Date of Award

1-2021

Document Type

Thesis

Degree Name

Master of Science (MS)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Sandra Passchier

Committee Member

Ying Cui

Committee Member

Josh Galster

Abstract

At the Eocene-Oligocene transition (EOT), approximately 34 million years ago (Ma), the Earth’s climate changed from a warm greenhouse to a cooler climate which resulted in ice-sheet growth and stable continental-scale ice sheets in Antarctica. Hole 696B of the Ocean Drilling Program Leg 113 drilled in 650 m of water depth on the South Orkney Microcontinent spans the entire EOT. Cores 53R and 54R are dated at lower Oligocene (~33.1 to ~33.5 Ma) and total ~14 meters in thickness from ~549 to ~564 mbsf. Ice-rafted debris (IRD) in sediment cores gives insight into the extent of glaciation in West Antarctica, as well as the evolution of deep-sea cooling during the EOT. Distinguishing between sea-ice rafted debris (SIRD) and iceberg rafted debris (IBRD) provides information about weathering processes and depositional environments.

Laser Particle Size Analysis was used to determine the volume percentage of sediment in different size classes, i.e. the grain size distribution of 113 samples. IRD was identified by examining quartz grains ˃150 μm. Samples with large volume percentages of coarse grains were sieved to obtain the sand fraction of grains >150 μm. 5 samples with the greatest yield of grains ˃150 μm were selected for microtexture analysis using the Scanning Electron Microscope (SEM). SEM with Energy Dispersive Spectroscopy (EDS) was used to identify quartz grains. SIRD and IBRD grains were distinguished by examining physical topography and microtextures in Secondary Electron images.

Quartz grains were categorized into 7 groups based on roundness, grain relief, amount of silica dissolution, and presence of grain fractures. The 7 types are further grouped by IRD type where IBRD types have little to no silica dissolution, angular/sub-angular grains, with fractures present; SIRD types have silica dissolution, rounded/sub-rounded grains, with little to no fractures present. 185 grains from 5 samples were analyzed using EDS and SEM, 105 of which were quartz grains. Based on the grain type groupings, 35% of the quartz grains are IBRD and 60% are SIRD, and 5% is not glacially influenced, and therefore, not an IRD type of grain. The ratio of SIRD to IBRD is uniform in sample 3. SIRD grain types are dominant in the rest of samples 1, 2, 4, and 5. This research concludes that IRD is present in the early Oligocene 33.48 Ma and supports that ice sheets were present in West Antarctica with widespread cooling and extensive glaciation during this time.

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