ABSTRACT: Middle Tertiary Sequence Stratigraphy, Southern San Joaquin Basin, California

PHILLIPS, SANDRA, ARCO Alaska, Inc., Anchorage, AK, and JAMES S. HEWLETT and WILLIAM J. M. BAZELY, ARCO Oil & Gas Co., Plano, TX

Middle Tertiary strata of the southern San Joaquin basin were deposited in a seaway within a subsiding forearc basin adjacent to the ancestral Sierran highlands. Six depositional sequences, encompassing the lower Eocene to middle Miocene section, can be mapped seismically throughout most of the basin. Deposition on the arc (east) side of the basin occurred along a stable, gently dipping ramp-margin. In contrast, multiple episodes of structural deformation on the western basin margin contributed to the development of localized, steep-sided depocenters.

Seismic onlap and truncation surfaces (sequence boundaries) separate the six depositional sequences. Biostratigraphic data indicate these sequences represent second- and third-order depositional cycles from 1 to 15 Ma in duration. Sequences and systems tracts do not coincide with lithostratigraphic units that are commonly used for correlation in the basin.

Along the eastern basin margin, seismic geometries and well data indicate a gradual transition from coastal plain to marine shelf environments. Overall, a vertical stacking of highstand wedges on the basin margin and lowstand shoreline systems further basinward is observed.

Major hydrocarbon accumulations are related to structural inversion of the center of this narrow depositional basin. Significant trap types include: (1) overlap of the seaward parts of east- and west-side derived progradational clastic wedges on the flank of a large anticline (Eocene, Coalinga East Extension), and (2) inversion of distal lowstand deltas into anticlinal folds (Oligocene, Kettleman North Dome). Transgressive marine shales serve as regional and reservoir-scale seal facies for most reservoirs in the basin.

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