Pangea B and the Late Paleozoic Ice Age

Abstract The Late Paleozoic Ice Age (LPIA) was the penultimate major glaciation of the Phanerozoic. Published compilations indicate it occurred in two main phases, one centered in the Late Carboniferous (~315 Ma) and the other in the Early Permian (~295 Ma), before waning over the rest of the Early Permian and into the Middle Permian (~290 Ma to 275 Ma), and culminating with the final demise of Alpine-style ice sheets in eastern Australia in the Late Permian (~260 to 255 Ma). Recent global climate modeling has drawn attention to silicate weathering CO2 consumption of an initially high Greater Variscan edifice residing within a static Pangea A configuration as the leading cause of reduction of atmospheric CO2 concentrations below glaciation thresholds. Here we show that the best available and least-biased paleomagnetic reference poles place the collision between Laurasia and Gondwana that produced the Greater Variscan orogen in a more dynamic position within a Pangea B configuration that had about 30% more continental area in the prime equatorial humid belt for weathering and which drifted northward into the tropical arid belt as it transformed to Pangea A by the Late Permian. The presence of widespread equatorial coal basins with Euramerica flora in the footprint of the Greater Variscan orogen during the Late Carboniferous is more compatible with a heterogeneous horst-and-graben morphology, characterized by uplifted crystalline massifs acting as loci of intense silicate weathering CO2 consumption and supplying sediment for proximal basins as venues of organic carbon burial, than a contiguous high mountain plateau, as assumed in recent climate modeling of the LPIA and its demise. The culminating phase of the LPIA occurred at about 275 Ma with the transformation from Pangea B to Pangea A and the attendant reduction of continental area in the equatorial humid belt, as well as with continued northward drift that placed what remained of the Greater Variscan orogen into the Zechstein arid belt in the Late Permian, by which time the geologic landscape was largely blanketed with siliciclastics. The resulting warming from reduced silicate weathering and thus increasing pCO2 was interrupted at 260 Ma with a cooling trend that coincided with emplacement of the Emeishan large igneous province on the equatorial South China Craton as well as the drift of the Cimmerian continental blocks through the equatorial humid belt due to opening of the Neo-Tethys. A return to ice age conditions from the increase in silicate weathering uptake of CO2 was avoided by drift of the Emeishan large igneous province out of the equatorial belt, that in conjunction with massive outgassing from emplacement of the Siberian Traps in high latitudes at the end of the Permian (252 Ma), helped steer the climate system to sustained non-glacial conditions.