REVISED STRATIGRAPHY OF PLIO-PLEISTOCENE SEDIMENTS SOUTH OF CENTERVILLE BEACH, HUMBOLDT COUNTY, NORTHERN CALIFORNIA, USA

The descriptive stratigraphy of Plio-Pleistocene stratigraphic units of the Wildcat Group in sea cliffs 0.5 – 1.5 km south of Centerville Beach has not been reinterpreted after mapping of the Eel River Basin by Burdette Ogle in 1953, who suggested that the sea cliffs consist of the Rio Dell (Pliocene) and Hookton (Pleistocene) formations. Using field observations of lithology and aerial photos, we propose a revised stratigraphy of the sea cliffs based on lithostratigraphic and biostratigraphic correlations with type sections defined by Ogle. The lowest unit present in our study area is a gray mudstone containing the marine fossil Patinopecten caurinus, which correlates with the marine Rio Dell Formation. An abrupt contact separates the Rio Dell from a series of nonfossiliferous interbedded sandstone and gravel deposits, which is interpreted as the Carlotta Formation. Sediments resembling the gray, fossiliferous Scotia Bluffs Sandstone appear to be absent between the Rio Dell and Carlotta. In the northern section of the sea cliffs, the top of the Carlotta is defined by an angular unconformity. Above the angular unconformity is poorly-consolidated sandstone and gravel containing wood fragments, correlating with the Hookton Formation. The angular unconformity continues south, until the Carlotta pinches out, at which point the angular unconformity separates the Hookton and Rio Dell. The absence of the Scotia Bluffs Sandstone may represent a facies change rather than a disconformity. The angular unconformity suggests a drop in base-level due to a combination of tectonism and Pleistocene sea level change. The revised stratigraphy offers a basis for future studies concerning formation ages in the Wildcat Group as well as understanding the history of neotectonic and eustatic changes in the area.