Date of Graduation

5-2015

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Suarez, Celina A.

Committee Member

Hays, Phillip D.

Second Committee Member

Zachry, Doy L.

Keywords

Earth sciences; Carbon isotopes; Central Atlantic Magmatic Province; Chemostratigraphy; Moenave Formation; Whitmore Point Member

Abstract

Earth's climate is predominantly controlled by the fluctuation of greenhouse gases, specifically CO2 and CH4, over geologic time. The late Triassic is a period of abrupt climate change that has been associated with a disruption to the global carbon cycle due the emplacement of the Central Atlantic Magmatic Province (CAMP). Evidence has shown that this global carbon cycle perturbation may be the culprit for the end-Triassic extinction. The Whitmore Point Member of the Moenave Formation is a lacustrine deposit with a disputed age of either late Triassic or early Jurassic and currently no absolute dating techniques can be applied to estimate an exact age. Therefore, I propose that identification of the CAMP carbon cycle perturbation through carbon isotope chemostratigraphy of the Whitmore Point Member will be the best current age constraint. δ13Corganic and δ13Ccarbonate were analyzed in the lacustrine deposits of the Whitmore Point Member of the Moenave Formation to construct a carbon isotope chemostratigraphic profile. Carbon isotope evidence indicates that the environmental perturbation caused by the emplacement of the CAMP is present within the Whitmore Point Member. Data was collected at two localities: 1) The Whitmore Point Reference Section (Potter Canyon, Arizona) and 2) Warner Valley, Utah. Carbon isotope data from Potter Canyon reveals a distinctive 5.5 / and 2.75 / decrease in δ13Corganic and δ13Ccarbonate, respectively, in the lower portion of the Whitmore Point Member. Warner Valley does not show a prominent negative carbon isotope excursion but has been correlated to the positive isotope excursion and main negative isotope excursion exhibited within Potter Canyon. Correlation of carbon isotope curves from different localities also helps to regionally correlate the Whitmore Point Member. The identification of the Potter Canyon negative carbon isotope excursion is the first terrestrial record of the CAMP in western Pangea and provides more compelling evidence on the global impacts of the CAMP. Carbon isotope data along with previously published conchostracan data indicates that the end-Triassic extinction is within the lower portion of the Whitmore Point Member while the Triassic - Jurassic boundary is present within the upper portion. Therefore, I propose the age of the Whitmore Point Member to be late Triassic to early Jurassic.

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