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Abstract: Timing of Sequence Deposition Related to the Development of the Eastern Venezuela Foreland Basin

Jason Crux, Sabrina Sarzalejo, Felipe Audemard, Celia Bejarano, Sandra De Cabrera, Diego Funes

The Eastern Venezuela Foreland Basin comprises the Guarico and Maturin Sub-basins. The Guarico Sub-basin developed first with a foredeep established and starting to fill by the end of the Eocene. A sudden shift of the depocenter from the Guarico Sub-basin to the Maturin Sub-basin occurred in the middle Miocene.

A seismic study of an area on the eastern margin of the Guarico Sub-basin and the western margin of the Maturin Sub-basin, together with biostratigraphic studies of three well sections, documents the shift in depocenter. Seismic sequence boundaries are identified by local onlap above and by truncation of reflectors below. These are mapped across the study area. The sequences below the depocenter shift thicken to the west into the Guarico Sub-basin, while those above thicken to the east into the Maturin Sub-basin. The biostratigraphic studies reveal: 1) An abrupt deepening event in the late early Miocene in the western part of the Maturin Sub-basin, 2) Condensing of sediments eastwards in a bathyal environment during the early middle Miocene, 3) Rapid sedimentation and several seismic equences deposited in the Maturin Sub-basin after the depocenter shift. These are of greater frequency than those documented for eustatically driven third-order depositional sequences.

The shift in depocenter coincides with one of our sequence boundaries. This boundary is dated as younger than the extinction of the nannofossils Cycllcargollthus floddanus but older than the extinction of Helicosphaera walbersdorfensis. No obvious correlation to the sequence boundaries shown in the sequence chronostratigraphy chart of Haq and his co-workers can be made.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela