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This study is centered around the spatial distribution and age structure of PSA in a section of floodplain in the upper reaches of Clear Creek Watershed in east central Iowa. The study area topography, climate, soil, and pre-settlement tallgrass prairie landcover are representative of the headwaters of many Midwest watersheds, making the findings applicable in other parts of the region. Through this investigation, I aim to further understand the volume and age structure of PSA sediments deposited on the floodplain after Euroamerican settlement. This will be done through multiple methods: the collection and measurement of PSA in soil cores, visual and spatial analysis of land use and stream channel morphology, PSA volume calculations, and isotope geochemistry. Using 210Lead (Pb) and 137Cesium (Cs) isotope geochemistry to calculate age structures of the PSA will provide a more detailed, temporal resolution of physical data than erosion and deposition model predictions can generate. A detailed land use history will further facilitate the understanding of depositional processes that have occurred in the study area and region. By understanding the age structure of the sediment on the floodplain, as well as sediment volumes that are stored in floodplain headwaters, tangible connections can be made between agricultural land use and floodplain sedimentation rates and the impact (if any) assessed of potential conservation practices. This research is supported by the Intensively Managed Landscape Critical Zone Observatory (IML-CZO) of the National Science Foundation’s CZO network, which aims to understand how land use changes affect the long-term resilience of the critical zone, where water, atmosphere, ecosystems, soil, and bedrock interact.

The Thelon basin, Nunavut, is similar to the uranium-producing Athabasca Basin, Saskatchewan; however, the uranium deposits associated with the Thelon Basin are poorly understood. The objective of this research is to develop a genetic model for the Bong uranium deposit, located in the Northeast Thelon region on the Kiggavik project of AREVA Resources Canada Inc. The Bong deposit formed in four stages. The first stage involved silicification of the host rocks. Stage 2 is characterized by pervasive argillization of the host rock and the formation of Stage A uraninite in veins and coating graphite (~1120 Ma). This stage is characterized by ~225°C fluids with calculated δ18O and δD values of -7.9‰ and -100.9‰, respectively. During Stage 3, organic matter formed, along fractures in permeable clay-rich alteration zones. At ~1040 Ma, an oxidizing fluid event (Stage 4) reconcentrated uraninite into redox fronts (Stage B) and altered Stage A uraninite to uranophane.

The Thelon basin, Nunavut, is similar to the uranium-producing Athabasca Basin, Saskatchewan; however, the uranium deposits associated with the Thelon Basin are poorly understood. The objective of this research is to develop a genetic model for the Bong uranium deposit, located in the Northeast Thelon region on the Kiggavik project of AREVA Resources Canada Inc. The Bong deposit formed in four stages. The first stage involved silicification of the host rocks. Stage 2 is characterized by pervasive argillization of the host rock and the formation of Stage A uraninite in veins and coating graphite (~1120 Ma). This stage is characterized by ~225°C fluids with calculated δ18O and δD values of -7.9‰ and -100.9‰, respectively. During Stage 3, organic matter formed, along fractures in permeable clay-rich alteration zones. At ~1040 Ma, an oxidizing fluid event (Stage 4) reconcentrated uraninite into redox fronts (Stage B) and altered Stage A uraninite to uranophane.

The Kianna deposit is an unconformity-related uranium deposit in the western Athabasca Basin of northern Saskatchewan, hosting uraninite in three distinct zones: 1) perched above the unconformity, hosted in sandstone; 2) at the unconformity, hosted in sandstone and basement rocks; and 3) below the unconformity in two separate pods, hosted by basement paragneiss. In situ secondary ion mass spectrometry (SIMS) was used to obtain radiogenic and stable isotope data to update the genetic model for the Kianna deposit. Primary basement-hosted ingress-style uraninite, associated with hematite and muscovite, has a minimum U-Pb age of ~1500 Ma. Recrystallization of basement uraninite occurred ~1100 Ma with the precipitation of coarse-grained illite. Late basement uraninite precipitated with fine-grained illite ~850 Ma. A separate, deeper basement pod formed ~1280 Ma. Egress-style uraninite at the unconformity, and perched uraninite in the sandstone, inter-grown with alumino-phosphate sulfate (APS) minerals and chalcopyrite, formed ~750 Ma. Later unconformity and perched uraninite precipitated with hematite, pyrite, and chalcopyrite ~500 Ma. Sulfides coeval with unconformity and perched uraninite have d34S values from -1.9 to 8.1‰ and 15.1 to 25.4‰, indicating two sources of sulfur: 1) sulfides in the metamorphosed basement and 2) APS minerals in the sandstone. Average d18O and dD mineral values for muscovite are 0.7 ± 4.3‰ and -33 ± 12‰, respectively, suggesting that muscovite formed from a marine brine. Average d18O and dD mineral values for coarse-grained illite are 0.4 ± 4.1‰ and -79 ± 16‰, respectively, indicating formation from hydrothermal fluids, whereas fine-grained illite d18O and dD mineral values are 6.5 ± 1.6‰ and -144 ± 21‰, respectively, suggesting formation from meteoric fluids.

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No description available.

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No description available.