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Marine Diatom Biostratigraphy in Pacific Coast Neogene Basins

John A. Barron

Marine diatoms offer a powerful tool for correlation in the Monterey Formation and related fine-grained siliceous rocks deposited in Pacific Coast basins during the late early Miocene (18 Ma) to the earliest Pliocene (4 Ma). In offshore regions, their biostratigraphic usefulness extends to the late Pliocene and Quaternary. In contrast to other microfossil groups, diatoms are abundant and diverse in cold waters, such as those that have typified the United States Pacific coast since 14 m.y. (latest Luisian benthic foraminiferal stage).

Miocene diatom zones can be readily correlated throughout the North Pacific. Correlations with standard tropical microfossil zonations are well established, and an age resolution approaching 200,000-300,000 years is possible. Diatom frustules, however, are readily destroyed by diagenesis, so they are absent in the porcelanite and chert that typify most lower units of the Monterey Formation. In such circumstances, diatoms are commonly preserved in primary dolomites (beds and concretions), and diatom biostratigraphy can be applied.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.