Print this pageAbstract: Tertiary Stratigraphic and Depositional Environments Near Indians Ranch, Monterey County, California
The Pleistocene through Miocene sequence exposed near the Indians Ranch, Monterey County, California, is the most complete Tertiary section of the central Salinian block and, therefore, is important for understanding the sedimentary history of the Salinian block. The upper Paleocene-Miocene sequence overlies with angular unconformity a poorly known Cretaceous-Paleocene section which lies on Salinian basement.
Upper Paleocene-lower Eocene rocks include sandstones and mudstones containing Foraminifera suggestive of lower bathyal (>2,000 m water depths), as well as local in-situ shallow-marine algal limestones. Middle and late Eocene depositional patterns are obscured by younger faulting, but apparently include in an east-to-west transect, shallow-marine basin-margin clastic rocks, slope(?) channel-fill conglomerates, and lower bathyal (>2,000 m) mudstone.
Upper Eocene deep-marine strata are overlain disconformably by lower Oligocene shallow-marine sandstones. These sandstones are succeeded by upper Oligocene mudstones containing an early middle bathyal microfauna (1,500 to 2,000 m). The lower and middle Miocene are telescoped into a thin sequence of phosphate-rich strata deposited at early middle bathyal water depths. Siliceous lithologies deposited at comparable depths characterize the overlying upper Miocene section. Paleocene deformation, possibly related to a proto-San Andreas fault system, shaped the local structural-topographic framework for the Eocene. Apparently, the Indians Ranch area was on the oscillating margin of an Eocene borderland-like basin. After uplift in early Oligocene time, deep-water conditions were reestablished in the late Oligocene and persisted through the Miocene. Viewed in the context of the Miocene sedimentary tectonics of adjacent areas, the phosphatic and siliceous Miocene strata of the Indians Ranch area probably reflect Neogene wrench-fault tectonism in the central Salinian block.
AAPG Search and Discovery Article #90976©1976 AAPG-SEPM-SEG Pacific Section Meeting, San Francisco, California