Upper slope sands: late Quaternary shallow-water sandy contourites of Campos Basin, SW Atlantic Margin
Published:January 01, 2002
Adriano R. Viana, Waldemar De Almeida, Jr., Cleide Wilhelm De Almeida, 2002. "Upper slope sands: late Quaternary shallow-water sandy contourites of Campos Basin, SW Atlantic Margin", 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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Upper slope sand deposits comprise a widespread but thin elongate accumulation of coarse to very fine-grained sand resulting from the action of slope boundary currents upon shelf-derived sediments. Sediment distribution on the Campos Basin upper slope responds to the action of the southward-flowing western boundary Brazil Current (BC). Linear, multi-source sediment supply to the slope is provided by shelf overspill due to the action of different forcing mechanisms: tides, storm fronts, and BC current onshelf penetration as gyres and meanders. On the slope, the sediment is pirated and redistributed by the BC Coarse-grained sediments (pebbles to very coarse sand) are found below the zone of maximum acceleration of the BC. Down–stream, fining is observed as a consequence of the morphologically controlled BC deceleration. The resultant accumulation is an elongate (c. 70 km long) and thin (> 50 m) wedge-shaped deposit. This depositional model is based on hydrographic, physiographic and sedimentologic characteristics of the modern Campos Basin margin, SE Brazil and characterizes a shallow water contouritic deposit
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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.