BOTTJER, DAVID J., KATHERINE WHIDDEN, and STEVE P. LUND, Department of Geological Sciences, University of Southern California, Los Angeles, CA

ABSTRACT: Sequence Stratigraphy and Upper Cretaceous Strata, Southern California

Upper Cretaceous (Turonian-Maastrichtian) strata in southern California on the Peninsular Ranges terrane (PRT) (Santa Monica Mountains to the United States-Mexico border) were deposited in a west-facing forearc basin. An unconformity throughout the PRT separates basement granites (early-middle Cretaceous) from the overlying Turonian Trabuco (Santa Monica and Santa Ana Mountains) and Lusardi (Carlsbad and San Diego areas) Formations, which were deposited in nonmarine alluvial fan and fan delta settings. Due to tectonics and erosion Upper Cretaceous stratigraphic sections in this region vary in completeness; the most complete stratigraphic section is found in the northern Santa Ana Mountains. There, the Trabuco Formation is overlain by the Turonian-Campanian Ladd Formation, which record onlap by shallow-marine (Baker Canyon Member) and shelf-slope (Holz Member) deposits. The top of the Ladd is marked by an unconformity, which is then overlain by the late Campanian Williams Formation, which records a return to fan delta and shallow-marine environments (Schulz Member) overlain by strata deposited in mid to outer shelf settings (Pleasants Member). The Paleocene Silverado Formation unconformably overlies the Pleasants. These unconformities are interpreted as sequence boundaries that define two Upper Cretaceous sequences. These sequences, at the present state of stratigraphic knowledge, cannot be traced to other southern California Upper Cretaceous strata, which were deposited primarily in deep-sea fan environments. Their identification, however, will allow re-examination o these deep-sea fan strata for features useful in sequence characterization, such as lowstand wedges, and a further assessment of the role of tectonics and eustacy in producing these southern California Upper Cretaceous strata.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.