Miocene Temblor Formation and Related Basin Evolution, Southwestern San Joaquin Basin, California

Blake W. Gillespie

The southwestern San Joaquin basin is an area of great importance for the energy industry and academic basin analysts. Understanding basin evolution is a key concern for explorationists in this essentially pristine province. Temblor Formation is exposed in an east-west-trending belt that comprises the north flank of the San Emigdio Mountains. Field and subsurface evidence were used to elucidate the geology, depositional environments, and age of the Temblor Formation. The formation represents sand-rich borderland sedimentation in a predominantly deep-marine setting. Deposition of Temblor clastics reflects deformation due to the impingement of the Farallon-Pacific ridge with the California-North American plate margin during the middle Oligocene. As a result, severe uplift a ong the margins of the southern San Joaquin basin, reinforced by a lowstand of global sea level, caused large volumes of coarse, immature clastics to be shed into the rapidly subsiding deep-marine depocenter. Deposition of the Temblor was thus concurrent with the transformation from a convergent margin tectonic regime to one of dextral strike-slip. This transformation was marked by an episode of transform-extension indicated by volcanism, rapid subsidence, and marine transgression during the early Miocene. The Maricopa trough or oceanic connection from the San Joaquin basin to the Pacific Ocean is inferred to have existed between Recruit Pass and Maricopa. The age of the Temblor Formation is late Oligocene to early Miocene. Petroleum production is limited to the upper member in small oil fields flanking the northern San Emigdio Mountains.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.