Thesis (Ph.D.)--Brown University, 2005. / Vita. Thesis advisor: Timothy Herbert. Includes bibliographical references (leaves 141-154). Also available online.

Thesis (Ph. D.)--University of Canterbury, 2007. / Typescript (photocopy). "April 2007." Includes bibliographical references (leaves 248-281). Also available via the World Wide Web.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2007. / Title from title screen (site viewed July 9, 2007). PDF text: xi, 202 p. : ill. UMI publication number: AAT 3252442. Includes bibliographical references. Also available in microfilm and microfiche formats.

Knowledge of the isotopic evolution of volcanic eruptions is essential to volcanologists, geochemists, and paleoclimatologists. I isotopically evaluate the evolution of magmas from their initial formation, to eruption, and then to their alteration during the diffusion of environmental waters into volcanic glass. I focus first on the formation and evolution of large, caldera-forming eruptions from both Gorely volcano in Kamchatka, Russia and 30–40 Ma caldera forming eruptions through Oregon in the United States of America. I utilize oxygen (δ18O), hafnium (εHf), strontium (87Sr/86Sr), and neodymium (143Nd/144Nd) isotopes to document the creation of caldera-forming eruptions at these eruptive centers through the melting of surrounding crust. I also use U-Pb and 40Ar/39Ar to document the timescales of the formation of these large-volume silicic eruptions. Following eruption, the volcanic glass in tephra and ash can slowly take in environmental water. It is thought that the hydrogen isotopic ratio (δD) of these waters can be used to determine paleoenvironments from the time that the volcanic glass was deposited. The latter portion of my dissertation focuses on the use of hydrogen isotopes of environmentally hydrated volcanic glass to determine paleoenvironments, and the calibration of the TCEA to analyze oxygen isotopes of hydrated volcanic glass. I first focus on the rate of diffusion of water at ambient temperature to better understand the time frame necessary to hydrate volcanic glass for use as a paleoenvironmental indicator. I also document the hydrogen isotopic ratios that result from the diffusion of water into volcanic glass, which is documented as a decrease in δD with an increase in secondary hydration in all regions worldwide except equatorial. Finally, I focus on the earliest stages of diffusion of water into volcanic glass by analyzing tephra deposits that were collected within days of the 1980 eruptions of Mount St. Helens as well as tephra deposits recently collected in 2015 to identify changes in water concentration and hydrogen isotopic ratios over an ~35 year period.

Stalagmites, or speleothems, are secondary cave deposits that record the isotope and trace element composition of the parent dripwaters within their crystal matrix. Changes in dripwater oxygen and carbon isotopes (δ18O and δ13C) and trace element to calcium (X/Ca) ratios are controlled by a number of parameters, including changes in rainfall intensity, vegetation regime, and hydrology above the cave. Cave and speleothem studies over the last fifteen years have demonstrated that in order to generate quantitative climate reconstructions, it is necessary to understand the transfer function between changing weather, and changing cave dripwater chemistry above the speleothem being used for reconstruction. In an effort to develop a deeper understanding of these transfer functions, three caves in Marianna, FL were instrumented for several years to monitor rainfall amount, ventilation, temperature, drip rates, dripwater chemistry, and calcite chemistry farmed atop stalagmites that had potential to yield a Holocene rainfall record. In two of the three caves it was found that dripwater X/Ca ratios increase during dry periods and decrease during wet periods, while drips in the third cave exhibited muted variations in X/Ca ratios. A mathematical model was developed to demonstrate that X/Ca ratios are a function of (1) mixing between dissolved limestone and dissolved dolomite, and (2) subsequent evolution away from the dissolved bedrock signature to higher X/Ca ratios as calcium is removed from solution by prior-calcite-precipitation (PCP) upstream of the speleothem. This model provides a diagnostic framework to judge whether dripwaters at each location are entirely controlled hydrologic saturation, and are thus suitable recorders of wet-versus-dry conditions. Timeseries measurement of rainfall amount and changing calcite chemistry allowed quantitative calibration of the transfer function between weather and the speleothem proxy record, a term dubbed 'speleochemical rainfall response'. This speleochemical rainfall response was then applied to stalagmite HRC2 to generate the first quantitative record of rainfall amount in the southeastern United States. The record shows that over the last 1,200 years there have been two significant dry periods. Rainfall in Marianna decreased by up to -60 mm month-1 during the Little Ice Age (650-150 years BP). An equivalent decrease in rainfall amount is only observed during the last 60 years. This record suggests that trends in modern climatic influence over Marianna rainfall have the potential to deliver north Florida into severe drought conditions within the next several decades. / A Dissertation submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester, 2015. / February 25, 2015. / Florida, Isotope, Paleoclimate, Rainfall, Speleothem, Trace Element / Includes bibliographical references. / Munir Humayun, Professor Directing Dissertation; James Elsner, University Representative; William Burnett, Committee Member; William Landing, Committee Member; Harley Means, Committee Member; Vincent Salters, Committee Member; Thomas Scott, Committee Member.

This dissertation presents biostratigraphic, taxonomic and paleoceanographic studies of sediment cores from low-latitude Ocean Drilling Program (ODP) Legs 154 (Site 929), 115 (Site 709), and 202 (Site 1237). Three major paleoceanographic events are featured: 1) the Oi-glacial events in the early-late Oligocene, 2) the Late Oligocene Warming Event (LOWE), and 3) the Oligocene/Miocene Boundary and Mi-1 glacial event. In Chapter Two, a new modified calcareous nannofossil zonation is proposed for the low latitudes that is composed of five major zones and three subzones between 24-30 Ma in age. The first occurrences of Sphenolithus avis, S. ciperoensis, Crassidiscus backmanii along with an increase in abundance of S. ciperoensis, and the last occurrences of S. predistentus, Crassidiscus backmanii and S. ciperoensis are synchronous and reliable throughout the tropics. The last occurrences of Sphenolithus distentus and S. avis are considered unreliable events due to a possible reworking of the former taxon and a diachronous occurrence of the latter. The last occurrences of Helicosphaera compacta and S. pseudoradians are only found in two out of three basins and thus are used as secondary events. The spatial and temporal distributions of calcareous nannofossil assemblages show major variations within the three tropical/subtropical sites. Sphenolithus taxa were found in low abundances in the Atlantic Ocean. Weak tolerance to low salinity is proposed since salinity declined in the Atlantic Ocean during the late Oligocene glacial events due to episodes of freshwater and terrigenous discharge from the Amazon River. This also lowered the δ18O values of seawater at Site 929 compared with the other sites. Furthermore, Site 929 was not far from its present-day position near the mouth of the Amazon River, thus, the low salinity levels best explains the observed major decline in Sphenolithus taxa. Calcareous nannofossil relative abundances (%) and bulk oxygen and carbon stable isotope data reveal a covariant response to glacial (Oi) events. During glacial events, temperate-, cool-water and eutrophic taxa dominated the tropical assemblage, whereas warm and oligotrophic taxa declined. This increase in temperate and cool-water taxa suggest that the tropical surface oceans witnessed a decrease in temperature that allowed cool-, and temperate-water taxa to extend their geographic range into the tropical zone. The Oligocene global glacial events (Oi-2*, Oi-2a, Oi-2b, and Oi-2c) were associated with accelerated upwelling in which eutrophic conditions prevailed and r-mode taxa dominated the total nannofossil abundance. Both Sphenolithus predistentus and Helicosphaera species show prominent increases during glacial (Oi) events. Unlike other Sphenolithus taxa that favored high salinity, S. predistentus increased in abundance during glacial events characterized by high δ18O and δ13C values. Similarly, Helicosphaera taxa show the same pattern with sporadic occurrences. This suggests that S. predistentus and Helicosphaera species were adapted to increased levels of nutrient (eutrophic or mesotrophic). Between 24-25 Ma, warm and oligotrophic taxa increased drastically and dominated the overall assemblage. However, bulk sediment δ18O and δ13C values at the three sites do not show a consistent decreasing trend similar to the global composite deep-sea isotopic record. Although the paleoecological group suggests oligotrophic conditions associated with dominate warm water, the paleotemperature of the sea surface during the LOWE was not as warm as during the Eocene hyperthermals. In Chapter Three, a new and significant late Oligocene Sphenolithus species is described from the tropical ODP materials. The new species, Sphenolithus avis, has a prominent short range spanning upper Zone NP23 to upper Zone NP25 with an age from ~29.9 Ma to 24.8 Ma. Sphenolithus avis is widely distributed and it differs from S. ciperoensis by more flaring proximal shields. In Chapter Four, high-resolution Oligocene/Miocene calcareous nannofossil biostratigraphy has revealed thirteen events, five of which are reliable and synchronous due to their similar ages in the Indian and Pacific Oceans. The synchronous events are: the last occurrences (LOs) of C. fenestratus and S. delphix, and first occurrence (FO) of S. disbelemnos and the beginning and ending of the S. conicus acme. The Sphenolithus conicus acme is documented in the Indian Ocean between 23.5 Ma and 22.8 Ma. This acme was first found in the Pacific Ocean across the Mi-1 glacial event which is characterized by high δ18O and δ13C values. This study supports a correlation of the S. conicus acme in the Indian Ocean with that of relatively similar age in the Pacific Ocean. / A Dissertation submitted to the Department of Earth, Ocean, and Atmospheric Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2016. / April 15, 2016. / Biostratigraphy, Calcareous Nannofossils, Glacial events, Oligocene, Paleoecology, Taxonomy / Includes bibliographical references. / Sherwood W. Wise, Jr., Professor Directing Dissertation; Laura R. Keller, University Representative; William C. Parker, Committee Member; Yang Wang, Committee Member.

The Late Miocene brought a sudden increase in the biomass of C4 plants that resulted in an expansion of grassland habitat and markedly changed the diets of vertebrate fauna in many places around the world. Concurrently, early pulses of Great American Biotic Interchange (GABI) migrations are evidenced by early first appearances of immigrant taxa in the fossil record, leading into the major GABI pulses in the Early Pliocene. The causes and environmental context of GABI migrations, however, are not well understood. Vertebrate fossils from Yepómera, western Chihuahua, represent one of the richest assemblages in Mexico and are a valuable paleo-environmental archive. This study examined the stable isotope compositions of tooth enamel samples of this fauna to provide broad insight into the environmental conditions of this region between 4.89 to 5.23 Ma, just after the arrival of C4 plants in North and South America and before the first major migration of GABI. The enamel carbon and oxygen isotope data suggest a relatively dry, open habitat (similar to savanna or prairie environments) with a strong C4 vegetation component, a mean annual temperature of 18 ± 10°C and a moderate annual precipitation of 657 ± 93 mm/yr. At Yepómera, there was distinct niche partitioning into pure C3 diets, mixed diets, and pure C4 diets. As such, C4 vegetation must have been a major component of the environment during the Late Miocene-Early Pliocene. Despite expectations, no niche partitioning between equid species (Dinohippus mexicanus, Nannippus aztecus, Astrohippus stockii, and Neohipparion eurystyle) can be determined from carbon isotope ratios. All four fossil horse species found in Yepómera had pure or nearly pure C4 diets, suggesting that they were hyper grazers or primarily grazers, consistent with the inference from their dental morphology. Pure C3 consumption was rare to absent in all other genera analyzed except for the genus Camelops, for which C3 vegetation was the dominant diet. Samples from Hemiauchenia varied between pure C3 diet and a mixed diet depending on the individual. The other genera in this study site (Gomphotheriidae, Hexobelomeryx fricki, and Platygonus) were primarily mixed feeders. Assuming a carnivorous life habit (based on dentition), Agriotherium schneideri, an immigrant large ursid, appears to have consumed primarily equids or an unsampled taxon with predominantly C4 diet. However, the enamel isotope data cannot exclude the possibility of an omnivorous life habit. Migrations are evidenced in the oxygen isotope ratios of several specimens indicating that there was mobility in these taxa before the GABI, with diets remaining consistent throughout this migration (suggesting strong dietary preferences and niche specialization). The carbon and oxygen isotope ratios of the Yepómera fauna are consistent with both the holding pen hypothesis for the GABI and a Central American rise in C4 biomass at least close in time to the expansion of C4 biomass in North America. Through adaptation to this ecosystem, these taxa would be well prepared to exploit and compete for the grassland habitats proposed to have developed on the Panama Isthmus. This could explain how equids, peccaries, gomphotheres, and short-faced bears related to these taxa had such success in arriving and diversifying in the South American mainland, where a similar habitat is believed to have expanded around the time of the exchange. Future work in this area will lead to a more complete understanding of biologic responses to changing climate and population dynamics. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / 2019 / November 14, 2019. / Diet, Enamel, GABI, Mexico / Includes bibliographical references. / Yang Wang, Professor Directing Thesis; William C. Parker, Committee Member; Jeremy Owens, Committee Member; Gregory M. Erickson, Committee Member.

Indiana University-Purdue University Indianapolis (IUPUI) / Late Holocene hydroclimate variability in the midcontinental United States is not well understood because there is a lack of high-resolution paleoclimate records constraining historical climate patterns for the region. Here, a 2500-year-long multi proxy lake sediment record from a northern Indiana kettle lake is used to examine spatial and temporal scales of drought and pluvial patterns in the Midwest. Oxygen (18Ocal) isotope analysis of authigenic carbonate and the sedimentary lithic abundance (%lithics) are the primary datasets used to evaluate hydroclimate trends with supporting information from total organic matter, total carbonate and magnetic susceptibility. We additionally derive a record of local evaporation by subtracting the isotopic composition of precipitation (18Oprecip) as characterized by the nearby Martin Lake, IN, record, from the Pretty Lake 18Ocal record. The combined Pretty Lake hydroclimate record documents climate variability during the last 2 millennia and shows that the Midwest has experienced a wide range of evaporative regimes during the late Holocene. We notice a consistent relationship between the Pretty and Martin Lake multi-proxy records; where reduced (increased) evaporative periods and higher (lower) lake levels at Pretty Lake mostly align with increased (decreased) Gulf sourced precipitation and stream erosion with longer (shorter) warm seasons at Martin Lake. Early periods of much drier, and weakened warm-season evaporation patterns dominated from 600 BCE to 900 CE. Evidence of a prolonged period of enhanced warm-season pluvial conditions, with less evaporation and higher lake levels, during the Medieval Climate Anomaly (MCA) between 900 to 1350 CE; and a pronounced century of arid conditions throughout the Little Ice Age (LIA) from 1350 to 1700 CE followed by a gradual decrease in evaporation and rising lake levels starting at 1700 CE and continuing to present. These trends track other Midwest regional hydroclimate climate records, but show an anti-phased relationship with records from the High Plains and western United States regions. This supports the idea that a hydrocilmate dipole exists between the Midwest and western United States driven largely by mean state changes in the Pacific North American teleconnection pattern, but with modification by local and in-lake responses to mean climate states.

No description available.

Thesis (Ph. D.)--University of Oregon, 2006. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 729-756). Also available for download via the World Wide Web; free to University of Oregon users.