Thesis (M.A.)--University of Wyoming, 2008. / Title from PDF title page (viewed on August 4, 2009). Interdisciplinary thesis in International Studies and Environment and Natural Resources. Includes bibliographical references (p. 58-63).

Thesis (D. Min.)--Western Seminary, Portland, OR, 2001. / Abstract. Includes bibliographical references (leaves 241-246).

Master of Science / Geology / Matthew E. Brueseke / The Upper Wind River Basin (UWRB) is located in north-central Wyoming, to the south of the Yellowstone National Park boundary and east of Jackson Hole. Both Lava Mountain and Spring Mountain are Quaternary volcanoes in the UWRB. Lava Mountain is a shield volcano composed of 26 separate lavas capped by a scoria cone. Spring Mountain is located about ~36 km east of Lava Mountain, north of Dubois, WY, where eruptions of basalt cut through Paleocene and Eocene strata. The goal of this study aims to reconstruct the petrogenesis of magmas erupted at both volcanoes using geochemical, petrographic, and isotopic analyses. Important local events in geologic history played a large role in the development of the UWRB. This includes a long history of ancient and Cenozoic subduction, regional extension, and also the migration of the North American plate over the Yellowstone hotspot. The few previous studies on Lava Mountain claim the rocks are mafic in composition, however this was based solely on reconnaissance geological mapping. Geochemical evidence presented in this thesis show Lava Mountain rocks range from basaltic andesite to dacite. Basaltic andesite and dacite are interstratified at the base until approximately 2774 m; the rest of the volcano is andesite. All Lava Mountain samples are largely aphanitic and crystal-poor. Conversely, at Spring Mountain, localized normal faulting controls the location of eruptions of olivine-rich basalt. Petrographic analysis for both Lava Mountain and Spring Mountain display a range of evidence for open system processes, including sieved and/or resorbed pyroxenes, olivines and feldspars, as well as xenocrysts that suggest an influence from crustal assimilation. A petrogenetic model is introduced that discusses how Lava Mountain magma production occurred via fractional crystallization of basalt to dacite, then magma mixing of basaltic andesite and dacite, coupled with small amounts of crustal assimilation, to form the locally erupted andesites. All samples, including Spring Mountain basalts, have ⁸⁷Sr/⁸⁶Sr isotopes of 0.70608 and 0.70751, with ¹⁴³Nd/¹⁴⁴Nd isotopes of 0.51149 and 0.51157 and εNd values of -18 to -22. Pb isotopes plot to the left of the Geochron and directly on to slightly above the Stacey-Kramers curve. Strontium, neodymium, and lead isotope data suggest that Spring Mountain basalts are melts of ancient (e.g., 2.8 Ga Beartooth province) lithospheric mantle. The high ⁸⁷Sr/⁸⁶Sr values and exceptionally low εNd values separate the UWRB rocks from both Yellowstone and Snake River Plain volcanics, and suggest they originated from a different magma source. Finally, thermal evidence suggests melting genesis for UWRB rocks may not be Yellowstone plume related; rather it is more likely linked to Cenozoic extension.

