I examined how predatory damage in bivalve shells can be used to assess the trophic importance of species, how oxygen isotope ratios in shells can be used to estimate past salinity, and how Colorado River flow affects growth rates in a bivalve mollusk. I devised methods to distinguish predatory damage from mechanical breakage in Mytilus trossulus at Argyle Creek, Washington. After 100 h of tumbling, live-collected mussel shells were abraded and disarticulated but not otherwise damaged. Eight percent of the dead-collected shells were broken during tumbling. Three types of diagnostic damage were inflicted by crab predation in lab experiments: nibbles, nibbles and chips, and peels; and trampling and tumbling caused three types of chipping: crescentic, angular, and slivered. Crushed shells and shells with fractured margins were caused by both predation and trampling. The source of damage could be correctly identified in ~ 75% of the shells. I also investigated the trophic importance of Mulinia coloradoensis in the Colorado River Delta (CRD). I analyzed the frequency of predatory damage on shells from before the era of upstream water diversions (the "predambrian"). I documented that five to 50% of the shells were attacked by predatory gastropods or crabs. The clam's population decline probably decreased the population sizes of its predators. I also reconstructed the pristine pre-impact salinity regime of the CRD. I estimated predambrian salinities by using oxygen isotopes in shells of M. coloradoensis. Since the construction of upstream water diversions, average salinity in the estuary has increased to 38; in the predambrian, M. coloradoensis grew when salinity ranged between 22-38. I studied the growth of M. coloradoensis by examining the sclerochronology of its shell and comparing growth rates in predambrian and dambrian specimens. Each micro-growth increment in M. coloradoensis consists of two semidiurnal growth increments showing a strong fortnightly periodicity reflecting tidal cycles. In shells of similar height, predambrian M. coloradoensis shells recorded twice the number of fortnights than dambrian shells, suggesting that dambrian shells grew twice as fast as predambrian shells. The observed differences in growth rate between pre-and post-dam M. coloradoensis are probably regulated by density-dependent processes.

The northwestern Chihuahuan Desert along the U.S.A.-Mexico border contains a rich mosaic of vegetation with high levels of biodiversity. A conspicuous gap in packrat midden coverage, however, exists for this area and paleovegetation data is scarce. The focus of this dissertation is the reconstruction of late Quaternary ecology, climatology, and biogeography of the northern Chihuahuan Desert.A new packrat midden chronology from Playas Valley, NM is the first installment of an effort to reconstruct paleovegetation and paleoclimate in the U.S.A.-Mexico Borderlands. Plant macrofossil and pollen assemblages from nine middens indicate late Pleistocene vegetation along pluvial lake margins consisted of open pinyon-juniper communities dominated by Pinus edulis, Juniperus scopulorum, Juniperus cf. coahuilensis and an understory of C4 annuals and grasses. This summer-flowering understory, characteristic of modern desert grasslands, suggests at least moderate late Pleistocene summer precipitation. By 10,670 14C yr B.P. Pinus edulis and Juniperus scopulorum had become rare or disappeared. The late Holocene was marked by arrival of Chihuahuan Desert scrub as vegetation became modern in character. A 36,200 cal yr B.P. midden record was also developed from the Peloncillo Mountains along the Arizona-New Mexico-Mexico border. Between 36,200-15,410 cal yr B.P., rocky areas above playa lakes supported Pinus edulis, Juniperus osteosperma, Juniperus cf. coahuilensis, and Quercus turbinella. This site also supported summer-flowering C4 annuals and grasses, indicating abundant summer rains and relatively warm temperatures. After ~15,410 cal yr B.P., Pinus edulis declined in abundance and disappeared briefly at 13,925 cal yr B.P., coincident with other evidence for Bølling-Allerød aridity, and then rebounded briefly during the Younger Dryas. Few middens date from the early to middle Holocene, while 35 middens from the late Holocene detail increasingly aridity.Bioclimatic envelopes were also applied to packrat midden series from the USA-Mexico borderlands. Bioclimatic envelopes for C4 grasses indicate winter temperatures were no more than 4.5ºC colder than present and summer temperatures no more than 4.4ºC colder during late Pleistocene, while summer precipitation was reduced by no more than 50%. The appearance of many desertscrub species around 5000-4000 yr B.P. appears to have been due, at least in part, to increasing winter temperatures.

