aggregates. Thickness maps of units 3 and 4 show that they have different depocentres, with unit 4 displaced northwest (downslope) relative to unit 3. Sedimentological trends in unit 3 are inconsistent and show no consistent transport direction. In contrast, clear across slope trends are seen in unit 4, with weak alongslope trends from the centre to both ends of the elongate contourite body. This suggests that the upper part of the contourite, unit 4, is derived from the downslope reworking of unit 3 sediment. There is no evidence for significant alongslope transport in either unit 3 or unit 4. The patchy occurrence of sandy contourites along the west Shetland slope is interpreted to result from localised export of sand from further upslope. The usefulness of the contourite sand in palaeoceanographic terms is limited. No meaningful dates can be derived from the sediments because of reworking and bioturbation. However, the presence of IRD within unit 3 shows that the Holocene circulation pattern, with strong bottom water flow through the Faroe–Shetland Channel, was established while there was still significant floating ice in the area. [Copyright &y& Elsevier]

The deep-marine environment is a complex setting in which numerous processes —settling of pelagic and hemipelagic particles in the water column, sediment gravity flows (downslope density currents; turbid flows), and bottom currents— determine sediment deposition, hence a variety of facies including pelagites/hemipelagites, contourites, turbidites and hyperpycnites. Characterization and differentiation among deep-sea facies is a challenge, and numerous features may be highlighted to this end: sedimentary structures, geochemical data, micropaleontological information, etc. Ichnological information has become a valuable, yet in some cases controversial, proxy, being in most of cases understudied. This paper gathers the existing ichnological information regarding the most frequent deep-sea facies —from those in which ichnological analyses are numerous and detailed (e.g. pelagites/hemipelagites and turbidites), to those for which ichnological information is lacking or imprecise (hyperpycnites and contourites). This review analyses palaeoenvironmental (i.e., ecological and depositional) conditions associated with deep-sea sedimentary processes, influence of these changes on the tracemaker community, and associated ichnological properties. A detailed characterization of trace fossil assemblages, ichnofabrics and ichnofacies is presented. Special attention is paid to variations in trace fossil features, approached through sedimentary facies models and the outcrop/core scale. Similarities and differences among deep-sea facies are underlined to facilitate differentiation. Pelagic/hemipelagic sediments are completely bioturbated, showing biodeformational structures and trace fossils, being characterized by composite ichnofabrics. The trace fossil assemblage of muddy pelagites and hemipelagites is mainly assigned to the Zoophycos ichnofacies, and locally to the distal expression of the Cruziana ichnofacies. Turbidites are colonized mostly from the top, determining an uppermost part that is entirely bioturbated, the spotty layer; below it lies the elite layer, characterized by deep-tier trace fossils. Turbidite beds pertain to two different groups of burrows, either "pre-depositional", mainly graphogliptids, or "post-depositional" traces. Turbidite deposits are mostly characterized by the Nereites ichnofacies, with differentiation of three ichnosubfacies according to the different parts of the turbiditic systems and the associated palaeoenvironmental conditions. There are no major differences in the trace fossil content of the hyperpycnite facies and the classical post-depositional turbidite, nor in the pelagic/hemipelagic sediments, except for a lower ichnodiversity in the hyperpycnites. Trace fossil assemblages of distal hyperpycnites are mainly assigned to the Nereites ichnofacies, while graphogliptids are scarce or absent. Ichnological features vary within contourites, largely related to palaeoenvironmental conditions, depositional setting, and type of contourite. Ichnodiversity and abundance can be high, especially for mud-silty contourites. The ichnological features of mud-silty contourites are similar to those of the pelagic/hemipelagic sediments (the tiering structure probably being more complex in pelagic/hemipelagic) or to the upper part of the muddy turbidites (contourites probably being more continuously bioturbated). No single archetypal ichnofacies would characterize contourites, mainly assigned to the Zoophycos and Cruziana ichnofacies. • A revision on the role of bioturbation in deep-sea sediments is presented. • Ichnological features refine previously proposed facies models. • Pelagites/hemipelagites and turbidites reveal diagnostic ichnological features. • Hyperpycnites and contourites show variability in ichnological properties. • Bioturbation reveals as a key to characterize and differentiate deep-sea facies. [ABSTRACT FROM AUTHOR]

