The idea of studying the colour of organisms in the fossil record has for a long timeseemed nothing more than the far flung dreams of a few idealistic palaeontologists.The last 5 years however have brought sweeping advances in this area, such that theidea is no longer hypothetical but an actual possibilty. Recent studies on the preserva-tion of fossilised pigment containing organelles, melanosomes, have hailed a new eraof palaeontological study and reconstruction. In this work geochemical techniques areapplied to study such structures in fossil feathers and an amphibian, to determine thenecessary level of confidence that these structures are not bacterial, discuss the relativeadvantages and disadvantages of the techniques used in the study of fossil melanin, andextend the study of fossil colour to other pigments in fossil algae. Fourier transforminfrared spectroscopy (FTIR) data is shown to provide some of the most consistentevidence of the presence of melanin, however it does not enable us to adequately dis-tinguish between the two major types, eu- and pheomelanin. Determining the presenceof bacteria in fossil stromatolites is shown to be most effective by using tetra-methylammonium hydroxide assisted pyrolysis gas chromatography mass spectrometry (Py-GCMS) to look for the distribution pattern of fatty acid methyl esters. Such analysisshows that samples identified as bacterial have identical patterns that differ signifi-cantly from those of fossil plants and animals. Such a biomarker is shown to be morereliable than hopanes, further commonly used bacterial biomarkers. The combination of FTIR and Py-GCMS suggest the presence of the red algal pigment phycoerythrin inthe Jurassic fossil Solenopora jurassica, strengthening its identification as a calcareousalga.

Pelagic clays cover nearly one half of the ocean floor, but are rarely used for paleoceanographic research because of their extremely slow sedimentation rates, post-depositional alteration(s), and the lack of biogenic material available to provide ages. My dissertation develops and applies approaches to study pelagic clays by targeting the largest marine sediment province in the world: the South Pacific Gyre (SPG). I present an unprecedented spatially and temporally extensive paleoceanographic history of the SPG and discuss authigenic processes in pelagic clays that are linked to changes in global seawater composition through the Cenozoic. My research was based on an extensive inorganic geochemical dataset I developed from samples gathered during Integrated Ocean Drilling Program Expedition 329. I applied multivariate statistical techniques (e.g., Q-mode factor analysis and constrained least squares multiple linear regression (CLS)) to the dataset in order to (a) identify the existence of six end-members in pelagic clay (namely, eolian dust, Fe/Mn-oxyhydroxides, apatite, excess Si, and two types of volcanic ash), (b) quantify their abundances, (c) determine their mass accumulation rates, and (d) infer major features in the paleoceanographic evolution of the SPG. Key parts of my research also developed improved MATLAB codes to facilitate and speed the search for best fitting end-member combinations in CLS modeling. Additionally, I expanded the natural gamma radiation instrumental capabilities on the D/V JOIDES Resolution to quantify concentrations of uranium, thorium, and potassium. I dated the pelagic clay at four of the IODP sites with a cobalt-based age model that I developed, and documented that the seawater behavior of cobalt determines the extent to which this method can be applied. Collectively, the results track the spatial extent of dust deposition in the SPG during the aridification of Australia, dispersed ash accumulation from episodes of Southern Hemisphere volcanism, and other features of Earth’s evolution during the Cenozoic. I further quantified two geochemically distinct types of authigenic ash alterations within the pelagic clay, indicating that altered ashes may be a significant and variable sink of magnesium in seawater over geologic timescales.

