ABSTRACT

Nolan first described the Sevy in the Gold Hill district of western Utah in 1935. His evidence pointed to Middle Devonian age for the non-fossiliferous formation.

In east-central Nevada and adjacent Utah the Sevy consists of 500–1,600 feet of aphanic, homogeneous, white-weathering dolomite. It unconformably overlies the Laketown dolomite (Silurian) and grades upward into the Simonson dolomite (Middle Devonian). Halysites, found in the lower part, indicates at least part of the Sevy is Silurian; the upper part is probably Devonian. The Sevy is tentatively correlated with the Lone Mountain formation of central Nevada.

A widespread, persistent dolomitic quartz sandstone at the top of the Sevy was derived from sources on the southeast. Evidence of this is based on geographic distribution of sorting, proportion of quartz sand, cross-lamination, and regional relationships.

The slowly deposited Sevy represents a calcareous mud which was dolomitized and reworked on a tidal flat or very shallow bay. The provenance, peripheral to the miogeosyncline, was a lowland underlain by Silurian and Upper Ordovician dolomites. These were removed by erosion, and the Middle Ordovician Eureka sands were exposed to provide the quartz in the sandy phase of the Sevy.

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