LATE ORDOVICIAN THROUGH MIDDLE SILURIAN GASTROPODA OF THE EASTERN GREAT BASIN

The geologic history of the Great Basin in the western United States is one of great complexity, and is one that has been well studied. This is in contrast to the understanding of preserved Ordovician and Silurian gastropod fauna within the Great Basin strata. This study deals with gastropods recovered by P. Sheehan during his work on Great Basin brachiopods and stratigraphy in 1980 and 1982. Collections are from the Late Ordovician, Ely Springs and Fish Haven Dolomites, as well as the Middle Silurian, Laketown Dolomite in Utah and Eastern Nevada. In addition, the Hanson Creek Dolomite of the Late Ordovician and Early Silurian was sampled southwest of Eureka, NV. The gastropods are silicified and were etched from dolotomized rock. The collection shows various degrees of preservation.

Late Ordovican gastropods include: Phragmolites sp., murchisonids, Gyronema, raphistomatids, and Cyclonema. Silurian taxa include: Euomphalopterus alatus, Trochonema, Umbospira, Fusispira, Oriostoma, and Platyostoma. This is the first reported occurrence of Phragmolites, Oriostoma, Umbospira, Euomphalopterus and Platyostoma from cratonic western North America. The gastropod faunas have North American (Laurentian) biogeographic affinities and lack any of the characteristic gastropods found in the terranes of northern California or Alaska.