The geologic context that fossils provide can be invaluable for understanding the history of a given stratigraphic sequence. Simply understanding the mode of life of a fossil organism can clarify which kind of environment that organism lived in, but a wealth of geochemical information can also be extracted from fossils. Here we present a new technique via advances in ICP-MS technology to directly date a multitude of vertebrate fossil materials, including biogenic apatite from several dinosaurs. Using U-Pb isochrons we are able to generate ages consistent with well-constrained stratigraphy, including Early and Late Cretaceous specimens and Middle to Late Miocene fossils. An initial study of a Zalmoxes dinosaur fibula from the late Cretaceous deposits of the Haţeg intramontane basin in western Romania yielded a U-Pb isochron age of fossilization of 74.4 ± 5.2 Ma. Subsequent analyses of an Early Cretaceous Hadrosaurid from Wyoming and a Late Miocene crocodilian coprolite from North Carolina have demonstrated the potential for this technique to be applicable across a variety of geologic questions. The prospect of better constraining the stratigraphic ages of vertebrates and their implications in our understanding of the timings of speciation and extinction events may make this an invaluable new tool in interpreting Earth’s history.

Copper deposits on the Colorado Plateau are well exposed variants on the theme of sediment-hosted copper systems. Study of two contrasting areas in the Colorado Plateau, Lisbon Valley and the northern Moab fault, allows evaluation of controls on mineralization and their possible relationships to broader basinal processes, through a combination of published work with new mapping, core logging, petrography, short-wave infrared spectroscopy (SWIR), and geochemical analyses. The focus of this study was on the GTO pit in the Lisbon Valley Mine and surface exposures along the northern Moab Fault. Both areas occur in the vicinity of step-over zones along major NW-trending normal faults. Both also areas also exhibit local bleaching of red beds and rare bitumen, suggesting flow of reduced fluids (hydrocarbons?). However, in detail, both areas differ in host, recognized alteration, and styles of mineralization. At Lisbon Valley, economic copper mineralization, composed principally of chalcocite and its weathering products, is mainly restricted to pyrite-depleted, carbonate-cement-poor strata in the variably pyritic sandstones and conglomerates of the Early Cretaceous Burro Canyon formation. In this area, bleaching is found throughout the stratigraphic column from the Permian to the Jurassic and are associated with formation of secondary kaolinite and other acid-stable sheet silicates. Rare hematite preserved under quartz overgrowths suggests that some of the Burro Canyon may have been red prior to (hydrocarbon-related?) bleaching. Mineralization typically occurs within 100 meters of major strands of the Lisbon Valley fault system. By contrast, along the northern Moab Fault the bleached upper part of the Moab Member of the Entrada formation contains widespread sparse copper mineralization, in the form of Cu(±Fe) sulfides and their weathering products. Fracture-controlled concentrations of Cu-Fe sulfides (now cuprian limonites) are locally abundant along structures at along the northern Moab fault. However, unlike at Lisbon Valley, the typical strata hosting Cu are Fe poor show little evidence for widespread early pyrite. The copper occurrences (now oxidized) have high Cu:Fe (>5:1) indicating a chalcocite-like, iron-poor precursor. Relatively pure calcite cement and nodules are abundant close to the fault splays whereas variably ferroan and manganoan carbonate is extensive in the lower Moab Member. Evidence of selective bleaching of original red beds near faults and in favorable (sandy) strata is well developed in both the Curtis and Slick Rock members of the Entrada Formation. Where present, copper occurs with bleaching indicating that it may have been localized by the presence of hydrocarbons or sour gas along the northern Moab fault and Lisbon Valley.. Mineralization postdates bleaching and broadly correlates with structures (second-order) if not specifically structurally controlled (first-order). Based on published work, these relationships imply that mineralization is Laramide (Late Cretaceous) or younger. Oxidized basinal brines, focused by faults and favorable stratigraphy, are inferred to have carried Cu and other metals which were then trapped by reaction with sulfide. The sulfide came from combinations of: (1) preexisting pyrite in the host rock, (2) H2S in a second fluid, and/or (3) S2- generated by thermochemical or bacterial sulfate reduction by organic carbon. At Lisbon Valley, stratigraphic control by preexisting pyrite and a reducing, perhaps sulfide-bearing fluid appear to have been the key traps in the Cretaceous rocks; along the Moab Fault, stratigraphic localization of copper at the top of the Curtis in iron-poor rocks suggests a hydrocarbon or gas (H2S-bearing?) trap. These results parallel evidence for similarly diverse controls on faults and stratigraphy elsewhere in the Paradox Basin.

