CARR, TIMOTHY R., ARCO Oil & Gas Co., Bakersfield, CA

Title: ABSTRACT: Stratigraphic Geometries of Miocene Reservoir Units in the Southern San Joaquin Basin, California: Implications for Sequence Analysis along Active Margins

Mesozoic and Tertiary rocks of the San Joaquin basin provide an on-land model for sequence geometries and sedimentary processes along tectonically active margins. As an example, middle to upper Miocene stratigraphic relationships interpreted from seismic, well log, core data in the southern San Joaquin basin differ significantly from relationships predicted from generally accepted depositional sequence models. Departures from standard sequence geometries and timing are numerous, but the most significant include basin starvation during lowstand (Monterey facies), deposition of the "lowstand fan" as an alluvial fan-fan delta (Chanac facies), and concentration of fan deposition in the latest lowstand and transgressive phases (Stevens facies).

Numerical simulation was used to investigate the empirical interpretations and to gain insight into the parameters influencing the position and timing of the deposition of observed facies. Synthetic stratigraphic sections were constructed based on model constraints on history of subsidence, sea level, and sediment supply. These models indicate that important parameters influencing the position and timing of major systems tracts include the relatively weak fluvial transport processes, narrow shelf/deep basin paleotopography, and the proximity of high relief source areas. Due to strong asymmetry in paleotopography and proximity of source areas from the east to the west side of the basin, changes in sequence geometries and timing are present within the basin. Such intrabasinal variations may be characteristic of other active convergent margins.

The modified sequence stratigraphic model has led to reinterpretation of known reservoir units, resulting in new interpretations of depositional patterns and processes, and has had direct economic impact in exploitation and exploration efforts in the Stevens and Santa Margarita reservoirs (example: Landslide field).

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