The equilibrium line altitude as a control on Gondwana glaciation during the late Paleozoic Ice Age.

ISBELL, J.L.; HENRY, L. C.; LIMARINO, C.O.; KOCH, Z.J.; CICCIOLI, P.L.; FRAISER, M. L.

Perth

Congreso; XVII International Congress on the Carboniferous and Permian; 2011

Much attention is given to environmental drivers during the late Paleozoic Ice Age (LPIA). However, the role that the equilibrium-line altitude (ELA) had on initiating and ending LPIA glacial events is undocumented. The ELA marks the altitude on glaciers that delineates areas of annual net accumulation from net ablation. The land surface must reside above the ELA for glaciers to form. Therefore, glaciation results from lowering of the ELA during global cooling or by tectonically elevating the landscape above the ELA. Latitude and precipitation also influence the ELA. LPIA glacial events varied in time, space, and volume across Gondwana; here, we speculate on how the ELA influenced glaciation during the LPIA.   The LPIA began in western and southern South America with the growth of small ice centers during the Viséan and Namurian. In western Argentina, alpine glaciation and glacimarine deposition occurred in fjords cut into the Protoprecordillera, a fold-thrust belt that developed during subduction of Chilenia beneath the Cuyania crustal block. Glaciation occurred due to uplift of the range above the ELA. Termination of glaciation occurred when the range collapsed below the ELA due to a transition into an extensional tectonic regime during the late Namurian .   During the Late Pennsylvanian and Early Permian LPIA acme, extensive glacimarine deposits indicate that glaciers reached sea level corresponding to a lowering of the ELA due to global cooling. An abrupt contact between glacial and postglacial deposits across polar and sub-polar Gondwana records global warming and the Sakmarian retreat of glaciers out of the basins.   Three additional glacial events in Eastern Australia, represented by small ice centers, ended in the Capitanian. The magnitude of global cooling during these events is debatable as there is an absence of glacial indicators in basins located farther south during the Permian (than the eastern Australia basins) in Tasmania, Antarctica, South Africa and Patagonia. From the late Sakmarian until the Capitanian, the Transantarctic Basin, which resided over the South Pole, was characterized by widespread deposition of fluvial coal measures; whereas glaciated eastern Australia lay outside of the polar circle. An absence of glacial deposits within the South Polar Circle indicates an elevated ELA located well above sea level. This suggests that severe global cooling was not the cause of the 3 Australian glaciations, but that conditions specific to eastern Australia drove these late phase events.