In this work we investigate the low-frequency (decadal-centennial) variability of the climate system in Monsoon Asia using a combination of instrumental, paleoclimate proxy, and climate model data. Understanding this critical component of the climate system is essential for accurately assessing the risk of low-probability extreme events such as megadroughts that may arise from the interaction of anthropogenic climate forcing and natural internal variability (Ault et al., 2014). In Appendix A, we use a network of hydroclimate proxies from Monsoon Asia as a case study to compare low-frequency variability in paleo-data to climate model simulations. We take a proxy system modeling approach, using climate output variables from isotope-enabled runs of iCESM, isoGSM, and iCAM5, to simulate synthetic proxy records, which creates a common ground for the comparison. We find that the pseudoproxies based on iCESM do not accurately capture the relative strength of multidecadal-century scale variability in the paleoclimate data. We find that the pseudoproxies based on isoGSM and iCAM5, which are constrained by instrumental observations, appear to match the scaling pattern of variability found in the proxy records. Our results indicate that state-of-the-art, fully coupled climate models are not able to generate a sufficient amount of multidecadal-century scale variability in hydroclimate. We find that one major source of multidecadal scale variability found in the proxies but not in the models comes from the combined interactions among the monsoon, El Niño-Southern Oscillation (ENSO), and the Indian Ocean sea-surface temperature variability. In Appendix B, we investigate the low-frequency variability found in multiproxy ENSO reconstructions, with the goal of understanding how this dominant source of hydroclimate variability on interannual scales may impact teleconnected regions on decadal-centennial time scales. Previous multiproxy reconstructions of ENSO have found a large amount of low-frequency variability but the time series of this low-frequency variability rarely matches between studies. We investigate potential biases in reconstructions of ENSO from the number and geographical distribution of sites, age model uncertainty, and sources of noise present in the individual proxy records. We conduct a series of sensitivity experiments using pseudoproxies to demonstrate that these factors have the potential to bias the spectrum of reconstructions causing them to overestimate the relative amount of decadal-century scale variability in the tropical Pacific. This could help explain why multiproxy ENSO reconstructions show greater multidecadal-century scale variability than is found in observations or climate model simulations. In Appendix C, we introduce a new paleo-monsoon proxy covering the last 2600 years based on grain size variability in a sediment core from Pale Daha, a small lake in western Nepal. We demonstrate that variability in grain size distribution over the last century matches with low-frequency precipitation variability found in 20th Century Reanalysis data (Compo et al., 2011). We identify a major pluvial from 950-1300 CE that matches with a similar pluvial in nearby Sahiya Cave (Sinha et al., 2015), and with increased monsoon circulation over the northern Arabian Sea (Anderson et al., 2002; Gupta et al., 2005). We find evidence that the monsoon precipitation at the site over the last 150 years has been particularly strong as compared to relatively weak monsoon rains from 1300-1800 CE. We then compare the trends found in paleo-monsoon proxies over the last 150 years and find that much of the apparently contradictory trends may be explained by the projected circulation and precipitation responses to anthropogenic forcing. This new interpretation is based on a simulated northward shift in circulation that may increase the relative fraction of precipitation at proxy sites received from the Arabian Sea and decrease the fraction from the Bay of Bengal. This shift in circulation could produce the trend in precipitation stable isotopes found in isotope based paleo-monsoon proxies. If true, these findings indicate that the South Asian Monsoon may already be experiencing the effects of anthropogenic climate change to a degree not yet fully appreciated, and that these changes are likely to continue into the future.

Global climate is changing at a rate that is unprecedented for the modern era, and atmospheric CO2 is at a level that has not been seen in ~3 million years. Recorded climate observations extend back only ~130 years. In order to understand how the Earth system may respond to present and future levels of CO2 forcing, we need to interpret ancient archives of climate and vegetation. The study of human evolution also involves studying past climate and vegetation, as it may have been influenced by climate change. Reconstructing past climate and vegetation often requires the use of robust molecular and microscopic fragments of plants. This dissertation uses microscopic plant opal silica phytoliths and microscopic charcoal from East Africa to reconstruct vegetation and hydroclimate for three important places and times in Earth and human history: (i) the Lake Malawi region after the Mount Toba supereruption at ~74 ka, (ii) the mid-Piacenzian Warm Period (MPWP) and the Plio-Pleistocene transition (3.29–2.57 Ma) in the Baringo Basin, Kenya, and (iii) the early Pleistocene (1.87–1.38 Ma) in the Turkana Basin, Kenya. These three study sites were investigated by drilling ancient lake sediments to recover soft sediment cores. From these cores, a total of 1029 samples were analyzed for phytoliths and microcharcoal. For the Mount Toba supereruption, we found no change in low elevation tree cover, or change in cool climate C3 and warm season C4 xerophytic and mesophytic grass abundance that was outside of normal variability for samples synchronous or proximal to the eruption. A spike in locally derived macrocharcoal and xerophytic C4 grasses immediately after the Toba supereruption indicated reduced precipitation and die-off of at least some afromontane vegetation, but did not signal volcanic winter conditions as had been hypothesized. For the Baringo Basin during the MPWP (3.26–3.01 Ma), which is the last time global atmospheric CO2 in a warm world was at levels similar to today, intervals with exceptionally high microcharcoal influx suggest regional turnover from woody to open habitats was driven in part by fire. After ~3.0 Ma, low elevation woody cover likely never exceeded 40% and mesic tall-grass vs. xeric short-grass savanna varied at precessional periodicities. For the Turkana Basin during the early Pleistocene, spectral analysis found that microcharcoal varied at precession (23–19 kyr), half-precession (9.6 kyr), and quarter-precession (5.1 kyr) periodicities, and linked orbital-forced peaks in precipitation with elevated fire on the landscape. Phytoliths show that C4 mesic and C4 xeric grasses varied at precession and quarter-precession periodicity. Identification of the Natoo Tuff in WTK13 allowed a direct linkage to the Nariokotome Boy Homo erectus/ergaster site. At the time that the Nariokotome Boy walked this ancient landscape, phytoliths indicate that the area was a seasonally wet and open environment dominated by short stature C4 Chloridoideae grasses, sedges, and other herbaceous plants.