Understanding the past sensitivity of ice sheets and sea level rise in a warmer climate is essential to future coastal planning under the threat of climate change, as accurately modeling impending scenarios depends primarily on data from the past. Extreme warm events during the Quaternary and Neogene periods hold much of the information needed to predict future global climate conditions due to anthropogenic and natural forcings, and may provide unique glimpses of how much future sea level rise can be expected on both short- and long-term timescales. Constraining global mean sea level (GMSL) during past warm periods becomes increasingly difficult the further back in time one goes, especially as precise dating of globally distributed paleoshorelines, along with long-term vertical displacement rates, is essential for establishing GMSL and ice volume history. However, placing chronological constraints on shorelines beyond the limit of U-series radiometric dating (~600 kyr), or at high latitude sites lacking coral, has remained elusive. Even relatively recent warm periods, such as the Last Interglacial (~117-129 ka) has proved challenging for reconstructing GMSL, primarily due to uncertainties in long-term vertical deformation rates and timing of when the highstand occurred. The first two chapters of this thesis address the dating of carbonate shorelines older than ~500 kyr through refinement of the strontium isotope stratigraphy dating methodology. I apply these techniques to a well-known location with numerous uplifted fossil shorelines (Cape Range, Western Australia) to provide the first geochemically derived ages on three fossil shorelines spanning the Pleistocene to the Miocene. Accurate dating and mapping at this location allows correction of long-term vertical displacement. In the last chapter, I use these rates of uplift, in conjunction with twenty new 230Th/U-ages on corals from Western Australia, to refine the timing and peak elevation of the Last Interglacial sea level highstand. Chapter 1 re-evaluates strontium isotope stratigraphy dating techniques for chronologically constraining fossil shorelines from ~0.5 to >30 Ma. Using marine terraces from South Africa, Western Australia, and the Eastern United States as examples, this chapter presents a refined sampling and dating methodology to overcome limitations on diagenetically altered samples, which are ubiquitous in older carbonate shorelines. Discussion on best practices for constraining maximum or minimum ages includes a novel scoring methodology for alteration and a sequential leaching procedure that is specifically suited for shallow-water biogenic carbonate fauna. In Chapter 2, I apply the revised strontium isotope stratigraphy dating methodology to three previously unknown aged terraces in Cape Range, Western Australia. The results obtained show Late-Miocene, Late-Pliocene and Mid-Pleistocene shorelines, which I then use to reconstruct the vertical uplift history of the anticlinal structure and relative rates of deformation. This study is the first to directly date the three terraces, and provides the deformation history necessary for constraining Last Interglacial sea level at Cape Range. In addition, we are able to place maximum relative sea level constraints on all three of these older shorelines. Chapter 3 builds upon the previous chapter by focusing on the Last Interglacial sea level history along ~300 km of coastline in Western Australia (Cape Range and Quobba). This chapter presents new U-series ages on multiple coral heads that are among the highest in-situ corals ever dated in Western Australia, with ages spanning from ~125.3 – 122.6 ka. Detailed geomorphic analysis, particularly at Cape Range, constrains the relative sea level highstand to 6.9 ± 0.4 m. When glacial isostatic adjustment models are applied to the age and elevation data, the resulting Eemian GMSL highstand occurred between 125.5-123.0 ka and reached an elevation between 4.9 and 6.7 m. This is later in the Interglacial and lower in elevation than many recent studies suggest. This dissertation focuses on refining sea level highstands from the Last Interglacial to the Late Miocene in a relatively small (but historically important) region of Western Australia. However, the methodologies presented here provide a powerful multi-proxy dating and mapping approach, which, when applied to regions with multiple marine terraces, can greatly improve the reliability of younger shoreline elevations by reducing neotectonic and dynamic topography uncertainties. The carbonate screening techniques and 87Sr/86Sr stratigraphy dating described here are applicable to a wide range of marine carbonates, with the ability to place accurate chronologic constraints on shorelines from 0.5 to >30 Ma. As I show in chapter 3, when combined with 230Th/U-dating on Late Pleistocene coral in places where multiple marine terraces exist, valuable long-term vertical deformation constraints can allow for far more accurate analysis of sea level in younger paleo shorelines (i.e. Last Interglacial).

The discovery of deep-sea hydrothermal vents in 1977 revealed an ecosystem supported by chemosynthesis with a rich diversity of invertebrates, Archaea and Bacteria. While the invertebrate vent communities are largely composed of endemic species and exist in different biogeographical provinces, the possible factors influencing the distribution patterns of free-living Archaea and Bacteria are still being explored. In particular, how differences in the geologic setting of vent fields influence microbial communities and populations associated with active vent deposits remains largely unknown. The overall goal of the studies presented in this dissertation was to examine the links between the geologic setting of hydrothermal vent fields and microorganisms associated with actively venting mineral deposits at two levels of biological organization. At the community level, bar-coded pyrosequencing of a segment of the archaeal and bacterial 16S rRNA gene was employed to characterize and compare the microbial communities associated with numerous deposits from several geochemically different vent fields. Results from these studies suggest that factors influencing end-member fluid chemistry, such as host-rock composition and degassing of magmatic volatiles, help to structure the microbial communities at the vent field scale. At the population level, targeted cultivation-dependent and -independent studies were conducted in order to expand our understanding of thermoacidophily in diverse hydrothermal environments. Results of these studies expanded the phylogenetic and physiological diversity of thermoacidophiles in deep-sea vent environments and provided clues to factors that are influencing the biogeography of an important thermoacidophilic archaeal lineage. Overall, these studies have increased our understanding of the interplay between geologic processes and microorganisms in deep-sea hydrothermal environments.

No description available.

Seamounts, or submarine volcanos, have two distinct phases: the formation phase when the seamount is magmatically active and the passive phase when the seamount is transporting on the seafloor until subduction. Being able to understand various aspects of seamounts both in the formation and passive phase can enhance our understanding of volcanic processes and how seamounts can influence other processes such as crustal deformation, plate subduction, and earthquake generation. The purpose of this thesis is to examine seamounts on the Juan de Fuca plate both in the formation and passive phases. The first three chapters of this thesis focuses on understanding the subsurface properties and volcanic processes of Axial Seamount, an active seamount located on the Juan de Fuca Ridge. The fourth and final chapter focuses on understanding how seamounts influence subduction and the seismogenic properties of the Cascadia Subduction Zone. In chapter 1, I analyze multichannel seismic data to characterize the internal crustal structure of the rift zones of Axial Seamount. The new reflectivity images reveal small and discontinuous crustal magma bodies beneath and in the vicinity of the rift zone lava flows from the three most recent eruptions. We also image wide magma bodies within the overlap regions between the rift zones and neighboring segments of Juan de Fuca Ridge. Collectively the new observations indicate that multiple small crustal magma bodies underlie Axial and likely contribute to rift zone magmatism with implications for interpretations of seismicity patterns and lava flow compositions. In chapters 2 and 3, I process over 7 years of continuous seismic noise at Axial Seamount and use cross-correlation functions to calculate the relative seismic velocity (dv/v) changes beneath the caldera. I find a long-term trend of decreasing velocity during rapid inflation, followed by slight increase in velocities as background seismicity increases and inflation rate decreases. I also observe small short-term increases in dv/v which coincide with short-term deflation events. The observations of changes in dv/v and their correlation with other geophysical data provide insights into how the top ~1 km of the crust at Axial Seamount changes in response to subsurface magma movement and capture the transition from a period of rapid reinflation to a period where the caldera wall faults become critically stressed and must rupture to accommodate further inflation. From the relative seismic velocity variations, I also observe a strong annual pattern constrained within the 0.1-0.2Hz filter band. This annual pattern correlates well with timing and location of storm activity within the Pacific Ocean. Through the comparison of annual variation with ocean data, we determine that the annual pattern observed is likely an apparent velocity change due to changes in the seismic noise source. Lastly, in chapter 4, I utilize multichannel seismic data and high-resolution P-wave velocity (Vp) models of the CASIE21 expedition to calculate residual Vp models to examine properties of the sediments relative to seamounts on the incoming plate. At one of the larger seamounts located within 25km of the deformation front, I show evidence consistent with predicted stress effects of buried topography where there is an increase in normal stresses landward and a stress shadow seaward of the seamount, which can alter and impact rupture patterns along the margin. I also show evidence for signatures of enhanced hydrothermal circulation at seamounts near the deformation front which show that seamounts can be potential carriers of additional fluid into the margin when subducted. In additional to looking at the sediments relative to the seamounts, I also evaluate properties of a high Vp basal layer that is prevalent on all of the lines which can provide insights into the earthquake rupture and tsunami potential for the area.

The Gorda Escarpment (40.4° N and from 126° W to 124.7° W) is a topographic high which is the eastern portion of the Mendocino Transform Fault. The Vizcaino Block is the anomalously shallow portion of the Pacific plate immediately south of the Gorda Escarpment. Sediments of the Vizcaino Block record a history of uplift and subsidence for itself and the Gorda Escarpment. Previous work on the Mendocino Ridge (the bathymetric expression of the Mendocino Transform Fault west of 126° W, where there is little sediment overlying basement) indicated that the ridge had been above sea level at some time in the past (Krause et al., 1964; Fisk et al., 1993). Assuming that the two bathymetric features have undergone the same response to tectonic forces, this study aims to constrain the timing of uplift and subsidence for the Gorda Escarpment, Vizcaino Block, and Mendocino Ridge by using the geological record of sediments of the Vizcaino Block. ODP Site 1022 drilling penetrated 379 meters into the Vizcaino Block's sediments. Age and lithologic constraints from the recovered cores, along with in-situ sampling by ROV and gravity cores, were integrated with a network of 25 seismic reflection lines. From these it is evident that uplift of the Gorda Escarpment and Mendocino Ridge began before 6 Ma, and was at a maximum at 2.7 Ma. Ocean circulation was likely altered by the uplift of the Gorda Escarpment and Mendocino Ridge. In turn, the altered ocean circulation regime may have had an impact on the regional climate in the Pliocene. From 2.7 Ma until the present the Gorda Escarpment, the Vizcaino Block and the Mendocino Ridge have been subsiding. / Graduation date: 2003

The Kane Oceanic Core Complex (OCC) is a valuable window into crustal architecture and chemical composition of the lithosphere beneath a slow-spreading ocean ridge. A suite of > 30 samples (comprised of whole rocks, mineral separates and basalt glasses) has been analyzed for ��He/���He isotope ratios and He concentrations. Gas extraction experiments included crushing in vacuum, step heating and fusion in a high-vacuum furnace. We found ��He/���He in the two freshest peridotites (harzburgite and olivine websterite) to be identical to ratios measured in basalt glasses collected from the Kane fracture zone-ridge axis intersection (8.4���8.7 R[subscript A]). Notably, the freshest and least deformed peridotite (a porphyroclastic harzburgite) has the highest helium content of any of the OCC ultramafic rocks (170 ncc STP/g), while the majority of its helium (70%) is released only upon melting. Lower helium contents (1-45 ncc STP/g) and more variable ��He/���He (2.0-6.3 R[subscript A]) are found in other more altered/deformed peridotite samples (whole rocks, clinopyroxene and orthopyroxene separates). For example, three mylonitized peridotites have lower helium contents compared to the less deformed peridotites. Troctolite intrusions from the Adam and Eve Domes appear to record very late-stage melt impregnation fed through dunite conduits near the MOHO. ��He/���He in these troctolites overlaps with values in the fresh peridotites and axial basalts, but extends to slightly higher values (8.6-9.0 RA). Collectively, fresh Kane peridotites and troctolites having He concentrations above 10 ncc STP/g show ��He/���He ratios of 8.4-9.0 RA that are higher than the median value (8.0-8.2 R[subscript A]) for mid-ocean ridge basalts. This suggests that domains of depleted upper mantle in the Kane region tend to have ��He/���He ratios of 9 RA or higher, similar to what is observed in the most trace-element depleted MORBs globally. Kane gabbroic rocks are more variable in 3He/���He. A subset of gabbros show systematically lower ��He/4He ratios (0.9-7.2 R[subscript A]), with He concentrations of 1-24 ncc STP/g, reflecting the increased importance of atmospheric and radiogenic components in several cases. Nonetheless, two whole rock gabbroic samples plus an amphibole separate have ��He/���He ratios of 7.6-8.0 R[subscript A] and He contents between 13 and 57 ncc STP/g. Variation in the sampling of a lithologically heterogeneous mantle source by the partial melting process may account for the observed ��He/���He variability of 7.6-9.0 R[subscript A] in peridotite, gabbro and basalt in the Kane area. / Graduation date: 2013

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Geological Sciences." Includes bibliographical references.

No description available.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 79-85). Also available on the World Wide Web.

Thesis (M.S.)--University of North Carolina at Wilmington, 2004. / Includes bibliographical references (leaves : 67-72).