Middle Cenozoic Benthic Foraminiferal Biofacies, Stratigraphic Events, and Unconformity-Bounded Stratigraphic Units: Key to Stratigraphic Analysis of Active Margin Basins

Martin B. Lagoe

An examination of the depositional history of two middle Cenozoic active margin basins in central California provides insights into the relative importance of tectonics and eustasy for controlling large-scale stratigraphic relationships. Both the Cuyama and southernmost San Joaquin basins were analyzed with respect to benthic foraminiferal biofacies, biostratigraphic and lithostratigraphic events, and the nature and extent of regionally important unconformities. The Cuyama basin exhibits two distinct cycles of basin subsidence and filing--one (late Oligocene to early Miocene) associated with the Vaqueros Formation and the other (early to late Miocene) associated with the Monterey Formation. The San Emigdio area of the southernmost San Joaquin basin exhibits only one major basin cycle (late Oligocene to late Miocene) associated with the Temblor and Monterey Formations. An analysis of the distribution of major unconformities, rapid bathymetric deepenings, periods of peak transgression, major shallow-marine progradational events, episodes of submarine fan development, and fluctuations in foraminiferal biofacies is used to compare basin history in the two areas. The timing of events is not always very well constrained but indicates that both eustasy and tectonics were important in shaping basin history. Several relationships suggest that tectonics is the relatively more important factor in these basins. Depositional history also is a key to understanding benthic foraminiferal biofacies distribution (particularly with respect to three-dimensional distribution f key marker species), which in turn provides insights into benthic foraminiferal biostratigraphy.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.