Abstract: Sedimentology and Facies Architecture of the Turonian Venado Sandstone (Great Valley Group) between Cache Creek and Berryessa Peak, California: a First Appraisal of Tectonic Versus Sedimentological Controls

LEVERENZ, AXEL, Stanford University, Stanford, CA

The Venado Sandstone, a sand-rich unit of the Great Valley Group, is exposed in the study area along an over 30 km long, NW-SE-trending ridge. This unit is characterized by distinct sandstone packages which appear to be continuous over distances of several kilometers, although vegetation cover and difficult access often hamper a detailed verification. Deposits in the sand-dominated packages mainly consist of very thick-bedded sandstones. Mud-dominated intervals are commonly characterized by thin-bedded turbidites. The most prominent feature of this unit is its north to south thinning from several hundred meters to less than 100 meters. In the north, three discrete sandstone packages, comprising high-concentration turbidites and minor debris flow deposits, can be distinguished ranging in thickness from 50 to >150 meters. They are separated by more mud-dominated intervals, including generally low-concentration turbidites, with a thickness between 40 and 100 meters. In contrast, only one prominent sand-dominated package is preserved in the south. Preliminary analyses indicate that relative thickness proportions of the three northern sandstone packages vary, with a tendency for the uppermost package to increase proportionally in thickness towards south, while the lower two packages decrease in relative thickness. Intervening mud-dominated units retain their relative thickness proportion. Various tectonic and sedimentological controls on the depositional processes will be discussed, such as: distal thinning or onlapping of turbidite system; sedimentological compensation of topographic lows; tectonic compartmentalization of turbidite system; changes in source regions, magnitude and direction of sediment supply.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California