The Okmulgee, Oklahoma fossil flora, a Mazon Creek equivalent: Spatial conservatism in the composition of Middle Pennsylvanian wetland vegetation over 1100 km

Abstract

Abstract Temporal compositional conservatism of late Middle Pennsylvanian wetland vegetation and persistence of its dominance-diversity structure through time spans of millions of years have been documented from many places in North America and Europe. This conservatism occurs within the context of glacial-interglacial fluctuations that force spatial migration of that vegetation or its restriction to refugia during periodic sea-level changes on the craton. Although known from long temporal sequences, there have been few studies of spatial variability in these wetland floras over more than relatively small distances, generally much less than a km. Here we report a late Middle Pennsylvanian (Desmoinesian) flora from above the Henryetta Coal, near Okmulgee, Oklahoma, in the American Midcontinent. This flora is exactly correlative with the Mazon Creek flora, above the Colchester Coal of northern Illinois; the Colchester Coal and its equivalents may have been the largest, contiguous peat accumulating swamp of the Pennsylvanian. Okmulgee and Mazon Creek are separated by 1100 km, but the depositional context of the two floras is the same and they can be considered isotaphonomic. Though a much smaller sample, and thus of lower overall biodiversity, the known composition of and dominance-diversity structure of the Okmulgee flora is convergent with Mazon Creek. The overwhelmingly dominant elements of both the Okmulgee and Mazon Creek floras are pecopterid tree-fern foliage mostly attributable to Lobatopteris vestita (Lesquereux) Wagner and the pteridosperm Macroneuropteris scheuchzeri (Hoffman) Cleal, Shute and Zodrow, Both of these floras likely represent wetlands that were being drowned during the early phases of sea-level rise associated with ice melting. Each sampled a broad area, and a variety of subhabitats that fringed the Pennsylvanian coastline.