Stratigraphic evolution of Eocene clinoforms from northern Santos Basin,offshore Brazil: Evaluating controlling factors on shelf-margin growth and deep-water sedimentation |
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| Affiliation: | 1. CNRS, Université de Bretagne Occidentale, Univ. Bretagne Sud, UMR6538 Laboratoire Géosciences Océan, IUEM, 1 place Nicolas Copernic, 29280 Plouzané, France;2. IFREMER, Laboratoire Géodynamique et enregistrements Sédimentaires, BP70, 29280 Plouzané, France;3. Sorbonne Universités, UPMC University Paris 06, CNRS, Institut des Sciences de la Terre de Paris (iSTeP), UMR 7193, 4 place Jussieu, 75005 Paris, France;4. Schlumberger Italiana SPA, Via dell’Unione Europea, 4 – Torre Beta, 20097 San Donato Milanese, Italy;5. GeoBioStratData.Consulting, 385 route du Mas Rillier, 69140 Rillieux la Pape, France;6. TOTAL, TG/ISS, CSTTF, Avenue Laribeau, 64018 Pau Cedex, France;1. Programa de Pós-Graduação em Geologia, Universidade Federal do Paraná, Caixa Postal 19001, CEP 81531-980 Curitiba, Brazil;2. Departamento de Geologia, Universidade Federal do Paraná, Caixa Postal 19001, CEP 81531-980 Curitiba, Brazil;1. Department of Marine Geology, Faculty of Marine Science, King Abdulaziz University, 80200, Jeddah 21589, Saudi Arabia;2. Geology Department, Faculty of Sciences, Tanta University, Tanta 31527, Egypt;3. GeoZentrum Nordbayern, Fachgruppe Paläoumwelt, Friedrich-Alexander-Universität Erlangen-Nürnberg, Loewenichstraße 28, 91054 Erlangen, Germany |
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| Abstract: | In order to assess the controlling factors on the evolution of a shelf margin and the timing of sediment transfer to deep waters, a seismic stratigraphic investigation was carried out in the Eocene interval of northern Santos Basin, offshore Brazil. The studied succession configures a complex of prograding slope clinoforms formed in a passive margin and encompasses five seismic facies and their respective depositional settings: shelf-margin deltas/shorefaces, oblique slope clinoforms, sigmoidal slope clinoforms, continental to shelfal deposits and mass-transport deposits. These are stratigraphically arranged as seven depositional sequences recording a total shelf-edge progradation of about 35 km and a progradation rate of 1,75 km/My. Two main types of sequences can be recognized, the first one (type A) being dominated by oblique slope clinoforms and shelf-margin deltas/shorefaces in which shelf-edge trajectories were essentially flat to descending and extensive sandy turbidites were deposited on the foreset to bottomset zones. Sequences of this type are dominated by forced-regressive units deposited during extensive periods of relative sea-level fall. Type B comprises an upper part represented by aggradational shelfal deposits and a lower part composed of mass-transport deposits and high-relief sigmoidal clinoforms with descending shelf-edge trajectory. Steep slump scars deeply cut the shelfal strata and constitutes the boundary between the two intervals observed in type B sequences. Sandy turbidites occur at the same frequency in both forced- and normal-regressive units but are more voluminous within forced-regressive clinoforms associated with shelf-margin deltas/shorefaces. Major slope failures and mass-transport deposits, by the other hand, occurred exclusively in type B sequences during the onset of sea-level fall and their volume are directly related to the thickness of the shelfal sediments formed during the pre-failure normal regressions. |
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| Keywords: | Sequence stratigraphy Shelf-edge trajectory Turbidites Mass-transport deposits Forced regressions |
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