https://homepages.uc.edu/~algeot/Algeo-Maynard-ChemGeol-2004.pdf

Trace-element behavior and redox facies in core shales of Upper Pennsylvanian Kansas-type cyclothems

The formation of upper Paleozoic (Visean to Sakmarian-Artinskian) Euramerican cyclothems, which resulted from base-level fluctuations of up to 100 m, commonly are attributed to large-scale waxing and waning of Gondwanan glaciers. However, evaluation of the geographic and chronostratigraphic distribution of Gondwana deposits reveals that glaciation was not the primary cause of base-level changes of that magnitude. Gondwana strata contain three non-overlapping glacial successions. Glacial I (Frasnian to possibly Tournaisian) and Glacial II (Namurian to lowermost Westphalian) rocks were deposited by alpine glaciers. Water sequestered by these glaciers was insufficient to account for the base-level changes. In contrast, Upper Carboniferous (Stephanian) to Lower Permian (Sakmarian-Artinskian) Glacial III rocks were widespread and indicate deposition by ice sheets that may have covered a total area of between 17.9 and 22.6 × 10 6 km 2 . Complete ablation of a single ice sheet of this size would produce eustatic changes of ~100 m. However, multiple ice sheets were likely present, which would have resulted in considerably smaller fluctuations in sea level during Glacial III deposition. The argument that Glacial I and II deposits were originally comparable in extent to those of Glacial III, but were eroded during the advance of Glacial III ice-sheets, is untenable. Weathered granite profiles on the pre-Glacial III unconformity occur scattered over a 1200-km length of the central Transantarctic Mountains. The profiles indicate prolonged subaerial exposure and, thus, an absence of ice cover. These and non-glacial successions in Gondwana constrain the size of ice sheets before Glacial III deposition and imply that glaciation prior to Glacial Episode III was not the primary cause of base-level changes linked to upper Paleozoic Euramerican cyclothems.

Timing of late Paleozoic glaciation in Gondwana: Was glaciation responsible for the development of northern hemisphere cyclothems?

Earth's glacial record and its tectonic setting

Continental glaciation, as recorded by sedimentary facies and by pavements scoured into underlying rocks, affected northern Africa at the end of the Proterozoic Era. This glaciation was followed in the Cambrian Period by a long, warmer interval without recorded ice sheets upon the Gondwana supercontinent. Strong glaciation ensued in Late Ordovician time in central northern Africa, and centers moved into then adjoining northern Brazil and on westward into southern Brazil, southern Africa, and Bolivia and into northern Argentina by the Early Silurian. From Middle Silurian time, world-wide and Gondwanan climate ameliorated until Late Devonian (Famennian) time, when glaciation again affected Brazil and perhaps parts of Africa. Glacial centers apparently waned after the late Famennian (latest Devonian) but waxed again in Andean regions and northern Brazil in Early and mid-Early Carboniferous times to begin the strong Late Paleozoic Ice Age. Many ice caps and ice sheets came and went across the wide reaches of Gondwana during the late Paleozoic, beginning on the west, culminating in southern Africa in the Late Carboniferous, continuing strongly in India and Australia in the Permian, and dying out in eastern Australia and in Antarctica in early Late Permian time. The path of ice-center migration closely follows published paleomagnetic wander paths. The record suggests that, among other terrestrial factors which cause ice ages, glaciation flourished when Gondwana lay in south polar regions and that glaciation disappeared when Gondwana glided, so that the pole lay in oceanic or coastal regions.

J. C. Crowell

Papers

Gondwanan glaciation, cyclothems, continental positioning, and climate change