Date of Award:
Master of Science (MS)
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.
Provow, Ashley W., "Ediacaran Depositional Age and Subsequent Fluid-Rock Interactions in the Mutual and Browns Hole Formations of Northern Utah" (2019). All Graduate Theses and Dissertations. 7468.
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