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The AAPG/Datapages Combined Publications Database
The Silurian rocks in the Great Basin can be assigned to two distinct facies: an eastern carbonate facies and a western shale facies. The line separating the two facies, actually a narrow transition zone, trends northeast from Independence, California, through Beatty, Eureka, and Elko in Nevada.
The rocks in the eastern carbonate facies are composed almost entirely of dolomite. The dolomite is heterogeneous, varying from fine- to coarse-grained, black to white, and from almost pure dolomite to very silty dolomite.
The dolomite facies is one of the poorest systems for paleontological studies in the Great Basin. Fossils are scarce and where present are usually poorly preserved. A few localities yield silicified fossils that can be etched and studied in detail. Both Middle and Upper Silurian fossils are present in the dolomite. The faunas seem to be most closely allied to those of Australia and the Orient, and have little similarity to the Silurian forms in eastern North America. No Lower Silurian fossils have been
recognized. Early references to Lower Silurian faunas in the Great Basin are Lower Silurian in the old European sense, that is, Ordovician.
The rocks in the western facies are predominantly black shale with minor amounts of sandy and calcareous shale and rare interbeds of limestone.
The fauna in the western shale facies is largely pelagic. Locally well preserved graptolites range from Middle to Late Silurian in age. The Upper Silurian shales locally contain eurypterids.
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