Master of Science / Geology / Matthew E. Brueseke / Previous K-Ar dating and petrography (Obradovich, 1978) have identified Pilot Knob as an ~3.4 (±0.06) Ma alkaline intrusive body. Bulk rock geochemistry obtained via XRF from four samples of Pilot Knob verifies the transitionally alkaline composition of the body, and new REE data also show enriched La, Ce, and Nd concentrations, consistent with rare earth element (REE) enrichment. Given the increased demand for REEs over the past ~30 years and China accounting for > 90% of global REE production (Kynicky, et al. 2012), it is important to evaluate new domestic REE sources. This includes those associated with alkaline intrusive complexes, because they are demonstrated to host high REE concentrations (Verplanck and Van Gosen, 2011). Such alkaline igneous occurrences show complex mineralization and consist of many minerals containing substitutional REEs (Mariano and Mariano, 2012). This study evaluates the petrogenesis and mineralogy of Pilot Knob (and a secondary field site, Wildcat Hill) and determines whether the intrusive body is consistent with an economically viable REE deposit. Additionally, given its geographic location and Pliocene faulting and magmatism (e.g., predating the earliest volcanism at Yellowstone), Pilot Knob may represent one of the earliest structural manifestations of the “arrival” of the Yellowstone hotspot at its current location under the North American lithosphere or magmatism associated with lithospheric extension to the south at the Leucite Hills, WY. Inspection of satellite imagery, which has been verified with field data, shows that other intrusive igneous bodies (e.g. - Wildcat Hill) exist, along an apparent normal fault zone along strike with a major extensionally related fault zone documented ~10 km northwest of Pilot Knob. Clinopyroxene geobarometry, coupled with Nd isotope data (εNd[subscript 3.5Ma] = -21.9), indicates that Pilot Knob formed via a multi-stage development history that initiated with melting of ancient lithospheric mantle, where crystallization occurred at a variety of depths. As an alkaline intrusive complex, Pilot Knob has been identified, based on mineral and chemical compositions, as a kersantite, and has been found to contain approximately 600 ppm total light-rare earth element ore lode with ~150 ppm Nd, ~175 ppm La, and ~338 ppm Ce enrichment. Apatite was found to be the primary REE-bearing mineral via petrography and electron microprobe analyses. Based on current technology and processing methods, REE concentrations were not found to be significant enough to denote an economically viable REE ore deposit at Pilot Knob.

The Twin Creek Limestone of Middle Jurassic age was studied in the Tunp, Salt River, and Wyoming Ranges in southwestern Wyoming. Modern carbonate environments and their ancient analogs were compared with information obtained from field study and petrographic analysis of samples of the Twin Creek Limestone in order to delineate environments of deposition, paleogeography, and diagenetic history. Six major lithofacies were recognized: (1) carbonate mudstone; (2) carbonate mudstone breccia; (3) fossiliferous wackestone; (4) packstone-grainstone; (5) terrigenous mudstone; and (6) sandstone. These lithofacies were deposited in a variety of environments, including outer shelf platforms (carbonate mudstone and fossiliferous wackestone), oolitic sand belts (packstone-grainstone), open to restricted lagoons (carbonate mudstone, fossiliferous wackestone, and terrigenous mudstone), tidal flats, and supratidal environments (terrigenous mudstone, sandstone and carbonate mudstone breccia). The Twin Creek epeiric seaway experienced two major transgressions (early Bajocian and late Bathonian-early Cal lovian) and two regressions (early Bathonian and middle Callovian). Lateral migration of the adjacent facies occurred in response to these changes in sea level. Eogenetic features include minor compaction, micritization, coarse fibrous rim cementation, granular cementation, syntaxial rim cementation and silicification of carbonates. These features were produced in environments ranging from freshwater phreatic to marine phreatic. Mesogenetic diagnesis was characterized by pressure-solution features and neomorphism. Telogenetic features are limited to calcite vein-fillings and oxidation coatings on carbonate and detrital gains and cements.

The Nugget Formation in the Anschutz Ranch East field, northeast Utah and southwest Wyoming, provides an exceptional example of how primary eolian rock properties have a considerable influence on the style of structural deformation. Both new and existing subsurface data were integrated for an overall characterization of sedimentologic and diagenetic heterogeneities, which demonstrate relationships with different styles of structural compartmentalization in reservoirs. The Anschutz Ranch East field is a large asymmetric anticlinal trap in the Utah-Wyoming thrust belt. Three cores were analyzed in order to investigate brittle deformation in eolian facies: dune, apron, and interdune. Selected cores are located along the back limb of the main structure and are nearly perpendicular to the fold axis. Each eolian facies appears to have an associated style of deformation that generally occurs within this tectonic setting. Within the dune facies, deformation bands are the most common style of deformation, unless a fault is present; when faults are present open fractures and breccia occur. In the apron facies, open fractures are more prevalent; however deformation bands are still very frequent. The primary styles of brittle deformation observed in interdune facies are breccias and closed fractures. This relationship between facies and rheology also correlates with porosity. These results support a hypothesis that high porosity rocks tend to be weaker and develop deformation bands, while low porosity rocks have a greater strength and will deform brittlely.