The inspiration for my topic was the use of hydrogen as a fuel source. Currently, the use of hydrogen is limited by the need to find a safe storage solution. I wanted to know how Nature stores hydrogen in minerals. The studies in my dissertation examine the nature of materials that contain hydrogen as OH groups through a variety of techniques. First, I examine the 450 known mineral species that contain isolated OH groups and have crystal structure determinations that include the location of the hydrogen atoms. I identify nine unique classes of OH hydrogen environments. The hydrogen environment exemplified by the mineral behoite is of particular interest because of behoite's structural relationship with SiO₂ cristobalite. I conducted two high-pressure studies exploring the similarities and differences in the behaviors of behoite and cristobalite as a function of pressure. In the process of categorizing the OH hydrogen environments in minerals I encountered minerals who's structures needed to be refined. Refinements for two minerals, despujolsite, a member of the fleischerite group of minerals, and kôzulite, an Mn rich amphibole, are presented and discussed. Two manuscripts, one on the new mineral bobdownsite, and the other on the mineral walstromite, are appended to this dissertation to highlight additional original research conducted throughout my graduate career.

In subduction zones, the dip of the downgoing oceanic lithosphere has a profound impact on the nature and extent of deformation as well as the generation of melt. In ~10% of subduction zones, the downgoing slab assumes a low-angle, or horizontal geometry, referred to as flat-slab subduction. The focus of this work is to better understand both the driving forces and impacts of flat-slab subduction on the Earth's lithosphere and asthenosphere. This is accomplished by focusing on three areas impacted by flat-slab subduction. The first area is the Pampean region of central Argentina and Chile, a modern flat-slab subduction zone. In this region, we invert Rayleigh-wave-dispersion data to produce a 3D shear velocity model. The flat slab is visible within the upper mantle as a high-velocity body containing low-velocity pockets that dissipate inboard from the trench. We interpret these velocities in the context of slab hydration and argue that the subducting Nazca plate is initially hydrated at the trench and dewaters as it subducts. The second area is southern California, which was impacted by Laramide flat-slab subduction. In this area, we use receiver functions to locate and parameterize anisotropy within the crust. Results show a persistent NE-SW oriented layer of lower crustal anisotropy. We conclude that this layer consists of schists that were emplaced during Laramide flat-slab subduction and have remained largely intact since. The final component of this work is a study of the Colorado Plateau in which we use ambient-noise tomography and receiver functions to study lithospheric structure. Results show fast crust, a complicated Moho and intact Laramide features throughout the crust beneath the Colorado Plateau while slower crust with a sharp Moho is observed along its margins. Based on these observations, published tomographic data and the volcanic and uplift history of the region, we argue that delamination of the lower crust has occurred beneath the Marysvale volcanic field. This process was driven by the gravitational instability of a dense mafic root that formed during mid-Tertiary magmatism related to the rollback of the Farallon flat slab.

Human activities are the main driver of environmental changes over the past 100-200 years, and threaten the stability of Earth's environmental systems. One part of Earth's environment already destabilized due to human activities is its climate. With human-caused changes to Earth's climate expected to continue, questions arise as to which, where, and when impacts to human and natural systems might occur. Understanding the vulnerability - the exposure, sensitivity, and resilience - of a system to changes in climate is essential to addressing these questions. This study represents an assessment of system vulnerability to climate change through the cases of modern sea level rise (SLR) and southwestern U.S. (SW) bioclimate. SLR is an important consequence of human-caused climate change, as higher seas have the potential to cause major social, environmental, and economic impacts. With a focus on sensitivity to SLR, we developed a new geospatial dataset that delineates low-lying coastal areas and overlaid this dataset with boundaries of U.S. cities with populations greater than 50,000 to determine areas prone to SLR impacts in this and subsequent centuries. Results demonstrate that potential SLR impacts to 180 U.S. cities will be very local and disproportionate. Recent warm and dry conditions have altered SW bioclimate, and expected further increases in regional temperatures raise concern that anomalous growing conditions will continue to occur and, in cases, worsen in the future. With a focus on exposure of SW vegetation to changing growing conditions, we compared the 1950s and 2000s droughts to take advantage of the opportunity to study mesoscale ecosystem responses to anomalously dry conditions before and during the regional warming. Higher temperatures and evapotranspirational demand during the more recent drought altered the degree to which climate limited foliar growth. These climatic conditions reduced effects of suboptimal temperatures on foliar growth at lower elevations in winter and higher elevations in summer. They also increased constraints of evapotranspirational demand on foliar growth at lower and middle elevations from spring through summer. Free-tropospheric air temperatures, a strong influence on climate in mountainous areas, support statistical downscaling of projected SW temperatures to assess if and when similar or more anomalous conditions will occur in upcoming decades. Assessing the vulnerability of a system to changes in Earth's climate like those taking place and projected to happen is a way for environmental sciences to help inform policy decisions that consequently stem from past or potential impacts of climatic hazards.

