Neogene sedimentation history as recorded in the seismostratigraphy of the Cape Basin.

eweigelt [ at ]


The Benguela Current System represents one of the largest upwelling regions world wide. Due to its high sedimentation rates it represents an excellent climate archive and offers the possibility to document modifications within the circulation system as well as the changing terrigenous component in the southern Cape Basin.As part of ODP Leg 175, three sites (Site 1085, 1086, 1087) were drilled in the southern part of the Cape Basin. Significant events as incursions of warm or cold waters (from Indian Ocean or Antarctica respectively), climate changes and slumpings are recorded in the deposited material. As pre site survey for this Leg multichannel seismic reflection data were collected in the Cape Basin during the METEOR Cruise M34/1 in 1996.The sedimentary properties are expected to be reflected in the signal structure of seismic data from this area. One major aim is the extrapolation of informations from the sites spatially by associating the results via synthetic seismograms to the seismic profiles.In this contribution we present a seismostratigraphy of the southern Cape Basin in view of three selected significant events:The first topic is the considerable increase in upwelling within the Benguela Current System (BCS) in late Miocene (about 5.7 Ma), reflected in the seismic profiles by a change in reflection pattern from weak signals of continuous layers to a chaotic transparent style. The layers show an increase in thickness towards the shelf and are disturbed by slide scarps.The second point concerns the observed landwards shift of the scarps with increasing age. The distribution in space and time probably reflects a shift of the Benguela Current upwelling system.A third item is the onset of glaciation of northern hemisphere about 3.2 Ma. In the seismic sections it corresponds to a change of reflection pattern from a more chaotic and transparent style to continuous reflectors with strong amplitudes running parallel to the seafloor. Additionally, the strongest of them corresponds to the abrupt cooling in late Pliocene (1.9-2.1 Ma) which is accompanied by an intensification of upwelling and increase in productivity. The time range accords also to the transition of lithostratigraphic unit IB to IA.

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Conference (Talk)
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Tagung der Deutschen Geophysikalischen Gesellschaft, 2002, Hannover..
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Weigelt, E. (2002): Neogene sedimentation history as recorded in the seismostratigraphy of the Cape Basin. , Tagung der Deutschen Geophysikalischen Gesellschaft, 2002, Hannover. .

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