Date of Award

May 2014

Degree Type

Thesis

Degree Name

Master of Science

Department

Geosciences

First Advisor

John L. Isbell

Second Advisor

Margaret L. Fraiser

Committee Members

Erik L. Gulbranson

Keywords

Argentina, Invertebrate Fossils, Late Paleozoic, Paleoecology, Patagonia, Stratigraphy

Abstract

The glacial and non-glacial intervals of the Late Paleozoic Ice Age (LPIA) are of great interest because they are our best deep time analogue for Pleistocene climate change. The changes and adaptations of the biota, as seen in the rock record, can serve as a proxy for understanding future trends in Earth's climate system. Most of the known LPIA marine faunal data come from low-latitudinal regions, and thus have been used as a global proxy. However, modern organisms in the low-latitudes (far-field basins) respond differently to a changing climate relative to marine organisms in the polar regions (near-field basins). In high-paleolatitude regions, glacial and non-glacial communities were ecologically dissimilar and may have had a dissimilar response to climate change relative to contemporaneous fauna at low-paleolatitudes. It is important to understand the how different global climate regimes affected the adaptability of the fauna that lived within them.

This study focuses on a high-latitude fauna from the Tepuel-Genoa Basin in Chubut Province in Patagonia, Argentina in order to better understand the responses of a high-latitude fauna to changing environmental conditions, and to develop a more robust understanding of climate change and its impacts on the biosphere. The Pampa de Tepuel Formation records Mississippian to Permian depositional history within the Tepuel Basin. Based on current age models for the basin, the analyzed section reported here occurs in the upper portion of the Lanipustula biozone, likely from the late Bashkirian to the early Moscovian. Field work consisted of counts of six fossil beds and a 276-meter stratigraphic section was measured and described in order to identify the lithofacies that indicate changes in depositional environments. The fossil count data was analyzed using various methods such as relative abundance comparisons, diversity indices and multivariate tests in order to determine and better define the paleoecology of the Lanipustula biozone and its fauna, which has not been accomplished to date.

This particular section of the Pampa de Tepuel Formation in the Sierra de Tepuel is representative of at least two depositional sequences, with evidence of a late highstand and falling stage systems tract in the lower portion of the section followed by a transgressive systems tract at the top of the section. There is also the appearance of slump and slide blocks throughout the section and clinoforms in the middle of the section suggesting that clastics periodically made it into the deeper parts of the basin. Much of the strata described in this study can be related to normal marine processes acting on the outershelf and slope of the Tepuel Basin rather than having occurred in a glacial marine setting. There are only minor glacial signatures observed within this portion of the formation. However, other parts of the Pampa De Tepuel Formation did accumulate in a glaciomarine setting. The paleoecology data suggest that there may be a new faunal composition near the top of the section that does not fit into the Lanipustula biozone, although there is no statistically significant difference taxonomically based on the relative abundance values and diversity indices. Results of the multivariate analyses of the paleocommunities seem to reflect that changes in the local depositional and environmental settings may be the cause for any changes seen in the faunal assemblages within the previously established Lanipustula biozone. By continuing research on the LPIA, we may be better able to understand the fundamental factors of species and ecosystem instability because of the substantial environmental and climatic shifts that occurred.

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