Upper Miocene Stevens Sands in the Maricopa Depocenter Southern San Joaquin Valley, California

QUINN, MICHAEL J., Chevron U.S.A., Inc., Houston, TX

During the late Miocene, the Maricopa depocenter was a northwest-southeast-trending trough located in the southeastern corner of the San Joaquin Valley. Uplifting granitic source terranes in the Salinian block to the southwest, the Sierra Nevada to the northeast, and the Tehachapi Mountains to the southeast shed coarse-grained quartz-rich sands into the subsiding basin in the form of deep marine turbidites. These upper Miocene turbidites are collectively referred to as the Stevens sands.

Based upon studies from several oil fields within the depocenter, a generalized model has been developed for the ramp, channel, and fan deposits seen within the Stevens system. This model, and the field studies are used to examine the size, morphology, sand distribution patterns, and seismic response of these sand-rich turbidite deposits. Within the Stevens system, the majority of the hydrocarbons are found within the middle to outer parts of the turbidites fans, with post depositional compaction, uplift, and folding providing three primary types of trapping mechanism: closure due to shale compaction over sand thicks, emplacement of sands across an anticlinal axis, and updip porosity pinch-outs.

Finally, the chronostratigraphy of the basin, developed from the field studies is used to examine upper Miocene strike-slip movement along the San Andreas fault, uplift of the Sierra Nevada, strike-slip and normal movement along the White Wolf fault, and how these various tectonic events relate to the Stevens deposition.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)