Geological Sciences electronic theses and dissertations (MU)
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The items in this collection are the theses and dissertations written by students of the Department of Geological Sciences. Some items may be viewed only by members of the University of Missouri System and/or University of Missouri-Columbia. Click on one of the browse buttons above for a complete listing of the works.
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Item Resolving taphonomic biases in lower Cambrian shelly fossil assemblages of the Mernmerna Formation, South Australia(University of Missouri--Columbia, 2025) Mate, Clarissa Lynn; Jacquet, Sarah[EMBARGOED UNTIL 12/01/2026] During the earliest Cambrian, a diverse group of small shelly faunas (SSFs) emerged, whose remains have been used to infer animal phylogenetic affinities, paleoecology, as well as to serve as valuable biostratigraphic markers. This record owes its high resolution to the pervasive phosphatization of several SSFs, yielding exceptional morphological detail, though also exhibiting selective taphonomic biases. In the MMF TAPH section of the Mernmerna Formation (Cambrian Series 2, Stage 3) in the Bunkers Range of South Australia, we quantify sources of introduced bias and assess their implications for interpreting the paleoecology and paleobiology of SSF assemblages. The study of SSF typically relies on destructive acid maceration to extract microfossils from host limestone. As effective as this process is for isolating fossils with insoluble elements (particularly phosphate), it preferentially dissolves calcareous material that may be present. In the first of two case studies, paired destructive and non-destructive methodologies reveal that this dissolution introduces taxonomic and mineralogical biases into the fossil assemblages obtained. The second case study focuses on a specific enigmatic microfossil, Stoibostrombus crenulatus, whose organismal affinity has eluded confident taxonomic placement. Using comparative anatomy in tandem with various microimaging techniques, we conducted a detailed examination of S. crenulatus, fossil priapulids, and the modern Priapulus caudatus, which supports a potential affinity between the fossil sclerites and the scalids of priapulid worms.Item The rise and flow of dacitic lavas : experimental insights into crystal-rich magma rheology, outgassing, and emplacement(University of Missouri--Columbia, 2025) Herbst, Thomas Gregory; Schiffbauer, James D.This research explores the rheological behavior and outgassing dynamics of crystal-rich silicic magmas. Using analogue experiments, the work in chapter 2 shows that magmas with 50–60 vol% crystals struggle to release gas efficiently due to competing viscous and brittle deformation, causing an increase in gas accumulation and explosive potential. Chapter 3 explores the rheological behaviors of dacite lava flows from the 1915 eruption of Lassen Peak volcano (USA). Field evidence suggests that the lavas advanced as thick rigid plugs sliding over a narrow basal shear zone. Having both rheological and temporal constraints, we inferred that the second lava flow was slightly hotter and/or wetter and extruded faster with fewer microlites than the initial lava dome. Chapter 4 presents the first rheological experiments on multiple andesitic-trachytic lava flows that extruded at the same time during the 1846 eruption of Volcán Quizapu (Chile). Crystal-poor Newtonian-like flows, characterized by a smooth morphology, likely traveled faster compared to their sibling flow with higher crystallinity and non-Newtonian rheology. Together, the findings from these field- and lab-based studies underscore the importance of crystallinity in controlling magma rheology, outgassing, and emplacement, offering critical insights into the eruptive behavior of silicic magmas.Item Digital spaces and Cambrian facies : terminological analyses and case studies in geoscience virtual fieldwork & paleoenvironments and taphonomic windows of Australian lower Cambrian deposits(University of Missouri--Columbia, 2025) Speir, Eury; Jacquet, Sarah[EMBARGOED UNTIL 08/01/2026] This dissertation is divided into two volumes, each encapsulating two stand-alone projects. Volume One examines virtual field education within the geosciences, including the pedagogical and experiential considerations in naming virtual field opportunities, and documents the implementation of a virtual field trip within the University of Missouri's introductory geology curriculum. Volume Two examines the sedimentological, geochemical, and environmental factors that influence fossil distribution and preservation through an analysis of the lower Cambrian deposits in South Australia. Virtual field opportunities provide a digital means for geoscience students to explore sites of interest, and their usage has increased in popularity in recent years. This rise in popularity has led to the use of varying terminology to describe similar experiences. We conducted a qualitative content analysis on 97 unique publications related to virtual field opportunities in the geosciences, followed by a series of multiple correspondence analyses to investigate the relationships between pedagogical and experiential factors and their impact on naming convention. We constructed a new lexicon to guide naming selection for future virtual field opportunities: virtual tour, virtual field trip, virtual field experience, and generated field environment. Using the newly developed lexicon, we developed a virtual field trip of Rock Bridge Memorial State Park for the introductory geology program at the University of Missouri. We employed an iterative design process that utilized student feedback to improve the functionality of the virtual field trip. Our findings suggest that providing students with both physical and virtual methods of interacting with a field site results in higher academic achievement, particularly when encountering the virtual medium first. The lower Cambrian deposits of the Arrowie Basin, South Australia, are host to well-documented small shelly fauna assemblages, with a large component often preserved through secondary mineralization. Understanding the sedimentological, environmental, and geochemical factors that enhance preservation potential, either through mobilization of phosphorus-rich waters or through primary distribution, can provide insight into the biostratigraphic utility of these faunas. We documented a condensed interval of repeated phosphatic hardgrounds in the Elder Range, Arrowie Basin, and