26 results on '"Praeg D"'
Search Results
2. Gravity complexes as a focus of seafloor fluid seepage : the Rio Grande Cone, SE Brazil
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Ketzer, João Marcelo, Praeg, D., Augustin, A. H., Rodrigues, L. F., Steiger, A. K., Rahmati-Abkenar, Mahboubeh, Viana, A. R., Miller, D. J., Malinverno, A., Dickens, G. R., Cupertino, J. A., Ketzer, João Marcelo, Praeg, D., Augustin, A. H., Rodrigues, L. F., Steiger, A. K., Rahmati-Abkenar, Mahboubeh, Viana, A. R., Miller, D. J., Malinverno, A., Dickens, G. R., and Cupertino, J. A.
- Abstract
Seafloor methane emissions can affect Earth’s climate and ocean chemistry. Vast quantities of methane formed by microbial decomposition of organic matter are locked within gas hydrate and free gas on continental slopes, particularly in large areas with high sediment accumulations such as deep-sea fans. The release of methane in slope environments has frequently been associated with dissociation of gas hydrates near the edge of the gas hydrate stability zone on the upper slope, with discharges in greater water depths less understood. Here we show, using data from the Rio Grande Cone (western South Atlantic), that the intrinsic, gravity-induced downslope collapse of thick slope sediment accumulations creates structures that serve as pathways for gas migration, unlocking methane and causing seafloor emissions via giant gas flares in the water column. The observed emissions in the study region (up to 310 Mg year−1) are three times greater than estimates for the entire US North Atlantic margin and reveal the importance of collapsing sediment accumulations for ocean carbon cycling. Similar outgassing systems on the Amazon and Niger fans suggest that gravity tectonics on passive margins is a common yet overlooked mechanism driving massive seafloor methane emissions in sediment-laden continental slopes. © 2023, The Author(s).
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- 2023
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3. Glacial tunnel-valleys in the southern North Sea Basin
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Praeg, D.
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551.7 - Abstract
Tunnel-valleys are morpho-stratigraphical entities within glaciated sedimentary lowlands, which record large-scale channelised drainage beneath ice sheets. The southern North Sea Basin contains large examples, locally over 400 m in relief, cut and filled during the maximum extent of the mid-Pleistocene Elsterian glaciation. These are examined over a 100 x 150 km area of the UK/Dutch sector using seismic reflection and downhole data, collected mainly in the course of hydrocarbon exploration. The reflection dataset comprises over 12,000 line-km of profiles (≤1 km grids), and a 3D-seismic volume over a 39 x 22 km area. New information on basal morphology and fill stratigraphy is used to support a model of time-transgressive formation by en- and sub-glacial drainage beneath the ice margin during its deglacial recession. Evidence for basal erosion to the south, erosional overlap to the north, and glaciofluvial fill progradation to the north are reconciled in a model of contemporaneous headward excavation and backfilling or elongate basins during ice margin recession. This resulted in an axially diachronous valley base and fill sequence, younger to the north. Clinoform surfaces (sequence I) are identified as sub-marginal backsets, not previously observed at such a scale. They are explicable as subaqueous outwash from a distributed system of subglacial streams feeding grounding line fans, within the outer 5-20 km of ice-filled basins. Overlying surfaces (sequence II) record proglacial outwash of sands, and increasingly distal accumulation of muds, in lake basins which elongated with ice recession and persisted until the interglacial marine transgression. The physical characteristics of the tunnel-valleys indicate reworking of Cenozoic sedimentary materials (most of which remain within them) by drainage beneath the outer 50 km of the former ice sheet margin during its recession. Their size and spacing in relation to substrate thickness, and their arborescent geometry, are consistent with non-catastrophic models of tunnel development as a form of stable subglacial drainage over and through deformable aquifers. Sub-marginal drainage is dominated by surface supply, which exceeds basal melting by two orders of magnitude or more during deglaciation. Tunnel-valleys are therefore argued to form in response to both substrate characteristics and englacial hydrology during deglaciation, in a marginal zone which migrates with the ice sheet as it melts and passes through its own margin.
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- 1996
4. Initial Results of Heat Flow Acquisition from a Gas Hydrate System on the Amazon Deep Sea Fan
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Poort, J., Praeg, D., Rolandone, F., Dano, A., Kaminski, N., Ketzer, M., Silva, C., Govin, A., and Scientific party, A.
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The Amazon deep sea fan is a dynamic setting in which widespread seafloor fluid vents record degassing of a gas hydrate system hosted within an upper slope thrust-fold belt linked to gravitational collapse of the depocentre. This system is to be investigated during the AMARYLLIS-AMAGAS campaign of the R/V Marion Dufresne, to take place in May-June 2023 as a collaboration between research groups in Europe and Brazil. One aim of the campaign is to study the spatial distribution and stability conditions of the shallow gas hydrate reservoir in relation to temperature changes in the past, fluid migration and venting, and to the triggering of the giant slope failures that have recurrently extended across the fan. Three heat flow transects within a 200 km2 area of the upper fan will target seismically-observed BSR (bottom simulating reflection) patches associated with fluid venting structures at the crests of thrust-fold anticlines. Temperature gradients will be measured using autonomous high-precision temperature probes attached to core barrels, while thermal conductivity will be measured onboard using a needle probe instrument on recovered sediment cores. Together with hydroacoustic and geochemical datasets to be acquired during the campaign, the results are expected to yield insights into the dynamics of the gas hydrate system in relation to subsurface fluid flow and changes in the heat flow in sediments, as well as new information on the poorly-constrained background regional heat flow regime of the Amazon deep-sea fan., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)
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- 2023
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5. Maximum extent and readvance dynamics of the Irish Sea Ice Stream and Irish Sea Glacier since the Last Glacial Maximum
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Scourse, J. D., Chiverrell, R. C., Smedley, R. K., Small, D., Burke, M. J., Saher, M., Van Landeghem, K. J. J., Duller, G. A. T., Cofaigh, C. Ó, Bateman, M. D., Benetti, S., Bradley, S., Callard, L., Evans, D. J. A., Fabel, D., Jenkins, G. T. H., McCarron, S., Medialdea, A., Moreton, S., Ou, X., Praeg, D., Roberts, D. H., Roberts, H. M., Clark, C. D., Scourse, J. D., Chiverrell, R. C., Smedley, R. K., Small, D., Burke, M. J., Saher, M., Van Landeghem, K. J. J., Duller, G. A. T., Cofaigh, C. Ó, Bateman, M. D., Benetti, S., Bradley, S., Callard, L., Evans, D. J. A., Fabel, D., Jenkins, G. T. H., McCarron, S., Medialdea, A., Moreton, S., Ou, X., Praeg, D., Roberts, D. H., Roberts, H. M., and Clark, C. D.
