THE MAGNITUDE OF CARBONIFEROUS–PERMIAN GLACIOEUSTATIC FLUCTUATIONS: A REVIEW

A comprehensive literature review shows that glacioeustasy varied systematically through the Carboniferous-Permian and that at least seven distinct subdivisions can be recognized. This interpretation is based on reliable, previously published estimates of glacioeustasy which were plotted against time and interpreted in light of recent advances in understanding of the spatial and temporal distribution of glaciers in Gondwana.

Facies juxtapositions in carbonate successions and erosional relief in clastic successions indicate that glacioeustatic fluctuations of at least 20-25 m, and possibly as much as 60 m, took place throughout the Early Mississippian (Tournaisian) – a widely recognized glacial period. Middle Mississippian (Chadian to mid-Brigantian) shallow marine carbonate and clastic successions indicate that glacioeustatic fluctuations never exceed 30 m, a decrease in amplitude that matches well with the paucity of coeval glacial deposits. Renewed glaciation in the Late Mississippian-earliest Pennsylvanian (mid-Brigantian to Langsettian) is accompanied by widely distributed cyclic successions that record glacioeustatic fluctuations of 50-100 m. Although Middle Pennsylvanian (Duckmantian to mid-Asturian) glacial deposits are present in eastern Australia, paleovalley depths suggest coeval glacioeustatic fluctuations did not exceed 30 m. Fluctuations of 60-120 m have been widely reported from Late Pennsylvanian-earliest Permian (mid-Asturian through mid-Sakmarian) successions in North America, an increase that corresponds to the growth of large ice sheets across much of Gondwana. Incision and facies juxtaposition in Early-Middle Permian (mid-Sakmarian to Wordian) successions in eastern Australia indicate that glacioeustatic fluctuations of 40-70 m occurred during the waning stages of this major glacial period. Erosional relief in paleoequatorial carbonates and the presence of coeval glacial deposits in Australia suggests that the final glacial event in the Middle Permian (Capitanian) may have caused glacioeustatic fluctuations of up to 20-30 m.

This review demonstrates that far-field cyclic successions recorded changing glacial conditions in Gondwana and that Carboniferous-Permian glacioeustasy was more variable than previously recognized.