Paleotropical climate oscillations from upper Mississippian and Pennsylvanian stratigraphic records of western Laurentia: A convolution of plate migration and Gondwanan ice dynamics

In the Rocky Mountain region of the western United States, upper Mississippian and Pennsylvanian stratigraphy in central Montana and northern Utah preserve a poorly documented, paleotropical stratigraphic record that spans the Carboniferous interval of the Late Paleozoic Ice Age (LPIA). Sedimentologic and stratigraphic investigation of the Otter Formation (Visean) to the Alaska Bench (Bashkirian) in central Montana, and the Humbug Formation (Visean) to the Weber Formation (Gzhelian) in northern Utah, facilitated an appraisal of paleotropical environmental change preserved in these successions. Paleoclimate records of central Montana and northern Utah that were documented during this investigation were compared with previously derived records throughout paleotropical Laurentia to elucidate the mechanisms responsible for preserved paleoclimate trends. From the Serpukhovian through the Pennsylvanian, paleoclimate records from tropical western Laurentia preserve a broad first-order trend of progressive aridification driven by northern plate migration through increasingly arid paleoclimate belts. Current biostratigraphic indicators suggest that discrete excursions in humidity (< 3 Myr in duration) preserved in the stratigraphic record of central Montana broadly coincide with estimates of the main eustatic signal of the LPIA, the C1 glacial interval, and initial onset of the C2 glacial interval, whereas northern Utah was characterized by a relatively consistent humid, to humid, seasonally-dry paleoclimate at that time. Paleotropical climate excursions (< 5 Myr in duration) that likewise broadly coincide with known glacial intervals are similarly recorded in stratigraphic records throughout the Laurentian paleotropics, though paleolatitude exerted an influence over the magnitude and character of these paleoclimate excursions. Late Mississippian and early Pennsylvanian paleoclimate oscillations preserved in central Montana that are superimposed on the first-order, tectonically-driven aridification trend were likely forced by a coupled northward migration and intensification of the ITCZ during glacial episodes. This pattern provides evidence of a teleconnection between paleotropical climate and Gondwanan ice dynamics during the LPIA.