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Abstract

AAPG Bulletin, V. 94, No. 6 (June 2010), P. 869887.

Copyright copy2010. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/11020909021

The Orinoco turbidite system: Tectonic controls on sea-floor morphology and sedimentation

Yannick Callec,1 Eric Deville,2 Guy Desaubliaux,3 Roger Griboulard,4 Pascale Huyghe,5 Alain Mascle,6 Georges Mascle,7 Mark Noble,8 Crelia Padron de Carillo,9 Julien Schmitz10

1Institut Francais du Petrole, Direction Geologie-Geochimie-Geophysique, 1-4 avenue du Bois Preau, F-92852 Rueil-Malmaison Cedex, France; present address: Bureau de Recherches Geologiques et Minieres, Service GEO/GSO, 3 av. Claude Guillemin, 45060 Orleans Cedex 2, France
2Institut Francais du Petrole, Direction Geologie-Geochimie-Geophysique, 1-4 avenue du Bois Preau, F-92852 Rueil-Malmaison Cedex, France; [email protected]
3Institut Francais du Petrole, Direction Geologie-Geochimie-Geophysique, 1-4 avenue du Bois Preau, F-92852 Rueil-Malmaison Cedex, France; present address: Gaz de France-Suez, 361, avenue du President Wilson, BP33, Saint Denis, France
4Departement de Geologie et Oceanographie, URA CNRS 197, Universite de Bordeaux-I, F-33000 Bordeaux Cedex, France
5Laboratoire de Geodynamique des Chaines Alpines, UMR 5025, Universite Joseph Fourier, F-38041 Grenoble Cedex, France
6Institut Francais du Petrole, Direction Geologie-Geochimie-Geophysique, 1-4 avenue du Bois Preau, F-92852 Rueil-Malmaison Cedex, France
7Departement de Geologie et Oceanographie, URA CNRS 197, Universite de Bordeaux-I, F-33000 Bordeaux Cedex, France
8Centre de Geosciences, UMR 7619 Sisyphe, Mines ParisTech, Fontainebleau, France
9Institut Francais du Petrole, Direction Geologie-Geochimie-Geophysique, 1-4 avenue du Bois Preau, F-92852 Rueil-Malmaison Cedex, France; Laboratoire de Geodynamique des Chaines Alpines, UMR 5025, Universite Joseph Fourier, F-38041 Grenoble Cedex, France; present address: Departamento de Ciencias de la Tierra, Universidad Simon Bolivar (USB), Apartado 89000, Valle de Sartenejas, Baruta. Edo. Miranda, Venezuela
10Institut Francais du Petrole, Direction Geologie-Geochimie-Geophysique, 1-4 avenue du Bois Preau, F-92852 Rueil-Malmaison Cedex, France

ABSTRACT

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.

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