<p>Metal alkyls have a variety of uses including important intermediates in a variety of  processes. In this research, a thorium bis-alkyl species was fully characterized and explored for its potential reactivity, specifically for the formation of thorium bis-amide complexes. A series of three thorium bis-amide complexes was synthesized and characterized in this work. Additionally, several pathways have been attempted to synthesize an actinide alkylidene within this project including the use of a homoleptic tetrabenzyl complex, the use of diazoalkanes through the loss of dinitrogen, deprotonation of alkyls, and reducing a metallacycle complex. However, many of these did not result in products that suggest that an alkylidene was formed. These reactions ranged from being thermally unstable, decomposing, not reacting, or forming multiple products and being unable to discern one major product.<br> </p>

<p dir="ltr">The origins and deposition of nitrate in dust traps in Mojave Desert are examined in this thesis. Two main hypotheses are tested: (1) most of the dust in the traps comes from local soil, implying that the nitrate content is primarily derived from the soil; and (2) wet deposition is the primary source of nitrate found in the environments, implying that precipitation processes play an important role in nitrate accumulation. To test these hypotheses, we collected data from 11 dust trap from locations in of the US Geological Survey's long-term investigation of dust composition and influx rates. Dust and soil samples were analyzed for ions to determine their origins and the contributions of local vs distant sources. Our findings show that the fraction of soil-derived nitrate (<i>f</i>_soilNO₃^-) is consistently low at all traps, hardly reaching 0.03, whereas the atmospheric nitrate percentage (<i>f</i>_atmNO₃^-) is usually close to or equal to 1. This shows that atmospheric sources play a substantial role in the nitrate levels detected in dust traps. Nitrate contributions are also significantly influenced by sedimentary and geological settings, such as the distinctions between alluvium and playa regions. Playas, which are composed of silt and clay, may have higher nitrate concentrations than alluvial plains, indicating that external dust inputs are significant. The second hypothesis's results show that nitrate deposition in the study area is primarily from dry sources, with dry deposition values ranging from 0.68 to 10.84 NO₃⁻/kg/ha/yr, averaging 4.12 NO₃⁻/kg/ha/yr, and wet deposition values averaging 1.09 NO₃⁻/kg/ha/yr. This observation challenges the hypothesis that wet deposition is the primary source of nitrate. The dominance of dry deposition is further supported by low amounts of precipitation and a weak correlation between precipitation and dust deposition. This study concludes that although local soil has a role in nitrate levels in dust traps in the study site, it is not the primary source, external sources and dry deposition account for the majority of nitrate in the dustpan</p>

Peat from the temperate regions has been used for paleoenvironmental reconstruction using diverse proxies for over a century now. Peat is rare and severely understudied in the tropics. The montane peat bogs of the Nilgiris, southern India have been found to preserve global climatic signals including the Holocene Optimum and the Last Glacial Maximum (LGM). At Sandynallah, one of the oldest peat accumulations in the world at >40 kyr BP, we had undertaken a high resolution paleoenvironmental reconstruction using multiple proxies which are yet to be evaluated in the tropical context. The study consists of 3 main objectives, i. Establishing an accurate high resolution chronology for the peat profile using radiocarbon dating, ii. Extracting vegetation and climate information from C/N ratio and Rock-Eval indices and iii. Using elemental profiles to establish the utility of inorganic geochemical proxies for processes such as weathering and dust transport. High resolution chronology for the site was built using Accelerator Mass Spectrometry (AMS) radiocarbon dates. To improve accuracy of the age-depth model, we also tested 4 samples for the effects of the AAA (Acid-Alkali-Acid) extraction method, the most common pre-treatment method for peat in the world. We compared ages on bulk samples (acid washed) and AAA treated samples from 4 different depths. We find that for all depths, the ages of the untreated samples do not lie within the internal uncertainty window and differ from the AAA treated sample age by at least an order of magnitude of the internal error, if not more. Based on these results we argue that the internal error should be used in conjunction with a reliable estimate of external error in an age-depth model for more realistic dating of paleoclimatic events. C/N ratios were explored for their paleoclimatic potential in conjunction with Rock-Eval indices and it was found that decomposition in tropical peat, as opposed to temperate peat, may not be sensitive to climatic perturbations. Inorganic geochemical proxies were also evaluated through this study. We see that the major and trace elements, except the lanthanide series do not show many significant trends for paleoenvironmental interpretation. But the lanthanides show some promise for identifying potential sources of dust and weathered material. Our study has addressed the gap in knowledge about the utility of recent geochemical proxies in tropical peat and has attempted to provide a solution to improve reliability in constructing age-depth models.

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