We present a multidisciplinary study of morphology, stratigraphy, sedimentology, tectonic structure, and physical oceanography to report that the complex geomorphology of the Palomares continental margin and adjacent Algerian abyssal plain (i.e., Gulf of Vera, Western Mediterranean), is the result of the sedimentary response to the Aguilas Arc continental tectonic indentation in the Eurasian–Africa plate collision. The indentation is imprinted on the basement of the margin with elongated metamorphic antiforms that are pierced by igneous bodies, and synforms that accommodate the deformation and create a complex physiography. The basement is partially covered by Upper Miocene deposits sealed by the regional Messinian Erosive Surface characterized by palaeocanyons that carve the modern margin. These deposits and outcropping basement highs are then covered and shaped by Plio-Quaternary contourites formed under the action of the Light Intermediate and Dense Deep Mediterranean bottom currents. Even though bottom currents are responsible for the primary sedimentation that shapes the margin, 97% of this region's seafloor is affected by mass-movements that modified contourite sediments by eroding, deforming, faulting, sliding, and depositing sediments. Mass-movement processes have resulted in the formation of recurrent mass-flow deposits, an enlargement of the submarine canyons and gully incisions, and basin-scale gravitational slides spreading above the Messinian Salinity Crisis salt layer. The Polopo, Aguilas and Gata slides are characterized by an extensional upslope domain that shapes the continental margin, and by a downslope contractional domain that shapes the abyssal plain with diapirs piercing (hemi)pelagites/sheet-like turbidites creating a seafloor dotted by numerous crests. The mass movements were mostly triggered by the interplay of the continental tectonic indentation of the Aguilas Arc with sedimentological factors over time. The indentation, which involves the progressively southeastward tectonic tilting of the whole land-sea region, likely generated a quasi-continuous oversteepening of the entire margin, thus reducing the stability of the contourites. In addition, tectonic tilting and subsidence of the abyssal plain favoured the flow of the underlying Messinian Salinity Crisis salt layer, contributing to the gravitational instability of the overlying sediments over large areas of the margin and abyssal plain. • Basement, Messinian canyons, contourites and mass movements dictate geomorphology. • Mediterranean bottom currents responsible for primary Plio-Quaternary sedimentation • Large-scale gravity-driven slides above Messinian salt deposits are characterized. • Tectonic tilting of the land-sea region triggers recurrent mass movements. • A model of offshore geomorphic responses to inland tectonic indentation is presented. [ABSTRACT FROM AUTHOR]

Abstract: Contourite depositional systems have been the focus of much recent research, but still relatively little is known about contourite erosive features and their associated processes. Based on multibeam bathymetry, side-scan imagery and different resolution seismic records, a detailed description and classification of the major erosive submarine valley features of the Contourite Depositional System of the Gulf of Cadiz middle slope is presented for the first time. Four types of erosive features have been differentiated, including contourite moats, contourite channels, marginal valleys and large isolated furrows, and interpreted in terms of their tectonic and oceanographic implications during the Quaternary. The study of the distribution and characteristics of erosive features is essential to better understand the present and past interaction of the Mediterranean Outflow Water (MOW) with the middle slope seafloor, and allows us to propose a new and more precise scheme for the MOW circulation patterns. This scheme includes a main along-slope circulation responsible for the excavation of the contourite moat and channels, and a secondary down-slope circulation responsible for the erosion of marginal valleys and isolated furrows. Three evolutionary stages have been observed in the development of the erosive system during the Quaternary, that can be related to changes in the distribution and splitting of the MOW as a consequence of the segmentation of the NE–SW diapiric ridges by neotectonic effects: 1) Early Pleistocene to Mid-Pleistocene: linear diapiric ridges; 2) Mid-Pleistocene to Late Pleistocene: diapiric reactivation and 3) Late Pleistocene to Holocene: main recent phase of diapiric ridges segmentation and rotation. This study provides important regional clues for establishing the evolution of the erosive features in relation with neotectonic effects, and represents a good example of the potential of erosive features as evidences for the reconstruction of the paleoceanography and recent tectonic changes. [Copyright &y& Elsevier]

