ALBERT

Description: Because of its location in an active margin context, the sand-rich Orinoco turbidite system is controlled morphologically and tectonically by the compressional structures of the Barbados prism, and as a consequence, the sedimentation system does not exhibit a classic fan geometry. The sea-floor geometry between the slope of the front of the Barbados prism and the slope of the Guyana margin induces the convergence of the turbidite channels toward the abyssal plain at the front of the Barbados accretionary prism. Also, whereas in most passive margins the turbidite systems are commonly organized upstream to downstream as canyon, then channel levee, then lobes, here, because of the control by active tectonics, the sedimentary system is organized as channel levee, then canyons, then channelized lobes. In shallow water, landward of the prism, the system has multiple sources with several distributaries, and progressively downward, the channel courses are more complex with frequent convergences or divergences that are emphasized by the effects of the undulating sea-floor morphologies. Erosional processes are almost absent in the upper part of the turbidite system shallower than 1500 m (4921 ft). Erosion along channels develops mostly between 2000 and 4000 m (6562 and 13,123 ft) of water depth, above the compressional structures of the Barbados prism. Incisions show irregular meandering and sinuous courses in the low-relief segments and less sinuous courses where channels incise the structures. Larger incisions (canyons) are 3 km (1.9 mi) wide and 300 m (984 ft) deep. The occurrence of different phases of successive incisions is responsible for the development of morphologically correlative terraces in both flanks of the canyons. This might be the consequence of two mechanisms: the tectonic activity of the deformation front characterized by progressive uplift and thrusting of recent sediments, and the superimposition of the cycles of the Orinoco turbidite system. Piston-core surveys have demonstrated that turbidite sediments moving through the channel and canyon system and deposited in the abyssal plain are mostly coarse sandy deposits covered by recent pelagic planktonic-rich sedimentation, which indicates that sand deposition slowed down during the postglacial sea level rise. 2nd revised manuscript received September 28, 2009 Yannick Callec received an M.Sc. degree in geosciences from the University d'Orsay, Paris XI in 1996 and a Ph.D. from the Paris School of Mines in 2001. He joined the Institut Français du Pétrole in 2002 doing research on the CARAMBA project. Since 2003, he has worked as a sedimentologist in the Bureau de Recherche Géologique et Minière for mapping projects and petroleum exploration in west Africa. Eric Deville received an M.Sc. degree in geosciences from the Pierre and Marie Curie University, Paris VI in 1983 and a Ph.D. from the University of Chambery, France, in 1987. He joined Institut Français du Pétrole in 1990 doing research on a wide range of sedimentary basins, notably in the Alps. His main research interests include deformation processes, thermicity, and fluid dynamics in convergent orogens and mud volcanism and shale mobilization processes. Guy Desaubliaux worked for two decades at the Institut Français du Pétrole as a sedimentologist. He joined Gaz de France in 2008 where he is now in charge of the coordination of research programs. Roger Griboulard is a researcher and teacher at the Bordeaux 1 University. His field of investigation concerns sedimentology and morphotectonics. He participated in several studies about the south Barbados accretionary prism and the deep Orinoco turbidite system. He was the initiator of the CARAMBA project. Pascale Huyghe is a researcher and teacher at the Grenoble 1 University. Her field of investigation concerns tectonics and sedimentation on either onshore or offshore. She participated on several studies about the south Barbados accretionary prism and its relationship with the deep Orinoco turbidite system. Alain Mascle received his M.Sc. degree in applied geophysics from the University of Paris VI in 1973, and his “Habilitation à Diriger des Recherches” from the University of Chambery-Savoie in 1998. He joined the Institut Français du Pétrole (IFP) in 1973 as a geologist in charge of the exploration of continental margins in collaboration with French oil companies. He moved to IFP in 1996 where he has been in charge of different M.Sc. programs in both petroleum geoscience and reservoir geoscience and engineering. George Mascle is a professor at Joseph Fourier Grenoble I University. He worked in many parts of the world, especially in Sicily and the Himalayas, and he participated in many marine surveys, notably in the Mediterranean Sea. Mark Noble received an M.Sc. degree in geophysics from the University of Paris Diderot (Paris VII) in 1986 and a Ph.D. from the Institut de Physique du Globe de Paris in 1992. He joined the geophysics research team of Mines ParisTech in 1992. His current research interests include theoretical seismology, seismic wave propagation, and tomography to characterize the near subsurface. Crelia Padrón de Carrillo received her B.Sc. degree in geophysics engineering from the Central University of Venezuela in 1997, an M.Sc. degree in science of the Earth from the Central University of Venezuela in 2002, and a Ph.D. from Joseph Fourier Grenoble 1 University, France, in 2007. She worked in PDVSA Exploration from 1996 to 2002. Her experience is in seismic interpretation focusing on exploration projects for the oil and gas industry, and her main research interests include tectonics and sedimentation and integration geophysics data. Since 2006, she has been a professor of geophysics and seismic interpretation for undergraduate and graduate students at Simon Bolivar University. Julien Schmitz joined the Institut Français du Pétrole in 1996. He participated in many marine surveys. His expertise during the CARAMBA project was in multibeam data processing and interpretation.