The geology of the inner basin margin, Newport Beach to Dana Point, Orange County, California

Geological and geophysical data, which include common depth point seismic profiles, velocity analysis displays, borehole and other information, were used to study the structural evolution and Neogene sedimentation of the inner basin margin between Newport Beach and Dana Point. Neogene time, as used in this study, includes the Miocene and Pliocene epochs. Using these data four seismic horizons were mapped in the study area: (1) top of the acoustic basement (top Catalina Schist); (2) top of the Delmontian (?) benthic foraminiferal stage; (3) top of the Repettian benthic foraminiferal stage; and (4) an arbitrary reflector within the Plio-Pleistocene stratigraphic section. Sedimentary rocks in the study area range from late Miocene to Recent. Late Miocene through Pliocene strata onlapped structurally high basement areas and downlapped structurally low basement areas to the south-southeast. The southerly direction of sediment transport in the upper Miocene through Pliocene stratigraphic section from the San Pedro Bay area to the study area suggests sediment was channeled through the northwest-trending Wilmington graben. These sediments were probably transported by density currents. In the study area, strata accumulated on a basement surface in which structural highs controlled or blocked sediment transport to the southeast. (See more in text.)