No abstract

High-resolution shallow seismic profiles from the Ventura shelf reveal two contrasting, structurally controlled styles of deposition. On the northern shelf, folded Plio-Pleistocene strata comprising the south limb of the Ventura Avenue anticline are unconformably overlain by undeformed late Quaternary strata. In contrast, a thicker section of undeformed, prograding deltaic sequences preserved on the subsiding southern shelf contains a detailed record of at least five middle and late Quaternary glacioeustatic sea-level oscillations. A transgressive surface at −140 m in upper Pleistocene Saugus deposits is overlain by transgressive and highstand systems tracts. A shelf-margin systems tract subsequently developed as the sea level lowered, marking the end of Saugus deposition. Thereafter, over 50 m of post-Saugus upper Pleistocene sediment accumulated during a period of smaller-scale sea-level oscillations, followed by the development of a pair of marine terraces, presently at −50 and −33 m, and a large fluvial channel, now buried at −113 m. Correlations of Saugus and terrace marker horizons with the middle to late Quaternary paleosea-level curve suggest development of the Saugus marker horizons during oxygen isotopic stages 7-5e and formation of the terraces during Wisconsinan high sea levels. Maximum rates of vertical separation on the Oak Ridge and Pitas Point faults are estimated to be 0.13 and 0.30 m/1000 yr, respectively.