Theses and Dissertations - Department of Geological Sciences

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Browsing Theses and Dissertations - Department of Geological Sciences by Author "Andrus, Fred"

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    First Report of Carbonate Mudbanks in Cuba: a Geospatial Comparison with Florida Bay, USA, and Implications on Underlying Controls
    (University of Alabama Libraries, 2021) Nibert, Lucas Allen; Minzoni, Marcello; University of Alabama Tuscaloosa
    Carbonate mudbanks and associated islands of Florida Bay are shallow-water to intertidal, linear Holocene sedimentary accumulations forming basins 1.5-3 m deep. The resulting reticulate-patterned banks and basins have only been documented in Florida Bay, where they developed landward of the shelf margin, protected by the Pleistocene ridge of the Florida Keys. Although extensively studied, the origin of mudbanks is unclear. Apparently similar depositional features occur south of Florida Bay in Bahia de Santa Clara, Cayo Santa Maria, and Cayería de Diego Pérez along the northern and southern coasts of Cuba. Comparative geospatial analysis of these sites establishes potentially novel localities for shallow-water carbonate mudbanks. The shallow lagoons of Florida and Cuba vary in size and are dissected into smaller basins or “lakes” by linear or arcuate sediment accumulations. Banks, keys, and platform-margin archipelagos were mapped using satellite images at each site to quantify and compare relative abundance and physical attributes of these major depositional environments. Florida Bay mudbanks cover at least twice the relative area as banks at the other sites. There is no clear relationship between the degree of open-ocean exchange and relative area of shelf elements. Banks are generally oriented perpendicular to winter storm winds in Florida Bay, Cayo Santa Maria, and Cayería de Diego Pérez in the Gulf of Batabano, but not in Bahia de Santa Clara. We conclude that there is not sufficient evidence to determine the processes responsible for bank genesis, but the initial configuration of banks was likely re-oriented by winter storm winds and other physical sedimentation processes. Mudbank-dominated lagoons may serve as modern analogues for transgressive carbonate strata in shallow, protected, land-attached shelf systems. Physical sampling in Cuba, when possible, and comparative stratigraphic analysis with Florida Bay will yield additional insight into Holocene evolution of carbonate shelf environments.
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    Floods and nutrients in Weeks Bay, AL: an evaluation of long-term environmental change and human impacts on coastal estuaries
    (University of Alabama Libraries, 2019) Parker, Lauren Elizabeth; Minzoni, Rebecca T.; University of Alabama Tuscaloosa
    Climate change and sea level rise are major concerns for coastal environments, with predicted increased storm intensity, coastal erosion, and ecological degradation. Long paleoenvironmental records can advance our understanding of these effects and help improve coastal resiliency to future sea level rise and climate change. Sediment archives are employed to build long paleo-environmental records for Weeks Bay, Baldwin County, AL. Grain size, organic carbon and nitrogen stable isotopes, elemental composition, and diatom assemblage and abundance are integrated to construct a multi-proxy paleoenvironmental record covering the past ~7000 years, from the Mid-Holocene to present based on 14C and 137Cs ages. The δ13C and δ15N, grain size, and terrestrial and marine elemental proxies indicate flooded marine conditions during the formation of the bay approximately 6600 years ago, and a transition from a more marine-influenced environment to a more brackish/freshwater bay environment as the estuary became more restricted approximately 2000 years BP. Anthropogenic influence in Weeks Bay over the past 200 to 300 years is expressed as changes in redox and nutrient-associated elemental proxies (Fe, Zn, Mn, Cr, V) with increase in C and N weight percent. Comparisons of TOC:TN to the Redfield Ratio confirms that nitrogen is a limiting factor in Weeks Bay, meaning nitrogen from anthropogenic sources potentially increased ecological feedback, signified by algal blooms. 34 flood events were interpreted from sand layers in the last 2000 years, with two periods of high flood activity coinciding with the Medieval Climate Anomaly and the Little Ice Age, illustrating potential correlation between geologically short-term climate changes and storm events. Stricter management of agricultural and industrial run-off with increased wetland conservation can aid in the reduction of algal blooms in Weeks Bay. Paleoenvironmental record studies of Weeks Bay and other estuaries across the Northern Gulf of Mexico help build a more complete understanding of past and present response of estuaries to sea level and climate events, which can be used to better predict their future.
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    Investigating Rare Biomineralization Structures in Trilobites
    (University of Alabama Libraries, 2020) Greenberger, Raya; Perez-Huerta, Alberto; University of Alabama Tuscaloosa
    Trilobites, a diverse class of arthropods, inhabited a range of marine environments from Early Cambrian to Permian time, and their abundance and various morphologies are significant in the interpretation of evolution, paleoenvironments and biostratigraphy. Their preservation is due to their calcitic structures formed by biomineralization. Investigating biomineralization processes in trilobite can enhance our understanding of the evolution of trilobites. This thesis presents two rare biomineralization structures in trilobites; the Asaphus trilobites, displaying stalk eyes, varying in length and width, and the Eldredgeops rana trilobites, displaying patterns on their shells that may have served as an additional visual system or amorphous calcium carbonate reservoirs. The eyes of Asaphus kowalewski, Asaphus cornutus and Asaphus punctatus and the spots on the Eldredgeops rana were characterized using a scanning electron microscope for imaging, energy dispersive x-ray spectroscopy and electron backscattered diffraction mapping to obtain elemental composition and crystallographic orientation and to observe microstructural arrangements. Further analyses were done on the Eldredgeops rana trilobites using atomic force microscopy and Raman spectroscopy to study the surface of the spots and their chemical bonding, respectively. This study reveals the stalked eyes main features are lenses and fibers. Asaphus kowalewski has lenses shaped as a truncated prism. Asaphus cornutus and Asaphus punctatus have lenses that are shaped as either a cone or an elongated prism. The cone shaped lens resembles ommatidium in the compound eyes of modern arthropods. The variation in lens shape within a specie could be explained by sexual dimorphism, which has been reported in modern arthropods. These findings suggest a stronger evolutionary link between trilobites and modern arthropods. Analysis of the spots on the Eldredgeops rana trilobite show that they cannot be lenses; there is no pathway connecting the spots to the exterior of the trilobite and no uniform orientation in the crystalline structures. Atomic force microscopy and Raman analyses of the spots show inconsistency with amorphous calcium carbonate. Overall, the results of this study demonstrate that by applying new concepts from the study of modern organisms and using advanced analytical techniques, we can enhance our understanding of the diversification of trilobites.
