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End date: 2023 × 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 × search.filters.applied.f.resourcesubtype: Undergraduate Thesis ×

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Now showing 1 - 10 of 12
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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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Characterizing iron reducing microorganisms from anoxic ferruginous lake sediments

2018-12 , Costa, Bianca Francesca

Lake Matano, Indonesia is a well-known ancient ocean analogue as its anoxic ecosystem in the subsurface sediments allow the growth of microorganisms capable of mediating anaerobic oxidation coupled to iron reduction. An anoxic, ferric iron rich BSR was kept for 163 days to culture iron reducing bacteria in an environmental sample from Lake Matano sediment. Microscopy analysis was performed periodically to look for morphology trends using DAPI staining. Phylogenetic analysis was performed using CARD-FISH microscopy to target the Geobacter genus, known for electroactive abilities through pilA and interactions with iron particles. Cell counts correlated with iron reduction throughout the culturing period indicating iron reducing microorganisms were present in the environmental sample. Filamentous, coccus, bacillus and vibrio morphologies were observed through the culturing period with vibrio and bacillus being predominant at later stages of the culture. Particle association instances were observed at days 20, 62, 86 and 126 and DIET interactions at day 86. Characterizing these microorganisms opens a broad range of possibilities for wastewater treatment (strip mining groundwater contamination), use in bioelectrochemical systems biofilms (due to external electron transport pilA) and understanding the importance of this microorganisms in Iron cycling.

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Stream Terraces in the Critical Zone - Lower Gordon Gulch, Colorado

2011-05-09 , Warrell, Kathleen Frances

As bedrock weathers into soil, erosional processes often carry loose sediment down slope into a stream channel. Higher weathering rates produce larger amounts of erodible soil, which then causes sediment in the stream to build up and raise the base level of the stream. Changes in climate and land use may cause changes in the stream's carrying capacity and result in stream incision. As the stream adapts to changes in climate and land use over time, a complex series of fill terraces may form. These terraces can store large amounts of sediment, and it may take thousands of years for the stream to remove this sediment. Gordon Gulch, a small catchment in Colorado's Front Range, is a prime example of a series of complex fill terraces. In this study, five terraces have been thoroughly mapped and characterized. The volume of sediment stored in the terraces is 50,000 cubic meters, and a time span for removal of this sediment is 1,300 years by the model developed by Mueller and Pitlick, (2005). The reliability of the results from this model are also discussed and contrasted with 14C dates obtained from the terraces.

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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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A Proposed Improvement for Measuring Hydroxylamine in Seawater

2019-12 , Sandler, Lily R.

Hydroxylamine is a chemical intermediate in the nitrogen cycle that can quickly react via biotic and abiotic processes to yield nitrous oxide, a potent greenhouse gas. Because of its high reactivity, hydroxylamine tends to be present at low concentrations in aquatic ecosystems. High reactivity and low concentrations also make hydroxylamine difficult to measure. Our goal was to improve the method for measuring environmental concentrations of hydroxylamine. The current method involves converting hydroxylamine to nitrous oxide with ferric ammonium sulfate at low pH and analyzing the nitrous oxide produced by gas chromatography. This method requires a recovery curve because the conversion of hydroxylamine to nitrous oxide does not always go to completion. Here, we propose a new method using a manganese oxide mineral pyrolusite, which rapidly oxidizes hydroxylamine and completely converts it to nitrous oxide, thus eliminating the need for a recovery curve and sample acidification. The method involves (1) crushing and sieving commercial pyrolusite to increase reactive surface area; (2) adding crushed pyrolusite to airtight bottles containing hydroxylamine in artificial seawater at neutral pH; (3) incubating for two hours; and (4) analyzing of the oxidized product, nitrous oxide, by gas chromatography. Hydroxylamine concentrations are calculated from the concentration of nitrous oxide in headspace before and after pyrolusite addition. Addition of crushed pyrolusite resulted in complete conversion of hydroxylamine to nitrous oxide within two hours, whereas minimal conversion occurred without pyrolusite. This method has a shorter reaction time and goes to completion, allowing for more rapid and accurate measurements of hydroxylamine in aquatic environments.

