Theses and Dissertations at Montana State University (MSU)
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Item Change in provenance and sediment routing history of the Miocene-Pleistocene Bengal Fan, Indian Ocean using detrital zircon (U-Th)/He thermochronology(Montana State University - Bozeman, College of Letters & Science, 2023) Dixon, Timothy Spencer; Chairperson, Graduate Committee: Devon A. Orme; This is a manuscript style paper that includes co-authored chapters.The Ganges-Brahmaputra river system carries thousands of tons of sediment from the Himalaya each year to the submarine Bengal Fan within the Indian Ocean. Deposition of sediments to the fan has been ongoing since at least late-Oligocene time (Krishna et al., 2016), preserving a record of Himalayan tectonics and topographic evolution (Blum et al., 2018). IODP Expedition 354 (2015) collected 1.7 km of sediment core from the Bengal Fan to expand the record of Himalayan sediment routing (France-Lanord et al., 2016). Detrital zircon U-Pb data from core samples reflect five major tectonostratigraphic sequences from the Himalaya-Tibet Orogen (Blum et al., 2018). Age populations appear to vary temporally, suggesting change in erosion rates and sediment routing through time, especially apparent during the Pliocene-Pleistocene transition. This research uses detrital zircon (U-Th)/He thermochronology, double dating analyses, and sediment mixing model approaches to fingerprint changes in sediment routing and river deposition to the Bengal Fan. (U-Th)/He analyses are used to quantify rock uplift and exhumation experienced in the Himalayas, facilitating lag-time interpretations across Miocene-Pleistocene time. To interpret the Bengal Basin sink record, a compilation of mid to low-temperature thermochronology datasets across the Himalaya-Tibet orogen is presented for characterization of modern-day thermochronologic age signals. This database highlights orogen wide trends in cooling dates that show younging apatite/zircon (U-Th)/He and fission tracks in the frontal Himalaya and syntaxes, and a younging trend in 40Ar/39Ar dates towards the orogen center. Zircon (U-Th)/He analyses of Bengal Fan sediments deposited 6.20 - 0.13 Ma reveal cooling dates from ~0.28 + or - 0.03 - 540.15 + or - 6.13 Ma. Age populations vary greatly between Miocene-Pleistocene time, with notable loss of >23 Ma populations between Miocene-Pliocene time and increasing 5.3 - 23 Ma populations across the Pliocene-Pleistocene transition with decreasing depositional lag-times. Comparison of age populations to previously recorded cooling dates from the orogen reveal shifts from Brahmaputra to Ganges sources between Miocene-Pliocene time before reaching a mixed drainage signal in the middle Pleistocene. Observed shifts in sediment provenance are attributed to coupled tectonic-climatic forces with regional acceleration of exhumation in the Himalaya, onset of northern hemisphere glaciation and increased denudation of the frontal-Himalaya during Miocene-Pleistocene time.Item Understanding the Coprophilous fungus Sporormiella as a proxy for megaherbivores(Montana State University - Bozeman, College of Letters & Science, 2020) Ulrich, Barbara Carol; Chairperson, Graduate Committee: Cathy WhitlockIn many studies, the presence of the coprophilous fungus Sporormiella in Quaternary sediments has been interpreted as evidence of past megaherbivore activity. Despite its use as an ecological proxy, little is known about the taxonomy and life history of Sporormiella, and the taphonomic processes that lead to its preservation in lake sediments. This information underlies its utility to interpret past herbivore presence and abundance. Present-day bison (Bison bison) dung from Yellowstone National Park was examined to explore the production, dispersal, transportation, deposition, and preservation of Sporormiella there. While Sporormiella was found in dung samples, sediments from two lakes frequently visited by bison failed to yield Sporormiella spores. Laboratory preparation techniques were modified to increase the likelihood of Sporormiella spore survival, yet no spores were identified with the new treatment. Although the occurrence of spores in lake-sediment samples may indicate herbivore presence, our study suggests that spore absence does not necessarily indicate an absence of herbivores. We attribute the absence of spores in sediments to local climatic and seasonal factors that may affect production and transport in the watershed, sedimentary processes that may destroy spores after deposition, and harsh laboratory processing techniques that may damage or destroy spores. More research remains to be done to evaluate the importance of these factors before using Sporormiella as a reliable proxy of herbivore activity.Item Channel morphology controls on the spatial distribution of trace metals in bed sediments in Soda Butte Creek, Montana(Montana State University - Bozeman, College of Letters & Science, 1995) Ladd, Scott ChristopherItem Field verification of predictive bedload formulas in a coarse bedload mountain stream(Montana State University - Bozeman, College of Letters & Science, 1988) Bugosh, NicholasItem Erosional impact of hikers, horses, off-road bicycles, and motorcycles on mountain trails(Montana State University - Bozeman, College of Letters & Science, 1991) Seney, Joseph PaulItem Sedimentological analyses of eggshell transport and deposition : implication and application to eggshell taphonomy(Montana State University - Bozeman, College of Letters & Science, 2013) Imai, Takuya; Chairperson, Graduate Committee: David VarricchioThe interpretation of fossil eggshell assemblages in the absence of nesting structures is problematic because eggshells can be transported by hydraulic flows in fluvial environments. Failure to recognize transported eggshells may lead to erroneous interpretation of the reproductive behavior and ecology of those animals. An inconsistent array of evidence has been used in past studies to assess eggshell transport. Here, a series of flume studies was conducted to establish analytical techniques for assessing eggshell hydraulic transport in the fossil record. Using modern eggshells in a flume, I investigated preferred eggshell orientation after transport, the relationship of flow competence with eggshell shape and size, and size of clastic sediment expected to be associated with transported eggshells. Emu, goose, and ostrich eggshell fragments were released in a rectangular flume with decelerating flow. The transport of each eggshell was observed five times on each of four substrates (coarse sand, sparse gravel, dense gravel, and polyvinylchloride). At eggshell deposition, eggshell orientation and flow depth were recorded. Critical bed shear stress for eggshell deposition was estimated based on the flow depth at the point of eggshell deposition. The probability of concave-down orientation for deposited eggshells was estimated for each eggshell type transported on each substrate. The relationship of the critical bed shear stress for eggshell deposition with eggshell shape and size was tested. Size of clastic grains deposited under the critical bed shear stress for eggshell deposition was estimated. The probability of concave-down orientation after transport was > 85% regardless of eggshell types and substrates. The bed shear stress at eggshell deposition was most closely related to eggshell height and volume. Estimated size of clastic sediment associated with transported eggshell was coarse sand or coarser sediment. One may consider a high proportion of concave-down oriented eggshells in fossil assemblages as indicative of transport regardless of eggshell types. In addition, eggshells may be sorted according to their height and volume. Coarse sand or larger particles observed in matrix of fossil eggshells may be used as evidence of eggshell transport. Further studies are necessary to test reliability of those techniques and broaden their applicability.