1. Holocene coastal changes along the Gironde estuary (SW France): new insights from the North Médoc peninsula beach/dune system
- Author
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Mathieu Bosq, Ane García-Artola, Serge Suanez, Gilles Arnaud-Fassetta, Florence Verdin, Frédérique Eynaud, Stéphane Costa, Frédéric Bertrand, Pascal Bertran, Clément Coutelier, Camille Culioli, Pierre Stéphan, Littoral, Environnement, Télédétection, Géomatique UMR 6554 (LETG), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Université d'Angers (UA)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Brest (UBO)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Géographie et d'Aménagement Régional de l'Université de Nantes (IGARUN), Université de Nantes (UN)-Université de Nantes (UN), Ausonius-Institut de recherche sur l'Antiquité et le Moyen âge, Université Bordeaux Montaigne-Centre National de la Recherche Scientifique (CNRS), Pôle de recherche pour l'organisation et la diffusion de l'information géographique (PRODIG (UMR_8586 / UMR_D_215 / UM_115)), Université Paris 1 Panthéon-Sorbonne (UP1)-Institut de Recherche pour le Développement (IRD)-AgroParisTech-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Pôle de recherche pour l'organisation et la diffusion de l'information géographique (PRODIG), Université Paris 1 Panthéon-Sorbonne (UP1)-Institut de Recherche pour le Développement (IRD)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris-Sorbonne (UP4)-AgroParisTech-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Universidad del Pais Vasco / Euskal Herriko Unibertsitatea [Espagne] (UPV/EHU), De la Préhistoire à l'Actuel : Culture, Environnement et Anthropologie (PACEA), Université de Bordeaux (UB)-Centre National de la Recherche Scientifique (CNRS), Littoral, Environnement, Télédétection, Géomatique (LETG - Brest), Université de Nantes (UN)-Université de Nantes (UN)-Université de Caen Normandie (UNICAEN), Institut national de recherches archéologiques préventives (Inrap), Littoral, Environnement, Télédétection, Géomatique (LETG - Caen), ANR-10-LABX-0052,LaScArBx,Using the world in ancient societies : processes and forms of appropriation of space in Long Time(2010), and ANR-10-IDEX-0003,IDEX BORDEAUX,Initiative d'excellence de l'Université de Bordeaux(2010)
- Subjects
010506 paleontology ,Marsh ,[SHS.ARCHEO]Humanities and Social Sciences/Archaeology and Prehistory ,010504 meteorology & atmospheric sciences ,Pleistocene ,01 natural sciences ,estuary ,law.invention ,dune ,Sedimentary depositional environment ,law ,TLS ,estuaire ,14. Life underwater ,Radiocarbon dating ,Sea level ,Holocene ,0105 earth and related environmental sciences ,Earth-Surface Processes ,geography ,geography.geographical_feature_category ,Aquitaine ,Geology ,sea-level rise ,15. Life on land ,aeolian sand drift ,vasière ,hausse du niveau marin ,salt marsh ,marais maritimes ,Oceanography ,Gironde ,Salt marsh ,Sedimentary rock ,mudflat ,Holocène ,ensablement éolien - Abstract
International audience; L’Amélie beach is located near the mouth of the Gironde estuary (south-western Atlantic coast of France). It has been greatly eroded by recent storms, especially in the winter of 2013-2014. Erosion of the dune front and beach has uncovered a set of estuarine and aeolian sediment deposits containing numerous archaeological remains. A campaign of topographic surveys was undertaken with DGPS and TLS equipment during the springs of 2014 and 2015 along the 2 km length of L’Amélie beach in order to reconstruct the elevation and stratigraphy of these deposits. Sedimentological analyses (grain size, micro-faunal) were performed to better constrain the depositional environment. Archaeological remains and several radiocarbon dates obtained from sediment samples collected in the field were used to propose a consistent chronological framework for this sedimentary sequence. Ten main lithofacies were distinguished from the lower part of the beach to the top of the dune. The base of the sedimentary sequence is composed of Pleistocene deposits dating from MIS 9 (unit 1a) to MIS 2 (unit 1b) (Bosq et al., 2019). The Holocene sedimentary infilling began around 5000 BC with an accumulation of coarse marine sands, which suggests the presence of a tidal inlet. On both sides of this tidal channel, archaeological remains dating from the early Neolithic period up to the Bronze Age testify to a human occupation of the coastal area. From ca. 5000 to ca. 3500 cal. a BP, a characteristic deposit of intertidal mudflats indicates the transformation