Colby Ford

Abstract

The Canyon Overlook Trail of Zion National Park follows an outcrop of Navajo Sandstone, which displays a uniquely well-exposed assemblage of features associated with failure of the lee face of a large eolian dune, and run-out over an expanse of interdune sediments downwind of that bedform. Exposed features include dramatic folds in the interdune succession and a stacked series of thrust sheets incorporating both interdune and overlying dune deposits. Thrust surfaces display consistent strikes, parallel to those of undeformed foresets, and incorporate zones of brittle failure and fluid deformation, including folds overturned in the direction of foreset dip. These features correspond to predictions made by the Horowitz (1982) model of dune collapse, formulated from less fortuitously exposed architectures in the Navajo Sandstone. Unlike the Horowitz (1982) model, however, this site preserves distinct indications that the bulk of deformed material accumulated above the level of the contemporary interdune surface, in an aggradational succession. Paleotopographic reconstruction, based on preserved facies relationships at this site, indicates the presence of a large dune, partially encroaching upon a well-developed wet interdune succession, made up of two half-meter carbonate mud layers, separated by a meter of medium-grained sand. Trapping of pore water pressure between these mud layers during liquefaction reduced shear strength in this interval, facilitating the collapse of the lee face of the upwind dune into the interdune area, and transmitted resultant shear forces to distal portions of the interdune expanse, in the shallow subsurface. Shear failure developed along bedding planes in the horizontally laminated carbonate muds, which provided both lubrication of the shear surfaces and structural support for the preservation of coherent thrust sheets during production of an imbricated succession of shear zones in the toe portion of the slump. Individual shear surfaces exposed in this outcrop extend for up to 50 m along strike and dip north up to 55°. Upturned mud layers in the toe of the slump resisted deflation, promoting preservation of an irregular interdune topography, over which the reorganized dune ultimately advanced.

LLU Discipline

Geology

Department

Earth and Biological Sciences

School

School of Medicine

First Advisor

Nick, Kevin E.

Second Advisor

Bryant, Gerald

Third Advisor

Buchheim, H. Paul

Degree Name

Master of Science (MS)

Degree Level

M.S.

Year Degree Awarded

2015

Date (Title Page)

12-2015

Language

English

Library of Congress/MESH Subject Headings

Sediments - Surfaces; Surfaces - Deformation of; Sediments (Geology) - Permeability; Geology; Stratigraphic - Jurassic; Geology; Stratigraphic - Triassic; Formations (Geology) - West (U.S.); Paleohydrology; Navajo Sandstone

Subject - Local

Dune collapse; Sand dunes; Soft-sediment deformation; Interdune

Type

Thesis

Page Count

72

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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