PLANTS IN THE LATE PALEOZOIC ICE AGE: INSIGHTS FROM LATE PENNSYLVANIAN AND EARLY PERMIAN FLORAS OF FRANCE

Abstract

The late Paleozoic ice age (LPIA) constitutes a unique framework in which to study deep time plant-climate interactions. Key research foci include (1) the onset of the first ice age on a vegetated planet and elucidating the role that plants played in this global cooling, (2) plant evolution and dynamics during LPIA glacial-interglacial oscillations, which have been compared to those of the Cenozoic, and (3) the establishment of polar forests with no extant equivalent as high latitudes became unglaciated in the Permian. The purpose of this talk is to present an overview of these major research topics and use the tropical floras from the Pennsylvanian and Permian of the Graissessac-Lodeve region in southern France as a case study of plant dynamics during the LPIA. The Graissessac basin contains one of the best-preserved examples of intramontane Late Pennsylvanian wetlands in southern Europe. Plant-yielding deposits have been extensively studied since the 19th century and document the vegetation of alluvial fans, fluvial channels, floodplains, and peat mires. Stands of arborescent lycopsids (Sigillaria) dominated the peat mires, while tree ferns (Psaronius), sphenopsids (Calamites, Sphenophyllum), and medullosan pteridosperms occupied different zones of the floodplains. Allochtonous logs and leaves of cordaitalean gymnosperms reflect the vegetation of higher/drier areas of the landscape. This vegetation contrasts with that of coeval coastal (paralic) wetlands from North America, which had a different spatial distribution of taxa. Permian deposits from the nearby Lodeve basin record a change towards increasingly drier conditions. The oldest macroflora in the basin is one of the most diverse Asselian plant assemblage known to date, with over 40 species. While some of the plants correspond to Carboniferous taxa that persisted in the early Permian, the flora is dominated by conifers, indicating a more seasonal and arid climate. It also contains an important diversity of peltaspermales (pteridosperms), as well as some occurrences of ginkgophytes and cycadophytes that started diversifying at that time. Younger assemblages from the basin are also dominated by conifers and other seed plants and reflect a transition to semi-arid conditions by the end of the early Permian (Artinskian-Kungurian).