Date of Graduation

8-2019

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor

Glenn Sharman

Committee Member

Celina Suarez

Second Committee Member

Barry Shaulis

Keywords

Detrital Zircon, end-Triassic extinction, Moenave Formation, Petrology, Provenance, Triassic-Jurassic Boundary, U-Pb Geochronology

Abstract

In southwestern Utah and northeastern Arizona, Moenave Formation (latest Triassic(?)-Jurassic) is bracketed by well-studied Mesozoic units extensively sampled for detrital zircon geochronology and is poorly documented in regard to provenance, representing an important gap in knowledge. The Moenave Formation provides a unique opportunity to employ detrital zircon U-Pb geochronology and sandstone petrography relevant to completing the paleogeographic, evolutionary, and climatic story of the region. This study aims to characterize the sedimentary provenance of the Moenave Formation and to identify, or at least improve constraints on, the stratigraphic position of the Triassic-Jurassic boundary (TJB) and placement of the end-Triassic extinction (ETE), if present at all, within the Moenave Formation. The present work (1) expands the database of detrital zircon data for the Moenave Formation with U-Pb ages from 5190 individual detrital zircon analyses from 22 samples collected from three study sites and (2) adds petrographic analyses using 400 modal point counts per thin section for 26 samples. This study reports individual and composite U-Pb age distributions and provenance ternary diagrams of the Moenave Formation and surrounding units, as well as apply nine different maximum depositional age (MDA) calculations from the resulting detrital zircon data. Comparison of composite U-Pb age distributions and petrographic detrital modes show strong similarities in sediment dispersal and composition between the Moenave and Kayenta formations. The age distribution of the Moenave Formation consists of dominant age peaks that indicate the Moenave Formation was derived from a number of sources including the Cordilleran arc, Appalachian Orogeny, Grenville Orogeny, Mesoproterozoic plutons, and Yavapai-Mazatzal sources. Conservative MDA estimates (YC2σ, Y3Zo, YSP, and the τ method) are consistent with a stratigraphic placement of the ETE within the lower DCM. These results are in agreement with existing provenance and chemostratigraphic interpretations regarding the stratigraphic location of the ETE.

Appendix A.xlsx (1026 kB)
Appendix B.xlsx (482 kB)

Available for download on Thursday, August 12, 2021

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