OSTRACOD EVIDENCE OF A BERRIASIAN AGE FOR THE LOWER YELLOW CAT MEMBER OF THE CEDAR MOUNTAIN FORMATION, UTAH

As part of a research project (German Science Foundation, M.E. Schudack, Freie Universität Berlin, in cooperation with Richard L. Cifelli, Sam Noble Oklahoma Museum of Natural History), Lower Cretaceous ostracods of the U.S. Western Interior were taxonomically revised and applied to biostratigraphy of the Cedar Mountain Formation (CMF). A sample from within the Yellow Cat Member of the CMF near the type locality of the Poison Strip Member northeast of Arches National Park, revealed a moderately diverse ostracod fauna consisting of at least four taxa of Cypridea Bosquet, an important index taxon in sediments of Purbeck/Wealden-like facies worldwide. All of these taxa occur in the Berriasian (145.5±4.0 to 140.2±3.0 Ma) of the English upper Purbeck Group (Durlston Formation) and lower Wealden Series (lower Ashdown Formation), and three of them in the Berriasian of NW Germany. Three of the four taxa are restricted to the Berriasian, the remainder occurs from the Berriasian to the Valanginian. Therefore, a Berriasian age of part of the Yellow Cat is most probable. A second sample from a site in central Yellow Cat exposures that produced Tithonian-Berriasian age palynomorphs, contained poorly preserved ostracods; one species could be identified that also occurs in the first sample and is restricted to the Berriasian in English Purbeck/Wealden deposits. New evidence inferred from ostracods strongly suggests that the lower part of the Cedar Mountain Formation is of Berriasian age, and considerably older than other published lines of evidence have indicated.