Abstract

The Permian Coconino Sandstone of northern and central Arizona is widely recognized as a classic eolian dune deposit, with conspicuous large-scale cross-beds that are interpreted as preserved dune foresets. On modern bedforms, fine-scale processes – which include grainflow, grainfall, and ripple migration – transport and deposit sediment, and these may provide useful analogs for interpreting ancient deposits. Even though the Coconino Sandstone is well known, such fine-scale process models have not been adequately developed to explain its cross-bed deposition. Furthermore, observed discrepancies between the sandstone and some eolian criteria suggest that additional study is needed to explore and refine these process models. To interpret cross-bed depositional processes, sedimentary textures and structures were described in multiple outcrops across northern Arizona. A methodology was developed to disaggregate the well-cemented sandstone, which is characteristic of most localities. These disaggregation methods are less tedious than petrographic approaches, and allow for expedited textural analysis of many samples. Cross-beds were observed to be laterally extensive along strike, with most dip angles ranging from the mid-teens to mid-twenties. Some cross-bed sets are coarser at their bases, but others exhibit variable changes in grain size with no significant vertical trends. While both massive and laminated textures occur, these do not show a preferred distribution within the studied cross-bed sets. Lamination – as observed in highresolution scans of thin sections – appears to exhibit both normal and reverse grading, but these trends are difficult to define where laminae contacts are diffuse. Diagenetic features, which include stylolite seams and large pores, mimic primary structures and likely relate to both depositional and post-depositional processes. These features also show no preferred vertical distribution within their respective cross-beds. Observed textures and sedimentary structures suggest that the cross-beds may consist of grainflow and grainfall deposits, but these are difficult to differentiate at outcrop and thin-section scales. Such a model explains massive textures and vertical coarsening in some outcrops, but also predicts that the beds may differ from those produced by modern grainflows (due to the inclusion of grainfall). This characterization of fine-scale processes will serve as a critical piece of the puzzle as researchers seek to understand the deposition of the Coconino Sandstone.

LLU Discipline

Earth Sciences

Department

Earth Science

School

School of Medicine

First Advisor

Leonard R. Brand

Second Advisor

Raúl Esperante

Third Advisor

Ronald Nalin

Fourth Advisor

Kevin E. Nick

Fifth Advisor

John H. Whitmore

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

2019

Date (Title Page)

6-2019

Language

English

Library of Congress/MESH Subject Headings

Sand dunes; Sandstone Sedimentary structures; Carbonate minerals; Scanning electron microscopy; Particle analysis

Type

Dissertation

Page Count

xvii, 434 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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