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The BRITICE‐CHRONO Project has generated a suite of recently published radiocarbon ages from deglacial sequences offshore in the Celtic and Irish seas and terrestrial cosmogenic nuclide and optically stimulated luminescence ages from adjacent onshore sites. All published data are integrated here with new geochronological data from Wales in a revised Bayesian analysis that enables reconstruction of ice retreat dynamics across the basin. Patterns and changes in the pace of deglaciation are conditioned more by topographic constraints and internal ice dynamics than by external controls. The data indicate a major but rapid and very short‐lived extensive thin ice advance of the Irish Sea Ice Stream (ISIS) more than 300 km south of St George's Channel to a marine calving margin at the shelf break at 25.5 ka; this may have been preceded by extensive ice accumulation plugging the constriction of St George's Channel. The release event between 25 and 26 ka is interpreted to have stimulated fast ice streaming and diverted ice to the west in the northern Irish Sea into the main axis of the marine ISIS away from terrestrial ice terminating in the English Midlands, a process initiating ice stagnation and the formation of an extensive dead ice landscape in the Midlands. © 2021 The Authors Journal of Quaternary Science Published by John Wiley & Sons, Ltd.
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- 2021
6. Quaternary ice sheet limits on the continental shelf west of Ireland
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McCarron, Stephen, Saqab, Mudasar, Craven, Kieran, Praeg, D, Thebaudeau, Benjamin, Monteys, Xavier, Department of Geography [Maynooth], National University of Ireland Maynooth (Maynooth University), University College Dublin [Dublin] (UCD), Geological Survey of Ireland (GSI), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Joyce Country and Western Lakes Geopark, European Project: 656821,H2020,H2020-MSCA-IF-2014,SEAGAS(2016), Daniel, Praeg, Multi-disciplinary Comparison of Fluid Venting from Gas Hydrate Systems on the Mediterranean and Brazilian Continental Margins over Glacial-Interglacial Timescales - SEAGAS - - H20202016-04-30 - 2019-04-29 - 656821 - VALID, National University of Ireland Maynooth (NUIM), and Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])
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[SDU.STU.GM] Sciences of the Universe [physics]/Earth Sciences/Geomorphology ,[SDU.STU.ST]Sciences of the Universe [physics]/Earth Sciences/Stratigraphy ,[SDU.STU] Sciences of the Universe [physics]/Earth Sciences ,[SDU.STU.ST] Sciences of the Universe [physics]/Earth Sciences/Stratigraphy ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,[SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology ,[SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology ,[SDU.STU.OC] Sciences of the Universe [physics]/Earth Sciences/Oceanography ,[SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography ,[SDU.STU.GL] Sciences of the Universe [physics]/Earth Sciences/Glaciology - Abstract
International audience; Recent investigations have shown that the continental shelf west of Ireland contains sedimentary landforms recording occupation by grounded, lobate ice sheet margins that extended from Ireland during at least the last glacial cycle. This paper reviews some of the offshore evidence of past glacial events available from high-resolution bathymetry, 2D/3D seismic datasets (Fig. 1), and shallow sediment cores providing information on the sedimentology, rheology and age of glacigenic stratigraphic units. The available data suggest that the continental shelf has been repeatedly occupied by tidewater ice margins characterised by ice streaming, possibly since the mid-Pleistocene transition. The offshore record provides as yet incomplete information on the extent and timing of glaciation from multiple centres of dispersal in Ireland. The dynamics of former ice sheets in Ireland, downwind of the climatically important central North Atlantic region, makes them of wider interest in the study of partially marine based ice sheet-ocean interactions in rapidly changing environments.
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- 2019
7. Submarine geomorphology of the Celtic Sea continental shelf and the southern extent of glaciation on the Atlantic margin of Europe
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Praeg, D, Mccarron, Stephen, Dove, Dayton, Accettella, Daniella, Cova, Andrea, Facchin, Lorenzo, Monteys, Xavier, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Department of Geography [Maynooth], National University of Ireland Maynooth (Maynooth University), British Geological Survey (BGS), Istituto Nazionale di Geofisica e di Oceanografia Sperimentale (OGS), Geological Survey of Ireland (GSI), European Project: 656821,H2020,H2020-MSCA-IF-2014,SEAGAS(2016), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), National University of Ireland Maynooth (NUIM), Daniel, Praeg, and Multi-disciplinary Comparison of Fluid Venting from Gas Hydrate Systems on the Mediterranean and Brazilian Continental Margins over Glacial-Interglacial Timescales - SEAGAS - - H20202016-04-30 - 2019-04-29 - 656821 - VALID
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[SDU.STU.GM] Sciences of the Universe [physics]/Earth Sciences/Geomorphology ,[SDU.STU.ST]Sciences of the Universe [physics]/Earth Sciences/Stratigraphy ,[SDU.STU] Sciences of the Universe [physics]/Earth Sciences ,[SDU.STU.ST] Sciences of the Universe [physics]/Earth Sciences/Stratigraphy ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,[SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology ,[SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology ,[SDU.STU.OC] Sciences of the Universe [physics]/Earth Sciences/Oceanography ,[SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography ,[SDU.STU.GL] Sciences of the Universe [physics]/Earth Sciences/Glaciology - Abstract
International audience; Ice sheets have occupied the Atlantic continental margin of Europe as far south as the Celtic Sea, where the maximum extent of glaciation remains in question. The Celtic Sea contains no obvious glacial landforms, but is dominated by a system of shelf-crossing seafloor megaridges, up to 60 m high and 10 km wide, that extend seaward up to 300 km in water depths of 100-200 m. The last British-Irish Ice Sheet (BIIS) was thought to have reached a limit on the mid-shelf, based on glacigenic sediments sampled on and between megaridges in the Irish-UK sectors, but recent work in this area has shown that the BIIS extended at least 150 km farther, at minimum to the UK shelf edge at 48˚20'N. Stratigraphic analysis of newly acquired core and seismic data has indicated the megaridges to be eroded sand bodies, which can be interpreted as a) glaciofluvial ridges modified by post-glacial megatides, or b) tidal banks truncated by wave energy. Here we examine megaridge morphology using a regional bathymetric grid and multibeam data across a 25x100 km area of the mid-shelf. At regional scale, the megaridges fan seaward to meet the shelf edge near-transversely along 600 km of its length, their axes rotating by 80˚ from W-E (Irish shelf) to almost N-S (French shelf). The fan-shaped network points to an apex in the north Celtic Sea, yet axial convergences are more common to seaward than landward. Individual megaridges consist of segments tens of kms long, of differing orientation, that form bathymetric highs. On the Irish-UK mid-shelf, multibeam imagery show that en echelon megaridge segments (up to 40 km long, 7 km wide, 55 m high) give way both axially and laterally to transverse 'ribs' (up to 10 km long, 10 m high). The ribs vary in form and spacing, distinct from asymmetric regularly-spaced sand waves within the multibeam data. Glacigenic sediments have been reported near seabed on and between both the megaridges and ribs, but subglacial lineations are not observed at seafloor. We hypothesise that the rectilinear network of megaridges and ribs are the eroded remnants of giant eskerine ridges flanked by glaciofluvial De Geer moraines, formed time-transgressively along an ice sheet margin during its retreat from the shelf edge. If correct, this interpretation would have broad implications for the dynamics of the last BIIS, and for the supply of meltwater and sediment across the shelf and slope to the North Atlantic at the LGM. Glaciofluvial vs tidal models for the formation of Celtic Sea bedforms invite testing through the targeted acquisition of core data, notably from areas of existing multibeam data in both the Irish-UK and French sectors.
