IMPACT OF LATE PENNSYLVANIAN (EARLY KASIMOVIAN) GLOBAL WARMING WAS GREATER on WETLAND THAN DRYLAND TROPICAL FLORAS

The North American regional Desmoinesian-Missourian boundary (early Kasimovian) appears to have been a time of global warming, accompanied by drier conditions, throughout equatorial west-central Pangea, east of the modern Appalachians. This vast area of tropical Euramerica records a sharp floristic turnover in wetland environments – coal beds, mineral soil coastal plains and floodplains. This turnover, occurring within a single glacial-interglacial cycle, resulted in a marked change in species composition and dominance-diversity patterns, and restructuring of wetland vegetational architecture. At the same time, vegetation of more seasonally dry regions in western Pangea, dominated by xeromorphic seed plants, appears to have been little affected by this event. In central New Mexico, a succession of paleofloras dominated by conifers, seed ferns, and callipterids occurs through a mixed marine-nonmarine section encompassing the Desmoinesian-Missourian boundary (age control by conodonts). These floras occur contemporaneously with the wetland vegetation of the central Pangean tropics. The different patterns in these areas suggest that distinct biomes may have very different “internal” responses to global warming, varying from minimal to catastrophic. Examination of the late Moscovian-through-Gzhelian indicates that xeromorphic floras of seasonally dry climates, occupants of diverse habitats, oscillated spatially across central and western Pangea during cyclic changes in ice-age climate. In contrast, the edaphically narrow wetland biome appears to have been unable to migrate widely due to physical habitat and climatic constraints and, instead, contracted into regional refugia during drier climatic phases.