Paper No. 10
Presentation Time: 3:30 PM
INTRACONTINENTAL EXPRESSION OF THE LATE PALEOZOIC ICEHOUSE AND ITS COLLAPSE IN EQUATORIAL PANGEA: THE MARITIMES BASIN, EASTERN CANADA
Comprehensive floral, faunal and sedimentological records from the intracontinental Maritimes Basin (MB) provide insight into environmental response of equatorial Pangea to global change during expansion and collapse of the Gondwanan cryosphere. Basinal patterns in depocentres of the MB during the Early Pennsylvanian (Bashkirian) show the importance of drainage and limits of seasonality, with coexisting red beds and coal-bearing strata. Wetlands and mires were seasonally dependant on groundwater, dominated by polycarpic lycopsids, pteridosperms and sphenopsids and were the habitat of a distinct, terrestrially adapted vertebrate fauna, including the earliest amniotes. Better drained surroundings and riparian habitats appear dominated by cordaitaleans. Increasing water deficit in these basinal depocentres in the Middle (Moscovian) and into the Late (Kasimovian) Pennsylvanian resulted in shrinking wetlands and their disappearance from west to east across the southern MB. At the same time however, expansion of mires in the eastern and central Maritimes Basin attended encroachment of the sea, presumably from Europe. Shifts between weakly and strongly seasonal climate at this time have been interpreted for alternating coal and calcrete at the timescale of orbital eccentricity, implicating glacially modulated sea level change, and underscoring the importance that proximity to the sea played in enhancing humidity. The limit of seasonality for peat formation was crossed by the Late Pennsylvanian (Gzhelian), however, as epeiric seas withdrew for the last recorded time during the Paleozoic coincidentally with expansion of the Gondwanan ice sheet. Wetland communities were replaced in lowland riverine environments as early as the Gzhelian by walchian conifers and reptilian dominated vertebrate communities that persisted through the Early Permian (Asselian to Sakmarian). Even as the Gondwanan ice sheet collapsed, aridification continued unabated, and by the Artinskian, desertification is recorded in eolian sandstones of Les Isles de la Madeleine as the Maritimes Basin moved from an equatorial position into ever drier northern latitudes.