Pennsylvanian to Lower Permian (Desmoinesian-Wolfcampian) fusulinid biostratigraphy of Midcontinent North America

Abstract

Midcontinent North American Middle Pennsylvanian-Lower Permian (Desmoinesian-Wolfcampian) fusulinid foraminiferal species range charts were plotted and new fusulinid zones were defined. The species range charts were plotted together with lithostratigraphic columns and cyclothemic sea level curves in order to compare biostratigraphic, lithostratigraphic, and glacio-eustatic patterns. The fusulinids Beedeina and Wedekindellina appeared during widespread early Desmoinesian transgressions and characterized that interval. The mid-Desmoinesian extinction of Wedekindellina and turnover of Beedeina species coincided with a lowstand followed by a widespread transgression, generally higher sea levels, and changing paleoclimatic patterns. Beedeina went to extinction near the Desmoinesian-Missourian sequence boundary. The earliest Missourian is barren of fusulinids in the Midcontinent, followed by a thin zone of Eowaeringella, and then the appearance of Triticites, which dominated fusulinid faunas through the remainder of the Upper Pennsylvanian. Lower and Middle Missourian Triticites have relatively small tests and plane septa. In the Upper Missourian, Triticites became medium-sized with more complex septal fluting, and Kansanella appeared. In the uppermost Missourian and lower Virgilian, most Triticites are medium-sized and evenly biconvex, and have weak septal fluting. Kansanella gradually declined through the lower Virgilian and disappeared in the lowest middle Virgilian. The middle Virgilian is dominated by medium to large Triticites with complex septal fluting, and Dunbarinella appeared and became locally common. The upper Virgilian has mostly large inflated Triticites and the first Leptotriticites. The uppermost Virgilian (‘Bursumian’) has large Triticites, diverse Leptotriticites, and the first primitive elongate Schwagerina. That fauna extends across the new conodont-based Pennsylvanian-Permian (Virgilian-Wolfcampian) boundary, and the first definitive Wolfcampian (Lower Permian) fusulinids did not appear until the Neva Limestone, which is a couple cycles above the new systemic boundary. Most significant fusulinid biostratigraphic changes correlate with major glacio-eustatic cyclothem boundaries, but not all major cyclothem boundaries have significant faunal turnovers. Fusulinid zonal boundaries that were based on only fusulinid species ranges were found to closely approximate maximum sea level lowstands. Most new genera and species appear in the regressive phases of the next cyclothem, probably because faunal migrations occurred during maximum flooding events, and subsequent highstand system tracts had more paleoenvironmental diversity and thus more niches to fill.