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Showing 1 to 20 of 26 for “"stable isotope geochemistry"”.
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Stable isotope geochemistry of nitrogen in marine particulates
Isotope studies of nitrogen and carbon were undertaken to investigate the fate of particulate organic matter (POM) during its residence in the water column and after deposition on the seafloor. The processes focused on were water-column transformations and sedimentary diagenesis. Sampling sites …
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Stable isotope geochemistry of nitrogen in marine particulates
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1983.
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Investigating nitrate attenuation in an urban stream using stable isotope geochemistry and continuous monitoring
Urbanization affects in-stream biogeochemical processes that control nutrient export. Attempts to restore urban streams will not be successful unless the biological and physical controls on water quality are thoroughly understood. The objective of this study was to identify the relative influences …
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Stable Isotope Geochemistry and Paleohydrology of the Poison Strip Sandstone, Early Cretaceous, Eastern Utah
… Through detailed petrographic, diagenetic, and stable isotopic analysis, we were able to determine that that the atypical δ18O values produced from the poikilotopic calcite cements of the Poison Strip Sandstone are the result of deep burial diagenesis. The precipitation of poikilotopic calcite …
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Stable isotope geochemistry of the Okenyenya igneous complex, Namibia : constraints on contamination and fluid interaction
… suite, are consistent with the attainment of isotope equilibrium and largely closed system conditions. The majority of the temperatures calculated by conventional mineral-pair thermometers are spurious, as a result of oxygen isotope diffusion during slow cooling. Closure temperatures for …
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Mercury stable isotope geochemistry as a tool for tracing sources and chemical transformations in the environment
… is a redox active global contaminant. Hg has two stable oxidation states in the environment, Hg(0) and Hg(II). Hg(0) is significantly less soluble than Hg(II) and is less reactive. Hg(II) is very soluble and highly reactive; being able to form methylmercury, a potent neurotoxin. Hg is a health …
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Climate and habitat reconstruction of hominid sites in northern China with paleosol stable isotopes
… faunal and floral assemblages, paleosols, and geochemistry are often contradictory. In order to understand paleoenvironments and the nature of hominid adaptations, evolution and behavioral change, more accurate reconstructions of their environments are needed. Stable isotope geochemistry of …
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Influence of climate and the expansion of C4 grasses on sequence-scale cyclicity and landscape development during the late Miocene to Pleistocene of West Texas.
… cycle thickness, and facies proportions. Stable isotope geochemistry of bulk paleosol samples and pedogenic carbonate suggest C₄ expansion at 7.25 Ma and provide a pCO₂ reconstruction of the late Miocene to Pleistocene. C₄ onset coincides with a decreasing sedimentation rate, less frequent …
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A biogeochemical investigation of Trunk River Lagoon, Falmouth, Massachusetts
… In chapter 2 we employ radiocarbon dating, stable isotope geochemistry, and lipid biomarker analyses on a 2-meter sediment core spanning 3000 years, revealing shifts from a freshwater to a brackish environment with evidence of anthropogenic contamination. In Chapter 3, biomarker analyses on …
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Inferring Extinct Reptilian Response To Global Warming: Insights From Modern Stable Isotope Ratios
… are disconnected from the taxon of interest. Stable isotope geochemistry, however, provides an independent test. I analyzed stable isotope ratios (δ¹⁸O, δ¹³C) from enamel, providing new data on the connection between morphology, diet, and environment. I find a trophic separation in δ¹³C, and …
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Depositional constraints on lacustrine carbonates from the Winnemucca Dry Lake Basin, Nevada, USA
… composition, particularly with respect to the stable isotopes of carbon and oxygen, and trace elements such as Mg and Sr. However, in order to best interpret these geochemical proxies, we must first understand the geochemical conditions under which deposition occurs. In addition to providing …
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Dinoflagellate Cyst Biostratigraphy, Palynofacies and Paleoenvironmental Analysis of the Maastrichtian and Basal Danian, Brazon River, Texas
… samples are combined with ?13C and ?18O stable isotope geochemistry and TEX86 and BIT Index organic geochemistry data for paleoenvironmental interpretations. Biostratigraphically important species of dinoflagellates divide the section into three intervals. Interval 1 occurs within the …
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Depositional and diagenetic controls on porosity evolution in the "C" zone, Red River Formation (Upper Ordovician), Divide County, North Dakota
… dolomitization model. </p><p> Carbon and oxygen stable isotope geochemistry suggests that the initial dolomitizing fluid was seawater or seawater-derived brines. This penecontemporaneous phase of dolomitization produced planar dolomites that were subsequently neomorphosed or recrystallized into …
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Experimental, geochemical and isotopic insights on melting and degassing behavior on Earth
… of experimental petrology (Chapters 2 and 3) and stable isotope geochemistry (Chapters 1 and 4). Chapter 1 explores the systematics of methane (CH4) isotopologues in geothermal systems, with a particular focus on the kinetics of isotopic exchange reactions in the vicinity of the supercritical …
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Kinematics and Dynamics of Continental Deformation
… published paleoaltimetry results based on stable-isotope geochemistry are used to provide constraints on vertical motions. These demonstrate that uplift is much slower than had previously been suggested from thermochronometric data. Numerical modelling of the time evolution of a …
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The stratigraphic and structural controls on copper-gold mineralization at Cassenha hill prospect, within the Archean to Paleoproterozoic Angolan shield, Congo craton, South Western Angola
… borehole core logging, petrography, whole-rock geochemistry (XRF and ICP-MS), and stable isotope geochemistry on samples collected on the surface and from exploration boreholes drilled as part of RVR exploration program. Overall, the petrographic and geochemical studies undertaken in the rocks …
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Birds of a Feather: Cultural and Ecological Relationships between the Unangax̂ and Seabirds in the Aleutian Islands, AK
… for raw materials and food. Results from my bulk stable isotope analyses suggest that seabirds stayed relatively stable in marine food webs over the last ~4,500 years. Noting record murre (Uria spp.) die-offs after the 2014-16 marine heatwave, my use of a novel compound-specific stable isotope …
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The nature and co-behaviour of volatile and non-volatile elements in the sub-continental lithospheric mantle
… (He and C) in mantle phases, together with their isotope compositions (3He/4H and 13C/12C), have been determined in 55 well-characterised peridotites and pyroxenites predominantly from off-craton mantle. The peridotites include spinel- and garnet-bearing lherzolites to harzburgites and are …
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Geochemistry and Basin Analysis of Laramide Rocky Mountain Basins
… This study uses the oxygen and strontium isotope geochemistry of freshwater bivalve fossils from six Laramide basins in order to reconstruct the spatial evolution of the paleotopography and Precambrian basement erosion in late Cretaceous-early Eocene. In addition it uses the sedimentology, …
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Holocene guano influences on eutrophication and lacustrine ecology at Kettle Lake, North Dakota
… the Holocene. I investigate this influence using stable nitrogen isotope values (𝛿15N) from lake sediment organic matter, with particular focus on periods of struvite deposition, a magnesium-ammonium-phosphate mineral formed from guano. I find that 𝛿15N is elevated throughout the Holocene in …
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