Earth and Atmospheric Sciences, Department of
Date of this Version
Spring 4-16-2010
Abstract
Determining how the tropics respond to glaciation is important for improving our global understanding of icehouse worlds. The impetus behind this study is to identify the far-field impacts of Gondwanan glaciation during the Early Permian. Impacts including climate and sea-level change should be evident in sensitive carbonate systems, such as the upper Paleozoic paleotropical strata in the Orogrande Basin. A sequence stratigraphic and stable isotopic approach is used to examine the effects of late Paleozoic climate change in the Orogrande Basin during the acme and subsequent demise of the late Paleozoic ice age.
Sequence stratigraphic analysis suggests the occurrence of a major unconformity at the Pennsylvanian-Permian boundary, which coincided with the onset of major Gondwanan glaciation. Additionally, two transgressive events during the Sakmarian and Artinskian broadly correlate with the end of major glacial epochs in eastern Australia.
Stable isotopic analysis suggests periods of subaerial exposure from the Gzhelian through the early Sakmarian, which are associated with lower carbon isotope values. Carbon isotope values return to global averages after the mid-Sakmarian. Two smaller negative isotope excursions (1.5‰ decrease in carbon isotope values) occur within upper Sakmarian-Kungurian strata. These lower carbon isotope values are associated with a facies change to shallower conditions that coincided with periods of renewed expansion of glacial ice across parts of Gondwana. Isotopic interpretations are consistent with the relative sea level reconstructions inferred from the sequence stratigraphic analysis.
Examination of other paleotropical records suggests that the overall stratigraphic pattern inferred for the Orogrande Basin reflects a global signal. Paleotropical carbonate platforms experienced significant subaerial exposure in the earliest Permian, which is represented by a sequence boundary or a basinward shift in facies. This eustatic drop coincided with the initiation of major glaciation across Gondwana. Results from this study suggest that carbonate strata from the Orogrande Basin responded to glacial epochs evident in the Gondwanan record. This suggests that these glacial events were of global significance.
Comments
A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Geosciences (Geology), Under the Supervision of Professor Tracy D. Frank. Lincoln, Nebraska: May, 2010
Copyright (c) 2010 Jesse Koch