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ABSTRACT: Flexural Subsidence Mechanism for the Late Cretaceous-Paleogene Great Valley Basin

Ian W. Moxon

Tectonic processes driving subsidence and syndepositional structural growth in forearc basins were examined in the Late Cretaceous-Paleogene Great Valley basin. Stratigraphic, structural, and foraminiferal data, combined with computer modeling studies, support a flexural mechanism of subsidence in response to thrust-stacking of Franciscan terranes and their displacement landward onto magnetic basement of the Great Valley.

The Great Valley experienced a dramatic shift in basin architecture during the late Albian or the Cenomanian to middle Campanian. The western part of the San Joaquin basin (Great Valley sediments exposed in the eastern flank of the Diablo Range) subsided to middle bathyal water depths (conservative estimates of 600-1000 m) during the upper Albian-Cenomanian, following a period of nondeposition or erosion of Hauterivian-middle Albian sediments. In the Sacramento and San Joaquin basins, the eastern limit of sediments migrated eastward by 50 km across foundering Sierran basement during the Turonian to middle Campanian time (^sim90-78 Ma). During the middle Campanian to latest Maastrichtian or the early Paleocene, the fluviodeltaic complexes prograded westward from the unroofing Sierran a c, and the western margin of the basin shoaled from middle bathyal to neritic water depths as ancestral folds developed.

The Turonian to middle Campanian pattern of eastward shoreline migration coupled with maintenance of middle bathyal water depths in the western part of the basin under conditions of rapid sedimentation can be simulated by modeling the flexural response of Sierran crust to overthrusting of tectonic loads with density and thickness characteristics similar to Franciscan terranes.

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