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- 2019
8. Gas hydrates, fluid venting and slope stability on the upper Amazon deep-sea fan
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Praeg, D., Silva, C, Reis, A, Ketzer, J-M, Migeon, S, Unnithan, Vikram, Perovano, Rodrigo, Cruz, Alberto, Gorini, Christian, Universidade Federal Fluminense [Rio de Janeiro] (UFF), Pontificia Universidade Catolica do Rio Grande do Sul (PUCRS), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Universidade do Estado do Rio de Janeiro [Rio de Janeiro] (UERJ), Linnaeus University, Jacobs University [Bremen], Sorbonne Université (SU), Institut des Sciences de la Terre de Paris (iSTeP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), The European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement No. 656821 (2016-2018, 2019-2020), and a Brazilian Visiting Foreign Researcher Fellowship (PVE CAPES Édital IODP 38/2014) at Universidade Federal Fluminense (2018-2019)., Programa de Geologia e Geofísica Marinha (PGGM), EC SEAGAS (656821), European Project: 656821,H2020,H2020-MSCA-IF-2014,SEAGAS(2016), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Linnéuniversitetet, Sweden, Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Daniel, Praeg, and Multi-disciplinary Comparison of Fluid Venting from Gas Hydrate Systems on the Mediterranean and Brazilian Continental Margins over Glacial-Interglacial Timescales - SEAGAS - - H20202016-04-30 - 2019-04-29 - 656821 - VALID
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[SDE] Environmental Sciences ,[SDE]Environmental Sciences ,[SDE.ES] Environmental Sciences/Environmental and Society ,[SDE.ES]Environmental Sciences/Environmental and Society - Abstract
International audience; Gas hydrates are ice-like compounds of water and volatiles (mainly methane) that are stable in deep-sea sediments due to high pressures and low temperatures. Changes in oceanographic conditions that reduce their stability field (e.g. sea level lowering, bottom water warming) have been suggested to trigger continental slope failures. The Amazon deep-sea fan is a major Plio-Quaternary depocentre associated with large-scale slope instabilities, in which the presence of gas hydrates has been reported from a discontinuous bottom simulating reflection (BSR) on the upper slope. Reductions in gas hydrate stability during lowered sea levels have been argued to trigger megaslides from the upper fan; megaslides have also been linked to tectonism within an extension- compression system on the upper fan recording its collapse above deep detachments. Here we present the first systematic mapping of the Amazon fan BSR using a regional grid of 2D/3D seismic reflection data, and argue the results to provide evidence for stability zone changes driven from below by fluid upwelling. The BSR is seen to extend over an area of at least 6800 km2 as elongate patches up to 10s km wide and >100 km long that coincide with the crests of thrust-fold anticlines. The BSR patches lie within 300 m of seafloor, in places rising beneath seafloor features that 3D seismic imagery show to be pockmarks and mud volcanoes. The BSRs are shallower than the methane hydrate stability zone calculated using regional datasets, and inversion of depths to temperatures yields spatially variable gradients up to 10 times background values in well data from the fan. We interpret the elevated BSR patches to record the upwelling of warm, gas-rich fluids via the thrust-folds. We propose that changes in heat flux due to episodic fluid flow, notably during fault movements, will result in gas hydrate dissociation to reduce pore pressures at the base of the stability zone. This mechanism could account for recurrent large-scale failures from the upper Amazon fan during its Plio-Quaternary collapse. Our model of 'bottom-up' gas hydrate dynamics driven by fluid migration is applicable to collapsing passive margin depocentres worldwide, and is independent of 'top-down' changes in gas hydrate stability due to climate-driven changes in ocean conditions.
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- 2018
9. Neogene evolution and demise of the Amapá carbonate platform, Amazon continental margin, Brazil
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Cruz, A.m., Reis, A.t., Suc, J.p., Silva, C.g., Praeg, D., Granjeon, D., Rabineau, Marina, Popescu, S.m., Gorini, C., Cruz, A.m., Reis, A.t., Suc, J.p., Silva, C.g., Praeg, D., Granjeon, D., Rabineau, Marina, Popescu, S.m., and Gorini, C.
