EES Geoscience Seminar Series: John Isbell (UW-Milwaukee): "Evaluation of proxies used to interpret past glaciations with a focus on the late Paleozoic Ice Age"

Dec 8, 2023

03:30 PM - 05:00 PM

Trowbridge Hall, 125 TH

123 South Capitol Street, Iowa City, IA 52240

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"Evaluation of proxies used to interpret past glaciations with a focus on the late Paleozoic Ice Age"

The late Paleozoic Ice Age (LPIA) was one of Earth's most important climatic events lasting for over 110 Mys from the Late Devonian until the Late Permian. Despite its importance, its history is controversial with two hypotheses that portray glaciation differently. Traditional views characterize the LPIA as a continuous glacial event with a massive ice sheet that covered Gondwana throughout this interval. This approach often uses only one or two proxies to define the glaciation. The other emerging hypothesis suggests that numerous ice sheets occurred in Gondwana with individual glacial events lasting up to 10 Mys alternating with glacial minima/non-glacial intervals of similar duration. Both views are prevalent in the literature. Both near- and far-field proxies are used to define the ice age. Here we will focus on the near field proxies. These proxies include the occurrence/absence of diamictites, glaciotectonic deposits/landforms, striated clasts and clast pavements, outsized clasts (dropstones), rhythmites, cyclic diamictite-bearing successions, glendonites, grooved and striated surfaces, streamline landforms, and U-shaped paleovalleys. Detrital zircons and chemical index of alteration (CIA) studies help to delineate the occurrence, extent, and location of glaciation. Multiple complexities occur with the use of these proxies as different non-glacial processes and driving factors can produce similar features or results. Here we discuss the limitations and use of these proxies and promote a multiproxy approach to investigating Earth's glacial intervals. We suggest that studies incorporate multiple proxies coupled with detailed environmental, paleoflow, and paleogeographic analyses to better constrain the occurrence, timing, and extent of glaciation and its influence on global systems. This approach provides a robust view of the LPIA and other glacial intervals. 


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