The Experts below are selected from a list of 2514 Experts worldwide ranked by ideXlab platform

Dorrik A. V. Stow - One of the best experts on this subject based on the ideXlab platform.

  • Unusual Components Within a Fine-Grained Contourite Deposit: Significance for Interpretation of Provenance and the Contourite Budget
    Minerals, 2020
    Co-Authors: Shereef Bankole, Jim Buckman, Dorrik A. V. Stow
    Abstract:

    Deep-water Contourite muds are an important component of many continental margin systems and are currently the focus of much interest amongst deep-water researchers. One outstanding gap in our knowledge of these systems is to understand and quantify a Contourite budget, both at the small (facies) scale and at the larger drift scale. A second problem concerns the establishing of robust criteria for discriminating between Contourites and associated deepwater facies—turbidites and hemipelagites. This paper contributes to these topics by detailed examination of sediment composition, with a particular focus on potentially diagnostic components, within Contourites and hemipelagites from the same depositional basin. Samples were selected from Pliocene to Quaternary muddy Contourites from the Gulf of Cadiz (IODP 339) and examined by scanning electron microscopy. The presence of tunicate spicules, micro-bored shell fragments, and a particular species of coccolithophore, Braarudosphaera biglowii, all indicate derivation from shallow waters and hence lateral off-shelf supply. In contrast, micro-mudclasts and fragmented bioclasts are indicative of alongslope transport in bottom currents. A normal planktic component of the Contourite muds shows a significant vertical input from pelagic settling. Such diagnostic components can also help in the discrimination between Contourites, turbidites and hemipelagites.

  • Contourite porosity, grain size and reservoir characteristics
    Marine and Petroleum Geology, 2020
    Co-Authors: Dorrik A. V. Stow, Zeinab Smillie, Ibimina Pepple Esentia, Rachel Brackenridge, Xinong Xie, Shereef Bankole, Emmanuelle Ducassou, Estefanía Llave
    Abstract:

    Abstract Contourites are now recognised as having a significant potential as hydrocarbon reservoirs in the subsurface, and several fields have been interpreted as comprising bottom-current reworked turbidite sands. However, very little has been published on the porosity characteristics of Contourites. This study documents porosity data from IODP Expedition 339 sites in the Gulf of Cadiz. We use grain size analyses, porosity-depth plots and exponential models to yield a better understanding of grain size characteristics and facies, porosity characteristics, and the reservoir potential of Contourites in the subsurface. New grain size data for over 350 samples from the Cadiz Contourites is presented, building on earlier work. These data confirm the distinctive trends in textural properties linked to depositional processes under the action of bottom currents. The finest muddy Contourites ( Porosity-depth relationships from four Cadiz sites show a moderately high initial porosity for both sand and mud facies (50–60%) and a systematic decrease with depth to around 35–40% near 500 m burial depth. According to the exponential models of porosity with depth, Contourite porosity should exceed 10% at 2500 m burial depth. We compare the data from the Gulf of Cadiz Contourite Depositional System, with those of the Eirik Drift, Newfoundland Drift, Gardar Drift and Canterbury Slope Drifts. Similar depth trends are observed, and all show anomalies linked to interbedded sandy and muddy facies, composition (carbonate vs siliciclastic), and the presence of hiatuses in the sediment record. These data provide good insight into the likely reservoir characteristics of Contourites, for both conventional and unconventional reservoirs. They are comparable with those of existing Contourite fields, most of which are mixed turbidite-Contourite systems.

  • Contourite facies model improving Contourite characterization based on the ichnological analysis
    Sedimentary Geology, 2019
    Co-Authors: Francisco J Rodrigueztovar, Heiko Hüneke, Estefanía Llave, F J Hernandezmolina, Dorrik A. V. Stow
    Abstract:

    Abstract The calcareous Contourites from the Late Oligocene and Early Miocene in the Petra Tou Romiou type section (southern Cyprus) have been studied in detail, being regarded as outstanding examples of fossil bioclastic Contourites and representative of the standard facies model of Contourite bigradational sequence. These bigradational sequences of sand-dominated Contourites consists of whitish calcarenite beds with wavy layering in the middle portion of the sequence. Gradual alternations of whitish and greenish calcilutites appear above and below these calcarenites. The internal wavy layering is composed by compacted interlayers and non-compacted interstratified layers. In the present study, an in-depth ichnological analysis of the bigradational sequence has been conducted, focusing on ichnological features such as length, shape, diameter, and orientation of individual burrow segments, the configuration of burrow systems, as well as external features, fill material, and finally taphonomy. Trace-fossil assemblages differ, containing Planolites isp., Chondrites isp., and ?Thalassinoides isp. at the compacted interlayers, and non-compacted layers bearing only Planolites structures. The compacted interlayer structures are flattened and elliptical, containing similar fill material as the calcilutite host sediment, though lighter in color. In the non-compacted layers, Planolites are near un-deformed, being cylindrical and tubular, with circular to sub-circular cross-sections. These are located mainly at the base or occupy the entire layer, locally showing longitudinal striae (Planolites reinecki Ksiąziewicz), and filled with calcarenite material. The different trace-fossil assemblages in the compacted layers and non-compacted interlayers, varying in fill material, evidence an original primary differentiation, presumably indicative of fluctuating paleoenvironmental conditions. In consecutive non-compacted layers, the distribution of Planolites is separated by compacted interlayers. This indicates that the middle portion of the Contourite type facies, with internal wavy layering, underwent a multiphase deposition. In the non-compacted layers, the almost undeformed Planolites, marked by striae, is consistent with a higher substrate consistency, which is interpreted as being associated with sedimentary condensation or omission, immediately before the next compacted interlayers were deposited. This evidence clearly supports the contention that sedimentary processes governing Contourite deposition were intermittent rather than continuous, as traditionally proposed. These findings raise basic questions regarding the bottom current processes, and consequent bedform development in these deep-marine environments.