- Abstract
The Amazon continental shelf hosted one of the world's largest mixed carbonate-siliciclastic platforms from the late Paleocene onwards - the Amapá carbonates. The platform architecture, however, remains poorly understood and causes and timing of the cessation of carbonate deposition are still controversial. Here we present a stratigraphic analysis of the Neogene succession of the Amapá carbonates, based on a grid of 2D/3D seismic data correlated to revised micropaleontological data from exploration wells. The results provide improved constraints on the age of the transition from predominantly carbonate to siliciclastic sedimentation, which is shown to have varied through time across three different sectors of the shelf (NW, Central and SE). Four Neogene evolutionary stages of carbonate deposition could be defined and dated with reference to the new age model: (1) between ca. 24 and 8 Ma a predominantly aggrading mixed carbonate-siliciclastic shelf prevailed across the entire region carbonate production gave way to siliciclastic sedimentation across the Central and SE shelves; (2) between 8 and 5.5 Ma carbonate production continued to dominate the NW shelf, as deposition was able to keep up with base level oscillations; (3) between 5.5 and 3.7 Ma (early Pliocene), sediment supply from the paleo-Amazon River promoted the progressive burial of carbonates on the inner NW shelf, while carbonates production continued on the outer shelf (until 3.7 Ma). Longer-lasting carbonate sedimentation on the NW shelf can be explained by a lesser influx of siliciclastic sediments due to the paleo-geography of the Central shelf, characterized by a 150-km-wide embayment, which directed most terrigenous sediments sourced from the paleo-Amazon River to the continental slope and deep ocean; (4) from 3.7 Ma onwards, when the Central shelf embayment became completely filled, continuous sediment supply to the NW shelf resulted in the final transition from carbonate to siliciclastic-dominated
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- 2019
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10. Geophysical and geochemical analysis of shallow gas and an associated pockmark field in Bantry Bay, Co. Cork, Ireland
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Jordan, S.F., O'Reilly, S.S., Praeg, D., Dove, D., Facchin, L., Romeo, R., Szpak, M., Monteys, X., Murphy, B.T., Scott, G., McCarron, S.S., Kelleher, B.P., Jordan, S.F., O'Reilly, S.S., Praeg, D., Dove, D., Facchin, L., Romeo, R., Szpak, M., Monteys, X., Murphy, B.T., Scott, G., McCarron, S.S., and Kelleher, B.P.
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An integrated geophysical, geological, and geochemical investigation of seabed fluid venting was carried out in upper Bantry Bay, a large marine inlet on the southwest coast of Ireland. The results provide evidence of the seafloor venting of gas rich fluids, resulting in the formation of a pockmark field identified here for the first time. The pockmarks occur in an area where sub-bottom profiles provide evidence of chimney-like features interpreted to record upward gas migration through Quaternary sediments to the seafloor. Three vibrocores up to 6 m long were acquired in water depths of 24–34 m, two from the pockmark field and one from outside. Methane of predominantly biogenic origin was quantified in all three cores by headspace analysis of sediment sub-samples. Well-defined sulfate methane transition zones (SMTZs) were observed in two of the cores, the shallowest (1.25 m below sea floor (mbsf)) inside the pockmark field and the other (3.75 mbsf) outside. It is likely that an SMTZ occurs at the location of the third core, also within the pockmark field, although deeper than the samples obtained during this study. Gas migration towards the seafloor is suggested to involve both diffuse pore fluid migration across wide areas and focused flow through the pockmarks, together driven by methanogenesis of pre-glacial lacustrine sediments preserved in a bedrock basin, and possible gas release from the Owenberg River Fault. Analysis of phospholipid fatty acids (PLFAs) and archaeal isoprenoid hydrocarbons was used to investigate the microbial ecology of these sediments. Anaerobic oxidation of methane (AOM) may play a role in controlling release of CH4 to the water column and atmosphere in this shallow gas setting, potentially mediated by syntrophic sulfate reducing bacteria (SRB) and anaerobic methanotrophic archaea (ANME).
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- 2019
11. A stratigraphic investigation of the Celtic Sea megaridges based on seismic and core data from the Irish-UK sectors
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Lockhart, E.A., Scourse, J.D., Praeg, D., Van Landeghem, K.J.J., Mellett, C., Saher, M., Callard, L., Chiverrell, R.C., Benetti, S., Cofaigh, C., and Clark, C.D.
- Abstract
The Celtic Sea contains the world's largest continental shelf sediment ridges. These megaridges were initially interpreted as tidal features formed during post-glacial marine transgression, but glacigenic sediments have been recovered from their flanks. We examine the stratigraphy of the megaridges using new decimetric-resolution geophysical data correlated to sediment cores to test hypothetical tidal vs glacial modes of formation. The megaridges comprise three main units, 1) a superficial fining-upward drape that extends across the shelf above an unconformity. Underlying this drape is 2), the Melville Formation (MFm) which comprises the upper bulk of the megaridges, sometimes displaying dipping internal acoustic reflections and consisting of medium to coarse sand and shell fragments; characteristics consistent with either a tidal or glacifluvial origin. The MFm unconformably overlies 3), the Upper Little Sole Formation (ULSFm), previously interpreted to be of late Pliocene to early Pleistocene age, but here shown to correlate to Late Pleistocene glacigenic sediments forming a precursor topography. The superficial drape is interpreted as a product of prolonged wave energy as tidal currents diminished during the final stages of post-glacial marine transgression. We argue that the stratigraphy constrains the age of the MFm to between 24.3 and 14 ka BP, based on published dates, coeval with deglaciation and a modelled period of megatidal conditions during post-glacial marine transgression. Stratigraphically and sedimentologically, the megaridges could represent preserved glacifluvial features, but we suggest that they comprise post-glacial tidal deposits (MFm) mantling a partially-eroded glacial topography (ULSFm). The observed stratigraphy suggests that ice extended to the continental shelf-edge.
