--> The Formation of Reservoir Compartments During Subsidence-Sea Level Interactions, San Joaquin Valley, California, by M. S. Clark, L. M. Beckley, and M. T. Singleton; #90986 (1994).

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Abstract: The Formation of Reservoir Compartments During Subsidence-Sea Level Interactions, San Joaquin Valley, California

Michael S. Clark, Lila M. Beckley, Mark T. Singleton

The Miocene Stevens sandstone produces oil on the Bakersfield Arch, San Joaquin basin, California from reservoir compartments that formed in response to tectono-eustatic controls. The "Arch Stevens" contains two seismic-scale (330-500 m thick) depositional sequences. The upper sequence contains amalgamated to shale-encased sandstones that were deposited by grain- and debris-flows in (approx.) 300 m water depths. This sequence is sand-rich (60-80% ss) on structural highs that were also paleotopographic highs during Stevens deposition (e.g., South Coles Levee, Paloma, and Strand anticlines). Thicker sections with less sand characterize the flanks. The sand distributions are anomalous since grain and debris flows preferentially deposit in bathymetric lows.

Backstripping calculations indicate that the flanks subsided faster than the paleohighs. Thus, increases in accommodation space were greatest on the flanks and resulted in aggradation with preservation of section. Less accommodation on the crests resulted in progradation with erosion and reworking. Through lobe-switching processes some sand reached all parts of the depocenter. Winnowing of fines and erosion of shale interbeds in slowly subsiding areas of progradation and reworking (crests) created sand-rich sections with amalgamated sands that are not additive to the section. Preservation of shale interbeds in areas of rapid subsidence (flanks) created shale-dominated sections with sands that are additive. Differential compaction of shale-encased flank sands creates compactional antic ines. Greater compaction of thicker, shale-dominated flanks equalizes the thicknesses of flank and crest sections. Thus, the reservoir architecture represents the integrated effects of compensation (lobe-switching), accommodation (subsidence + sea level), and compaction.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994