The late Carboniferous–earliest Permian age estimate (300–280 Ma) for maximum ice volume during late Paleozoic glaciation of Gondwana is challenged. Past estimates assume a direct relation between extent of depositional glacial record and former ice cover; this assumption cannot be sustained, given that the glacial record is composed predominantly of glacially influenced marine strata that accumulated on the margins of ice-covered areas. We argue that Gondwana ice cover expanded in the Early Carboniferous in response to polar position, availability of moisture from a mediterranean sea, and epeirogenic uplift of the Gondwana interior. In Namurian time (ca. 325 Ma), Gondwana ice cover attained a maximum extent of about 21 × 106 km2, nearly the area of maximum Pleistocene ice cover. Despite extensive ice cover, the depositional record is meager; continental glacial deposits are poorly preserved on a regional unconformity. Thereafter, extensional subsidence of intracratonic basins promoted marine flooding, fragmentation of the ice cover, and the accumulation of thick glacially influenced marine deposits. In Stephanian-Asselian time (ca. 285 Ma), ice cover had decreased to about 15 × 106 km2, but glacial marine strata were being deposited and preserved across a very large area of the Gondwana supercontinent.
- Geological Society of America