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The AAPG/Datapages Combined Publications Database

Pacific Section of AAPG

Abstract


Geology of the Northern San Joaquin Basin Gas Province, 1997
Pages 1-12

Regional Upper Cretaceous Stratigraphy and Depositional Systems of the Northern San Joaquin Basin, California

Tor H. Nilsen, Donald W. Moore

Abstract

Campanian, Maestrichtian, and Danian strata of the northern San Joaquin portion of the Great Valley forearc basin form a complex assemblage of varied siliciclastic lithofacies derived from the Mesozoic Sierran magmatic arc to the east. Along the eastern margin of the basin, two major deltaic complexes prograded southwestward into the deeper parts of the basin and record final filling of the basin to sea level. The older deltaic complex, the Starkey Formation, is of middle Campanian to middle Maestrichtian age, reaches almost 3,000 feet thick, restricted to the subsurface, and consists of four principal stacked progradational wave-dominated deltas separated by transgressive shale intervals. The younger deltaic complex, the Garzas Formation, is of middle Maestrichtian to Danian age, is as thick as 1,750 feet, is present as a progradational sequence over the entire basin and crops out along the western flank of the basin, and is truncated by a regional post-Danian unconformity.

The deltaic deposystems grade laterally southwestward into slope shale units, submarine-fan systems, and basin-plain shale with some interbedded turbidites. The submarine-fan deposits form the principal reservoirs in the basin. The slope and correlative fan deposits have been divided in ascending stratigraphic order into the Lathrop, Tracy, and Blewett formations. Basinwide highstand condensed-section shale units form the base (Sacramento Shale) and top (Hall Shale) of the middle Campanian to Danian succession. Two additional basinwide shale units, the Sawtooth Shale and Ragged Valley Shale, separate the Lathrop/Tracy formations and the Tracy/Blewett formations, respectively. Numerous other subsurface shale markers have been used to correlate and subdivide the stratigraphic succession.

The middle Campanian to Danian strata in outcrop have been assigned in ascending stratigraphic order by most workers to the Panoche Formation and Moreno Formation; however, a large number of names have been assigned to numerous outcropping fine-grained and coarse-grained subunits by several generations of field geologists. In this report, we recommend that the subsurface units be extended to outcrop and show the correlation from several nearby wells to measured outcrop sections. The subsurface stratigraphy provides a three-dimensional understanding of two-dimensional outcrop data, and the basinwide highstand shales provide a basis for correlation from outcrops of deep-marine deposits to subsurface nonmarine and shallow-marine deposits.


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