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Transport Pathways of Shelf Source Micronutrients to the Southern Ocean

2015-08-18 , Birmingham, Ryan W.

We use a numerical ocean model to evaluate the hypothesis that the continental shelves are significant sources of dissolved iron to the Southern Ocean. We simulate the distribution of passive tracers released from the 18 different continental shelf regions of the extra-tropical southern hemisphere oceans using an offline, eddy-permitting transport model. The circulation fields are taken from the Southern Ocean State Estimate, and we only simulate the transport of inert tracers focusing on the physical transport pathways. The resulting tracer fields are then compared with the remotely sensed ocean color data, revealing a remarkable resemblance between the distributions of shelf-source tracers and the climatological surface chlorophyll-a concentrations. We further analyze the spatial pattern of simulated tracer fields in relation to satellite ocean color data. Dynamic ocean features such as the Southern Ocean fronts and coastal waters are reflected in both the tracer model and the observed biological productivity. Our results support the overall importance of continental shelves as a potential source region for dissolved iron. The relative importance of different shelf regions is found to vary significantly depending on the relevant circulation features.

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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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Earth's oxygen and phosphorus cycle and the evolution of animal life

2019-05 , Liu, Xinyi

The purpose of this study is to reconstruct an environmental context for the emergence and expansion of early animal life during the Middle Proterozoic (∼1.8–0.8 billion years ago). Specifically, we examined the spatially and temporally evolving Earth surface ocean oxygen (O2) concentration impacted by atmospheric partial pressure of oxygen (pO2) and phosphorus levels. We exploited a quantitative biogeochemical model - the Grid ENabled Integrated Earth system (cGENIE) model, which consists of a reduced physics 3-D ocean circulation model coupled to a 2-D energy-moisture balance model of the atmosphere and a dynamic-thermodynamic sea-ice model. Our results suggest a challenging evolutionary landscape for basal metazoan life characterized by spatiotemporal variation in surface ocean oxygen level and prevalent benthic anoxia even with surface ocean-atmosphere oxygen level sufficient to support basal biological activities. By studying the environmental variability presented during the evolutionary history of complex life on Earth, we are thus equipped with a valuable tool to examine the potential biotic complexity throughout the universe.

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Measuring present-day strain rates along the Fish Lake Valley fault system, Pacific-North America plate boundary

2012-05-07 , Johnson, Christopher William

The eastern California shear zone (ECSZ) is located east of the San Andreas fault and contains a complex network of structures that accommodate ~25% of the relative displacement between the Pacific and North American plates. Geodetic data indicate strain accumulation at a rate of 12±2 mm/yr along four main structures in the ECSZ. The Death Valley-Fish Lake Valley fault, the prominent and longest fault in the ECSZ at ~300km, is observed to be the fastest slipping fault in the region storing elastic strain at a rate of 3-8 mm/yr. Recently determined long-term slip rates (103 106 year timescale) indicate a pattern of decreasing velocity moving north through Fish Lake Valley (FLV) from ~6 mm/yr to zero, presumably because strain is transferred onto extensional faults located to the east. This study intends to determine the short-term (decadal timescale) displacement field along the FLV fault using Global Positioning System (GPS) derived velocities to test whether spatial patterns of geodetic and geologic rates are consistent through time. In a series of two GPS campaigns in 2010 and 2011, nine geodetic monuments, spaced 15-20 km apart, were surveyed in and around FLV. In addition, campaign data from previous surveys has been acquired from UNAVCO. The combined data sets are used to calculate the relative motion along the fault. Modern strain rates determined using an elastic half space model resulted in a slip rate of ~3.8 mm/yr across the FLV fault. This rate is examined with respect to previously determined Quaternary rates along the FLV fault

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