Abstract: Regional Stratigraphy and Depositional Systems of Campanian and Maestrichtian Reservoirs, Northern San Joaquin Basin, California

NILSEN, TOR H. and DONALD W. MOORE

The northern San Joaquin basin forms a major gas-producing region characterized by continuing exploration activity. On the basis of a regional stratigraphic and structural study of Campanian and Maestrichtian reservoirs for the petroleum industry conducted by Applied Earth Technology, Inc., the overall stratigraphic framework and principal reservoir geometries were defined. The Upper Cretaceous forearc basin generally contains a series of shelfal deltaic deposits along its eastern and northeastern flanks, south- and southwest-dipping slope deposits with associated submarine canyons and gullies in the central parts of the basin, and a series of submarine-fan and basin-plain deposits in the western part of the basin that also crop out to the west in the Diablo Range. Deposition of the assemblage of shallow-, intermediate-depth-, and deep-marine reservoirs was interrupted by a series of basinwide highstand condensed sections, which include in ascending stratigraphic order the Dobbins Shale, the Sacramento Shale, the Sawtooth Shale, the Ragged Valley Shale, and the Hall Shale. The Santonian to middle Campanian reservoirs consist of submarine canyons and fans shed westward off the Sierran shelf. The principal middle Campanian to middle Maestrichtian reservoirs include a stack of progradational wave-dominated deltas assigned to the Starkey Formation and related canyon and mostly sandwich fan deposits of the Lathrop, Tracy, and Blewett Formations. The upper Maestrichtian to Danian reservoir consists principally of the Garzas Formation, a major deltaic system that prograded westward across the entire basin, recording final filling of the basin to sea level.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California