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    Source, composition, and biodegradability of dissolved organic matter in the Parlung Zangbo river in southern Tibet, China
    (University of Alabama Libraries, 2019) Warren, Olivia Marie; Lu, Yuehan; Zheng, Chunmiao; University of Alabama Tuscaloosa
    Regions of the Tibetan Plateau are experiencing increasing temperatures and decreasing glacial mass at a faster rate than the global average. Our study area, the Parlung Zangbo River basin, is within the southeastern region of the Tibetan Plateau which is experiencing the greatest degree of glacial mass loss. Glacial loss could mobilize organic matter from the terrestrial landscape to lakes and rivers and thereby influence watershed carbon cycles, water quality, and aquatic ecological functioning. However, the present-day dissolved organic matter (DOM) pool of the river, which could serve as a baseline for future predictions, has not been characterized. This project will characterize spatial distribution of the amount, source, and biodegradability of DOM exported from the Parlung Zangbo River basin. Samples were collected along the main stem of the river over 170 km, nearby tributaries, and a headwater lake and analyzed for DOC concentration and DOM quality based on absorbance and fluorescence properties. The excitation emission matrix coupled with parallel factor analysis (EEM-PARAFAC) yielded three humic-like fluorophores and two protein-like fluorophores. A subset of samples analyzed with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) analysis showed that the DOM pool was dominated by lignins. Incubation experiments showed microbial utilization of DOM increased with increasing temperature up to an optimum temperature (between 17°C and 25°C) before declining. Lake samples showed characteristics indicative of glacial contribution, including greater proportions of Nitrogen-rich DOM and microbially-derived DOM, as well as higher β:α values that suggest lower degrees of diagenesis and higher bioreactivity. Our results suggest that increasing glacial loss in the future may shift the composition and increase the bioreactivity of DOM pool in Tibetan rivers. Consequently, these shifts in the DOM pool will contribute to global warming through a positive feedback loop.
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    Sulfur, carbon, and oxygen isotopes of coexisting sulfides and carbonates in gas and oil seeps from the Gulf of Mexico
    (University of Alabama Libraries, 2019) Morelli, Erica C.; Wielicki, Matthew; Aharon, Paul; University of Alabama Tuscaloosa
    Microbial processes consisting of bacterial sulfate reduction (BSR), bacterial disproportionation of sulfur (BDS), and BSR coupled with anaerobic oxidation of methane (BSR-AOM) occur in the Gulf of Mexico (GOM) at sites where hydrocarbon oil and gas seep through conduits to the seafloor. Thus far, no studies have measured the solid-phase sulfides from GOM seeps in-situ that provide a superior analogue to sulfides from the geologic record. This study employs in-situ sulfur isotope measurements by secondary ion mass spectrometry (SIMS) in authigenic sulfides associated with barites and carbonates, and isotope measurements of carbon and oxygen by isotope ratio mass spectrometry (IRMS) in coexisting carbonates from 5 sites (GC-140, GC-185, GC-272, MC-929, and GB-382) in the GOM. Pyrite grains (FeS₂) yield variable δ³⁴S values and are considerably more ³⁴S-depleted in seeps with dominant carbonate phase (GC-140 & GC-185: range of -50.5 to -9.0‰ CDT) compared to seeps with minor to dominant barite phase (GC-272 & MC-929: range -23.9 to 19.5 ‰ CDT; GB-382: range 5.3 to 25.9‰). Measurements of carbonate reveals variably ¹³C-depleted and ¹⁸O-enriched δ¹³C and δ¹⁸O values in all seeps (GC-140 & GC-185: -36.7 to -3.5‰ VPDB and 2.5 to 5.3‰ VPDB, respectively; GC-272 & MC-929: -38.0 to -1.2‰ VPDB and 1.6 to 2.5‰ VPDB, respectively; GB-382: -31.4 to -1.2‰ VPDB and -0.5 to 4.1‰ VPDB; respectively). The isotope data suggest a strong influence of: (i) BSR and BDS processes using crude oil and unlimited SO₄²⁻ supply near the sediment-water interface (GC-140 & GC-185); (ii) BSR using crude oil/ non-methane sublimated gas hydrate and variable availability of SO₄²⁻ at depth within the sediment column (GC-272 & MC-929; GB-382), or (iii) possible BSR-AOM using sublimated methane hydrate and SO₄²⁻ near the sulfate-methane transition zone (GC-272 and GB-382). Additionally, Fe-oxides reported in association with pyrites at GC-140, GC-185, and GC-272, could potentially influence fractionation of sulfur isotopes during microbial processes by promoting greater sulfur recycling and thus muting fractionation effects. The results of this study offer important insights on the high variability of sedimentary pyrites in cold seeps that has implications for the biogeochemical cycling of sulfur and carbon in marine environments.