Abstract

Lower Jurassic fluvio-lacustrine deposits of the Kayenta Formation and Whitmore Point Member reveal past climatic and tectonic conditions in SW Utah. Fluvial overbank deposits and sparse channel belts characterize the Kayenta’s intermittent fluvial system. Reconstructed dune morphology matches that of modern rivers. Downstream bar accretion, as in braided channels, is indicated by numerical reconstruction. Vertical succession of cross-set thickness and grain size shows covariance drop up-section. This, along with a decreasing sand/mud ratio of sandstones suggests that suspended load increased up-section. The Kayenta vertically progresses from poorly-channelized sandsheets to wide channel-fills. Paleohydraulics-derived sandstone body widths are smaller than those measured in the field, pointing to very wide paleoflow, which was relatively shallow. Calculations suggest paleodischarge and area of drainage comparable to the Indus River (Pakistan). Since channel style did not change longitudinally, greater preservation of overbank deposits distally was likely due to a greater rate of tectonic subsidence. Kayenta Formation and Whitmore Point Member lacustrine deposits, with variegated mudstones, contain widespread carbonate beds, mostly fine-grained but also including oolitic grainstone, rudstones, and ostracodal and peloidal packstones. Fossils xv include ostracods, bivalves, microbialites, and ganoid fish scales associated with iron concretions. Carbonate eogenesis was complex, with pedogenesis, intrasediment sulfate, early silicification, and dolomitization. Dolostones show higher δ18O and lower δ13C than limestones. Lacustrine dolomite, with higher Fe, Na, and Sr, formed under reducing waters, highly-evaporative conditions, and very early in diagenesis. It contrasts with lower Fe, Na, and Sr dolomite of fluvial floodplain carbonates, formed under less-reducing waters, less evaporation, and during late diagenesis. Temporal trends include decrease in lake size, increase of carbonate to siliciclastic ratio, intensified evaporation and lake recessions, and shift in lake water chemistry, from occasionally saline-alkaline to occasionally sulfate-rich. Lake basins were likely balanced-filled, with depocenter towards NW and lake margins towards SE. Lakes were shallow, low-grade, low-energy, and at times ephemeral. Lamination in carbonates possibly ensued from salinity stratification. Climate was seasonal, semi-arid to sub-humid. Vertical trends suggest long-term aridification. Lack of mature paleosols despite pedogenesis likely results from relatively fast rates of tectonic subsidence in the region at the time.

LLU Discipline

Earth Sciences

Department

Earth Science

School

School of Medicine

First Advisor

Kevin E. Nick

Second Advisor

Roberto E. Biaggi

Third Advisor

Benjamin L. Clausen

Fourth Advisor

V. Leroy Leggitt

Fifth Advisor

Ronald Nalin

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

2020

Date (Title Page)

5-2020

Language

English

Library of Congress/MESH Subject Headings

Sedimentary rocks--Utah.

Type

Dissertation

Page Count

xv, 195 p.

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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