Radiolarian biostratigraphy of siliceous Eocene deposits in central California

Abundant Eocene siliceous deposits in California are located in the San Joaquin and Sacramento valleys. The white shales to buff mudstones are characterized by radiolarians, diatoms, and silicoflagellates. Taxonomic descriptions and abundance data of key radiolarian species in existing monographs have limited biostratigraphic and paleoenvironmental interpretation. The California fauna is similar to faunas from the Norwegian Sea, Russian Platform, and southern oceans of Antarctica. Eocene faunas from the equatorial Pacific Ocean and Caribbean Sea differ considerably in diversity. In this study, the taxonomy and biostratigraphic information of species comprising more than 2% of the population are evaluated. Two radiolarian zones are erected for the middle Eocene of California, the Podocyrtis fasciata and Calocyclas semipolita Zones. Paleoenvironmental information suggests that some differences in the fauna may be environmentally controlled due to deposition in submarine canyons. -Authors