Constraining the depositional age of Neoproterozoic stratigraphy in western North America has implications for correlating global glaciation and tectonic events. The depositional ages of the Neoproterozoic Mutual and Browns Hole formations of northern Utah are controlled by two conflicting datapoints. However, new U-Pb geochronological data from 95 detrital apatite grains refines the maximum depositional age of the volcanic member of the Browns Hole Formation to 613 ± 12 Ma (2σ). This places new restrictions on the time available for the deposition of underlying units. Due to debate regarding the age models for underlying stratigraphy, two scenarios for sediment accumulation rates are explored. These results highlight a need for further exploring regional unconformities. Evidence for several post-depositional fluid-rock interaction events are observed in the Mutual and Browns Hole formations. Cross-cutting relationships identified via petrography, scanning electron microscopy, and electron microprobe analysis show at least seven fluid mediated events: (1) early grain-rimming hematite cement, (2) quartz overgrowth and cement development, (3) feldspar dissolution, (4) phosphate dissolution, (5) partial quartz dissolution, (6) authigenic mineral precipitation in cluding clays, sericite, monazite, and apatite cement, and (7) later hematite cementation. Constraining the timing of these events is challenging due to a limited of datable material. Using basic geochemical modeling and consideration of expected mineral formation conditions, a paragenetic sequence is placed into context of the known geologic history.

Detrital zircon U-Pb geochronology is a useful tool for analyzing provenance in the sedimentary record. Differentiating recycled and first cycle populations in the detrital record, however, is not a straightforward process. A second potential problem in using detrital signatures to determine provenance of sediment lies in the assumption that detrital signatures of modern rivers reflect input from each exposed unit in the catchment boundaries. To investigate each of these problems, I present U-Pb analysis of detrital zircon (DZ) from modern river sand collected from 20 watersheds, 6 detrital apatite (DA) signatures from modern river sand, and 6 DA signatures from exposed strata, all within the Talkeetna Mountains (south-central Alaska). DA rarely survives past the first cycle of erosion and deposition due to its inability to survive chemical weathering, and thus dominantly represent igneous input in detrital signatures, whereas zircon can be of igneous origin or can survive multiple cycles of erosion and deposition. By comparing the DA signatures with the DZ signatures, I present a method to better differentiate first cycle, igneous sediment contributions from recycled populations within a detrital signature. The results of these comparisons show that DA signatures provide ages of igneous input into the detrital record; these ages are also reflected in the DZ signature, thus signaling these DZ populations as igneous in origin. This study also investigates the potential for DA recycling and DA input from recycled strata. To address the second problem, I present a method using GIS software and the most recent map of Alaska to create simulated signatures that records input on a scale proportionate to the exposed surface area of each bedrock unit. In ~35% of the watersheds tested, the simulated signatures predict trends similar to the DZ signatures from the modern river sands, in 55% of the watersheds tested the simulated signatures missed one or more populations present in the DZ signature, and in 10% of watersheds tested, the simulated signature predicted trends very different from the DZ signatures. In cases where the DZ and simulated signatures do not match, I believe this represents influences of climate and relief and zircon fertility.

The evolution of mountain landscapes is controlled by complex interactions between large-scale tectonic, surficial and climate conditions. Dominant processes are attributed to creating characteristic features of the landscape, but topographic features are the cumulative result of coupled surficial processes, each locally effective in a different climate or elevation regime. The focus of erosion by glacial, fluvial, or mass wasting processes is highly sensitive to small changes in boundary conditions, therefore spatial and temporal variability can be high when observed over short time scales. This work evaluated methods for dissecting the history of complex alpine landscapes to understand the role of individual processes influenced by changing climate and underlying bedrock. It also investigated how individual and combined mechanisms of surficial processes influenced the evolution of topography in the Teton Range in Wyoming. Detrital apatite (U-Th)/He thermochronology and cosmogenic radionuclide erosion rates were applied to determine spatial and temporal variability of erosion in the central catchments of the range. Spatial variability existed between the glacial and fluvial systems, indicating that sediment erosion and deposition by these processes was controlled by short-term variability in climate conditions. Effective glacial incision also controlled other processes, specifically enhancing rock fall activity and inhibiting fluvial incision. Short-term erosion rates were highly variable and were controlled by stochastic processes, particularly hillslope failures in response to slope oversteepening due to glacial incision and orientation and spacing of bedrock fractures. Erosion rates averaged over 10 ky time scales were comparable to long-term exhumation rates measured in the Teton Range. The similarity of spatial erosion patterns to predicted uniform erosion and the balance between intermediate and long-term erosion rates suggests the landscape of the Teton Range is approaching steady-state, but frequent stochastic processes, short-term erosional variability and coupled processes maintain rugged topographic relief. / Ph. D.