ABSTRACT: Upper Cretaceous Hydrocarbon-Rich Depositional Systems of the Sacramento Basin, California

Tor H. Nilsen, G. M. Barats, D. P. Imperato, D. W. Moore, D. B. Serena

Large volumes of gas have been produced from the uppermost (Santonian to Maestrichtian) part of the Great Valley sequence in the Sacramento basin. The deposystems consist principally of deltaic, slope, deep-sea fan, and basin-plain units that prograded southward and westward into the basin. Magmatic-arc sources to the north and east supplied large volumes of quartzofeldspathic detritus. The eastern basin margin formed a stable, shallow, gently west-dipping shelf underlain by the Sierran magmatic-arc complex; the axial and western parts of the basin formed a more unstable, deep-marine, south-plunging trough underlain by the Coast Range Ophiolite. The western basin margin was a submarine ridge underlain by the Franciscan accretionary wedge.

Deposystems of the productive sequence include (1) shelf sandstone and shale units of the eastern flank of the basin (Chico Formation); (2) deltaic complexes that prograded southward down formation and southwestward across the basin axis (Starkey and Mokelumne River formations); (3) shale-rich slope deposits with sandstone-filled gullies and submarine canyons (upper Forbes Formation, shale units transitional between the Starkey and Winters formations); (4) submarine-fan complexes that include mud-rich systems (middle Forbes Formation), mixed-sediment systems (part of the Guinda Formation; Marsh Creek and Lathrop formations), and sand-rich systems (part of the Guinda Formation; Winter, Tracy, and Blewett formations); (5) basin-plain deposits (part of the Winters, Lathrop, Tracy, and Bl wett formations); and (6) basinwide shale units deposited during regional high sea level stands (Dobbins Shale Member of the Forbes Formation, Sacramento Shale, Sawtooth Shale, Ragged Valley Shale, H&T Shale, and Hall Shale). The deposystems generally record tectonically induced southward and eastward migration of depocenters.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990