Biostratigraphy and depositional environments of calcareous microfossils in the lower Monterey Formation (lower to middle Miocene), Graves Creek area, Central California

• Published in: Micropaleontology 1990, Vol.36 (1), p.1-55
• Main Authors: Finger, Kenneth L, Lipps, Jere H, Weaver, John C. B, Miller, Peter L
• Format: Article
• Language: English
• Subjects: algae; Arthropoda; Biostratigraphy; California; Cenozoic; Central California; Crustacea; Etymology; Foraminifera; Geology; Graves Creek; Holotypes; Invertebrata; lower Miocene; Mandibulata; Marine; Microfossils; Micropaleontology; middle Miocene; Miocene; Monterey Formation; nannofossils; Neogene; New species; Ostracoda; paleo-oceanography; paleobathymetry; Paleoecology; paleogeography; Paratypes; Plantae; Protista; Salinas Basin; San Luis Obispo County California; Specimens; stratigraphy; Tertiary; thallophytes; United States
• ISSN: 0026-2803; 1937-2795
• DOI: 10.2307/1485663

In 1905, Rufus M. Bagg, Jr., described an assemblage of foraminifers from an outcrop sample of the Sandholdt Member of the Monterey Formation collected along Graves Creek, San Luis Obispo County, California. The Graves Creek section has since been referred to often in the regional literature, and has become an important reference section for the Miocene of California and the Salinas Basin in particular. However, microfossils from the Graves Creek section have never been documented in detail. We recovered 187 species/subspecies of Foraminifera, 11 species of Ostracoda, and 24 species of calcareous nannoplankton from 19 samples. Nearly half of the foraminiferal species are new and 31 of them and Kleinpella, n. gen., are described herein. Many of the previously described species require significant extensions of their published biostratigraphic ranges. The benthic foraminiferal succession is representative of the provincial Saucesian to Luisian stages. Planktic foraminifera represent lower Miocene zones N6 to N8, and the calcareous nannofossils indicate zones CN2 to CN4. Strontium isotope ratios reveal that the sampled section dates from 17.85±0.10 Ma to 16.1±0.1 Ma, which implies that the Luisian assemblages are coeval with the upper part of the Relizian stratotype. Paleobathymetrically mixed faunal associations and sedimentary patterns indicate that the strata were deposited as turbidites at water depths between 1500 and 2000 meters. Species indicative of low-oxygen conditions are present in most of the assemblages, indicating that an oxygen-mimimum zone persisted in the Salinas Basin during the early and middle Miocene.