The Magnitude of Late Paleozoic Glacioeustatic Fluctuations: A Synthesis

Abstract

Abstract A comprehensive literature review shows that the magnitude of eustatic fluctuations varied throughout the Carboniferous and Permian and that at least eight distinct phases can be recognized. Facies juxtapositions in carbonate successions and erosional relief in clastic successions indicate that glacioeustatic fluctuations of 20–25 m, and occasionally as much as 60 m, took place throughout the early Mississippian (Tournaisian)—a widely recognized glacial period. Middle Mississippian (mid-Chadian through Holkerian) shallow marine carbonate and clastic successions indicate that eustatic fluctuations were 10–25 m, a decrease that matches well with the paucity of coeval glacial deposits. Late Viséan (Asbian through mid-Brigantian) glacioeustatic fluctuations of 10–50 m record the initial phases of ice accumulation in advance of the widespread mid-Carboniferous glacial event. The latest Mississippian–earliest Pennsylvanian (mid-Brigantian through Langsettian) was a time of widespread glaciation, and strata of this age commonly exhibit evidence of glacioeustatic fluctuations of as much as 40–100 m. Although middle Pennsylvanian (Duckmantian through Asturian) glacial deposits are present in eastern Australia, paleovalley depths suggest that coeval glacioeustatic fluctuations were less than 40 m. Glacioeustatic fluctuations of as much as 100–120 m have been widely reported from late Pennsylvanian–earliest Permian (Stephanian through mid-Sakmarian) successions in North America, an increase that corresponds to the growth of large ice sheets across much of Gondwana and the accumulation of ice in the northern hemisphere. Incision and facies juxtaposition in Early–middle Permian (mid-Sakmarian through Kungurian) successions in eastern Australia indicate that glacioeustatic fluctuations of 30–70 m occurred during the waning stages of major glaciation. Erosional relief in paleoequatorial carbonates and the presence of coeval glacial deposits in Australia suggests that eustatic fluctuations of 10–60 m occurred during the final stages of glaciation in the middle to Late Permian (Roadian through Capitanian), but the modest size of most of these fluctuations makes it difficult to isolate the glacioeustatic signature. This review demonstrates that far-field cyclic successions record changing glacial conditions in Gondwana, that the magnitude of glacioeustatic fluctuations was directly related to the volume of glacial ice, that Carboniferous–Permian glacioeustasy was more variable than previously recognized, and that generalizations from short temporal intervals are probably not representative of the late Paleozoic ice age as a whole. Although any attempt to quantify the magnitude of ancient eustatic changes is based on caveats and assumptions, this review incorporates the results of over 100 published papers on the topic in an attempt to minimize the errors inherent in any one study.