Abstract: Buried contourites located offshore Capo Suvero (Calabria, Southern Italy) have been investigated using analysis of Sparker profiles. The deposits onlap an erosional surface produced by a slide in the upper slope Pleistocene units. The overall seismic characters of the deposits suggest an interpretation as infilling drift deposits formed by the activity of a northward bottom-current flowing along the paleoslope. The deposits, with thickness up to ~140 m, are made up of 3 units, including 8 sub-units with an upward-convex shape on dip profile and a lenticular shape on strike profile. The stacking pattern of sub-units highlights a general upslope migration, interrupted by two downslope shifts accompanied by erosion; a general migration toward the north has also been recognized. This evolution could be explained by autocyclic processes, due to the seafloor modification during the growth of the deposits; otherwise it could also be related to variations of the oceanographic conditions or eventually to sea-level changes. Formation of the deposits (located in the present-day 110–240 m bathymetric range) could have been significantly deeper than present location as a consequence of the regional uplift affecting the area since Pleistocene. Under this hypothesis, an intermediate current may be inferred for the formation of the deposits. These deposits are quite rare along the Tyrrhenian margins and their formation–preservation seems to be related to the peculiar morphological setting of the area, characterized by a morpho-structural high and a slide scar. Their presence is relevant for the stratigraphy of the eastern Tyrrhenian margin as they underline the importance of bottom-current processes, with implications on paleocirculation reconstructions of the Mediterranean Basin. [Copyright &y& Elsevier]

Abstract: Multichannel seismic data collected off Western Wilkes Land (East Antarctica) reveal widespread sediment mass movement events, mainly in the form of mega debris flows deposited on the continental rise. In places, they have a seaward extent of more than 200 km and a thickness of up to 400 m. Debris flow units are commonly separated by thin deposits of well-stratified facies, interpreted as glaciomarine mixed contouritic and distal turbidite deposits, possibly with some hemipelagic sediments. These units, due to a dominant contouritic component, represent weakened layers and could then play a major role in the slope instability. Based on stratigraphic correlation with DSDP Site 268, it is suggested that slope failures in the Western Wilkes Land occurred mostly during the Miocene. Inferred high sedimentation rates, due to large amounts of sediment delivered from a temperate, wet-based ice sheet, would have constituted a key factor in the sediment failures. The distribution of mass wasting-related features appears also strongly related to the amount of meltwater discharge. The main trigger mechanism would probably have been earthquakes, enhanced by isostatic rebounds following major ice sheet retreats. [Copyright &y& Elsevier]

Abstract: In the Gulf of Cadiz, the hydrodynamic process acting on particle transport and deposition is a strong density-driven bottom current caused by the outflow of the saline deep Mediterranean water at the Strait of Gibraltar: the Mediterranean Outflow Water (MOW). New high resolution acoustic data including EM300 multibeam echo-sounder, deep-towed acoustic system SAR and very high resolution seismic, completed by piston cores collected during the CADISAR cruise allow to improve the understanding of the hydrodynamics of the MOW in the eastern part of the Gulf of Cadiz. Interpretation of data corrects the previous model established in this area and allows, for the first time, the accurate characterization of various bedforms and erosive structures along the MOW pathway and the precise identification of numerous gravity instabilities. The interaction between the MOW, the seafloor morphology and the Coriolis force is presently the driving force of the sedimentary distribution pattern observed on the Gulf of Cadiz continental slope. [Copyright &y& Elsevier]

Recently acquired Parasound and high resolution multi-channel seismic reflection data have afforded a more detailed investigation of the Mauritania Slide Complex. The slide is more complex than previously reported, and has affected an area in the order of 34,000 km2 between ∼ 600 and > 3,500 m water depths. The ovate-shaped slide displays a long run-out distance > 300 km. Slide formation was pre-conditioned mainly by uninterrupted deposition of upwelling-induced organic-rich sediment in an open slope environment which gave rise to rapid accumulation of poorly consolidated bedded sediment intercalated with thin weak layers. The stages of slide development were characterised by multiple failure events probably occurring mainly as retrogressive sliding which exploited widespread weak layers as glide planes. The study suggests excess pore pressures as being the most important trigger mechanism for slide formation. Earthquakes associated with nearby Cape Verde Islands may have played a mostly complementary or, at one time, a leading role in triggering sediment failures. Diapiric growths have locally triggered minor instability events which resulted in remobilizing of pre-existing debris flows as well as translational sliding. The combined activities of all these triggering factors are the most like cause of the complex morphology of the Mauritania Slide Complex. [ABSTRACT FROM AUTHOR]