  • Contourite Drifts and Associated Bedforms
    Submarine Geomorphology, 2017
    Co-Authors: Ibimina Pepple Esentia, Dorrik A. V. Stow, Zeinab Smillie
    Abstract:

    Contourites, also known as alongslope deposits, are sediments that have been deposited or significantly affected by the persistent action of contour (bottom) currents. Contourite drifts are the large-scale morphological expression of Contourite deposition, up to 106 km2 in area and >1 km in thickness. They are a common feature in some parts of the ocean basins and are found covering large areas of the present-day seafloor beneath modern bottom current systems. They typically co-occur with erosional features caused by bottom currents in very large-scale Contourite depositional systems. Contourite drifts are classified into four principal types—sheeted drifts, mounded-elongate drifts, patch drifts, and channel-related drifts—, and four specific types linked to their mode or location of formation, including confined drifts, infill drifts, fault-controlled drifts, and mixed-drift systems. The principal erosional elements include: depositional hiatuses; regional erosive surfaces—erosional terraces, abrasive surfaces, channel scour and sub-circular scour; and linear erosion—Contourite channels, moats, marginal valleys and isolated furrows. Seismic criteria for the identification of drifts and erosional elements must be applied carefully at three scales of observation—whole drift, seismic element and seismic facies. Bottom-current bedforms are common over drifts and erosive features and provide important insights into the flow characteristics and depositional mechanisms. The wide range of longitudinal and transverse bedforms can be linked to flow velocity and sediment grain-size in a bedform-velocity matrix. The principal controls on Contourite systems are: the nature and style of bottom current flow; the slope gradient and other topographic features; and the sediment supply.

  • Contourite vs gravity-flow deposits of the Pleistocene Faro Drift (Gulf of Cadiz): Sedimentological and mineralogical approaches
    Marine Geology, 2016
    Co-Authors: Belén Alonso, Dorrik A. V. Stow, Francisco J. Rodríguez-tovar, Gemma Ercilla, David Casas, Javier Dorador, F.j. Hernández-molina
    Abstract:

    Abstract Pleistocene succession at Sites U1386 and U1387 (IODP 339) from palaeo-moat and drift domains of the Faro Drift has been examined to characterize the lithofacies and to identify the most useful criteria for distinguishing between Contourite and gravity-flow deposits. Three lithofacies, A, B, and C, are defined based on a combination of sedimentological and mineralogical analyses. The dominant lithofacies A corresponds to Contourite deposits; lithofacies B and C comprise turbidites and debrites respectively. Three main criteria have been utilized to distinguish between these deposits: (i) the vertical trend of the grain-size and the sedimentary structures. The Contourites show complete sequences (C1 to C5 divisions) and truncate sequences (basecut-out divisions, e.g., C3–C2–C1, and C3). The turbidites display mainly Td–Te divisions, although Tc division is also present to a lesser extent. The debrites display deformational and shearing structures; (ii) the modal frequency distribution. The Contourite sequences show similar mode grain-size values in different textures suggesting that the steady conditions of supply are maintained over time. In contrast, turbidite and debrite sequences display different modes, primarily conditioned by mixing of components from allochthonous sources and their downslope gravitational transport; (iii) the sediment composition (clay mineral, bulk mineral and sand fraction) and provenance that reflect long- and short-distance transport modes. Most of the terrigenous components of the Contourites come from the Guadalquivir drainage basin, whereas for the turbidites and debrites these are sourced from the neighbouring fluvial drainage basins (Guadiana, Tinto-Odiel). The biogenic components in the latter indicate shallow depositional environments prior to seafloor failure. The spatial and temporal distributions of the lithofacies reflect the different (palaeo) environments of the Faro Drift. Debrite and incomplete turbidite sequences characterize the palaeo-moat domain during the Early Pleistocene. Complete Contourite sequences (C1 to C5) and basecut-out sequences (C3–C4–C5, and C3) characterize the proximal palaeo-drift domain during the Early and Middle Pleistocene and the complete Contourite sequences represent the distal drift domain during the Late Pleistocene.

Michele Rebesco - One of the best experts on this subject based on the ideXlab platform.

  • 4 A Turbulent Story: Mediterranean Contourites and Cold-Water Corals
    Mediterranean Cold-Water Corals: Past Present and Future, 2019
    Co-Authors: Michele Rebesco, Marco Taviani
    Abstract:

    Dynamic bottom current regimes govern cold-water corals as well as Contourites. We provide an overview of the general aspects of both research fields, with specific attention to the Mediterranean Sea region, which has the particularity to be a climatically-sensitive mid-latitude semi-enclosed basin. In this area there are many examples of along-slope Contourite deposits (known as Contourite drifts), typically with an along-slope, elongated mounded shape adjacent to a concave moat. Likewise, a number of thriving coral sites, together with sparse occurrences, are present in the central and western Mediterranean, with large coral mounds known so far only in the Alboran Sea. In the Mediterranean Sea both Contourite drift and cold-water corals seem mainly related to the Levantine Intermediate Water, but their strict co-existence has still to be ascertained in many cases. Further research should address this aspect and the great potential of combining the two complementary kinds of climate paleo-archives provided by cold-water corals and Contourites.

