DID WAXING AND WANING OF GONDWANAN GLACIERS CAUSE UPPER PALEOZOIC CYCLOTHEMS?

Late Paleozoic cyclothems in Euramerica commonly are attributed to waxing and waning of Gondwanan ice sheets. We tested whether or not Gondwana glaciation could be responsible for the 60-100 m sea-level fluctuations associated with cyclothems by evaluating the timing and extent of Gondwana ice sheets. Were they large enough throughout the cyclothem interval (Visean to Sakmarian) to have caused the global sea-level fluctuations? Gondwanan glaciation occurred in three non-overlapping intervals. Glaciation during both glacial episodes I (Fammenian to Tournaisian) and II (Namurian to earliest Westphalian) was restricted mostly to alpine and tidewater glaciers at convergent plate boundaries. Glacial deposition is recorded primarily by glacimarine and glacially-influenced marine deposits; glaciterrestrial deposits are rare. The record indicates insufficient ice to account for the sea-level fluctuations recorded by cyclothems of this age. In contrast, Glacial III deposits include extensive sub-glacial tillites reflecting glaciterrestrial deposition by large ice sheets during the Stephanian to Asselian/Sakmarian. The argument that Glacial I and II deposits were originally comparable in extent to those of Glacial III, but were eroded during advance of Glacial III ice-sheets, is untenable. Pre-glacial III weathered granite profiles, indicating prolonged subaerial exposure, occur scattered over 1200 km of the Transantarctic Mountains. These and other complete successions of non-glacial deposits in Gondwana constrain the size of ice sheets between Glacial II and III. Fluctuations in the size of ice sheets prior to Glacial III were not responsible for contemporaneous cyclothems.