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Enregistrements sédimentaires des changements environnementaux séculaires à millénaires par la micro- et la macrofaune benthiques littorales

Abstract : Unraveling the respective influence of human activities and natural processes on recent environmental changes is a critical issue. In this respect, fossil molluscs and foraminifers of the Pertuis Charentais area (western France) as well as the sediments deposited during the Holocene they originate from have been studied. The study is focused on a mud drape that corresponds to the upper, most recent sediment infill of the area. The results show that it is composed of fine grained sediments originating from the adjacent catchments deposited from 1400 AD onwards. This major environmental change was the consequence of an increase in soil erosion promoted by intense deforestation started during the Middle Ages. Mud sedimentation rate increased suddenly in ca. 1760 AD, owing to a short-lived increase of winter rainfall which triggered more intense soil erosion on vulnerable deforested lands. The sharp deposition of fine grained sediments in the Pertuis Charentais has had few consequences on the past benthic mollusc communities, except the local extinction of the bivalve \textit{Lepton squamosum} in the Marennes-Oléron Bay. On the contrary, the increase in mud supply has triggered an ecological succession among benthic foraminifer communities (resistance - disturbance - adaptation). As a whole, the results demonstrate that environments disrupted by human activities become more sensitive to high-frequency climate changes. They also highlight the potential of paleoecology for a better understanding of recent environmental changes occurring within coastal areas at a millennial to centennial scale.
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Clément Poirier. Enregistrements sédimentaires des changements environnementaux séculaires à millénaires par la micro- et la macrofaune benthiques littorales. Sciences de la Terre. Université de La Rochelle, 2010. Français. ⟨NNT : 2010LAROS318⟩. ⟨tel-00580982⟩

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