The Vema contourite fan in the South Brazilian basin
Published:January 01, 2002
Jean-Claude Faugères, S. Zaragosi, M. L. Mézerais, L. Massé, 2002. "The Vema contourite fan in the South Brazilian basin", 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 Vema contourite fan is a Neogene mud-rich accumulation (200-400 m thick), fed by Antarctic Bottom Water bottom currents and located downstream of the Rio Grande Rise. It forms one single, mounded, fan-shaped body deposited between two major channels through which the main part of the deep AABW circulation is funneled. A suite of cores and seismic lines have been collected over the whole area. The sediments deposited below the shear zone between the two current branches consist almost exclusively of muddy contourites, either homogeneous in structure or micro-brecciated. Manganiferous deposits occur in the vicinity of the channels and on the channel floors. As a result of the morphological and hydrological background, the contourite drift has prograded mostly downstream. It is composed of several depositional units bounded by widespread discontinuities showing erosional patterns. This geometry results from an alternation of episodes of strong and unstable erosive currents, and periods of relatively weak and stable depositional currents
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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.