Faro–Albufeira drift complex, northern Gulf of Cadiz
Published:January 01, 2002
Dorrik A. V. Stow, Jean-Claude Faugères, Eliane Gonthier, Michel Cremer, Estefania Llave, F. J. Hernández-Molina, Luis Somoza, V. Díaz-Del-Río, 2002. "Faro–Albufeira drift complex, northern Gulf of Cadiz", 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 northern margin of the Gulf of Cadiz is swept by Mediterranean Outflow Water between about 500 and 1000 m water depth. This warm, saline, thermohaline, bottom current attains velocities in excess of 1 m s−1 through the narrow and relatively shallow Gibraltar gateway, and then descends and slows as it moves towards the north and west around the Iberian margin. It was established in its present form in the latest Miocene, following tectonic re-opening of the Gibraltar gateway, and has since helped to sculpt the slope region in conjunction with downslope processes and diapiric intrusion. The principal area of contourite deposition, up to 600 m in thickness, is the Faro–Albufeira drift complex in a mid-slope setting some 30 km south of Faro. This comprises an elongate low-mounded drift (Faro–Albufeira) and adjacent broad sheeted drifts (Faro and Bartolomeu Dias Planaltos), flanked and partly dissected by deep, erosional, bottom-current channels and buried channels. The seismic character is one of progradational-aggradational depositional units with laterally extensive sub-parallel reflectors, widespread discontinuities and a large-scale cyclicity in seismic facies. The upper 10 m of cored section comprises muddy, silty and sandy contourites of mixed terrigenous and biogenic composition, that show small-scale cyclicity in grain size and associated sedimentary features. Rates of accumulation varied from < 1 to 14.5 cm ka−1 (cores), and 3.5 to 29.5 cm ka−1 (seismics). The large and small-scale cyclicity noted can be related to fluctuation in bottom current velocity related to climate and sea-level changes, although the precise correlation between these events remains uncertain.
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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.