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Sedimentologic and Stratigraphic Investigation of Carboniferous Strata in Central Montana and Northern Utah: A Record of Environmental Change in the Paleotropics of Western Laurentia
The Late Paleozoic Ice Age (LPIA) was a ~76 myr icehouse characterized by dynamic glaciations, glacio-eustatic sea-level fluctuations, and paleoclimate oscillations. As a broad analog for the Quaternary icehouse in which humans currently reside, the LPIA provides a unique opportunity to better understand future climate patterns in a world where climate change is ever more apparent. Outcrop, core, and thin-section observations facilitated a sedimentologic and stratigraphic investigation of late Mississippian to late Pennsylvanian strata in central Montana and northern Utah, from which new estimates of LPIA onset and more resolved paleoclimate records were derived for these successions. In Chapter 2 a stratigraphic pattern indicating a shift from low-magnitude sea-level oscillations in the Otter Formation, to a pattern entailing at least 6 fourth-order, high-frequency and high-magnitude (at least 18–36 m) sea-level fluctuations in the Heath Formation was recognized. A comparison to global stratigraphic records and current biostratigraphic constraints for the lithostratigraphy of central Montana, suggests that this pattern records the main eustatic signal of the LPIA in central Montana between 331 and 327 Ma (base Serpukhovian). In Chapter 3 high magnitude relative sea-level oscillations were first observed in the lower third of the Manning Canyon Formation. Onset of this stratigraphic signal was followed by a depositional pattern entailing at least 9 fourth-order, high-frequency and high-magnitude (at least 40 m) sea-level fluctuations throughout the remainder of the formation. A comparison to global stratigraphic records and current biostratigraphic constraints for the lithostratigraphy of northern Utah suggests that this stratigraphic pattern records the main eustatic signal of the LPIA in northern Utah between 331 and 328 Ma (base Serpukhovian). In Chapter 4 paleoclimate records from central Montana, northern Utah, and additional paleotropical successions in the literature were examined. These records preserve a first-order trend of progressive paleotropical aridification in step with northern plate migration through increasingly arid paleoclimate belts during the late Mississippian and Pennsylvanian. Discrete paleoclimate excursions (less than 3–5 Ma in duration) that stray from this trend are broadly coincident with known glacial intervals, which suggests a teleconnection between high-latitude ice dynamics and tropical climate at that time.
Ahern, Justin, "Sedimentologic and Stratigraphic Investigation of Carboniferous Strata in Central Montana and Northern Utah: A Record of Environmental Change in the Paleotropics of Western Laurentia" (2019). ETD collection for University of Nebraska-Lincoln. AAI27666150.