Middle-late Pennsylvanian fusulinid faunas from Midcontinent North American and the Paradox Basin, Utah and Colorado
Nail, Robert S
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The utility and limits of using fusulinids for biostratigraphy in cyclical depositional sequences are evaluated in two studies on Middle-Late Pennsylvanian strata in North America. The first study concentrates on the fusulinid succession in Missourian-Virgilian transitional strata within the type region of the North American Midcontinent. The fusulinid faunas from the Captain Creek Limestone Member, Stanton Limestone Formation through the Amazonia Limestone Member, Lawrence Formation are described and illustrated. The fusulinid succession consists dominantly of Triticites species, and nine new species and subspecies are recognized. Species oí Kansanella constitute a minor part of the flisulinid succession, and one new species is recognized. Fusulinid distribution is analyzed in six depositional cycles (cyclothems): the Stanton, South Bend, latan, Westphalia, Haskell, and Amazonia cycles. The transgressive limestone facies of each cycle extends throughout the study area, but the regressive limestone facies is not always present. Fusulinid faunas are not only cycle specific, but some species are restricted to the transgressive or regressive phase. Thus, flisulinid faunas may delimit time intervals less than the duration of a cyclothem. Many biostratigraphic datums can be defined by diagnostic species and are intimately associated with glacioeustatic cycles, which enables a high level of correlation within the Midcontinent region. Unfortunately, few of the biostratigraphic datums defined by Midcontinent fusulinid species can be recognized in other geographic regions due to provincialism. The second study documents Middle-Late Pennsylvanian fusulinids from the Paradox Basin in Utah and Colorado. Detailed biostratigraphic data for Paradox Basin strata do not exist due to the dominance of shallow-water depositional environments, and a paucity of significant biostratigraphic fauna. Several outcropping and subsurface fusulinid horizons from the Hermosa Group yielded species of Triticites, Beedeina, Fusulinella?, and Oketaella. The fusulinid faunas indicate the presence of Desmoinesian, Missourian, and Virgilian age strata. The flisulinid succession provides data with which to assign ages to depositional sequences, and permit the correlation of these cycles within the basin and with major eustatic events in the Midcontinent region.