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- 2018
12. Mud extrusion and ring-fault gas seepage – upward branching fluid discharge at a deep-sea mud volcano
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Loher, M., Pape, T., Marcon, Y., Römer, M., Wintersteller, P., Praeg, D., Torres, M., Sahling, H., Bohrmann, G., Center for Marine Environmental Sciences [Bremen] (MARUM), Universität Bremen, Pontifícia Universidade Católica do Rio Grande do Sul [Porto Alegre] (PUCRS), Oregon State University (OSU), European Project: 656821,H2020,H2020-MSCA-IF-2014,SEAGAS(2016), Pontifical Catholic University of Rio Grande do Sul (PUC-RS), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])
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lcsh:R ,[SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology ,lcsh:Medicine ,lcsh:Q ,lcsh:Science ,Article - Abstract
International audience; Submarine mud volcanoes release sediments and gas-rich fluids at the seafloor via deeply-rooted plumbing systems that remain poorly understood. Here the functioning of Venere mud volcano, on the Calabrian accretionary prism in ~1,600 m water depth is investigated, based on multi-parameter hydroacoustic and visual seafloor data obtained using ship-borne methods, ROVs, and AUVs. Two seepage domains are recognized: mud breccia extrusion from a summit, and hydrocarbon venting from peripheral sites, hosting chemosynthetic ecosystems and authigenic carbonates indicative of long-term seepage. Pore fluids in freshly extruded mud breccia (up to 13 °C warmer than background sediments) contained methane concentrations exceeding saturation by 2.7 times and chloride concentrations up to five times lower than ambient seawater. Gas analyses indicate an underlying thermogenic hydrocarbon source with potential admixture of microbial methane during migration along ring faults to the peripheral sites. The gas and pore water analyses point to fluids sourced deep (>3 km) below Venere mud volcano. An upward-branching plumbing system is proposed to account for co-existing mud breccia extrusion and gas seepage via multiple surface vents that influence the distribution of seafloor ecosystems. This model of mud volcanism implies that methane-rich fluids may be released during prolonged phases of moderate activity.
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- 2018
13. Features of mass wasting along the submarine scope of the Ionian Calabrian margin
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Ceramicola, S., Civile, D., Caburlotto, A., Cova, A., Cotterle, D., Diviacco, P., Caffau, M., Praeg, D., Accettella, D., Colizza, Ester, Critelli, S., Cuppari, A., Dominici, R., Fanucci, Francesco, Morelli, Danilo, Muto, F., Romano, C., Ramella, R., Ceramicola, S., Civile, D., Caburlotto, A., Cova, A., Cotterle, D., Diviacco, P., Caffau, M., Praeg, D., Accettella, D., Colizza, Ester, Critelli, S., Cuppari, A., Dominici, R., Fanucci, Francesco, Morelli, Danilo, Muto, F., Romano, C., and Ramella, R.
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MaGIC Project ,Multibeam ,Marine Geomorphology ,Ionian Sea - Abstract
The Ionian slopes of the Calabrian continental margin have been affected by mass movements of varying style, scale and age. Here we present examples of seabed and subsurface features identified from recently acquired multibeam morpho-bathymetric data and sub-bottom profiles, being interpreted in the framework of the MAGIC project. Four different types of mass wasting phenomena are recognized: mass transport complexes (MTCs) within intra-slope basins, isolated slide scars on slopes, possible features of gravity sliding above Messinian salt and headwall scarps in canyons. An improved understanding of past and present processes of mass failure on the Calabrian margin is strategic for assessments of the geohazards they may represent.
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- 2009
14. Anomalous Cenozoic subsidence along the 'passive' continental margin from Ireland to mid-Norway
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Ceramicola, S., Stoker, M., Praeg, D., Shannon, P.M., De Santis, L., Hoult, R., Hjelstuen, B.O., Laberg, S., Mathiesen, A., Ceramicola, S., Stoker, M., Praeg, D., Shannon, P.M., De Santis, L., Hoult, R., Hjelstuen, B.O., Laberg, S., and Mathiesen, A.
- Abstract
Two-dimensional flexural backstripping and thermal modelling (assuming uniform stretching and cooling) is applied to four interpreted, depth-converted seismic profiles across the Rockall, Faroe–Shetland and Vøring basins, along 1600 km of the Atlantic continental margin of NW Europe. The results reveal a significant discrepancy between the modelled palaeo-depths for the base of the Cenozoic succession and those proven by geological evidence at control points (subaerial conditions or depositional depth ranges in wells). The discrepancy is of Rm-scale, much larger than the possible range of parameter error determined by sensitivity tests (up to 0.5 km). Assuming a Cretaceous rift episode (100 Ma), the discrepancy is at least 1.7 km in the Rockall Basin, up to 2.1 km in the Faroe–Shetland Basin and at least 1 km in the Vøring Basin (which also contains evidence of kilometre-scale uplift of the inner margin). Assuming (unproven) a second rift in the early Cenozoic (60 Ma), the discrepancy remains of kilometre-scale in the Rockall and Faroe–Shetland basins. The restorations also provide evidence of uplift, both above compressive structures and across the modelled profiles as seaward rotations of palaeo-bathymetric records. The palaeo-bathymetric discrepancy corresponds to an anomaly in subsidence that is the cumulative product of all the tectonic episodes that have affected the NW European margin, and may incorporate both permanent effects of the last episode of lithospheric extension and transient responses to the interaction of the margin with mantle convective flow. Any explanation must accommodate both the large magnitude of anomalous subsidence along the margin and evidence of its episodic character.
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- 2011
15. Structure and Driver of Cold Seep Ecosystems
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Foucher, J. P., Westbrook, G. K., Boetius, Antje, Ceramicola, S., Dupre, S., Mascle, J., Mienert, J., Pfannkuche, O., Pierre, C., Praeg, D., Foucher, J. P., Westbrook, G. K., Boetius, Antje, Ceramicola, S., Dupre, S., Mascle, J., Mienert, J., Pfannkuche, O., Pierre, C., and Praeg, D.
- Published
- 2009
16. Structure and drivers of cold seep ecosystems
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Foucher, J.-P., Westbrook, G. K., Boetius, A., Ceramicola, S., Dupré, S., Mascle, J., Mienert, J., Pfannkuche, Olaf, Pierre, C., Praeg, D., Foucher, J.-P., Westbrook, G. K., Boetius, A., Ceramicola, S., Dupré, S., Mascle, J., Mienert, J., Pfannkuche, Olaf, Pierre, C., and Praeg, D.
- Abstract
Submarine hydrocarbon seeps are geologically driven “hotspots” of increased biological activity on the seabed. As part of the HERMES project, several sites of natural hydrocarbon seepage in the European seas were investigated in detail, including mud volcanoes and pockmarks, in study areas extending from the Nordic margin, to the Gulf of Cádiz, to the Mediterranean and Black seas. High-resolution seabed maps and the main properties of key seep sites are presented here. Individual seeps show ecosystem zonation related to the strength of the methane flux and distinct biogeochemical processes in surface sediments. A feature common to many seeps is the formation of authigenic carbonate constructions. These constructions exhibit various morphologies ranging from large pavements and fragmented slabs to chimneys and mushroom-shaped mounds, and they form hard substrates colonized by fixed fauna. Gas hydrate dissociation could contribute to sustain seep chemosynthetic communities over several thousand years following large gas-release events.