  • Contourites and associated sediments controlled by deep water circulation processes state of the art and future considerations
    Marine Geology, 2014
    Co-Authors: Michele Rebesco, Javier F Hernandezmolina, David Van Rooij, Anna Wahlin
    Abstract:

    Abstract The Contourite paradigm was conceived a few decades ago, yet there remains a need to establish a sound connection between Contourite deposits, basin evolution and oceanographic processes. Significant recent advances have been enabled by various factors, including the establishment of two IGCP projects and the realisation of several IODP expeditions. Contourites were first described in the Northern and Southern Atlantic Ocean, and since then, have been discovered in every major ocean basin and even in lakes. The 120 major Contourite areas presently known are associated to myriad oceanographic processes in surface, intermediate and deep-water masses. The increasing recognition of these deposits is influencing palaeoclimatology & palaeoceanography, slope-stability/geological hazard assessment, and hydrocarbon exploration. Nevertheless, there is a pressing need for a better understanding of the sedimentological and oceanographic processes governing Contourites, which involve dense bottom currents, tides, eddies, deep-sea storms, internal waves and tsunamis. Furthermore, in light of the latest knowledge on oceanographic processes and other governing factors (e.g. sediment supply and sea-level), existing facies models must now be revised. Persistent oceanographic processes significantly affect the seafloor, resulting in large-scale depositional and erosional features. Various classifications have been proposed to subdivide a continuous spectrum of partly overlapping features. Although much progress has been made in the large-scale, geophysically based recognition of these deposits, there remains a lack of unambiguous and commonly accepted diagnostic criteria for deciphering the small-scaled Contourite facies and for distinguishing them from turbidite ones. Similarly, the study of sandy deposits generated or affected by bottom currents, which is still in its infancy, offers great research potential: these deposits might prove invaluable as future reservoir targets. Expectations for the forthcoming analysis of data from the IODP Expedition 339 are high, as this work promises to tackle much of the aforementioned lack of knowledge. In the near future, geologists, oceanographers and benthic biologists will have to work in concert to achieve synergy in Contourite research to demonstrate the importance of bottom currents in continental margin sedimentation and evolution.

  • Contourites and associated sediments controlled by deep-water circulation processes: state-of-the-art and future considerations
    2014
    Co-Authors: Michele Rebesco, Francisco Javier Hernandéz-molina, David Van Rooij, Anna Wahlin
    Abstract:

    The Contourite paradigm was conceived a few decades ago and about 120 major Contourite areas are presently known associated to myriad oceanographic processes, which involve dense bottom currents, tides, eddies, deep-sea storms, internal waves and tsunamis. The increasing recognition of these deposits is influencing palaeoclimatology & palaeoceanography, slope-stability/geological hazard assessment, and hydrocarbon exploration. Nevertheless, there is a pressing need for a better understanding of the sedimentological and oceanographic processes governing Contourites. Persistent oceanographic processes significantly affect the seafloor, resulting in a continuous spectrum of depositional and erosional features. Although much progress has been made in the large-scale, geophysically based recognition of these deposits, there remains a lack of unambiguous and commonly accepted diagnostic criteria for deciphering the small-scaled Contourite facies and for distinguishing them from turbidite ones. Similarly, the study of sandy deposits generated or affected by bottom currents offers great research potential: these deposits might prove invaluable as future reservoir targets. Expectations for the forthcoming analysis of data from the IODP Exp. 339 are high, as this work promises to tackle much of the aforementioned lack of knowledge. In the near future, geologists, oceanographers and biologists will have to work in concert to achieve synergy in Contourite research.

  • Quaternary Contourite drifts of the Western Spitsbergen margin
    Deep Sea Research Part I: Oceanographic Research Papers, 2013
    Co-Authors: Michele Rebesco, Anna Wahlin, Jan Sverre Laberg, Ursula Schauer, Agnieszka Beszczynska-möller, Renata G. Lucchi, Riko Noormets, Daniela Accettella, Yulia Zarayskaya, Paolo Diviacco
    Abstract:

    The study of Contourite drifts is an increasingly used tool for understanding the climate history of the oceans. In this paper we analyse two Contourite drifts along the continental margin west of Spitsbergen, just south of the Fram Strait where significant water mass exchanges impact the Arctic climate. We detail the internal geometry and the morphologic characteristics of the two drifts on the base of multichannel seismic reflection data, sub-bottom profiles and bathymetry. These mounded features, that we propose to name Isfjorden and Bellsund drifts, are located on the continental slope between 1200 and 1800 m depth, whereas the upper slope is characterized by reduced- or non-deposition. The more distinct Isfjorden Drift is about 25 km wide and 45 km long, and over 200 ms TWT thick. We revise the 13 years-long time series of velocity, temperature, and salinity obtained from a mooring array across the Fram Strait. Two distinct current cores are visible in the long-term average. The shallower current core has an average northward velocity of about 20 cm/s, while the deeper bottom current core at about 1450 m depth has an average northward velocity of about 9 cm/s. We consider Norwegian Sea Deep Water episodically ventilated by relatively dense and turbid shelf water from the Barents Sea responsible for the accumulation of the Contourites. The onset of the drift growth west of Spitsbergen is inferred to be about 1.3 Ma and related to the Early Pleistocene glacial expansion recorded in the area. The lack of mounded contouritic deposits on the continental slope of the Storfjorden is related to consecutive erosion by glacigenic debris flows. The Isfjorden and Bellsund drifts are inferred to contain the record of the regional palaeoceanography and glacial history and may constitute an excellent target of future scientific drilling.

