Date of Award

Spring 1-1-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geological Sciences

First Advisor

Gifford H. Miller

Second Advisor

Robert S. Anderson

Third Advisor

John T. Andrews

Abstract

Evidence is poorly preserved in the geologic record for the evolution of Laurentide Ice Sheet (LIS) erosion, dynamics, and basal thermal regime patterns. It has been hypothesized that changes in LIS subglacial conditions and erosional efficiency drove the enigmatic mid-Pleistocene transition (MPT) from 41- to 100-ka climate cyclicity. In this dissertation, a variety of archives and tools are used to explore the 2.7+ Ma history of ice-sheet erosion on Baffin Island in the eastern Canadian Arctic and the possible role of the LIS in the MPT.

We compile till geochemistry and cosmogenic radionuclide data to identify a coherent spatial pattern of fresh till and older, more weathered till on the landscape. We interpret the presence of such weathered till to be the result of an expansion in cold-based ice cover prior to 1 Ma, and by that time the fiorded Baffin Island coastline must have developed close to its modern configuration.

Subglacially precipitated calcite crusts preserved at several sites on the interior plateaux of Baffin Island provide unique insight into LIS erosion during the last glaciation. U-series dating and O, C, and Sr isotope analyses reveal that the majority of erosion during the last glaciation must have occurred prior to 25-15 ka, and the extent of cold-based ice expanded during deglaciation.

The Clyde Foreland Formation (CFF) records at least seven Plio-Pleistocene glaciations. Combining amino acid racemization and 10Be-26Al isochron burial dating, we construct the first absolute chronological framework for the CFF. The oldest sediments are Early Pleistocene or latest Pliocene and contain an exceptionally high meteoric 10Be inventory consistent with regolith erosion. Younger tills both pre- and post-dating the MPT contain no detectable geochemical or mineralogical evidence of regolith erosion.

Regolith was most likely removed from beneath the Foxe Dome of the LIS prior to the MPT, and the subglacial deformation of such sediment was not responsible for any regional changes in ice sheet dynamics related to the MPT. However, changes in the LIS basal thermal regime on Baffin Island occurred coincident with or prior to the MPT and may have contributed to the MPT.

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