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- 2009
- Full Text
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17. Mid- to Late Cenozoic canyon development on the eastern margin of the Rockall Trough, offshore Ireland
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Elliott, G.M., Shannon, P.M., Haughton, P.D.W., Praeg, D, O'Reilly, B.O., Elliott, G.M., Shannon, P.M., Haughton, P.D.W., Praeg, D, and O'Reilly, B.O.
- Abstract
The sediment-undersupplied eastern margin of the Rockall Trough, west of Ireland, is incised by numerous canyons and slope failure features. Swath multibeam bathymetry has been integrated with 2D seismic profiles to constrain the Neogene evolution of the slope and its canyons. The morphology varies along the margin, with canyon heads located at mid-slope depths in the south but extending onto the shelf in the north. West of Porcupine Bank, slope gullies connect with a distributative channel system on the trough floor, while north of Porcupine Bank the basin floor is flat and featureless. Draped fault-blocks and deep structures exerted an important influence on slope gradients, canyon extent and geometry. A ‘bottom driven’ upslope–retrogressive slope failure mechanism is inferred for canyon formation. They were initiated by failure localisation following widespread slope rotation and instability linked to differential subsidence that produced a latest Eocene–early Oligocene (C30) regional unconformity. In the NE Rockall, where the greatest density of canyons occurs, a large mass failure wedge directly overlies the C30 surface and the seabed canyons have incised the upper part of the wedge. Axial profile data indicate that canyons in the NE Rockall Trough formed in Mid-Cenozoic times but were locally reutilised as sediment conduits during Plio-Pleistocene slope progradation.
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- 2006
18. Sedimentary and oceanographic responses to early Neogene compression on the NW European margin
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Stoker, M.S., Hoult, R.J., Nielsen, T., Hjelstuen, B.O., Laberg, J.S., Shannon, P.M., Praeg, D., Mathiesen, A., van Weering, T.C.E., McDonnell, A., Stoker, M.S., Hoult, R.J., Nielsen, T., Hjelstuen, B.O., Laberg, J.S., Shannon, P.M., Praeg, D., Mathiesen, A., van Weering, T.C.E., and McDonnell, A.
- Abstract
The lower Neogene stratigraphy of the NW European Atlantic margin, from the Vøring to the Porcupine basins, is interpreted to record a discrete phase of compressional tectonism that spanned at least 8 Ma from the earliest to the early mid-Miocene. This compressional tectonism may be coeval with a local reorganisation of the NE Atlantic plate system with the transfer of the Jan Mayen micro-plate from Greenland to Europe. The compressional tectonics has resulted in a number of stratigraphic sequences of complex character bounded by regional base Neogene and intra-Miocene unconformities. These are traceable across a range of depths and record distortion of the basin margins and changes in deep-water circulation patterns. This episode of compressional tectonics has also resulted in the creation of a number of anticlinal domes along the Norwegian, Faroese and UK Atlantic margins. The stratigraphic and structural evidence are interpreted to record two stages in the development of the margin: the first being characterised by a prolonged period of regional flexure in response to the build-up of compressive stresses; the second stage is the development of anticlinal structures that led to a rapid release of stress. In the Wyville–Thomson–Faroes region, compressional deformation influenced the creation of the present-day deep-water conduit of the Faroe Bank Channel, which is interpreted to be an early Neogene syncline. Together, the Faroe Bank and Faroe–Shetland channels represent the deepest water passageway across the Greenland–Scotland Ridge. The early Neogene development of this conduit is considered to mark the onset of deep-water exchange across this oceanic gateway.
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- 2005
19. Sequence stratigraphic analysis in deep-water, underfilled NW European passive margin basins
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Shannon, P.M., Stoker, M.S., Praeg, D., van Weering, T.C.E., de Haas, H., Nielsen, T., Dahlgren, K.I.T., Hjelstuen, B.O., Shannon, P.M., Stoker, M.S., Praeg, D., van Weering, T.C.E., de Haas, H., Nielsen, T., Dahlgren, K.I.T., and Hjelstuen, B.O.
- Abstract
Sequence stratigraphic analysis is now carried out routinely on Mesozoic–Cenozoic sedimentary basins with a view to understanding their post-rift stratal geometries and predicting facies architecture. The conventional method embodies two concepts; the physical division of strata into unconformity-bounded units and their genetic interpretation on the assumption that hierarchical changes in sea-level represent the primary control on sedimentary architecture. The genetic model is reflected in a complex descriptive terminology and derives from the development of the method in shallow-water basins, where the results of analyses typically accord with geological data constraints. Applied to deep-water underfilled basins, however, the sea-level assumption yields results that are unsatisfactory and in many cases misleading, reflecting the influence of additional controls, including tectonic movements, deep-sea currents and climate (e.g. glaciation) on stratal geometries and facies architecture. This is illustrated by comparative analyses of examples from the deep-water Cenozoic basins of the NW European Atlantic passive margin, which contain a set of seismic megasequences, bounded by unconformable to conformable surfaces, correlative from shelf to slope to basinal settings. The deep-water successions contain regional, locally diachronous, submarine unconformities that were generated in response to changes in deep-water current circulation and slope processes, rather than subaerial erosion. These bound aggradational contourite drifts that include upslope accretion against basin margins. The deep-water successions interfinger at two levels with seaward-prograding shelf-slope wedges that reflect differential tectonic movements, involving coeval uplift and subsidence. The youngest wedges formed in the last 4 Ma and record seaward progradation of the margin by up to 100 km, overprinting high-amplitude variations in sea-level and coeval with changes in deep-ocean currents. Sedimen
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- 2005
20. Neogene evolution of the Atlantic continental margin of NW Europe (Lofoten Islands to SW Ireland) : anything but passive.
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Dore, A.G., Vining, B., Stoker, M.S., Praeg, D., Shannon, P.M., Hjelstuen, B.O., Laberg, J.S., Nielsen, T., van Weering, T.C.E., Sejrup, H.P., Evans, D., Dore, A.G., Vining, B., Stoker, M.S., Praeg, D., Shannon, P.M., Hjelstuen, B.O., Laberg, J.S., Nielsen, T., van Weering, T.C.E., Sejrup, H.P., and Evans, D.