The long-lived radionuclide ¹²⁹I (half-life: 15.7 × 10⁶ yr) is well-known as a useful environmental tracer. At present, the global ¹²⁹I in surface water is about 1-2 orders of magnitude higher than pre-1960 levels. In order to understand the spread of ¹²⁹I in the Pacific Ocean, ¹²⁹I time series from corals and seawater were reconstructed. Two iodine extraction methods were tested and compared to optimize the yield and precision of the measurements. A solvent extraction method was chosen over a resin column preparation technique giving that it provides higher signal and lower error. Coral ¹²⁹I time series records from the Western Pacific including Con Dao and Xisha Islands, in the South China Sea; Rabaul, Papua New Guinea, in the South Pacific; and Guam in the North Pacific were reconstructed and pathways and sources of ¹²⁹I from the 1950s onward were assessed. Nuclear weapons testing was the primary ¹²⁹I source to the ocean, notably from testing in the Marshall Islands and radiogenic iodine was carried primarily through surface ocean currents. A seawater ¹²⁹I monitoring program was instituted with seawater samples from Scripps Pier, La Jolla, California, USA a few months after the Great East Japan Earthquake, which involved the accidental release of substantial amounts of ¹²⁹I from the Fukushima Daichi nuclear power plant. These data were used to construct a 4-year record of surface water ¹²⁹I with monthly resolution. ¹²⁹I in Hanford site vicinity is also surveyed to understand the background value of the California Current System. It is clear that the California Current System is influenced by the Hanford site which can explain the higher ¹²⁹I/¹²⁷I background values observed along the west coast of the U.S. compared to other surface sites in the Pacific Ocean. Our result shows that the highly contaminated seawater from the Fukushima Daiichi Nuclear Power Plant accident has not yet seen at the Scripps Pier, La Jolla, California, USA four years of ocean transport.

The Amazon Craton is one of the largest Precambrian landmasses on Earth, yet its crustal growth history and evolution are relatively poorly constrained. This dissertation addresses the timing and modes of continental growth and deformation of a sizable portion of the central and western Guyana Shield, mostly using a combination of texturally-resolved U-Pb, Lu-Hf and δ¹⁸O analysis of zircon. These results provide a wealth of new information that have major implications for the role of Amazonia in Precambrian supercontinent models, its significance in the global record of crustal generation and the possible tectonic processes that were involved in its construction. It is argued that, contrary to the previously accepted Proterozoic accretionary model for the growth of northwestern Amazonia, the new data suggest that sizable portions of the shield formed during an episodic extraction event in the Neorchean. This hypothesis challenges the current tectonic model for the evolution of Amazonia, and provides evidence for the continued importance that mechanisms inducing episodic crustal generation had after subduction-driven plate tectonics had been established on Earth. During the last decade, the study of crustal growth processes by means of U-Pb-Hf-O analysis of zircon has considerably improved our understanding of the mechanisms that drive planetary differentiation. However, zircon has a significant limitation, and is that basic and ultrabasic rocks have very low fertility to form this mineral owing to their low SiO₂ composition. Therefore, the global zircon U-Pb-Hf repository is biased towards the felsic portion of the crust, leaving the mafic archive mostly unconstrained. Undersaturated rocks can form baddeleyite, a phase with high affinity for Hf and U, low affinity for Yb, Lu and Pb, and slow diffusion rates with respect to all these chemical species. Consequently, baddeleyite is an extremely robust carrier of geochronological (by using the U-Pb system) and tracer (by using the Lu-Hf system) information for the origin of mafic rocks. This dissertation provides a method for the fast, accurate and precise analysis of U-Pb-Hf isotopes in baddeleyite, a tool that in the future may prove crucial for studying the timing and processes associated with the formation of mafic crust on Earth.

In east-central Arizona, overlapping sets of Tertiary normal faults dismembered, variably extended, and exposed up to 15 km of the upper crust including portions of several Late Cretaceous to Paleocene (Laramide) igneous centers and their associated porphyry copper systems. These exposures enable both a rigorous evaluation of the nature of extension in the upper crust and systematic reconstruction of the 3-dimensional distribution of several major porphyry copper centers.Synthesis of existing geological data and new mapping provide the basis for reconstructions of district and regional scale cross sections through an area comprising about 4,000 km2 centered on the Dripping Spring Mountains of east-central Arizona. The study area is located within a highly extended portion of the Basin and Range province and encompasses the Globe-Miami, Superior, and Mineral Creek (Ray) mining districts and numerous other deposits and related occurrences.The field evidence and the reconstructions demonstrate that sequential sets of initially steeply dipping normal faults generated multiple half-grabens and associated sedimentary fill. Complex overlap of >10 sets of these half-grabens led to aggregate extension of about 100% across the study area, but the amount of extension locally varies from less than 20% to well over 400% depending on the amount of overlap and direction and amount of displacement on the various fault sets. These fault sets were not kinematically linked and do not merge into a master fault at depth, but are inferred to feather into a broader zone of mid-crustal flow, which may resemble the characteristics of nearby metamorphic core complexes.Reconstructions at regional (10's of kms) to copper deposit (a few kms) scales demonstrate that multiple deposits, prospects, and other hydrothermal features in the Globe-Miami, Superior and Ray districts are dissected portions of originally fewer, larger hydrothermal centers. These restorations delineate exposures ranging from near paleosurface to locally >10 kms paleodepth and enable comparisons of different systems and of well mineralized portions along with their roots, tops, and margins.

Over the past two decades, several competing dynamic models have emerged to explain the tectonic evolution of the Himalayan thrust belt. Basic aspects of the geology of the range remain relatively poorly known, however, limiting the accuracy of dynamic and kinematic models. For example, the location of a mega-thrust now exposed in the interior of the range, the Main Central thrust (MCT), is only approximately known across much of the Himalaya. Both because the MCT accommodated at least 150 kilometers of slip during the mid-late Tertiary and because it carries in its hanging wall the highest-grade metamorphic rocks exposed in the range, the MCT is a prominent feature in all models that seek to explain the tectonic evolution of the Himalaya. Whole-rock Nd isotopes and detrital zircon U-Pb ages allow the discrimination of hanging wall and footwall rocks of the MCT. Application of these techniques in the Annapurna Range of central Nepal unambiguously locates the MCT. Microstructural analyses confirm the presence of a thrust-sense ductile shear zone superimposed on this isotopic boundary.With improved locations of the MCT and other faults, it is now possible to understand thermobarometric and kinematic data in more correct structural context. Thermobarometric estimates demonstrate that rocks exposed in fault-bounded blocks in the Modi Khola transect experienced approximately constant peak conditions, and that peak conditions change dramatically across large faults. Pressure-temperature estimates combined with constraints on the extent of metasomatism indicate the presence of a large normal fault one kilometer structurally above the MCT. Preliminary Th-Pb dating of monazite suggests that this normal fault may have been active during slip on the MCT. The presence of such a proximal normal fault slipping synchronously with the MCT challenges some current representations of dynamic models for the evolution of the thrust belt. In situ Th-Pb ages of monazite inclusions in garnet, chemical and age zoning in the inclusions, and textural relationships between monazite, garnet, and nearby minerals demonstrate that interpretation of the tectonic significance of Tertiary Th-Pb ages from matrix monazite is simpler than interpretation of ages from inclusions in garnet.

The Santonian to Campanian Telegraph Creek and Eagle formations in south-central Montana contain a series of regressive to transgressive cycles deposited on the western margin of the Cretaceous Western Interior Seaway. This study focuses on depositional environments, stratal stacking patterns, and syndepositional faulting. Four cycles are identified and mapped regionally over an area of 30,000 km2 using outcrop and subsurface data to correlate 100 km up paleoslope from their maximum seaward extent. Each cycle of progradation and subsequent transgression left behind an upward-coarsening shoreface and/or deltaic sandstone body, capped by either a transgressive sand, an erosional top or maximum flooding surface. The stratigraphically lowest cycle studied, the Telegraph Creek Formation, contains a single regressive sandstone topped by a transgressive ravinement surface with chert and quartz pebble lag. The overlying Eagle Formation is composed of three genetically related regressive to transgressive cycles: 1) a basal cycle consisting of a detached low-stand delta capped by a ravinement surface which is overlain by transgressive chamosite-rich green marine sands and a maximum flooding surface; 2) a middle cycle composed of a highstand normal regressive delta and a sharp-based forced regressive shoreface that are erosionally incised into indicative of base-level fall and representing a sequence boundary, which is overlain by a subsequent transgressive tidally-influenced valley-fill; and 3) a top cycle consisting of normal regressive shoreface and deltaic deposits capped by a transgressive ravinement surface containing black-chert pebbles, representing the Claggett transgression. Each successive regressive to transgressive cycle steps consecutively basinward creating a larger progradational wedge. Sediment dispersal patterns indicate two separate and distinct controls on deposition, eustatic sea level fluctuations and tectonic overprint. Eustatic fluctuations affect the paleodip distribution of sediment (i.e. systems tracts) with a drop in eustatic sea level attributed to the valley incision within the middle member of the Eagle. The tectonic overprint, caused by activation of the Lake Basin Fault Zone, controls the paleostrike variability with an overall creation of accommodation space to the south of the fault zone.