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Bassins de rift à des stades précoces de leur développement: l'exemple du bassin de Makgadikgadi-Okavango-Zambezi, Botswana et du bassin Sud-Tanganyika (Tanzanie et Zambie). Composition géochimique des sédiments: traçeurs des changements climatiques et tectoniques

Abstract : This thesis presents the results of a multidisciplinary study of sediments, with an emphasis on geochemistry, with the following objectives : 1) improve our understanding of geochemical processes occurring as a result of erosion, transport and deposition in two rift b asin in their early stage of development; 2) reconstruct environments in these two regions of the rift during the Late Pleistocene and Holocene and 3) define sedimentary and geochemical criteria to allow us to discriminate tectonic setting and climate change in nascent and early stage rift basins. The two basins chosen to represent early stagerift development were 1) the Makgadikgadi-Okavango-Zambesi basin located in NW Botswana and 2) the Mpulungu Basin, located at the south-western extremity of Lake Tanganyika. The geochemical study of sediments and water of the Okavango Delta revealed the presence of elevated arsenic in the groundwater occuring as a result of the dissolution of oxides under reducing conditions. The presence of elevated arsenic in the sediments in linked to organic rich clays, deposited under lacustrine conditions during periods of higher rainfall and possible impoundment of the river by the Thamalakane Fault. The geochemical results were used as a proxy fro climate change in the Mpulungu basin. The results indicate a remarkable excursion which coincides with the Younder Dryas event. This environmental event appears to be the most important event in southern lake Tanganyika during the period 23-3 ka, which is characterized by the transport of weathered material into the basin due to a change in vegetation cover in the catchment area.
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Submitted on : Tuesday, July 10, 2007 - 10:34:58 AM
Last modification on : Tuesday, February 2, 2021 - 9:52:02 AM
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  • HAL Id : tel-00161196, version 1

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Philippa Huntsman-Mapila. Bassins de rift à des stades précoces de leur développement: l'exemple du bassin de Makgadikgadi-Okavango-Zambezi, Botswana et du bassin Sud-Tanganyika (Tanzanie et Zambie). Composition géochimique des sédiments: traçeurs des changements climatiques et tectoniques. Géochimie. Université de Bretagne occidentale - Brest, 2006. Français. ⟨tel-00161196⟩

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