- Abstract
A regional stratigraphic framework for the Neogene succession along and across the NW European margin is presented, based on a regional seismic and sample database. The stratigraphy provides constraints on the timing and nature of the mid- to late Cenozoic differential tectonic movements that have driven major changes in sediment supply, oceanographic circulation and climate (culminating in continental glaciation). The overall context for Neogene deposition on the margin was established in the mid-Cenozoic, when rapid, km-scale differential subsidence (sagging) created the present-day deep-water basins. The Neogene is subdivided into lower (Miocene–lower Pliocene) and upper (lower Pliocene–Holocene) intervals. The lower Neogene contains evidence of early to mid-Miocene compressive tectonism, including inversion anticlines and multiple unconformities that record uplift and erosion of basin margins, as well as changes in deep-water currents. These movements culminated in a major expansion of contourite drifts in the mid-Miocene, argued to reflect enhanced deep-water exchange across the Wyville-Thomson Ridge Complex, via the Faroe Conduit. The distribution and amplitude of the intra-Miocene movements are consistent with deformation and basin margin flexure in response to enhanced intra-plate compressive stresses during a local plate reorganisation (transfer of the Jan Mayen Ridge from Greenland to Europe). The upper Neogene records a seaward tilting (<1°) of the margin from the early Pliocene, in which km-scale uplift and erosion was accompanied by increased offshore subsidence, resulting in a major seaward progradation of the shelf–slope wedge as well as deep-marine erosion during a reorganisation of bottom current patterns. The large amplitude of tilting cannot be accounted for by intra-plate stress variations, but is consistent with a dynamic topographic response to upper mantle convection, in particular edge-driven flow beneath the continental margin. Sedimentary a
- Published
- 2005
21. A comparison of the NW European glaciated margin with other glaciated margins
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Nielsen, T., De Santis, L., Dahlgren, K.I.T., Kuijpers, A., Laberg, J.S., Nygard, A., Praeg, D., Stoker, M.S., Nielsen, T., De Santis, L., Dahlgren, K.I.T., Kuijpers, A., Laberg, J.S., Nygard, A., Praeg, D., and Stoker, M.S.
- Abstract
The present paper provides an overview of glacial related seabed features and sedimentary sequences found along the formerly glaciated NW European margin and compare it with those found on contemporary glaciated margins from both the Southern and Northern Hemispheres. A brief review of the seabed physiography and strata architecture of the margins under consideration is followed by comparison of the most relevant similarities and differences. Comparison of the present-day bathymetric setting of both former and contemporary glaciated margins reveals no clear link to the effect of neither ice sheet or sediment load. Three different types of glacially eroded shelf transverse troughs have been identified, while marginal troughs seem connected to similar geological settings everywhere. Beyond the shelf edge interaction between downslope and alongslope processes has occurred resulting, amongst others, in the formation of large sedimentary mounds on the rise. More frequent large-scale mass wasting occurs on the former glaciated NW European margin than the Greenland and Antarctic margins in the latest Neogene to recent times. A two-stage evolution of the shelf prograding wedges is observed on all margins under consideration, which may reflect a general development of an ice cover from an initial phase of non- to restricted glaciation, evolving to a mature stage of expansive glaciation.
- Published
- 2005
22. Episodic Cenozoic tectonism and the development of the NW European 'passive' continental margin
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Praeg, D., Stoker, M.S., Shannon, P.M., Ceramicola, S., Hjelstuen, B., Laberg, J.S., Mathiesen, A., Praeg, D., Stoker, M.S., Shannon, P.M., Ceramicola, S., Hjelstuen, B., Laberg, J.S., and Mathiesen, A.
- Abstract
The North Atlantic margins are archetypally passive, yet they have experienced post-rift vertical movements of up to kilometre scale. The Cenozoic history of such movements along the NW European margin, from Ireland to mid-Norway, is examined by integrating published analyses of uplift and subsidence with higher resolution tectono-stratigraphic indicators of relative movements (including results from the STRATAGEM project). Three episodes of epeirogenic movement are identified, in the early, mid- and late Cenozoic, distinct from at least one phase of compressive tectonism. Two forms of epeirogenic movement are recognised, referred to as tilting (coeval subsidence and uplift, rotations <1° over distances of 100s of Kilometres) and sagging (strongly differential subsidence, rotations up to 4° over distances <100 km). Each epeirogenic episode involved relatively rapid (<10 Ma) km-scale tectonic movements that drove major changes in patterns of sedimentation to find expression in regional unconformity-bounded stratigraphic units. Early Cenozoic tilting (late Paleocene to early Eocene, c. 60–50 Ma) caused the basinward progradation of shelf-slope wedges from elongate uplifts along the inner continental margin and from offshore highs. Mid-Cenozoic sagging (late Eocene to early Oligocene, c. 35–25 Ma) ended wedge progradation and caused the onset of contourite deposition in deep-water basins. Late Cenozoic tilting (early Pliocene to present, <4±0.5 Ma) again caused the basinward progradation of shelf-slope wedges, from uplifts along the inner margin (including broad dome-like features) and from offshore highs. The early, mid- and late Cenozoic epeirogenic episodes coincided with Atlantic plate reorganisations, but the observed km-scale tectonic movements are too large to be accounted for as flexural deflections due to intra-plate stress variations. Mantle–lithosphere interactions are implied, but the succession of epeirogenic episodes, of differing form, are difficult to r
- Published
- 2005
23. Pliocene-Quaternary mass wasting along the Ionian Calabrian margin, offshore southern Italy
- Author
