Abstract

A thick marine turbidite succession, dominatly coarse sandstone, underlies the southern portion of the San Joaquin Valley of California. Deposited in paleontologically defined water depths of 6,000 feet or more, the sands are pebbly and gritty to fine-grained, poorly sorted, quartzose to arkosic, and are interbedded with dark foraminiferal shales. Graded bedding is common and, in conjunction with depth determinations, is taken to indicate turbidity current origin for most of the sands. The deep Paloma test was extensively cored, providing good definition of the thick Lower to Upper Miocene turbidite section in the basin deep and allowing comparisons with the electric log. The most widely spread turbidites are the Upper Miocene Stevens sands, which are oil productive and closely drilled, providing data for studies of sand distribution in relation to Miocene tectonics and bathymetry.

Oligocene to Early Miocene sands were swept far to the southwest from their Sierra Nevada provenance but by latest Miocene anticlinal barriers were rising from the sea floor, restricting most of the Stevens sands to the northeastern side of the deep basin. Earliest Late Miocene sands there entered from discrete troughs or canyons but later sands came from more widely dispersed sources as shelf sands encroached. Deep basinal transport was both axially northwestward from Tejon and westward from Edison and the incipient Bakersfield Arch. Locally, thick Stevens synclinal sands spread eastward off the rising Temblor Range. Sudden cessation of sand-carrying turbidity currents was followed by deposition of chert, shale, and Pliocene neritic sediments.

Detailed subsurface correlations show that Stevens sand bodies include sinuous channel fills bounded by major anticlines, sands flanking and covering lower structures, and lobate and branching apron or fan sands in simple homoclinal areas. Compaction structures are shown to control later sand deposition and to offer clues for continuing exploration.