Pennsylvanian upland vegetation and its implications for the demise of the peat-forming tropical biome

Abstract

Gymnosperm-dominated vegetation replaced pteridophytic, peat-forming lowland rainforests across tropical Euramerica in Late Pennsylvanian times. Some of the gymnosperm elements appear to have evolved in upland environments and expanded down into the lowlands in response to continental-scale changes in edaphic conditions. This paper reviews the cryptic evidence for the composition of Pennsylvanian upland vegetation. Specifically, three datasets are critically analyzed: plant assemblages associated with marine maximum flooding surfaces, plant assemblages hosted in fluvial channels adjacent to basin margins, and the plant assemblages of elevated, intermontane basins. These data show that while peat-forming, pteridophytic ecosystems occupied localized, intermontane basins at altitudes of up to a few hundred metres above sea-level, most higher elevation upland zones were dominated by diverse gymnosperm forests containing conifers, cordaites, and pteridosperms. The principal hypotheses that explain the expansion of these latter gymnospermdominated ecosystems into lowland terrains in Late Pennsylvanian times are discussed in light of these data.