Author ORCID Identifier

https://orcid.org/0000-0002-0615-9181

Semester

Spring

Date of Graduation

2023

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Geology and Geography

Committee Chair

Kathleen Benison

Committee Co-Chair

James Lamsdell

Committee Member

Amy Weislogel

Abstract

Bedded evaporites and associated red bed siliciclastics record saline lake and groundwater systems from Permo-Triassic Pangea. A major component of these red bed and evaporite systems is bedded gypsum. However, little attention has been paid to the textures of ancient gypsum. Observations of gypsum textures can refine interpretations of depositional environment and diagenetic history. This project describes textures of bedded gypsum from an outcrop of the Triassic Red Peak Formation (Chugwater Group) near Greybull, Wyoming.

This thesis uses fieldwork, petrography, and x-ray diffraction to describe an outcrop of the upper Red Peak Formation, with a focus on textures of bedded gypsum, to make interpretations about depositional environments. The study outcrop is comprised of alternating units of bedded gypsum and red bed siliciclastic mudstone. The red mudstone units are massive, rich in blocky peds, host abundant cross-cutting gypsum veins, and are interpreted to be paleosols. Three distinct lithologies of bedded gypsum are described and identified: bottom- growth gypsum, laminated gypsum, and clastic gypsum. Bottom-growth gypsum is interpreted to have precipitated at the bottom of shallow saline surface water bodies. Laminated gypsum likely formed in shallow saline lakes and mudflats; here, gypsum cumulates precipitated and were later reworked. Clastic gypsum units are composed of eolian-reworked bottom growth gypsum crystals deposited in sandflats and dunes. The study section of the Red Peak Formation was formed in shallow saline lakes and associated mudflats, sandflats, dunes, and desert soils.

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