of the tidal inlet into estuarine marshes protected by a coastal dune barrier. Between ca. 3500 and ca. 3000 cal. a BP, the dune barrier records a phase of erosion resulting in the exposure of the marsh to stronger hydrodynamic conditions. From ca. 2800 to 1650 cal. a BP, a second phase of estuarine sedimentation is recognized. This period is characterized by significant human occupation as indicated by the presence of numerous archaeological remains of the Iron Age and Gallo-Roman periods, associated with the exploitation of a saltwater-to-brackish environment. From 1650 to 1250 cal. a BP, the estuarine salt marsh is gradually overrun by northward migrating coastal-dune fields. After 1250 cal. a BP, the marsh is completely covered by aeolian sands. These results are consistent with previously published data and allow us to detail the local sequence of palaeogeographic changes of the north-Médoc peninsula. Using the ‘sea-level index points’ method (Hijma et al., 2015), the analysis of radiocarbon dated levels also provides new relative sea level records for this part of the French Atlantic coast. Finally, the phases of coastal dune activity/stability recognized along L’Amélie beach are synchronous with those in the wider Aquitaine coastal region, suggesting a regional driving factor. We propose that the shared sedimentary dynamics are the consequence of the onshore migration of intertidal and subtidal sand banks distributed at the mouth of the Gironde.; L’Amélie beach is located near the mouth of the Gironde estuary (south-western Atlantic coast of France). It has been greatly eroded by recent storms, especially in the winter of 2013-2014. Erosion of the dune front and beach has uncovered a set of estuarine and aeolian sediment deposits containing numerous archaeological remains. A campaign of topographic surveys was undertaken with DGPS and TLS equipment during the springs of 2014 and 2015 along the 2 km length of L’Amélie beach in order to reconstruct the elevation and stratigraphy of these deposits. Sedimentological analyses (grain size, micro-faunal) were performed to better constrain the depositional environment. Archaeological remains and several radiocarbon dates obtained from sediment samples collected in the field were used to propose a consistent chronological framework for this sedimentary sequence. Ten main lithofacies were distinguished from the lower part of the beach to the top of the dune. The base of the sedimentary sequence is composed of Pleistocene deposits dating from MIS 9 (unit 1a) to MIS 2 (unit 1b) (Bosq et al., 2019). The Holocene sedimentary infilling began around 5000 BC with an accumulation of coarse marine sands, which suggests the presence of a tidal inlet. On both sides of this tidal channel, archaeological remains dating from the early Neolithic period up to the Bronze Age testify to a human occupation of the coastal area. From ca. 5000 to ca. 3500 cal. a BP, a characteristic deposit of intertidal mudflats indicates the transformation of the tidal inlet into estuarine marshes protected by a coastal dune barrier. Between ca. 3500 and ca. 3000 cal. a BP, the dune barrier records a phase of erosion resulting in the exposure of the marsh to stronger hydrodynamic conditions. From ca. 2800 to 1650 cal. a BP, a second phase of estuarine sedimentation is recognized. This period is characterized by significant human occupation as indicated by the presence of numerous archaeological remains of the Iron Age and Gallo-Roman periods, associated with the exploitation of a saltwater-to-brackish environment. From 1650 to 1250 cal. a BP, the estuarine salt marsh is gradually overrun by northward migrating coastal-dune fields. After 1250 cal. a BP, the marsh is completely covered by aeolian sands. These results are consistent with previously published data and allow us to detail the local sequence of palaeogeographic changes of the north-Médoc peninsula. Using the ‘sea-level index points’ method (Hijma et al., 2015), the analysis of radiocarbon dated levels also provides new relative sea level records for this part of the French Atlantic coast. Finally, the phases of coastal dune activity/stability recognized along L’Amélie beach are synchronous with those in the wider Aquitaine coastal region, suggesting a regional driving factor. We propose that the shared sedimentary dynamics are the consequence of the onshore migration of intertidal and subtidal sand banks distributed at the mouth of the Gironde.
- Published
- 2019
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