Contourites on the Agulhas Plateau, SW Indian Ocean: indications for the evolution of currents since Palaeogene times
Published:January 01, 2002
Gabriele Uenzelmann-Neben, 2002. "Contourites on the Agulhas Plateau, SW Indian Ocean: indications for the evolution of currents since Palaeogene times", Deep-Water Contourite Systems: Modern Drifts and Ancient Series, Seismic and Sedimentary Characteristics, D. A. V. Stow, C. J. Pudsey, J. A. Howe, J.-C. Faugères, A. R. Viana
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The area south of South Africa is one of the most important gateway regions for the interchange of watermasses from the Atlantic, Indian and Southern oceans. This results in a very complex flow pattern which up to now has been known only in general terms. For this study, a set of seismic reflection lines from the southern Agulhas Plateau has been analysed. These show strong indications for the effect of bottom currents on sedimentation in the form of sediment drifts, channels, erosional unconformities and sediment waves. These observations have been used to infer the development of palaeocircu-lation over the southern Agulhas Plateau since Paleogene times. Three different currents have been identified. The oldest observed flows across the Agulhas Plateau from the southwestern tip to the northeast, and probably dates from the early Eocene times. It is believed to comprise an Antarctic Bottomwater component derived from its source in the south. The eastern Agulhas Plateau is characterized by a south-flowing current, which has been active since the Lower Oligocene and appears to have remained stationary to within a distance of 10 km. The Agulhas Retroflection is considered as its most likely source. The third current observed flows along the western flank of the plateau, dates from the Middle Miocene and probably results from an Antarctic Bottomwater component re-circulated via the Cape Basin.
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Deep-Water Contourite Systems: Modern Drifts and Ancient Series, Seismic and Sedimentary Characteristics
Countourites are a widespread but poorly known group of sediments linked to the action of powerful bottom currents in deep water. Although we know they are especially common along continental margins and through oceanic gateways, they have been surrounded by contoversy since they were first recognized in the early 1960s. Where correctly recognized and decoded they can provide one of the keys to our better understanding of bottom water circulation and of the ocean–climate link. They are part of the spectrum of deposits that confronts the oil industry as exploration moves into progressively greater water depths.
This memoir is an important outcome of the International Geological Correlation Project 432 on Bottom Currents, Contourites and Palaeocirculation. It includes 30 papers involving over 75 key scientists from around the world. Following an introductory state–of–the–art paper by the editors, there are 25 separate case studies on modern drifts and four on ancient contourite series. Each contribution highlights the specific geological and oceanographic setting, bathymetry, physiographic and stratigraphic context, seismic attributes and sedimentary characteristics of that drift. Case studies range from some of the well-documented North Atlantic drifts to those much less known from the Mediterrenean, from important syntheses of the Gulf of Cadiz and Vema Channel Gateway, to completely new data on South Atlantic, Pacific and Antartic margin systems. The four papers on ancient series from Japan, China and Cyprus serve to emphasise the complex nature and subtle characteristics of contourites, which make their identification a scientific challenge.
This volume is dedicated to the memory of Charlie Hollister (1936–1999), one of the founding fathers and pioneers of countourite research.