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Date Permissions Signed

7-1-2021

Date of Award

Fall 2021

Document Type

Masters Thesis

Department or Program Affiliation

Department of Geology

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Foreman, Brady

Second Advisor

Dahl, Robyn

Third Advisor

Mitchell, Robert J. (Geologist)

Fourth Advisor

Pfeiffer, Allison

Abstract

Earth's climate experienced a set of hyperthermal events during the greenhouse climate state of the early Paleogene. The Paleocene-Eocene Thermal Maximum (PETM) was the largest of these abrupt global warming events, occurring at ~56 Ma and lasting for ~200,000 years. The PETM is identifiable by a large negative carbon isotope excursion and associated with significant changes in global temperature, hydrology, ocean chemistry, and biology. Subsequent smaller hyperthermal events appear to have commensurately smaller effects on marine environments, but the scaling of the complementary nonmarine environmental responses is unclear.

The Bighorn Basin of northwest Wyoming contains the most detailed nonmarine record of the PETM, and recent work has identified a significant perturbation of fluvial deposition associated with it. The PETM generated a thick and laterally extensive sandbody likely due to enhanced channel mobility potentially mediated by higher sediment flux related to an increase in rainfall variability. This study compares and contrasts fluvial deposition spanning a younger hyperthermal event at ~53 Ma, the ETM2 event, which was approximately 50,000 years in duration and displays a carbon isotope excursion with half the magnitude of the PETM. Herein I present sandbody geometries, lithofacies patterns, flow depths, and paleocurrent patterns spanning the ETM2 for comparison to PETM-induced fluvial changes. I find channel-fills are dominated by fining upward sequences of trough crossbedding and ripple cross lamination and abundant bar clinoform deposition. Sandbodies are typically single-storied and 3 meters in thickness. Notably, there are no significant changes in fluvial deposition across the ETM2. Several hypotheses may explain this observation: (1) there were no major hydrologic changes associated with the ETM2; (2) there were no major changes in vegetation associated with the ETM2; and/or (3) environmental perturbations were insufficient to overcome the internal autogenic thresholds of the river systems. These three hypotheses are not mutually exclusive, and each is evaluated in the context of existing datasets.

Type

Text

Keywords

fluvial, stratigraphy, hyperthermal, ETM2, Bighorn Basin, signal shredding

Publisher

Western Washington University

OCLC Number

1286695774

Subject – LCSH

Geology, Stratigraphic--Eocene; Sedimentary basins--Wyoming; Alluvium--Wyoming; Lithofacies--Wyoming

Geographic Coverage

Bighorn Basin (Mont. and Wyo.)

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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