Date of Award
Doctor of Philosophy
John L Isbell
Kathy J Licht, Mark T Harris, Lindsay J McHenry
detrital zircon geochronology, glacial sedimentology, Late Paleozoic Ice Age, sedimentology, Tasmanian Basin, Transantarctic Basin
The Late Paleozoic Ice Age (LPIA; ~ 374 – 256 Ma) is the longest Phanerozoic icehouse interval. this interval in Earth’s history was largely defined by extensive glaciation of the southern hemisphere at both polar and temperate latitudes. Glaciers are powerful climatic and geologic actors, especially during icehouse periods, and widespread glaciation can have a significant influence on both regional and global climate and geology. Therefore, constraining the characteristics of LPIA glaciers is essential to developing a global-scale understanding of this key climatic event in Earth’s history. The manuscripts in this dissertation examine the sedimentology, transport directions, stratigraphy, and detrital zircon provenance of the Pennsylvanian – Permian glacigenic succession from the LPIA at locations in the Transantarctic (Antarctica) and Tasmanian (Australia) basins.
The Transantarctic and Tasmanian basins share many characteristics that make them interesting and important places to study LPIA glacigenic rocks. In both basins, sediments were deposited during a ~ 14 Myr icehouse interval spanning the Pennsylvanian-Permian boundary during which time glaciation is thought to have been the most extensive of the LPIA. During this interval, both basins were located at high (> 60˚) southern latitudes along the Panthalassan margin of southeastern Gondwana. The similarities in paleogeographic, geologic, and temporal contexts between the Transantarctic and Tasmanian basins mean that characterizing and comparing LPIA glaciations in both areas is critical to understanding the late Paleozoic glacial maximum at polar latitudes. The works presented in this dissertation demonstrate that building an accurate, nuanced understanding of global glaciations during the LPIA, requires beginning at the local scale and building outward.
Chapter 2 examines the Pagoda Formation of the Transantarctic Basin at four locations in the Shackleton Glacier Region of Antarctica. The dominant lithology in the Pagoda Fm at those locations is a massive, sandy, clast-poor diamictite. Depositional processes governing these diamictites were proglacial, subaqueous glacial processes, likely a combination of mass transport, iceberg rain-out, iceberg scouring, plume sedimentation, and subglacial till deposition. Some of the deposits are part of grounding-line fan systems. All glacigenic sediments in the Pagoda Fm at these locations were likely deposited during the retreat phase of a single, up to 90 m thick glacial sequence. Flow directions from these successions support the hypothesis that an ice center was present toward the Panthalassan margin of East Antarctica (Marie Byrd Land) during the LPIA.
Chapter 3 describes the basal 415 m of the type section of the Wynyard Formation of the Tasmanian Basin, which outcrops along the coast of northwestern Tasmania. Facies associations in this succession include muddy massive diamictite, sandy massive diamictite, and rhythmically laminated fine-grained facies. Respectively, these sediments were deposited as a grounding-zone wedge, proglacial, proximal grounding line fan or morainal bank, and proglacial, glacier-distal cyclopelites. In this succession, the basal Wynyard Fm was deposited in glacier-proximal to glacier-distal, marine environments on a continental shelf at water depths below storm wave base. All facies associations contain mass transport and turbidite deposits that could have been driven by slope instability due to rapid deposition. The “Wynyard Glacier” was most likely an outlet glacier or ice stream draining a large ice cap or ice sheet.
Chapter 4 is a detrital zircon geochronology provenance study of sandstones from the Wynyard Formation. These data represent the first such measurements from the Wynyard Formation anywhere in the basin. With these data, and using a “local first” approach, we demonstrated that all measured detrital zircon dates from the Wynyard Fm can be attributed to zircon sources that occur within 33 km of the sample location along the glacier’s flow path. Therefore, while the detrital zircon provenance signature of the Wynyard Fm also supports the hypothesis that the Wynyard Glacier flowed from south to north, this information does not impart insight into where the ice center was nucleated.
Ives, Elizabeth Rosa Woodford, "A South Polar View of Late Paleozoic Glaciation: Physical Sedimentology and Provenance of Glacial Successions in the Tasmanian and Transantarctic Basins" (2021). Theses and Dissertations. 2793.