Abstract: Stratigraphy and Sedimentary Facies of the Eocene Gobernador Formation, Barinas Basin, Western Venezuela.
BEJARANO, CELIA A., Corpoven S.A., Laboratorio Geol¢gico, Puerto La Cruz, Venezuela. GEORGE P. ALLEN, Queensland University of Technology, Brisbane, QLD 4001. Australia. LIONEL TORRES, Corpoven S.A., Gerencia General de Geologia, Caracas, Venezuela.
The Gobernador Formation is an important hydrocarbon reservoir in the Barinas Basin and forms a regional extensive sand sheet, covering more than 26,000 km2. The formation overlies a major unconformity extending from the upper Cretaceous to the middle Eocene which marked the transition from a passive to a foreland tectonic setting. The sandstones were deposited on a fluvial-eroded Cretaceous surface affected by synsedimentary tectonism and onlaps onto uplifting arches to the north and south, and the Guayana shield to the south-west, which constituted the primary source of fluvial sand.
The Gobernador thickness varies from 40 to 300 feet and was controlled by synsedimentary folding and fluvial incision. In the zones of fluvial incision, the base of the formation is constituted by medium to coarse-grained conglomeratic cross-bedded sandstones deposited within large bedload-dominant braided rivers. These rivers flowed to the north from the Guayana shield and accumulated multistory channel-fill deposits. These lowstand fluvial sediments were subsequently transgressed and overlain by a regional extensive sheet of braid-delta front sands which onlap the intrabasinal fold axes and uplifting basin margins.
The upper transgressive unit consists of fine to medium-grained bioturbated sands organised into small-scale sequences representing high frequency regressive-transgressive deltaic cycles. Regional facies patterns indicate a northward evolution into more open marine conditions, with fiiner-grained sandstones overlain by bioclastic carbonates. These regional facies variations as well as the effects of synsedimentary tectonism on sandstone thickness have an important implication for regional exploration strategies in the basin.
AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah