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Item Hydrothermal influences on the Holocene environmental history of central Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2020) Schiller, Christopher Michael; Chairperson, Graduate Committee: Cathy Whitlock; Cathy Whitlock, Kathryn L. Elder, Nels A. Iverson and Mark B. Abbott were co-authors of the article, 'Erroneously old radiocarbon ages from terrestrial pollen concentrates in Yellowstone Lake, Wyoming, USA' in the journal 'Radiocarbon' which is contained within this dissertation.; Rosine Cartier, Cathy Whitlock and Lisa A. Morgan were co-authors of the article, 'Multi-proxy record of Holocene paleoenvironmental conditions from Yellowstone Lake, Wyoming, USA' submitted to the journal 'Quaternary science reviews' which is contained within this dissertation.; Cathy Whitlock, Sabrina R. Brown and Petra Zahajska were co-authors of the article, 'Holocene geo-ecological evolution in Lower Geyser Basin, Yellowstone National Park' submitted to the journal 'Geological Society of America bulletin' which is contained within this dissertation.; Cathy Whitlock, Mio Alt and Lisa A. Morgan were co-authors of the article, 'Vegetation responses to Quaternary volcanic and hydrothermal disturbances in the northern Rocky Mountains and Greater Yellowstone Ecosystem' in the journal 'Palaeogeography, Palaeoclimatology, Plaeoecology' which is contained within this dissertation.The postglacial vegetation history of Yellowstone National Park is well established by past paleoecological studies, but the role of hydrothermal activity--pervasive in areas of the park--in that history is poorly understood. To address this unknown, pollen and charcoal records were examined from lake sediment cores at multiple sites in central Yellowstone National Park to reconstruct Holocene vegetation. First, radiocarbon ages obtained from pollen concentrates were compared with other age controls at Yellowstone Lake, revealing ages that were up to 4300 cal years too old. Erroneous ages were due to either old carbon contamination from magmatic or hydrothermally degassed CO 2 or old pollen reworked from an unknown source. Second, Holocene vegetation and fire history were reconstructed from a Yellowstone Lake sediment core. The record was characterized by gradually increasing closure or extent of Pinus contorta forest and increasing fire activity to the present, consistent with reduced summer insolation creating cooler, effectively wetter conditions in central Yellowstone National Park. No impact of hydrothermal activity was detected in the regional Holocene-long vegetation and fire histories. Third, Holocene vegetation and fire history were studied at Goose Lake in Lower Geyser Basin, an area with abundant modern hydrothermal activity. The vegetation and fire history diverged from the regional trend at 3800 cal yr BP, synchronous with geochemical indicators indicating reorganization of hydrothermal activity in the basin, suggesting an abrupt ecological response to shifting hydrothermal activity. Finally, a variety of volcanic and hydrothermal processes were investigated as disturbances in the Northern Rocky Mountains and Yellowstone National Park through high-resolution pollen analysis. Hydrothermal explosion deposits were found to be synchronous with conifer morality, in some records, indicating that the effects of hydrothermal explosions are local and short-lived. At a regional scale, it is evident that vegetation changes were chiefly responding to millennial-scale, insolation-driven climate change. However, the impacts of hydrothermal activity were locally important where pervasive, as in Lower Geyser Basin, and in areas recently affected by hydrothermal explosions.Item Structurally-controlled hydrothermal diagenesis of Mississippian reservoir rocks exposed in the Big Snowy Arch, central Montana(Montana State University - Bozeman, College of Letters & Science, 2014) Jeffrey, Sarah Rae; Chairperson, Graduate Committee: David R. LagesonThe subsurface characterization of three-dimensional structural traps is becoming increasingly important with the advent of new technologies for the sequestration of anthropogenic carbon dioxide, which often takes place within preexisting, sealed reservoirs to permanently store greenhouse gasses that are detrimental to the global climate. Within the Big Snowy Arch, central Montana, reservoir units that are targets for carbon sequestration have experienced Laramide and younger deformation and widespread Eocene igneous activity, which introduced a heating mechanism for hydrothermal fluid flow and created anisotropy in Mississippian strata. One particular region of interest is the western flank of the Big Snowy Mountains, which contains a northeast-southwest striking, high-angle fault zone which has acted as a conduit for hydrothermal brine solutions into the overlying Phanerozoic rocks. Such fault zones often branch and bifurcate as they propagate up-section through the overburden, until a loss of thermally-driven hydrodynamic pressure terminates the upward movement of carbon dioxide-rich brines, leaving a distinct assemblage of collapse breccia rich in hydrothermal minerals, such as saddle dolomite and sulfide precipitates. To determine the degree of structurally-induced anisotropy within the reservoir units, field techniques (detailed structural measurements and lithologic descriptions) coupled with analytical methods (X-ray diffraction spectrometry, stable carbon and oxygen isotope analyses, secondary electron imagery, and petrography) were utilized. These techniques presented concrete evidence of hydrothermal mineralization and episodic fluid flow within the brecciated region of the fault zone. These areas are major avenues of enhanced porosity and permeability in the subsurface, which has important applications at some sites in Montana where carbon sequestration is under consideration (e.g., Kevin Dome).Item Structural controls on subsurface fluid migration through thrust sheets of the Stewart Peak culmination, northern Salt River Range, Wyoming(Montana State University - Bozeman, College of Letters & Science, 2012) Lynn, Helen Beatrice; Chairperson, Graduate Committee: David R. LagesonThe Stewart Peak culmination is a duplex fault zone of the Absaroka thrust sheet, which is part of the Sevier fold-and-thrust belt in western Wyoming. Duplex structures can serve as subsurface oil, gas and carbon dioxide (CO 2) traps. The culmination lies east and up-dip from naturally occurring CO 2 traps in Idaho and west of the Moxa arch in Wyoming, another naturally occurring CO 2 trap and potential target for CO 2 sequestration. The culmination has been uplifted and breached by erosion, exposing traps and reservoir rocks analogous to proximal subsurface structures, thus allowing for outcrop-scale investigation of the elements that comprise a complex trap and an analysis of the relative timing of faulting, fracturing, fluid migration and structurally-controlled diagenesis. The purpose of this study was to characterize structural elements of the Stewart Peak culmination that controlled fluid flow. Field-based analyses of fractures, fault damage zones and breccia pipes were conducted in order to assess how these structures affected fluid flow. Rocks were sampled in order to elucidate the diagenetic characteristics of alteration associated with episodes of fluid migration and document the qualities of reservoir rocks. Faulting has led to extensive fracturing and brecciation of rocks in the culmination. The geometry of faults and fracture sets initially controlled fluid migration pathways. Brecciated fault zones of large-displacement thrusts served as focused fluid conduits. Fracturing also facilitated fluid flow, locally enhancing porosity and permeability. The protracted history of deformation in the culmination helped maintain fluid flow pathways through fractures and fault zones. Fault zones and fractures display complex diagenetic alteration as a result of multiple eposodes of deformation and fluid migration. Sub-vertical fracture swarms and breccia bodies dissect some fault zones and represent discrete vertical fluid pathways through which CO 2-charged hydrothermal fluids were focused. Hydrothermal brines may have enhanced structurally-controlled fluid migration pathways through interrelated processes of effervescence-induced brecciation and dolomitization. Faulting, fracturing, brecciation and diagenetic alteration generally enhanced the quality of reservoir rocks and increased the hydraulic connectivity within the culmination. The enhanced porosity and permeability of the Madison Limestone and Bighorn Dolomite indicate that these reservoirs have good potential for CO 2 sequestration.