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End date: 2023 × Start date: 2020 × search.filters.applied.f.isOrgUnitOfPublicationTitle: College of Sciences × search.filters.applied.f.isOrgUnitOfPublicationTitle: School of Earth and Atmospheric Sciences × search.filters.applied.f.isSeriesOfPublicationTitle: Undergraduate Research Option Theses × Type: Text ×

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Provenance Analysis of the Bouse Formation, Lower Colorado River from Detrital Zircon (U-Th)/Pb Geochronology

2023-01-18 , Motz, Samantha L.

The timing and mechanism of Colorado River integration from the Grand Canyon to the Gulf of California have long been debated. Early research proposed river integration developed “bottom-up” due to Pliocene marine incursion and regional uplift. However, mapping, stratigraphy, and geochemical analyses of early Colorado River deposits instead support a “top-down” integration by progressive filling of lake basins connected by the Colorado River. Key to this debate are interpretations of the depositional environment of the Pliocene Bouse Formation. Here we present a new dataset of detrital zircon (U-Th)/Pb geochronology (n = 1774 single-grain ages) to explore the sedimentary provenance of sand horizons in the Bouse Formation. Our results span 13 Bouse samples from four sub-basins in the lower Colorado River corridor: Mohave, Chemehuevi, Parker, and Cibola. Additional samples of underlying Pyramid gravel and modern sediment from the Colorado River, Bill Williams River, and Silver Creek are presented for comparison. Except for three samples from the Mohave sub-basin, statistical comparison of grain-age populations illustrates that the Bouse Formation has a non-local provenance consistent with a large drainage area comparable to the modern Colorado River. The excepted samples reflect derivation from local source rocks. Within the Bouse Formation’s stratigraphy, grain-age populations do not vary. Still, inter-sub-basins vary geographically, which we attribute to the progressive admixture of zircons from local source rocks and tributaries. Overall, our provenance analysis is consistent with the deposition of Bouse sand horizons as delta-front turbidities originating from a river with a well-mixed and lithologically diverse sediment load. Exceptional samples from the Mohave sub-basin may be explained by interbedding of transverse fan-deltas from local tributaries. Our analysis does not support the deposition of the Bouse Formation in separated and locally sourced lake systems. Instead, it promotes deposition by a single, high-discharge river rapidly progressing southward, integrating previously separated sub-basins.

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Mapping and Quantifying Tortuous Ridges on Europa

2021-05 , Babcock, Michelle

Double ridges are the most common surface feature on Europa and account for both some of the oldest and newest surface features on the moon. Ridges with linear and cycloidal trajectories have been well-studied, with established hypotheses for their formation and trajectories. We find that a number of ridges consistently deviate from either linear or cycloid trajectories in an irregular pattern. Tentatively described as “tortuous” ridges, these have not been previously mapped, classified, or studied in detail. To gain a better understanding of their distribution and context, I mapped ridges with tortuous, linear, and cycloid trajectories across four regions of Europa using regional Galileo SSI images having resolutions < 1 km/px and analyzed ridge trajectory using fractal dimension analysis. Fractal dimension, D, is used to characterize patterns in nature by quantifying their self-similarity or self-affinity. I test fractal analysis as a way to quantify the tortuosity of ridges on Europa and classify some ridges as distinctly non-linear and non-cycloidal (i.e., as tortuous). The fractal dimension of a line is D ~ 1 and Brownian noise is D ~ 1.5, so we would expect a higher fractal dimension for tortuous trajectory (i.e., 1 < D < 1.5) compared to both linear and cycloid features. This analysis explores fractal dimension analysis as a quantitative means for classifying tortuous ridges on Europa, which would enable more focused research on the topic that could inform future models for ridge and fracture formation on Europa and lend insight into the moon’s ice shell properties.

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Sorption of Rare Earth Elements onto Kaolinite

2022-05 , Wise, Paige

Rare earth elements (REEs), defined as yttrium (Y), scandium (Sc), and the 15 lanthanides, have become prominent areas of focus in the geochemistry field. REEs are used in many alternative energy technologies and as geochemical tracers that assist in understanding geochemical processes in aqueous settings. The biogeochemical transport of REEs is dependent on factors such as concentration, pH, ionic strength, and the presence of sorbents and due to their trivalent charge, can undergo adsorption to negatively charged mineral surfaces. The sorption process is greatly affected by the sudden change in pH and salinity during the transportation of REEs from freshwater to seawater[1]. In this study, the behavior of REE adsorption and desorption on clay minerals was investigated under varied solution chemistry, to simulate the mobilization of REE from freshwater sources to seawater and to understand the behavior of REE desorption when introduced to ocean conditions. The phyllosilicate, clay mineral kaolinite was employed as our representative sorbent due to its large surface area and negatively charged surface which allows for adsorption to occur[2] Understanding and quantifying the sorption of REE on clay in different pH conditions implies the adsorbent contribution to the dissolved REE budget. Batch experiments were conducted to model the sorption of REE to kaolinite and the mineral adsorbent was introduced into simulated freshwater with a pH of 6. After 24-hour reaction, REE-bearing mineral were rinsed and resuspended in artificial seawater at pH 8. Suspension samples were taken at different time points during the experiments to monitor the rate of desorption once introduced to simulate seawater. At the end of reaction, the solid and final aqueous sample were collected and analyzed for REE concentration using inductively coupled plasma-mass spectrometry (ICP-MS) and plotted as isotherms.

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The Impact of Elevation-SMB Feedbacks on the Evolution of Thwaites Glacier, West Antarctica

2021-05 , Verboncoeur, Hannah

The Amundsen Region of the West Antarctic Ice Sheet is one of the major active contributors to global sea level rise. Thwaites Glacier is a large, fast-flowing glacier in this region which is experiencing mass loss, flow acceleration, and rapid grounding line retreat, indicative of the marine ice sheet instability. Although there are many factors that may influence the potential destabilization and collapse of Thwaites Glacier, surface mass balance is an important factor as the balance of precipitation and ablation change with changing glacier geometry. This study investigates a surface elevation-SMB relationship and its influence on projected future stability at Thwaites Glacier. Observational data and regional climate model outputs are used to identify a strong elevation-SMB relationship at Thwaites Glacier. The Ice-Sheet and Sea-Level System Model is then then used to simulate Thwaites Glacier’s evolution with an added elevation-SMB feedback. Incorporating an elevation-SMB feedback increases the model prediction for ice mass loss by 5%-10% over a 200 year transient simulation.

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