Biostratigraphy and Paleoecology of Desmoinesian (Pennsylvanian) Brachiopods, Bird Spring Group, Arrow Canyon, Clark County, Nevada
David L. Moffett, Ralph L. Langenheim, Jr.
The Bird Spring group is abundantly fossiliferous, appears free from hiatus, and is being considered for several Pennsylvanian stratotypes. Thus, its brachiopods are of widespread interest. Twenty-nine species and 18 genera occur in the Desmoinesian at Arrow Canyon. Twenty-one species are shared with both the Rocky Mountain and Midwest areas, and seven occur in Ohio. Orthotichia morganiana (Derby), previously recorded in the Itaituba Series, reinforces an association with faunas of the Amazon basin, as also indicated by an Atokan Brasilioproductus at Arrow Canyon.
Microfacies 0 through 5 define 13 complete cycles from relatively deep to shallow-water deposition in the Bird Spring Desmoinesian. Only Orbiculoidea sp., Buxtonia sp., and Composita ovata, all adapted to soft substrates, occur in microfacies 0. Twelve species from microfacies 1, calcisiltite with as much as 30% calcarenite, lived in somewhat shallower water. There, productids dominate and are accompanied by Composita spp. and two alate spiriferids. Microfacies 2, calcisiltite with 30-50% calcarenite in a microcrystalline matrix from just below wave base, contains 24 brachiopod species. Spiriferids dominate productids, and the genera Rhipidomella, Orthotichia, Derbyia, Mesolobus, and Hustedia are restricted to this microfacies. Microfacies 3, grain-supported calcarenite in calcisiltit from just above wave base, yielded only Composita ovata, Neospirifer dunbari, and Punctospirifer kentuckensis. However, brachiopod bioclasts reportedly peak in microfacies 3. Microfacies 4 and 5, from shallower environments, lack brachiopods.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.