Lacustrine Ostracod Biostratigraphy in Neogene Rocks of Basin and Range Province, Western United States

F. M. Swain

Freshwater Ostracoda are well represented in lacustrine rocks ranging from Cretaceous to Holocene in the Basin and Range province of Nevada, western Utah, and southern Idaho. The present study deals mainly with Miocene and Pliocene faunas represented in the Esmeralda Formation (Miocene) of western Nevada, the Humboldt and North Creek Formations (Miocene) of northeastern Nevada, the Hay Ranch Formation (Pliocene) of northeastern Nevada, and the Glenns Ferry Formation (Pliocene) of southern Idaho, from which about 125 species of freshwater Ostracoda have been obtained. The rocks in individual lake basins range from tens to thousands of meters and include major volcanic episodes.

The formations that yielded the Ostracoda were deposited in nearly isolated lake basins; therefore, only a few species are common to deposits of nearly the same age, but which lie in separate basins. Each basin apparently tended to develop a variety of endemic species.

The Miocene Esmeralda, Humboldt, and North Creek Formations yielded mesotrophic-eutrophic faunas dominated by Eucypris and and Cypricercus spp., and by a new nodose genus. The Pliocene (and early Pleistocene?) Hay Ranch Formation contains abundant Elkocythereis and Eucypris as well as cladoceran ephippia. The Pliocene Glenns Ferry Formation is dominated by Candona and Tuberocypris and by several new exotic ostracods.

The lacustrine environments represented by these faunas probably ranged from mesotrophic through several eutrophic stages and included alkaline conditions at various times. In addition to the biofacies, several ostracod assemblage zones can be recognized.

Paleogene deposits at several localities in Nevada yielded ostracod faunas, which are being studied.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.