Some remarks on the study of subsidence of sedimentary basins Application to the Gulf of Lions margin (Western Mediterranean) |
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| Institution: | 1. Panorama Petroleum Pty Ltd, Melbourne, Australia;2. Departmnet of Exploration Geophysics, Curtin University, Perth, Australia;1. Department of Geology and Geophysics, Louisiana State University, E-235 Howe-Russell, Baton Rouge, LA 70803, USA;2. Key Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Institute, Chinese Academy of Sciences, Lanzhou 730000, China;3. Museum of Natural Science, Louisiana State University, 109 Foster Hall, Baton Rouge, LA 70803, USA;1. Université de Bordeaux-CNRS, UMR 5805 EPOC, Allée Geoffroy Saint-Hilaire, CS 50023, 33615 Pessac Cedex, France;2. College of Petroleum Engineering and Geosciences, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia;3. Dept. of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, Houston, TX 77005, USA;4. CSL – Center for Carbonate Research, RSMAS, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA;5. Aix Marseille University, CNRS, IRD, Collège de France, CEREGE, Aix-en-Provence, France;6. Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, CNRS, 1, rue Jussieu, 75238 Paris Cedex 5, France;7. Section of Earth and Environmental Sciences, University of Geneva, 1205 Geneva, Switzerland;8. IFPEN, 1-4 avenue de Bois-Préau, 92852 Rueil-Malmaison, France;1. Laboratoire des Géosciences Appliquées LGA, Université Mohamed 1er, faculté des sciences, Oujda, Morocco;2. UMR CNRS 5243 Géosciences Montpellier, Université de Montpellier, CC 060, Pl. Eugène Bataillon, 34095 Montpellier Cedex 05, France;3. National Institute of Marine Geology and Geo-ecology (GeoEcoMar), Str. Dimitrie Onciul, nr 23-25, RO-024053 Bucarest, Romania;4. Université Lyon 1, ENS de Lyon, CNRS UMR 5276 LGL-TPE, F-69622 Villeurbanne, France;5. National and Kapodistrian University of Athens, Faculty of Geology and Geoenviromment, Athens, Greece;6. Institut des Sciences de l''Évolution, Université de Montpellier, CNRS 5554, IRD, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France;7. Departamento de Estratigrafía y Paleontología, Universidad de Granada, Fuenta Nueva S/N, 18002 Granada, Spain;8. Département de Géologie, Université Abdelmalek Esaadi, 93003 Tetuán, Morocco;9. Laboratoire Biodiversité et dynamique des écosystèmes, Université Cadi Ayyad, Faculté des Sciences Semlalia, Boulevard Prince-Moulay-Abdelah, Marrakech, Morocco;1. Institute of Geology and Geoinformation, Geological Survey of Japan, AIST, Tsukuba, Ibaraki 305-8567, Japan |
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| Abstract: | The study of basin subsidence is a helpful geological tool for understanding the tectonic and thermal evolution of sedimentary basins. Subsidence is clearly one major aspect of the geodynamics of ‘rifted’ basins. It is controlled by the inner lithospheric and crustal processes of mechanical, thermal and also tectonic origin. The load of sediments which fill the initial rift depression amplify these vertical movements, according to the laws of isostatic compensation.The purpose of the backstripping method is to separate these two components of subsidence. The subsidence due to both controlling factors (geodynamics and sediments loading), called total subsidence, can be estimated by a precise reconstruction of paleotopography in the basin during past sedimentation. This geohistorical reconstruction is based on observational data, mainly the chronostratigraphy of the sedimentary cover, lithologies and paleoenvironments, all data being constrained by the global geological context in the basin studied.The tectonic subsidence, which corresponds to the driving lithospheric phenomena, is computed according to a model of the response of lithosphere to sediment loading. Two models are considered, the Airy or local isostasy model and flexure models. In flexure models, the main difficulty is to estimate the history of the flexural rigidity of the lithosphere below continental margins and rifted basins. The influence of compensation models on subsidence history will be discussed.The present paper brings out some remarks on the use of backstripping techniques. In particular, the two-dimensional approach is emphasized because it gives better constraints on the geological validity of the paleotopographic reconstruction and the distribution of subsidence in space and time. Discussion is illustrated by the study of the young passive margin of Gulf of Lions, in the northwestern part of the Mediterranean Basin. The rifting was initiated during upper Oligocene and lasted until Aquitanian time. A seismic survey in the Gulf of Lions and on-shore geological studies of the bordering areas (Sardinia, Camargue) have shown that the postrift history mainly consists of a regional subsidence of the whole margin. The hypothesis of a thermal control of the postrift subsidence, as predicted by geodynamical models (McKenzie, 1978), will be discussed. The geohistorical reconstruction deals with two main problems. (1) Determination of paleobathymetry is not accurate enough from observation data. (2) A strong erosional event, known as the Messinian Event, is superimposed to the geodynamic evolution of the margin. Thus, the complete paleotopographic reconstruction will be based on observations and also geological hypotheses, mainly the likely continuity of the geological phenomena during the postrift history of the margin, since they are controlled by the thermal evolution at depth. |
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