The Greys River fault is the easternmost active normal fault associated with Basin and Range extension in the lntermountain seismic belt. It is a north south trending normal fault, located in the Sevier-age fold and thrust belt of western Wyoming , and bounds the west side of the Wyoming Range . The fault is at least 54 km long , and juxtaposes Permo-Pennsylvanian Wells Formation against various Triassic formations . Throw ranges from 100-1000 m. Seismic reflection data suggest that the Greys River fault is a listric normal fault that soles into the Darby thrust at depth. The fault offsets late Quaternary deposits on the west flank of the Wyoming Range. These deposits were mapped and differentiated on the basis of provenance and weathering characteristics. Four sets of moraines were identified in the study area. The moraines segregated into a local four-fold relative age sequence based on topographic position and relative dating parameters. The four-fold relative age sequence was correlated to Blackwelder's original Rocky Mountain glacial chronology. The most extensive glacial deposits were correlated to the late Pinedale glacial advance. Alluvial deposits associated with the Pinedale glacial cycle also contain evidence for late Quaternary faulting on the Greys River fault. Maximum vertical surface displacements of late Quaternary deposits range from 8.6 m in Blind Bull Creek to 8.3 m in Box Canyon, 25 kilometers to the south. Between these points, vertical surface offset ranges from 3 to 8.2 meters. Three trenches were excavated in a late Pinedale alluvial terrace complex in Sheep Creek across a 7.5-meter scarp, a 3.1-meter scarp, and a 7.5-meter scarp-graben. The trenches revealed evidence for two paleoseismic displacements, the ages of which were constrained by eight radiocarbon dates. The most recent event involved a maximum displacement of 4.5 meters and occurred between 2110 +/- 60 and 2910 +/- 60 14C years BP. The earlier event was associated with a maximum observed displacement of 3.2 meters and occurred between 5080 +/- 60 and 5310 +/- 60 14C years BP. The moment magnitudes for these events, calculated from displacement and surface rupture length , range from Mw = 6.9 to 7.4 for both events. Scarp heights indicate an uplift rate of 1.11 mm / year. If the late Pinedale alluvium is 14,000 years old, then it appears no events occurred between 14,000 yr BP and 5310 14C yr BP, and two events have occurred between 5310 14C yr BP and 2110 14C yr BP. Such irregular recurrence interval is typical for normal faults in the Basin and Range and makes long-term prediction difficult.

The decline of greater sage-grouse (Centrocercus urophasianus) populations across western North America has intensified conservation, research, and management efforts. Predator-prey interactions have been the focus of widespread scientific study, but little research has been conducted on the effects of predation and predator removal on sage-grouse ecology. This study had three main objectives: 1) identify the types of predators impacting hen survival and nest success, 2) compare the effect of predator removal on vital rates, and 3) evaluate habitat selection and movement. Over two years (2011-2012), an observational study and field experiment were used to test the effects of predation and predator removal on sage-grouse survival, nest success, and spatial ecology in Bighorn Basin, Wyoming. In year one, I quantified the impacts of predators on sage-grouse demographics and developed a basis for monitoring sage-grouse and predator populations. In year two, predator removal was modified to remove the primary nest and hen predator in this system: coyote (Canis latrans). I evaluated the impact of anthropogenic features and management on sage-grouse home range size, seasonal movement, and habitat selection for potential behavioral responses. Resource selection functions (RSFs) were used to determine habitat selection and identify differences at multiple spatial extents (seasonal and annual scales). Hen survival was improved in sites treated with coyote removal over the nesting period (P = 0.05) but no improvement was seen in annual hen survival (P = 0.19). Observed nest success was higher at the site without coyote removal (P < 0.0001). RSF modeling showed sage-grouse to be sensitive to predator removal, avoiding areas close to roads, with high well density, and steep slopes. While this study suggests predator removal does not benefit observed nest success, provides only short-term enhancement to survival, and may disrupt habitat selection, potentially benefits to other life stages could exist and be detected with more time and monitoring. By taking an experimental approach to examining the effects of predation and predator removal, this study advances our knowledge of sage-grouse ecology by identifying changes in demographic vital rates and habitat selection, propagating the best management possible for sage-grouse populations.

