Sequence Stratigraphy, Tectonics and Hydrocarbon Trap Geometries of Middle Tertiary Strata in the Southern San Joaquin Basin, California

Sandra Phillips, James S. Hewlett, and W. J. M. Bazeley

Tectonic evolution of the southern San Joaquin basin exerted a fundamental control on Cenozoic sequence boundary development, reservoir, source and seal facies distribution, and hydrocarbon trap development. Spatial and temporal variations in Tertiary sequence architecture across the basin reflect differences in eastside versus westside basin-margin geometries and de formation histories. Deposition of Tertiary sequences initiated in a forearc basin setting, bounded on the east by a ramp-margin adjacent to the eroded Sierran arc complex and on the west by the imbricated accretionary wedge of the Coast Ranges thrust.

The major stages of Cenozoic basin evolution are: 1) Episodic compressional folding and thrusting associated with oblique convergence of the Farallon and North American plates (Late Cretaceous to Oligocene), 2) localized folding and onset of basin subsidence related to Pacific Plate reorganization, microplate formation and rotation (Oligocene to Early Miocene), 3) transtensional faulting, folding and basin subsidence associated with initiation of the San Andreas transform and continued microplate rotation (Miocene to Pliocene), and 4) compressional folding, extensional and strike-slip faulting related to evolution of the Pacific-North American transform boundary (Plio-Pleistocene).

Complex stratigraphic relationships within Eocene to Middle Miocene rocks provide examples of tectonic influences on sequence architecture. These include development of: (1) Tectonically enhanced sequence boundaries (Early Eocene base Domengine unconformity) and local mid-sequence angular unconformities, (2) westside-derived syntectonic "lowstand" systems (Yokut/Turitella Silt wedge and Leda Sand/Cymric/Salt Creek wedge), (3) regional seals associated with subsidence-related transgressions (Round Mountain Silt), and (4) combination traps formed by structural inversion of distal lowstand delta reservoirs (e.g. Coalinga East Extension field).

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California