  • Deep-water Circulation: Processes & Products (16–18 June 2010, Baiona): introduction and future challenges
    Geo-Marine Letters, 2011
    Co-Authors: Francisco Javier Hernandéz-molina, Dorrik A. V. Stow, Estefanía Llave, Michele Rebesco, Gemma Ercilla, Anxo Mena, David Rooij, Juan-tomás Vázquez, Antje H. L. Voelker
    Abstract:

    Deep-water circulation is a critical part of the global conveyor belt that regulates Earth’s climate. The bottom (contour)-current component of this circulation is of key significance in shaping the deep seafloor through erosion, transport, and deposition. As a result, there exists a high variety of large-scale erosional and depositional features (drifts) that together form more complex Contourite depositional systems on continental slopes and rises as well as in ocean basins, generated by different water masses flowing at different depths and at different speeds either in the same or in opposite directions. Yet, the nature of these deep-water processes and the deposited Contourites is still poorly understood in detail. Their ultimate decoding will undoubtedly yield information of fundamental importance to the earth and ocean sciences. The international congress Deep-water Circulation: Processes & Products was held from 16–18 June 2010 in Baiona, Spain, hosted by the University of Vigo. Volume 31(5/6) of Geo-Marine Letters is a special double issue containing 17 selected contributions from the congress, guest edited by F.J. Hernández-Molina, D.A.V. Stow, E. Llave, M. Rebesco, G. Ercilla, D. Van Rooij, A. Mena, J.-T. Vázquez and A.H.L. Voelker. The papers and discussions at the congress and the articles in this special issue provide a truly multidisciplinary perspective of interest to both academic and industrial participants, contributing to the advancement of knowledge on deep-water bottom circulation and related processes, as well as Contourite sedimentation. The multidisciplinary contributions (including geomorphology, tectonics, stratigraphy, sedimentology, paleoceanography, physical oceanography, and deep-water ecology) have demonstrated that advances in paleoceanographic reconstructions and our understanding of the ocean’s role in the global climate system depend largely on the feedbacks among disciplines. New insights into the link between the biota of deep-water ecosystems and bottom currents confirm the need for this field to be investigated and mapped in detail. Likewise, it is confirmed that deep-water Contourites are not only of academic interest but also potential resources of economic value. Cumulatively, both the congress and the present volume serve to demonstrate that the role of bottom currents in shaping the seafloor has to date been generally underestimated, and that our understanding of such systems is still in its infancy. Future research on Contourites, using new and more advanced techniques, should focus on a more detailed visualization of water-mass circulation and its variability, in order to decipher the physical processes involved and the associations between drifts and other common bedforms. Moreover, Contourite facies models should be better established, including their associations with other deep-water sedimentary environments both in modern and ancient submarine domains. The rapid increase in deep-water exploration and the new deep-water technologies available to the oil industry and academic institutions will undoubtedly lead to spectacular advances in Contourite research in terms of processes, morphology, sediment stacking patterns, facies, and their relationships with other deep-marine depositional systems.

Elda Miramontes - One of the best experts on this subject based on the ideXlab platform.

  • Contourite distribution and bottom currents in the NW Mediterranean Sea: Coupling seafloor geomorphology and hydrodynamic modelling
    Geomorphology, 2019
    Co-Authors: Elda Miramontes, F. Javier Hernández-molina, Pierre Garreau, Matthieu Caillaud, Gwenael Jouet, Romain Pellen, Michael A. Clare, Antonio Cattaneo
    Abstract:

    Abstract Contourites are common morphological features along continental margins where currents encounter the seafloor. They can provide long-term archives of palaeoceanography, may be prone to sediment instability, and can have a great potential for hydrocarbon exploration. Despite their importance and increasingly recognised ubiquitous occurrence worldwide, the link between oceanographic processes and Contourite features is poorly constrained. In particular, it is unclear under which specific conditions sediments are mobilised, modified and deposited by bottom currents. Here, we aim to determine key bottom current characteristics (velocity and bottom shear stress) affecting Contourite deposition, by assuming that recent oceanographic regimes may be extended back in time over the past glacial-interglacial cycles, with strong winter circulation assumed similar to glacial conditions and weak summer circulation to interglacials. We present an integrated study from the NW Mediterranean Sea that couples results of the MARS3D hydrodynamic model with high-resolution sedimentological and geophysical data (piston cores, multibeam bathymetry and high resolution seismic data). Near bottom circulation was modelled during winter and summer 2013 as representative of past periods of high and low current intensity, respectively. Model results match well with the extent of Contourite depositional systems and their different localised morphologic elements. We deduce that higher intensity events control the formation of erosional features such as moats and abraded surfaces. The heterogeneous distribution of bottom-current intensity on slopes explains the development of different types of Contourite drifts. Plastered drifts form in zones of low bottom-current velocities constrained upslope and downslope by higher current velocities. Separated elongated mounded drifts develop where fast bottom-currents decelerate at foot of the slope. In contrast, no mounded Contourite morphologies develop when the current velocity is homogeneous across the slope, especially in margins prone to downslope sediment transport processes. In confined basins, gyres may transport sediment in suspension from a margin with a high sediment supply to an adjacent starved margin, favouring the development of fine-grained Contourites in the latter. Our results provide new insights into how detailed bottom-circulation modelling and seafloor geomorphological analyses can improve the understanding of palaeoflow-regimes, at least over time spans when the overall paleogeography and the distribution of Contourite drifts is comparable to present-day conditions. The approach of coupled hydrodynamic models and geomorphological interpretations proposed here for depositional, erosional and mixed Contourite features may be used to understand other areas affected by bottom currents, and for a better conceptual understanding of bottom-current processes and their interactions with the seafloor.

  • Reservoir Potential in Contourites: Evidence of Coarse-grained Contourite Facies in the Mozambique Margin
    80th EAGE Conference and Exhibition 2018, 2018
    Co-Authors: Nathalie Babonneau, A. Genet, M. Rabineau, Laurence Droz, Cécile Robin, François Raisson, Elda Miramontes, D. Belleney, S. Révillon, M. Moulin
    Abstract:

    Summary Although Contourites and mixed turbidite/Contourite depositional systems are significant to the oil industry, they are still relatively poorly known by this sector, and there is no present-day accepted sedimentological model for sandy Contourites. Our goal here is to better understand the possibility of occurrence of contouritic sands susceptible to form potential reservoirs for hydrocarbons, and therefore possible new plays. After the Gulf of Cadiz ( Hernandez-Molina et al., 2013 ) and the Brazilian margin ( Mutti et al., 2014 ), the discovery of coarse granulometry Contourite facies in Plio-pleistocene deposits offshore Mozambique is a great step toward the proof of concept of reservoir potential for these objects. The results presented derive from the Pamela (PAssive Margin Exploration Laboratories) project, led by Ifremer and TOTAL in collaboration with Universites de Bretagne Occidentale, Rennes-1, P&M Curie, CNRS and IFPEN. First class outcome, the PAMELA-MOZ-3 cruise has revealed occurrence of coarse-grained Contourite facies deposited in a condensed layer wedging on a Contourite terrace. Sandy Contourite facies (siliciclastic or carbonate) is now proved to occur where favorable conditions gather. Consolidated with state-of-the art techniques of subsurface data interpretation, the new model integrating geometrical and amplitude characters should give keys to help interpreters predict the reservoir potential of Contourites.

  • Morphological control of slope instability in Contourites: a geotechnical approach
    Landslides, 2018
    Co-Authors: Elda Miramontes, S. Garziglia, N. Sultan, G. Jouet, A. Cattaneo
    Abstract:

    Contourite drifts are sediment bodies formed by the action of bottom currents. They are common features found on continental slopes and are often affected by slope failure. However, processes controlling slope instability in Contourite depositional systems are still not well constrained, and it is not clear whether Contourites have particular properties that make them more susceptible to slope failure. In this study, we compare sedimentological and geotechnical properties of contouritic and hemipelagic sediments within the Corsica Trough (northern Tyrrhenian Sea) using geophysical data sets and sediment cores in order to get a better understanding of the controlling factors of slope stability. Geomorphological and slope stability analyses reveal that differences in sediment properties have little influence on the location of submarine landslides, in comparison with the morphology of the drifts. Hence, the steep downslope flanks of plastered drift deposits are the most susceptible zones for local failure initiation. Moreover, as erosion is common at the foot of plastered drifts, undercutting is thought to contribute to the development of large-scale failure up to the point that submarine landslides are triggered.

  • Submarine landslides in the Northern Tyrrhenian Sea and relationship with the turbiditic and contouritic deposits: morphology, stratigraphy, geotechnics and modelling
    2016
    Co-Authors: Elda Miramontes
    Abstract:

    The Corsica Trough is an asymmetric confined basin located between the Corsica Island and the Tuscan Archipelago, with the western flank dominated by turbiditic and hemipelagic processes and the eastern flank by mass transport and contouritic processes. The present PhD project aims to develop our understanding of the mechanisms that control the formation of submarine landslides within muddy Contourites (sediment deposits related to bottom currents) during the Plio-Quaternary. The broad data set available for this PhD project includes: multibeam bathymetry, seismic reflection data, sediment cores, in situ geotechnical measurements, current ADCP measurements and results of a hydrodynamic model. The Contourites of the Corsica Trough are mainly composed of mud with sandy layers formed by enhanced bottom currents during periods of sea level fall. The Contourite drifts grow slowly during sea level high-stands and rapidly during sea level low-stands due to the high sediment availability provided by an active turbidite system. Bottom currents control the seafloor morphology and generate plastered drifts on the slope. This is a convex-shaped Contourite with steep slope gradients in the lower part limited by a moat (incision created by bottom currents). The Pianosa Slump was initiated in this lower part of the plastered drift. The occurrence of continuous erosive processes during cold periods could undercut the slope and trigger submarine landslides. Another predisposing factor for slope instability identified is the presence of a potential weak layer with a post-peak strain softening behaviour (strength loss with increasing strain). This particular property is caused by the presence of zeolites (product of the alteration of volcanic rocks). This layer originated the basal failure surface of the Pianosa Slump. In summary, the two main factors predispose the formation of submarine landslides in the Pianosa Ridge are: the morphology of the plastered drift with steep slopes in the lower part and a potential weak layer composed of zeolitic muddy sediment. The main triggering factor seems to be undercutting by bottom currents.

  • the pianosa Contourite depositional system northern tyrrhenian sea drift morphology and plio quaternary stratigraphic evolution
    Marine Geology, 2016
    Co-Authors: Elda Miramontes, Gwenael Jouet, Antonio Cattaneo, Estelle Thereau, Yannick Thomas, Marzia Rovere, E Cauquil, Fabio Trincardi
    Abstract:

    Abstract The Pianosa Contourite Depositional System (CDS) is located in the Corsica Trough (Northern Tyrrhenian Sea), a confined basin dominated by mass transport and contour currents in the eastern flank and by turbidity currents in the western flank. The morphologic and stratigraphic characterisation of the Pianosa CDS is based on multibeam bathymetry, seismic reflection data (multi-channel high resolution mini GI gun, single-channel sparker and CHIRP), sediment cores and ADCP data. The Pianosa CDS is located at shallow to intermediate water depths (170 to 850 m water depth) and is formed under the influence of the Levantine Intermediate Water (LIW). It is 120 km long, has a maximum width of 10 km and is composed of different types of muddy sediment drifts: plastered drift, separated mounded drift, sigmoid drift and multicrested drift. The reduced tectonic activity in the Corsica Trough since the early Pliocene permits to recover a sedimentary record of the Contourite depositional system that is only influenced by climate fluctuations. Contourites started to develop in the Middle–Late Pliocene, but their growth was enhanced since the Middle Pleistocene Transition (0.7–0.9 Ma). Although the general circulation of the LIW, flowing northwards in the Corsica Trough, remained active all along the history of the system, Contourite drift formation changed, controlled by sediment influx and bottom current velocity. During periods of sea level fall, fast bottom currents often eroded the drift crest in the middle and upper slope. At that time the proximity of the coast to the shelf edge favoured the formation of bioclastic sand deposits winnowed by bottom currents. Higher sediment accumulation of mud in the drifts occurred during periods of fast bottom currents and high sediment availability (i.e. high activity of turbidity currents), coincident with periods of sea level low-stands. Condensed sections were formed during sea level high-stands, when bottom currents were more sluggish and the turbidite system was disconnected, resulting in a lower sediment influx.

Raul Merinero - One of the best experts on this subject based on the ideXlab platform.

  • ferromanganese nodules and micro hardgrounds associated with the cadiz Contourite channel ne atlantic palaeoenvironmental records of fluid venting and bottom currents
    Chemical Geology, 2012
    Co-Authors: Francisco Javier Gonzalez, Rosario Lunar, Trinidad Torres, Jose E Ortiz, Jesus Martinezfrias, Teresa Medialdea, Ricardo León, Luis Somoza, Raul Merinero
    Abstract:

    Abstract Ferromanganese nodule fields and hardgrounds have recently been discovered in the Cadiz Contourite Channel in the Gulf of Cadiz (850–1000 m). This channel is part of a large Contourite depositional system generated by the Mediterranean Outflow Water. Ferromanganese deposits linked to Contourites are interesting tools for palaeoenviromental studies and show an increasing economic interest as potential mineral resources for base and strategic metals. We present a complete characterisation of these deposits based on submarine photographs and geophysical, petrographic, mineralogical and geochemical data. The genesis and growth of ferromanganese deposits, strongly enriched in Fe vs. Mn (av. 39% vs. 6%) in this Contourite depositional system result from the combination of hydrogenetic and diagenetic processes. The interaction of the Mediterranean Outflow Water with the continental margin has led to the formation of Late Pleistocene–Holocene ferromanganese mineral deposits, in parallel to the evolution of the Contourite depositional system triggered by climatic and tectonic events. The diagenetic growth was fuelled by the anaerobic oxidation of thermogenic hydrocarbons (δ 13 C PDB  = − 20 to − 37‰) and organic matter within the channel floor sediments, promoting the formation of Fe–Mn carbonate nodules. High 87 Sr/ 86 Sr isotopic values (up to 0.70993 ± 0.00025) observed in the inner parts of nodules are related to the influence of radiogenic fluids fuelled by deep-seated fluid venting across the fault systems in the diapirs below the Cadiz Contourite Channel. Erosive action of the Mediterranean Outflow Water undercurrent could have exhumed the Fe–Mn carbonate nodules, especially in the glacial periods, when the lower core of the undercurrent was more active in the study area. The growth rate determined by 230 Th excess / 232 Th was 113 ± 11 mm/Ma, supporting the hypothesis that the growth of the nodules records palaeoenvironmental changes during the last 70 ka. Ca-rich layers in the nodules could point to the interaction between the Mediterranean Outflow Water and the North Atlantic Deep Water during the Heinrich events. Siderite–rhodochrosite nodules exposed to the oxidising sea-bottom waters were replaced by Fe–Mn oxyhydroxides. Slow hydrogenetic growth of goethite from the seawaters is observed in the outermost parts of the exhumed nodules and hardgrounds, which show imprints of the Mediterranean Outflow Water with low 87 Sr/ 86 Sr isotopic values (down to 0.70693 ± 0.00081). We propose a new genetic and evolutionary model for ferromanganese oxide nodules derived from ferromanganese carbonate nodules formed on continental margins above the carbonate compensation depth and dominated by hydrocarbon seepage structures and strong erosive action of bottom currents. We also compare and discuss the generation of ferromanganese deposits in the Cadiz Contourite Channel with that in other locations and suggest that our model can be applied to ferromanganiferous deposits in other contouritic systems affected by fluid venting.

  • ferromanganese nodules and micro hardgrounds associated with the cadiz Contourite channel ne atlantic palaeoenvironmental records of fluid venting and bottom currents
    Chemical Geology, 2012
    Co-Authors: Francisco Javier Gonzalez, Rosario Lunar, Trinidad Torres, Jose E Ortiz, Jesus Martinezfrias, Teresa Medialdea, Ricardo León, Luis Somoza, Raul Merinero
    Abstract:

    Abstract Ferromanganese nodule fields and hardgrounds have recently been discovered in the Cadiz Contourite Channel in the Gulf of Cadiz (850–1000 m). This channel is part of a large Contourite depositional system generated by the Mediterranean Outflow Water. Ferromanganese deposits linked to Contourites are interesting tools for palaeoenviromental studies and show an increasing economic interest as potential mineral resources for base and strategic metals. We present a complete characterisation of these deposits based on submarine photographs and geophysical, petrographic, mineralogical and geochemical data. The genesis and growth of ferromanganese deposits, strongly enriched in Fe vs. Mn (av. 39% vs. 6%) in this Contourite depositional system result from the combination of hydrogenetic and diagenetic processes. The interaction of the Mediterranean Outflow Water with the continental margin has led to the formation of Late Pleistocene–Holocene ferromanganese mineral deposits, in parallel to the evolution of the Contourite depositional system triggered by climatic and tectonic events. The diagenetic growth was fuelled by the anaerobic oxidation of thermogenic hydrocarbons (δ 13 C PDB  = − 20 to − 37‰) and organic matter within the channel floor sediments, promoting the formation of Fe–Mn carbonate nodules. High 87 Sr/ 86 Sr isotopic values (up to 0.70993 ± 0.00025) observed in the inner parts of nodules are related to the influence of radiogenic fluids fuelled by deep-seated fluid venting across the fault systems in the diapirs below the Cadiz Contourite Channel. Erosive action of the Mediterranean Outflow Water undercurrent could have exhumed the Fe–Mn carbonate nodules, especially in the glacial periods, when the lower core of the undercurrent was more active in the study area. The growth rate determined by 230 Th excess / 232 Th was 113 ± 11 mm/Ma, supporting the hypothesis that the growth of the nodules records palaeoenvironmental changes during the last 70 ka. Ca-rich layers in the nodules could point to the interaction between the Mediterranean Outflow Water and the North Atlantic Deep Water during the Heinrich events. Siderite–rhodochrosite nodules exposed to the oxidising sea-bottom waters were replaced by Fe–Mn oxyhydroxides. Slow hydrogenetic growth of goethite from the seawaters is observed in the outermost parts of the exhumed nodules and hardgrounds, which show imprints of the Mediterranean Outflow Water with low 87 Sr/ 86 Sr isotopic values (down to 0.70693 ± 0.00081). We propose a new genetic and evolutionary model for ferromanganese oxide nodules derived from ferromanganese carbonate nodules formed on continental margins above the carbonate compensation depth and dominated by hydrocarbon seepage structures and strong erosive action of bottom currents. We also compare and discuss the generation of ferromanganese deposits in the Cadiz Contourite Channel with that in other locations and suggest that our model can be applied to ferromanganiferous deposits in other contouritic systems affected by fluid venting.

John A Howe - One of the best experts on this subject based on the ideXlab platform.

  • bottom currents Contourites and deep sea sediment drifts current state of the art
    Geological Society London Memoirs, 2002
    Co-Authors: Dorrik A. V. Stow, J C Faugeres, John A Howe, Carol J Pudsey, Adriano R Viana
    Abstract:

    Abstract This paper provides both an introduction to and summary for the Atlas of Contourite Systems that has been compiled as part of the International Geological Correlation Project - IGCP 432. Following the seminal works of George Wust on the physical oceanography of bottom currents, and Charley Hollister on Contourite sediments, a series of significant advances have been made over the past few decades. While accepting that ideas and terms must remain flexible as our knowledge base continues to increase, we present a consensus view on terminology and definitions of bottom currents, Contourites and drifts. Both thermohaline and wind-driven circulation, influenced by Coriolis Force and molded by topography, contribute to the oceanic system of bottom currents. These semi-permanent currents show significant variability in time and space, marked by periodic benthic storm events in areas of high surface kinetic energy. Six different drift types are recognized in the ocean basins and margins at depths greater than about 300 m: (i) Contourite sheet drifts; (ii) elongate mounded drifts; (iii) channel related drifts; (iv) confined drifts; (v) infill drifts; and (vi) modified drift-turbidite systems. In addition to this overall geometry, their chief seismic characteristics include: a uniform reflector pattern that reflects long-term stability, drift-wide erosional discontinuities caused by periodic changes in bottom current regime, and stacked broadly lenticular seismic depositional units showing oblique to downcurrent migration. At a smaller scale, a variety of seismic facies can be recognized that are here related to bottom current intensity. A model for seismic facies cyclicity (alternating transparent/reflector zones) is further elaborated, and linked to bottom current/climate change. Both erosional features and depositional bedforms are diagnostic of bottom current systems and velocities. Many different Contourite facies are now known to exist, encompassing all compositional types. We propose here a Cl-5 notation for the standard Contourite facies sequence, which can be interpreted in terms of fluctuation in bottom current velocity and/or sediment supply. Several proxies can be utilized to decode Contourite successions in terms of current fluctuation. Gravel lag and shale chip Contourites, as well as erosional discontinuities are indicative of still greater velocities. There are a small but growing number of land-based examples of fossil Contourites, based on careful analysis using the recommended three-stage approach to interpretation. Debate still surrounds the recognition and interpretation of bottom current reworked turbidites.

  • deep water Contourite systems modern drifts and ancient series seismic and sedimentary characteristics
    Geological Society Memoir, 2002
    Co-Authors: Dorrik A. V. Stow, J C Faugeres, John A Howe, Carol Pudsey, Adriano R Viana
    Abstract:

    Countourites are a widespread but poorly known group of sediments linked to the action of powerful bottom currents in deep water. Although we know they are especially common along continental margins and through oceanic gateways, they have been surrounded by contoversy since they were first recognized in the early 1960s. Where correctly recognized and decoded they can provide one of the keys to our better understanding of bottom water circulation and of the ocean–climate link. They are part of the spectrum of deposits that confronts the oil industry as exploration moves into progressively greater water depths. This memoir is an important outcome of the International Geological Correlation Project 432 on Bottom Currents, Contourites and Palaeocirculation . It includes 30 papers involving over 75 key scientists from around the world. Following an introductory state–of–the–art paper by the editors, there are 25 separate case studies on modern drifts and four on ancient Contourite series. Each contribution highlights the specific geological and oceanographic setting, bathymetry, physiographic and stratigraphic context, seismic attributes and sedimentary characteristics of that drift. Case studies range from some of the well-documented North Atlantic drifts to those much less known from the Mediterrenean, from important syntheses of the Gulf of Cadiz and Vema Channel Gateway, to completely new data on South Atlantic, Pacific and Antartic margin systems. The four papers on ancient series from Japan, China and Cyprus serve to emphasise the complex nature and subtle characteristics of Contourites, which make their identification a scientific challenge. This volume is dedicated to the memory of Charlie Hollister (1936–1999), one of the founding fathers and pioneers of countourite research.

  • Contourite sedimentation in the Falkland Trough, western South Atlantic
    Geological Society London Memoirs, 2002
    Co-Authors: Alex P. Cunningham, John A Howe, Peter F. Barker
    Abstract:

    Abstract The Falkland Trough is a west-east bathymetric deep that separates the Falkland Plateau from the North Scotia Ridge in the western South Atlantic. It lies in the path of Circumpolar Deep Water flowing within the Antarctic Circumpolar Current (ACC), and Weddell Sea Deep Water flowing beneath the ACC east of Shag Rocks passage. Marine geophysical and sediment core data demonstrate the influence of ambient bottom currents on deposition in this area, and reveal two styles of Contourite sedimentation: (1) deposition of glauconite-rich sandy Contourites in exposed areas of the Falkland Plateau and Falkland Trough, where vigorous ACC bottom currents control sedimentation, and (2) deposition of biogenic sandy Contourites, muddy Contourites and hemipelagites (western Falkland Trough), and muddy diatom ooze (eastern Falkland Trough), in the form of two elongate sediment drifts, which have developed in the presence of more sluggish bottom currents. The drift sediments contain a depositional record of bottom current flow through the glacial cycle (southern-origin bottom water flow in the east, and probably ACC flow in the west); analyses of core data from the western Falkland Trough suggest a reduction in bottom current strength during the Last Glacial Maximum at present depths of > 2500 m below sea level.

  • Sediment drifts and Contourites on the continental margin off northwest Britain
    Sedimentary Geology, 1998
    Co-Authors: Martyn S. Stoker, John A Howe, Maxine Akhurst, Dorrik A. V. Stow
    Abstract:

    Abstract Seismic reflection profiles and short cores from the continental margin off northwest Britain have revealed a variety of sediment-drift styles and Contourite deposits preserved in the northeast Rockall Trough and Faeroe-Shetland Channel. The sediment drifts include: (1) distinctly mounded elongate drifts, both single- and multi-crested; (2) broad sheeted drift forms, varying from gently domed to flat-lying; and (3) isolated patch drifts, including moat-related drifts. Fields of sediment waves are locally developed in association with the elongate and gently domed, broad sheeted drifts. The contrasting styles of the sediment drifts most probably reflect the interaction between a variable bottom-current regime and the complex bathymetry of the continental margin. The bulk of the mounded/gently domed drifts occur in the northeast Rockall Trough, whereas the flat-lying, sheet-form deposits occur in the Faeroe-Shetland Channel, a much narrower basin which appears to have been an area more of sediment export than drift accumulation. Patch drifts are present in both basins. In the northeast Rockall Trough, the along-strike variation from single- to multi-crested elongate drifts may be a response to bottom-current changes influenced by developing drift topography. Muddy, silty muddy and sandy Contourites have been recovered in sediment cores from the uppermost parts of the drift sequences. On the basis of their glaciomarine origin, these mid- to high-latitude Contourites can be referred to, collectively, as glacigenic Contourites. Both partial and complete Contourite sequences are preserved; the former consist largely of sandy (mid-only) and top-only Contourites. Sandy Contourites, by their coarse-grained nature and their formation under strongest bottom-current flows, are the most likely to be preserved in the rock record. However, the very large scale of sediment drifts should be borne in mind with regard to the recognition of fossil Contourites in ancient successions.

  • PLIOCENE-HOLOCENE Contourite DEPOSITION UNDER THE ANTARCTIC CIRCUMPOLAR CURRENT, WESTERN FALKLAND TROUGH, SOUTH ATLANTIC OCEAN
    Marine Geology, 1997
    Co-Authors: John A Howe, Carol J Pudsey, Alex P. Cunningham
    Abstract:

    The eastward-flowing Antarctic Circumpolar Current (ACC) has influenced sedimentation on the slope and floor of the western Falkland Trough, where the axis of the current is topographically constrained. Deep-water flow (below 3000 m) has produced a symmetrical sediment drift on the trough floor, with non-depositional margins indicating higher current velocities at the base of slope. To the southeast of the Falkland Islands there is a gap in the North Scotia Ridge, north of which the floor of the trough is swept clean of sediment by the ACC. Both echo character mapping and GLORIA side-scan data indicate that currents follow the bathymetric contours along the slope, redistributing sediment and locally eroding furrows. From six cores on the drift and on the northern slope, two styles of Contourite deposition have been identified. On the drift, Holocene biogenic sandy Contourites overlie Last Glacial Maximum muddy Contourites and fine-grained diatomaceous hemipelagites. Sedimentation rates here average 3–4 cm ka−1. The sandy Contourites present in four of the cores from the sediment drift are sharply underlain by the finer-grained, diatomaceous hemipelagites. The lack of a coarsening upward sequence, commonly associated with an increase in current velocity may be indicative of high current activity eroding away the finer (negative) sequence. Pliocene and Mid-Pleistocene glaucony-rich sandy Contourites containing radiolaria characterise the Falkland Plateau and the floor of the trough near the gap in the North Scotia Ridge. We suggest that the glaucony is derived from a combination of authigenic formation and erosion of locally outcropping Cretaceous and Tertiary strata; this is supported by dinoflagellate analysis. Sedimentation rates in these current-swept areas average < 1 cm ka−1.