employed sedimentological, compositional, and geochemical techniques to investigate the relationship between faunal preservation and hardground development. Additionally, we applied a suite of geochemical proxies to contrasting fossil-rich and fossil-poor localities to determine whether primary distribution or secondary alteration was the cause of an unusual absence of fauna in the Chace Range. Results show that phosphatic hardgrounds formed over multiple phosphogenic cycles, thereby enhancing the preservation potential of calcareous faunas through secondary mineralization; however, the hardgrounds themselves hinder recovery. These phosphogenic cycles foreshadow a regional unconformity and subsequent sea level rise. Results from carbon and sulfur isotopic records suggest the development of anoxic deep waters in the Chace Range while shallower environments remained oxygenated. This stratification of the water column discouraged the distribution of faunas in deeper, anoxic waters, which ultimately resulted in the paucity of fauna observed in the Chace Range.Item Seismic anisotropy, attenuation, and site amplification study of Southeast Asia and northern Los Angeles Basin(University of Missouri--Columbia, 2025) Islam, Md Mohimanul; Sandvol, Eric A.[EMBARGOED UNTIL 08/01/2026] Understanding the structure and dynamics of the Earth's crust and upper mantle is fundamental to advancing our understanding of plate tectonics and seismic hazard assessment. This dissertation presents four integrated studies focused on high-resolution imaging of the upper mantle, lithosphere, and near-surface effects of ground amplification, using seismic anisotropy, attenuation, and site amplification analyses. Together, these four chapters span diverse tectonic environments, from the highly oblique Indo-Burma subduction system in Southeast Asia to the sediment-filled basins of northern Los Angeles, providing critical insights into mantle deformation, crustal rheology, and seismic ground motion amplification. First, shear wave splitting analysis of teleseismic phases (SKS, SKKS, and PKS) is used to characterize mantle flow and deformation beneath the Indo-Burma subduction zone and the eastern Indochina Peninsula. Results reveal trench-parallel N-S mantle flow beneath the forearc region, induced by prolonged northward motion of the Indian plate and preserved lithospheric fabric due to ongoing convergence, as well as E-W fabric in the east of the Sagaing Fault, likely associated with asthenospheric flow from the Hainan Plume. Second, lithospheric-scale attenuation structures are investigated across Southeast Asia by seismic quality factor (Q) tomography of regional seismic phases. Using both the two-station method and reverse two-station method applied to regional Lg and Sn phases, this study uncovers a heterogeneous attenuation structure that correlates strongly with crustal thickness, volcanic centers, and tectonic boundaries. Particularly notable is the low Q and frequency-dependent attenuation beneath the Tengchong volcanic arc and Indo-Burman Ranges, indicating the presence of partial melt and pervasive crustal scattering. Third, a novel site response mapping is conducted in Yangon, Myanmar, using a dense nodal seismic array, demonstrating that dense small-aperture arrays can resolve site amplification variability at city-block scales, crucial for improving urban seismic hazard models. Finally, reverse two-station analysis is used to map crustal attenuation and site response across the northern Los Angeles Basin, revealing complex amplification patterns tied to basin depth, geometry, and fault proximity. Collectively, this work addresses critical observational gaps in tectonically complex and urbanized regions, enhances our understanding of deep and shallow Earth structures, and provides a framework for improving physics-based ground motion simulations and seismic hazard models.Item Gravitational instabilities in the lithosphere : numerical studies(University of Missouri--Columbia, 2025) Gou, Yiren; Liu, Mian[EMBARGOED UNTIL 08/01/2026] Gravitational instability is one of the fundamental mechanisms controlling the evolution of planets. It drives convection in the Earth's mantle and core, as well as in the atmosphere. However, being cold and stiff, the Earth's lithosphere is supposed to resist the growth of internal gravitational instability. In this dissertation, I integrate numerical experiments with geophysical observations and geological data to explore three Earth's lithospheric deformation processes where gravitational instability plays a major role: salt diapirism in sedimentary basins, Archean dome-and-keel structures, and small-scale removal of mantle lithosphere beneath the central Andes. In the study of salt diapirism, high-resolution thermomechanical models reveal that an interplay of salt buoyancy, differential loading, and tectonic stresses drives salt diapirs. Findings challenge the conventional dichotomy of active versus passive diapirism and underscore the importance of plastic deformation in allowing the piercement of salt rocks into stiff overburdens. For Archean dome-and-keel structures, numerical experiments indicate that their formation through partial convective overturn is more difficult than previously assumed. The favorable conditions for forming dome-and-keel structures are synchronous voluminous mafic-ultramafic magma eruption and TTG (Tonalite--Trondhjemite--Granodiorite) magma intrusion, possibly related to mantle plume activity. Therefore, dome-and-keel structures are products of localized thermal anomalies rather than evidence of a globally dominant vertical tectonic regime suggested in previous studies. To explore the formation of discrete low-velocity zones beneath the central Andes, numerical experiments highlight that composition-induced convective dripping can cause the small-scale removal of the mantle lithosphere, triggered by rheological weakening and lithospheric heterogeneity. The small-scale removal of the mantle lithosphere may account for the seismic low-velocity zones, magmatism, and topographic evolution in the central Andes. This dissertation highlights that the lithosphere can be locally weakened to permit the growth of gravitational instability. Gravitational instability plays a major role in lithosphere tectonics across diverse spatial scales and geological timeframes. By integrating numerical methods with geophysical and geological studies, this dissertation enhances our understanding of lithosphere evolution from the perspective of gravitational instability.