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Provenance analysis of siliciclastic beds of the Wilkins Peak member of the Lower Eocene Green River formation, Wyoming

Gregorich, Holly Gina (2021) Provenance analysis of siliciclastic beds of the Wilkins Peak member of the Lower Eocene Green River formation, Wyoming. Masters thesis, Northern Arizona University.

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The rock record of fluvial systems provides important information about provenance, sediment transport, fluvial architecture, and climate patterns throughout foreland basins by the way they respond to tectonics and greenhouse climates. Here we evaluate these parameters in the Eocene Wilkins Peak Member of the Green River Formation. There are nine laterally continuous alluvial siliciclastic intervals within the Wilkins Peak Member that record an alluvial distributary network that spanned across the floor of an ancient closed-lake system in southwest Wyoming during the Early Eocene. Samples collected from these alluvial intervals throughout the Bridger sub-basin and parts of the greater Green River Basin were analyzed using petrography, detrital zircon geochronology, and X-ray fluorescence to document the provenance of these beds and the distributary systems that fed them. Detrital zircon populations from the uppermost alluvial bed of the Wilkins Peak Member were split into chronofacies in order to connect sediment ages with adjacent source terrains and are shown to be dominated by Archean (4.0-1.9 Ga), Yavapai/Mazatzal (1.9-1.3 Ga), and Grenville ages (1.3-0.9 Ga), with minor contributions from Appalachian (900-350 Ma) and Cordilleran sources (350-0 Ma). XRF was used to measure the elemental concentrations of the sandstone and mudstone samples within the Wilkins Peak Member alluvial intervals. Principal component analysis of XRF results define three major chemofacies within the data set and were used in combination with sandstone petrography to understand mineral abundances within Wilkins Peak Member alluvial beds and reconstruct provenance of rivers that drained to Lake Gosiute. The first principal component is primarily controlled by the relative abundance of Rb, K, Al, Ti, Fe, and Zn, with samples of arkosic composition fed by the Aspen paleoriver coinciding with greater concentrations of these elements, whereas samples with greater Zr and Si concentrations have more quartzose compositions. Among the quartzose samples, sandstones derived from the Uinta Uplift and the Sevier fold and thrust belt can be differentiated by the second principal component, with greater concentrations of Mg, Mn, and Sr associated with more carbonate-rich compositions characteristic of fold and thrust belt-derived sandstones. Based on the data collected, two major paleorivers and a series of short steep streams on the north side of the Uinta Mountains drained into the depocenter of ancient Lake Gosiute during the deposition of the Wilkins Peak Member. Streams from the Uinta Mountains were the primary source for quartzose and conglomeratic detritus transported into the southern portion of the Bridger sub-basin throughout the WPM interval. Streams that were headed in the Sierra Madre, Gore, and Sawatch ranges joined streams that flowed down the eastern side of the Uinta Mountains and delivered arkosic sediment into the central and southeastern parts of the Bridger sub-basin and into the adjacent Washakie and Sand Wash sub-basins through the paleo Aspen River system. Streams that drained the Sevier fold-thrust belt were able to prograde out into the central parts of the Bridger sub-basin after the filling of the adjacent Fossil Basin and western Bridger sub-basin during the deposition of the lower Wilkins Peak Member, which underlies the marker beds. Sediment patterns within the Uinta Mountains streams and the paleo Aspen River system suggest that fine-grained siliciclastics were able to prograde out into the northern and central parts of the Bridger sub-basin after faulting along the Henrys-Fork Thrust fault ceased around the middle of Wilkins Peak Member time. Our results help define the dynamics of these river systems that drained into ancient Lake Gosiute during the deposition of the Wilkins Peak Member between 51.6-49.8 Ma and are necessary to understand the climate signals that are present within the Green River Early Eocene Climate Observatory Solvay Core, which contains one of the most complete and well-preserved archives of this ancient lake system.

Item Type: Thesis (Masters)
Publisher’s Statement: © Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords: alluvial; Eocene; Laramide; siliciclastic; Wyoming; Wilkins Peak member; Green River Formation
Subjects: Q Science > QE Geology
NAU Depositing Author Academic Status: Student
Department/Unit: Graduate College > Theses and Dissertations
College of the Environment, Forestry, and Natural Sciences > School of Earth Sciences and Environmental Sustainability
Date Deposited: 09 Feb 2022 17:11
Last Modified: 09 Feb 2022 17:11
URI: https://openknowledge.nau.edu/id/eprint/5674

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