LATE DEVONIAN SHELLY FOSSILS FROM THE JEFFERSON FORMATION, GRANDVIEW CANYON, EAST-CENTRAL IDAHO

Located in the East-Central part of Idaho is a well-developed Late Devonian reef from the Jefferson Formation in the Grandview Canyon region (Isaacson and Dorobek 1989). The fossils that make up the majority of life on the reef are the colonial rugose coral, Peneckiella sp.; three tabulate corals, Coenites sp., Thamnopora sp., and Syringopora sp.; two gastropods, Donaldina micra and Naticopsis naticopsis; a sponge species, Hormospongia sp.; four brachiopods: Cyrtospirifer whitneyi, Tenticospirifer utahensis, Radiatrypa multicostellata, and Floweria prava; and stromatoporoids in both domal and bulbous forms. These species are found abundantly throughout this section of the Jefferson Formation.

Collected from a section stratigraphically below the reef, the samples were dissolved in hydrochloric acid and the fossils were separated and identified. Several of the fossils, including the brachiopods and corals, have been recorded in other locations throughout the Western United States and Canada. Others, like Hormospongia sp., are documented very sporadically and are found only in limited areas. Also found in this section are unique symbiotic growth patterns of the stromatoporoids, rugose, and tabulate corals. The dark dolomite layer and the excellent condition of the fossil preservation suggest a deep-water environment, the fore-reef. The collection of species indicate deposition during the Frasnian period.