Coccoliths recovered at 69 localities from the northwest coast of San Miguel Island provide definitive biostratigraphic criteria for subdivision of more than 1,425 m of submarine fan strata of the Mirounga formation of Late Cretaceous age. The seven coccolith zones recognized from the stratigraphic distribution of 38 species suggest that San Miguel Island has one of the most complete sequences of Upper Cretaceous strata in southern California. The zones are, from oldest to youngest: Quadrum gartneri, Eiffellithus eximius, Marthasterites furcatus, Micula staurophora, Broinsonia parca, Quadrum trifidum, and Arkhangelskiella cymbiformis zones. These coccolith zones are known elsewhere in the world. They appear to represent a time interval from the early Turonian to the middl Maestrichtian, although coccolith criteria for the Santonian stage interval were not observed, possibly because of ecological restrictions.

Coccolith localities along the northwest coast of San Miguel Island indicate Upper Cretaceous strata where the Paleogene Pozo-Canada Formations and South Point sandstone had been mapped previously. These new data may add more than 500 m of rock to the previously recognized Late Cretaceous stratigraphic column. On the basis of coccolith criteria, various parts of the Mirounga formation correlate with Upper Cretaceous rocks of the southern California mainland such as: the Jalama Formation (western Santa Ynez Mountains), the Chatsworth Formation (Simi Hills), the Holz Shale Member of the Ladd Formation (Santa Ana Mountains), and the Point Loma Formation of the Rosario Group (San Diego area). Correlations are possible also with the Valle Formation of Mexico (Vizcaino Peninsula).

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