Oscar R. López-Gamundí1, Marcos A. Mozetic2, Eduardo A. Rossello3
(1) Texaco, Bellaire, TX
(2) YPF-REPSOL, Buenos Aires, Argentina
(3) University of Buenos Aires, Buenos Aires, Argentina
ABSTRACT: Asymmetric Half Graben Fill in Triassic Rifts of Western Argentina: Interaction between Sedimentation and Tectonics
Extension along the margins of Gondwanaland during the Triassic led to the creation of nonmarine rift basins in western Argentina. The Cuyo basin, the largest of these basins and with over one billion barrels of oil produced from Triassic and Tertiary reservoirs, branches northward into two arms: the Tamberias-Barreal and the Ischigualasto basins.
The Cuyo and Tamberías-Barreal basins are linked through a crossover offset or accomodation zone where fault polarity reverses. The basin bounding master fault in the Cuyo basin lies on the western flank of the basin. The master fault on the Tamberías-Barreal basin constituted the eastern margin. Reconstructions for this basin indicate the presence of an NNW-SSE elongate, 60 km - wide trough. The basal coarse fill on the fault margin reaches a thickness in excess of 1,100 m, thining to 10 m on the flexural margin. The overlying lacustrine interval exhibits a similar thickness trend, reflecting contrasting subsidence rates for the ramp and fault basin margins. East- and west-directed paleocurrents from the flank and fault basin margins respectively suggest strong transverse sediment supply.
Evidence of half graben asymmetry and growth faulting in the Ischigualasto basin has been provided by 2D seismic lines orthogonal to the strike of the rift. Faning of the intra-Triassic horizons and the thickening of the entire Triassic section toward the SW suggest that the master fault was active during sedimentation. Hanging wall onlap of the horizons on the NE flexural side indicates sedimentation in asymmetric half grabens with differential subsidence.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado