Permian climate development in the northern peri-Tethys area — The Lodève basin, French Massif Central, compared in a European and global context

Abstract

The Lodève basin, which contains an exceptional long and nearly uninterrupted profile of Early to Late Permian continental red beds, is well correlated to the other European Permocarboniferous basins. Together they cover the time span from the Late Pennsylvanian to the Permian–Triassic boundary. Although these basins were placed within the equatorial belt for the whole Permian, several climatic changes are recorded in the sediments. Terrestrial sedimentation is governed by the interaction of climate and tectonics as well as by volcanism to a variable degree. Therefore, small scale climatic variations of the Milankovitch band are hardly discernable and if so, they could not be correlated between different basins. Indeed, larger scale climatic shifts could be identified. It is shown, that the shift from the Carboniferous icehouse to the Mesozoic warmhouse was a multi-stage process. This global warming resulted in a general aridisation of northern Pangea, indicated by outspreading playa and sabkha red beds, aeolianites and evaporites. Several short phases of increased humidity interrupted this trend, indicated by wet red beds, lake sediments and coal deposits. In central and southern Europe, these wet periods are traceable within the Late Stephanian/Lower Rotliegend (Gzhelian/Asselian), topmost Lower Rotliegend (Asselian/Sakmarian), Upper Rotliegend I (late Artinskian/early Kungurian) and Upper Rotliegend II/Zechstein (Wuchiapingian). The aridisation of the northern Pangea which accelerated near the Sakmarian/Artinskian transition is attributed to a reorganisation of the major ocean currents. Cold water currents along the western flank of the Pangea, indicated by the Permian chert event, blocks moisture transport from West onto the continent. During Roadian and Wordian the onset of an additional cold water current along the Cimmerian continents, blocks moisture transport from the East. Both phenomena together are responsible for the maximum of aridity at the Early to Middle Permian transition. Additionally, the equatorial climate has been affected by an increasing seasonality within the Late Pennsylvanian and Permian, caused by the wide shifting of the Zone of Inter-tropical Convergence (ITC) over the equator. Based on a new reconstruction of the Pangean assembly in this paper, climatic changes in the Permian are interpreted and causes of the arid-humid-arid shifts are examined . Phases of higher humidity are often related to events of global impact, like the waxing and waning of the Gondwanan glaciation, obtained in the South African Karoo Basin (Dwyka Group). But also regional events had strong climatic influence. The Zechstein transgression in the Northern and Southern Permian Basin as well as the Bellerophon transgression of the Southern Alps caused the wet phase in the Wuchiapingian.