Late Miocene to early Pliocene marine diatom and silicoflagellate floras from the Oregon coast and continental shelf

A diatomite outcrop at Bandon Beach, Oregon and some diatom-rich mudstone outcrops from the Oregon continental shelf were examined for diatom and silicoflagellate remains. Samples from these sites are compared, the floras are documented, and the outcrops are related to a modern diatom stratigraphy. Seven silicoflagellate and 91 diatom taxa are recorded from these assemblages, of which two diatom taxa are described as new (Rhizosolenia twistata and Thalassiosira multipora). The abundance of planktonic marine microfossils indicates that these diatomites and mudstones were deposited in a highly productive deep-water marine environment. Sample ages are Early Pliocene for Bandon Beach and Cape Arago, and Late Miocene for Heceta Bank samples, indicating a possible progression from west to east with oldest material seaward (Heceta Bank) and youngest material landward (Bandon Beach and Cape Arago).