Date of Award

1-2019

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

Matthew Gorring

Committee Member

Huan Feng

Abstract

Antarctic sediment cores collected during Leg 113 of the Ocean Drilling Program (ODP) provide important paleoclimatic evidence over the Eocene-Oligocene transition (EOT) – a period of global cooling from greenhouse to icehouse approximately 34 million years ago. The cores, collected thirty years ago, offer new research opportunities with the application of an updated age model for the EOT in West Antarctica (Houben et al., 2013). The core from ODP Site 696 in the Weddell Sea contains a complete EOT record, with a remarkably green stratum attributed to glauconite dated to the late Eocene. The sediment composition, clay mineralogy, and geochemistry of this interval was investigated in the context of recent particle size data and an improved age model.

Smear slide and X-ray diffraction analyses confirm the green mineral is an authigenic, incipient form of glauconite with a minor contribution of expandable montmorillonite to the clay fraction. Major and trace element analysis show deposition occurred under reducing, suboxic conditions with low detrital input for samples with a high fraction of glauconite. Alteration of illite by Fe2+ substitution is the likely formation mechanism, possibly catalyzed by an increase in oceanic productivity. The highest-glauconite sediment interval, dated to ~34.5-35 mya, suggests a marine transgression peak in the South Orkney Microcontinent region during this time caused by crustal subsidence prior to the onset of full continental glaciation. These results document early effects of ice sheet advance in the Weddell Sea, though more research is needed to determine whether the impacts are caused by glaciation from East or West Antarctica.

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