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Foreland-Style Flexural Subsidence of San Joaquin Basin, California

Mark S. Rentschler

A cross section has been constructed through the central San Joaquin basin, California, from the San Andreas fault near Lost Hills to the Owens Valley fault near Mt. Whitney. Tertiary subsidence is approximated from the depths to Pliocene Etchegoin, upper Miocene Monterey, upper Oligocene Vaqueros, and middle Eocene Domengine Formations, and depth to basement.

A finite-element code was used to mathematically model the central California lithosphere in two dimensions as a beam floating on a fluid asthenosphere. Preliminary results of modeling show that (1) east-vergent thrust loading in the Coast Ranges was driving San Joaquin basin subsidence throughout much of the Tertiary, and (2) buoyant root-driven uplift and westward tilting of the Sierra Nevada increased basin subsidence in the last 10 m.y. in response to weakening of the lithosphere at the Owens Valley fault.

Thrust loading was active by the Paleogene and migrated eastward during the Neogene, causing eastward onlap of Tertiary strata onto the Sierran high. These results provide independent evidence for the existence of a thrust wedge along the west side of the basin. Thrust loading is still a major contributor to basin subsidence, however, as required by the concave-down basin profile and westward-thickening sedimentary units.

Results from the San Joaquin suggest that landward-vergent accretion and/or terrane obduction played an important role in California's forearc tectonics, and that compressional tectonics may be controlling sedimentary basin formation in the Neogene transform regime.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.