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SINK MEASUREMENT OF THE ZAMBEZI SYSTEM (DELTA TO DEEPSEA FAN): A RECORD OF THE EAST AFRICAN RIFT UPLIFT AND ASSOCIATED CLIMATE CHANGES

Abstract : The Zambezi deltaic system is one of the largest in Africa after the Niger, the Congo and the Nile. This passive margin-scale delta is characterized by a topographically and tectonically segmented depositional profile studied in the frame of the project PAMELAPassive Margin Exploration Laboratoriesfounded by TOTAL and IFREMER): (1) an upstream 10 km thick deltaic wedge with no gravitary tectonics, (2) the Angoche pounded deep depositional area and (3) the Zambezi deep-sea fan, bounded fromm the Angoche are by a major contouritic drift. The sink measurement was based on the seismic stratigraphic analysis of numerous regional seismic lines (from the upstream part of the margin to the abyssal plain) merge of industrial and academic data, calibrated in ages and lithologies on reevaluated wells to get the best possible ages. Volumes measured between successive time-lines, were compacted for a comparison with solid eroded volumes. Uncertainties were calculated (including ages, time-depth conversion law, porosities...) using the VolumeEstimator software. Four main periods of sediments delivery were identified: (1) 94-66 Ma (Turonian-Maastrichtian) first silicilastic imput, (2) 66-34 Ma (Paleocene-Eocene) – very low siliciclastic supply, (3) 34-5.5 Ma (Oligocene- Miocene) – second input of siliciclastic sediments and 5.5-0 Ma (Plio-Pleistocene) – sharp increase of the sediment supply. These changes correspond to major deformation and/or climate changes. The reconstruction of the climate (precipitation) evolution was based on a palynological study along wells of the Zambezi Delta and summarized as follows: 100 to 90 Masemi-arid, 90 Ma (base Coniacian)sharp increase to very humid conditions up to 40 Ma, 40-30 Ma and 15-11 Ma dryer periods, 30-20 Ma and 11-7 Ma very humid conditions again. (1) The 94-66 Ma first siliciclastic sediments supply can be related to the uplift of the South African Plateau and the erosion of the Bushveld reentrant. This can be enhanced after 90 by the sharp increase of the humidity. (2) The 66-34 Ma period of low siliciclasctic supply is both a period of tectonic stability, very humid conditions and then of intense weathering with carbonate platforms. (3) The 34 Ma second increase of siliciclastic sediments results from an African-scale upliftrelated to mantle dynamics – onset of a mechanical erosion of the Eocene weathering profiles. (4) The sharp increase of sediment supply around 5.5 Ma result from more local processes. They are no major climate changes with an amplitude higher than the other Neogene variations. This even is related to a major change of the drainage pattern of the Zambezi River at time of the initiation of the Malawi Rift.
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Submitted on : Tuesday, February 27, 2018 - 10:50:36 AM
Last modification on : Friday, April 5, 2019 - 8:17:58 PM

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  • HAL Id : insu-01718138, version 1

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Cécile Robin, Jean-Pierre Ponte, François Guillocheau, Massimo Dall’asta. SINK MEASUREMENT OF THE ZAMBEZI SYSTEM (DELTA TO DEEPSEA FAN): A RECORD OF THE EAST AFRICAN RIFT UPLIFT AND ASSOCIATED CLIMATE CHANGES. International Meeting of Sedimentology 2017, Oct 2017, Toulouse, France. pp.763. ⟨insu-01718138⟩

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