Sedimentation and Trapping Mechanism in Upper Miocene Stevens and Older Turbidite Fans of Southeastern San Joaquin Valley, California

Abstract Most of the stratigraphic oil production in the southern San Joaquin Valley comes from the sandstones of the upper Miocene turbidites. Updip, time-equivalent rocks of the shallow-marine environment are second in productivity. Third in importance are the deep-marine, fractured, siliceous shales deposited beyond distal margins of the fan complex. Many underexplored areas remain in the San Joaquin Valley despite many years of field development and wildcat drilling. The Miocene of the Bakersfield arch is representative of the classic arcuate type of turbidite deposits characteristic of modern submarine fans. Further paleogradient of the fans has been accentuated and not reversed through geologic time; stratigraphic oil fields are numerous. As in most California deep-marine troughs, the turbidite facies most easily reached by the drill, and in which most of the oil reserves have been developed, are in the mobile zone of basin-margin wedging. Two additional trapping aspects related primarily to depositional stratigraphy within the midfan facies are (1) intrabasin contemporaneous faults (analogous to Gulf Coast growth faults) resulting in expanded section and reverse drag on the downthrown block, and (2) compaction anticlines formed by post-sedimentary accommodation over submarine channel sands resulting in structural inversion with depth. South of the Bakersfield arch is an earlier (pre-late Mohnian) turbidite basin, virtually unexplored and referred to informally as the “Maricopa subbasin,” where drilling depths to potential Miocene pays range from 12,000 to 20,000 ft (3,600 to 6,000 m). Basic stratigraphic relations recognized in the Bakersfield arch may be applied in the subbasin to develop new hydrocarbon reserves.