ABSTRACT: Sequence Stratigraphy and Trapping Styles in Sandy Miocene Turbidite Systems, San Joaquin Valley, California

HEWLETT, J. S., ARCO Oil and Gas Co., Houston, TX, and D. W. JORDAN, ARCO International Oil and Gas Co., Plano, TX

The Upper Miocene Stevens Sandstone on the Bakersfield arch (San Joaquin Valley, CA) was deposited in a narrow forearc basin and consists of three newly defined, sandstone-rich, lowstand turbidite systems (LTS). Each LTS is bounded by regionally extensive siliceous shales comprising condensed sections. The oldest LTS (Coulter) was transported through distinct submarine canyons cut into the Monterey Shale, whereas the stratigraphically younger Gosford LTS and Bellevue LTS were transported through smaller gullies on the high-relief slopes of the Santa Margarita deltas (highstand systems tract). Each LTS consists of sandy, high-density (primarily) and low-density turbidites and debris flows deposited in channelized and nonchannelized complexes. These deepwater systems stack in a compensa ory manner and were influenced by pre-existing structural highs and depositional topography.

As of 1986, approximately 92% of cumulative hydrocarbon production in the Stevens was from the Bellevue LTS. Within the three turbidite systems, four stratigraphic or combination structural-stratigraphic trap types are distinguished (based on an integration of seismic, log, and core data), and these trap types may be indicative of hydrocarbon occurrences in many sandy, deep water basins: (1) permeability (facies) changes within thin-bedded sandstones in distal parts of turbidite wedges pinching out on anticlinal flanks (hundreds of MMBOE), (2) channelized sandstones that thin onto anticlines or cross structural noses (tens to hundreds of MMBOE), (3) numerous small traps (<10 MMBOE) formed by compactional, low-relief, four-way closure, and (4) pinch out of gully-fill turbidites on t e largely unexplored middle and lower slope of the youngest Santa Margarita deltaic wedge.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)