Pelecypoda and Rostroconchia of the Amsden Formation (Mississippian and Pennsylvanian) of Wyoming

Stratigraphy and geologic history of the Amsden Formation (Mississippian and Pennsylvanian) of Wyoming

“…The taxon identified by Burk (1954, p. 11) as Spirifer opimus Hall is here regarded as distinct; it is redescribed as Anthracospirifer shawi exoletus Gordon, n. subsp. (Gordon, 1975). This subspecies is an advanced form of A. shawi Gordon n. sp.…”

“…The following conclusions are evident from these data: (Dutro and Sando, 1963a). Gordon (1975) concludes that a brachiopod fauna of mixed origins, associated with a coralline facies, migrated to the Wyoming shelf from the miogeosyncline beginning in middle Chesterian time. The fauna spread eastward, diversified, and became highly endemic during the remainder of the Chesterian.…”

“…Our collections contain almost four times as many individuals as the rest of the megafauna combined. Gordon (1975) describes, figures, and discusses 66 taxa of brachiopods, including 7 subspecies. The scheme of local zonation adopted for this region is based primarily on the distribution of these fossils and some of the corals.…”

“…The brachiopods provide possibly the strongest evidence of geographic separation of the Montana and Wyoming areas during Mississippian time followed by marine continuity during the PEmnsylvanian. Gordon (1975) describes 66 brachiopod species and subspecies from the Amsden Formation of Wyoming, of which 41 are restricted to the Mississippian, 20 are restricted to the Pennsylvanian, and 5 occur in both Mississippian and Pennsylvanian strata. Only 18 of the Wyoming taxa have been identified by Gordon in the collections reported by Gardner and others (1946) and Easton (1962) from the Mississippian and Pennsylvanian of Montana.…”

“…In this summary of the stratigraphy and geologic history of the Amsden Formation, we have integrated the paleontologic data with lithostratigraphic and petrographic data. The following reports, which are part of this study, deal with the systematic paleontology of the Amsden : Foraminifera and algae (Mamet, 1975), Coelenterata (Sando, 1975), Brachiopoda (Gordon, 1975), Pelecypoda and Rostroconchia (Gordon and Pojeta, 1975), Gastropoda, Cephalopoda, and Trilobita (Gordon and Yochelson, 1975), and Ostracoda (Sohn, 1975). Other paleontologists who contributed identifications of Amsden fossils are: Betty Skipp, Foraminifera; Helen Duncan, Bryozoa; J. W. Huddle, conodonts; and D. H. Dunkle, fish remains.…”