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Candoni, Oliviero, Ceramicola, Silvia, Praeg, Daniel, Zecchin, Massimo, Brancatelli, Giuseppe, Gorini, Christian, Bohrmann, Gerhard, Cova, Andrea, Istituto Nazionale di Geofisica e di Oceanografia Sperimentale (OGS), Università degli studi di Trieste = University of Trieste, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Pontifical Catholic University of Rio Grande do Sul (PUC-RS), Institut des Sciences de la Terre de Paris (iSTeP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Center for Marine Environmental Sciences [Bremen] (MARUM), Universität Bremen, The European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement No. 656821, EC SEAGAS (656821), European Project: 656821,H2020,H2020-MSCA-IF-2014,SEAGAS(2016), Praeg, Daniel, Multi-disciplinary Comparison of Fluid Venting from Gas Hydrate Systems on the Mediterranean and Brazilian Continental Margins over Glacial-Interglacial Timescales - SEAGAS - - H20202016-04-30 - 2019-04-29 - 656821 - VALID, EGU General Assembly Conference, Candoni, O., Ceramicola, S., Praeg, D., Zecchin, M., Brancatelli, G., Gorini, C., Bohrmann, G., Cova, A., Università degli studi di Trieste, Pontifícia Universidade Católica do Rio Grande do Sul [Porto Alegre] (PUCRS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), and Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)
- Subjects
[SDE] Environmental Sciences ,mass wasting ,Plio-Quaternary ,[SDE]Environmental Sciences ,[SDE.ES] Environmental Sciences/Environmental and Society ,Crotone-Spartivneto basin ,[SDE.ES]Environmental Sciences/Environmental and Society - Abstract
International audience; The Ionian Calabrian margin, offshore southern Italy, is a tectonically active area, located above a subduction zone dominated by rollback of the African plate. A variety of mass wasting features are known to occur along the inner continental slope, based on seafloor mapping during the Italian project MaGIC (Marine Geohazards Along the Italian Coasts). New high-resolution geophysical data are available from a wider area following two surveys, in 2014 of the German RV Meteor, which acquired multibeam bathymetry (50 m DTM) and Parasound sub-bottom profiles, and in 2015 of the Italian RV OGS Explora, which acquired Chirp sub-bottom and multichannel seismic reflection profiles. Here we integrate these data with existing geophysical datasets and published exploration wells to map submarine slope failures and mass wasting deposits within the Pliocene-Quaternary succession. The results show that features of mass failures are widespread along the steep (higher than 10˚) slopes of the Ionian margin south of Calabria, and within the intra-slope basins of the margin east of Calabria. Seafloor features range from small-scale features (hundreds of meters in extent), mainly located on the canyon headwalls and sidewalls, to larger slides (up to 10 km in extent) on open slopes. Subsurface profiles across open slopes and intra-slope basins provide evidence of repeated failures, particularly in the upper Quaternary. The stratigraphic distribution of failures suggests that widespread mass wasting features occur above an unconformity tentatively dated to the Middle Pleistocene (
- Published
- 2018
24. Report and preliminary results of R/V METEOR cruise M112, Dynamic of Mud Volcanoes and Seeps in the Calabrian Accretionary Prism, Ionian Sea, Catania (Italy) - Catania (Italy), November 6 - December 15, 2014
- Author
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Bohrmann, Gerhard, Alvarez, R., Biller, T., Buchheister, S., Büttner, H., Canoni, O., Dehning, K., Ferreira, C., Geprägs, P., Heinken, S., Hüttich, D., Johansen, C., Klar, S., Klüber, S., Leymann, T., Mai, H.A., Marcon, Y., Mary, F., Meinecke, G., Menapace, W., Nowald, N., Pape, T., Praeg, D., Raeke, A., Rehage, R., Renken, J., Reuter, C., Rohleder, C., Römer, M., Sahling, H., Sans i Coll C., Schade, T., Seiter, C., Spalek, P., Spiesecke, U., Tamborrino, L., Torres, M., von Wahl, T., Wiebe, M., Wintersteller, P., and Zarrouk, M.
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550 Earth sciences and geology ,ddc:550 - Abstract
1 217 306
- Published
- 2015
25. Gas hydrate dissociation linked to contemporary ocean warming in the southern hemisphere.
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Ketzer M, Praeg D, Rodrigues LF, Augustin A, Pivel MAG, Rahmati-Abkenar M, Miller DJ, Viana AR, and Cupertino JA
- Abstract
Ocean warming related to climate change has been proposed to cause the dissociation of gas hydrate deposits and methane leakage on the seafloor. This process occurs in places where the edge of the gas hydrate stability zone in sediments meets the overlying warmer oceans in upper slope settings. Here we present new evidence based on the analysis of a large multi-disciplinary and multi-scale dataset from such a location in the western South Atlantic, which records massive gas release to the ocean. The results provide a unique opportunity to examine ocean-hydrate interactions over millennial and decadal scales, and the first evidence from the southern hemisphere for the effects of contemporary ocean warming on gas hydrate stability. Widespread hydrate dissociation results in a highly focused advective methane flux that is not fully accessible to anaerobic oxidation, challenging the assumption that it is mostly consumed by sulfate reduction before reaching the seafloor.
- Published
- 2020
- Full Text
- View/download PDF
26. Mud extrusion and ring-fault gas seepage - upward branching fluid discharge at a deep-sea mud volcano.
- Author
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Loher M, Pape T, Marcon Y, Römer M, Wintersteller P, Praeg D, Torres M, Sahling H, and Bohrmann G
- Abstract
Submarine mud volcanoes release sediments and gas-rich fluids at the seafloor via deeply-rooted plumbing systems that remain poorly understood. Here the functioning of Venere mud volcano, on the Calabrian accretionary prism in ~1,600 m water depth is investigated, based on multi-parameter hydroacoustic and visual seafloor data obtained using ship-borne methods, ROVs, and AUVs. Two seepage domains are recognized: mud breccia extrusion from a summit, and hydrocarbon venting from peripheral sites, hosting chemosynthetic ecosystems and authigenic carbonates indicative of long-term seepage. Pore fluids in freshly extruded mud breccia (up to 13 °C warmer than background sediments) contained methane concentrations exceeding saturation by 2.7 times and chloride concentrations up to five times lower than ambient seawater. Gas analyses indicate an underlying thermogenic hydrocarbon source with potential admixture of microbial methane during migration along ring faults to the peripheral sites. The gas and pore water analyses point to fluids sourced deep (>3 km) below Venere mud volcano. An upward-branching plumbing system is proposed to account for co-existing mud breccia extrusion and gas seepage via multiple surface vents that influence the distribution of seafloor ecosystems. This model of mud volcanism implies that methane-rich fluids may be released during prolonged phases of moderate activity.
- Published
- 2018
- Full Text
- View/download PDF
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