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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 38 (1954)

Issue: 2. (February)

First Page: 284

Last Page: 305

Title: Harding and Fremont Formations, Colorado

Author(s): Walter C. Sweet (2)

Abstract:

The Harding and Fremont formations crop out coextensively throughout a large, erosionally isolated province in central Colorado. The Harding is dominantly a very fine-grained sandstone which becomes more shaly toward the east. Prominent physical unconformities exist between the Harding and the underlying Manitou, and between the Harding and the Fremont. The known invertebrate fauna of the Harding is dominantly molluscan and indicates a Black River age for the formation; the large conodont fauna further suggests a correlation with the Glenwood beds of Minnesota, the Icebox shale of the Black Hills, and pre-Lander, post-Deadwood strata in the Bighorn Mountains of Wyoming. The Fremont dolomite is divided into two lithologic and faunal members: a lower massive dolomite with a contained fauna of Receptaculites, Halysites, Calapoecia, and 17 genera of nautiloid cephalopods; and an upper thin-bedded, argillaceous dolomite which bears a characteristic assemblage of corals and brachiopods. The name Priest Canyon is proposed for the upper member. The fauna of the lower member of the Fremont is like that known best from the Red River formation of southern Manitoba and the Bighorn dolomite of Wyoming, whereas the fauna of the Priest Canyon suggests a correlation with the Maquoketa of Iowa. It is concluded that the massive member is early Upper Ordovician (Covington), and that the Priest Canyon member is Richmond.

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