Year of Publication

2017

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Arts and Sciences

Department

Earth and Environmental Sciences (Geology)

First Advisor

Dr. Kevin M. Yeager

Abstract

East Matagorda Peninsula in southwestern Texas is characterized geologically by active, regional-scale and near-surface growth faulting. Decimeter scale (up to 0.42 m) vertical displacement was recorded at the study site over a period of four years, not believed to be associated with growth faulting. This research tested the hypotheses that fault slip rates were correlated with sediment accumulation rates, and that the observed vertical displacement was produced by shrink-and-swell clays in near surface sediments. To quantify sediment accumulation rates, a suite of radionuclides (7Be, 137Cs, and 210Pb) were used. To understand the effects of shrink-and-swell clays, analyses including particle size distribution, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were completed. Additionally, the free swell index test (FSI) was used to record the swelling potential of the sediment. Strong correlation (R2 = 0.99) indicates coupling between mean fault slip rates and mean sediment accumulation rates. Near surface sediment clay size fraction percentages ranged from 0.96 - 6.26% containing more than 90% smectite. Based on FSI results, maximum volume change in the top six cm was determined to be 208%. The presence and behavior of shrink-and-swell clay minerals in the region is an important contributor to the vertical displacement observed.

Digital Object Identifier (DOI)

https://doi.org/10.13023/ETD.2017.271

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