Fractures and faults in the Jakey's Fork area, northeastern Wind River Range, Wyoming, caused by brittle Laramide deformation in the Precambrian granitic basement have been studied in detail at airphoto, outcrop, and thin-section scales. The study area is bounded on the south by the approximately east-west and vertical Jakey's Fork Fault and on the east by the approximately northwest-southeast and vertical Ross Lakes Fault. Both were active during Laramide deformation. Four distinct structural domains, defined by fracture pat terns and proximity to the two major faults nave emerged in this study. The areas are: 1) Along Ross Lakes Fault granite cores a fold defined by shallowly and steeply east dipping Cambrian Flathead Sandstone. Laramide movement on Ross Lakes Fault appears to have post-dated, Jakey ' s Fork Fault movement and was discordant with Precambrian zones. Fractures at all scales studied strike approximately northeast-southwest, consistent with the inferred maximum Laramide principal stress. 2) Along east-west striking Jakey's Fork Fault, Laramide movement appears to have reactivated Precambrian mylonite zones as evidenced by the chlorite-rich, foliated cataclasite along its trace. Fractures at all scales have an approximate east-west orientation. 3) Near the intersection of the two faults, deformation was intense, as shown by mylonitic, breccia, and veined clasts. Discrete airphoto fractures were not recognized due to intense deformation in this interaction zone. 4) In the central area, away from the two faults, airphoto and outcrop fracture orientations have a north to northeast strike. Fracture orientations at the thin-section scale are more variable and do not agree with macroscopic orientations; they strike west to northwest. The central area is a 'block', possibly divided into 'sub-blocks' , bounded by zones along which much of the deformation occurred. Thus, these zones had an insulating effect at thin-section scale. The Paleozoic rocks were at least partially decoupled from the basement during deformation, suggested by gouge along the contact and different fracture orientations on opposite sides of the contact. At least two fluid systems are represented in the study area. Relatively wide-spread, pre-Laramide chlorite development occurred at temperatures and pressures higher than those present during Laramide deformation. A Laramide (or post-Laramie ) pervasive fluid system (especially near Ross Lakes Fault) is reflected by abundant fracture porosity, advanced feldspar alteration, and kaolinite development.

Most people are at least aware that, in the past, companies that owned mines, lumber mills, and other large-scale industrial projects in isolated areas also ran company towns. For many people, such towns conjure up images miserable working conditions, exploitative company stores, and inadequate shacks for most workers, while managers live in relative luxury up on “snob knob.” Most people are also fairly certain that such towns, at least in the United States, died out about the same time as the horse and buggy. Several industries in Wyoming, however, continued to support company towns through the end of the 20th century, with one such town surviving into the early 2000s. This project looks at two of these towns supported by the uranium mining and milling industry that dominated central Wyoming’s economy for about 30 years starting in the mid-1950s. These towns, Gas Hills and Jeffrey City, along with Wyoming’s other modern company towns represent a new era in the history of these communities. Furthermore, they actually had many advantages for inhabitants, companies, and the local economy, especially compared to a small conventional community located near a resource boom. Often, and in contrast to the towns in this thesis, conventional towns must scramble to meet the demands of a massive migration, only to be left with unpaid bonds when the resource dries up or becomes no longer profitable.