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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

RE–OS and PGE geochemistry of organic-rich sedimentary rocks and petroleum

Finlay, Alexander James January 2010 (has links)
The research in this thesis is presented in paper format with each of four chapters representing one complete study. Chapter two presents Re–Os and geochemical fingerprint data for UK Atlantic margin oils. organic and δ13C geochemical data demonstrate that the oil is sourced from Upper Jurassic marine shales and the Re–Os data yields an age of 68 ± 13 Ma. Comparison of this date with published basin histories and Ar-Ar geochronology demonstrate that Re–Os ages correspond with the timing of oil generation. Furthermore the similarities between oil and source rock 187Os/188Os at the time of oil generation (Osg) indicates that Osg can be used to identify oil source units. Chapter three demonstrates, through the analysis of Kimmeridge Clay Fm. core and North Sea oil, that unradiogenic mantle like values within oils from wells in the Viking Graben and East Shetland Basin cannot be inherited from source. It is hypothesised that they are caused by contamination by a hydrothermal fluid sourced from either Cenozoic intrusive units or the mantle. Strain localisation is suggested to have caused the main basin bounding faults within the Viking Graben and East Shetland Basin to be of sufficient depth to act as conduits for hydrothermal fluid to propagate through and contaminate oils within reservoirs. Chapter four investigates how Osi values across the Ordovician/Silurian boundary GSSP at Dob’s Linn, Scotland, tracks the Hirnantian glaciation within a globally important source unit: the Ordovician/Silurian “Hot” Shales. During the Late Katian, Osi values increase from 0.28 – 1.08, providing evidence for increased silicate weathering of radiogenic continental crust. A decrease to less radiogenic Osi (~0.60) occurs at the base Hirnantian and marks the onset of the Hirnantian Glaciation. This is ascribed to Hirnantian ice cover and reduced chemical weathering rates cutting the supply of radiogenic material. In the Late Hirnantian an abrupt increase in Osi values to ~1.1 over 19 cm of stratigraphy, is attributed to the leaching of exposed radiogenic glacial deposits and increased weathering of silicate terrane during deglaciation. Chapter five applies the Platinum Group Elements, specifically Pt/Pd ratios, to identify oil source units. It is demonstrated that asphaltenes from the well constrained UK Atlantic margin petroleum system contain similar Pt/Pd and Osg values to the known source unit. A further study of the poorly constrained West Canadian Tar Sands demonstrates that Pt/Pd ratios in source rocks are not affected by hydrocarbon maturation and are distinct between differing potential source units. Comparison of the Tar Sands with potential source units demonstrates that the Tar Sands are mainly sourced from the Lower Jurassic Gordondale Fm., with minor input from the Devonian/Mississippian Exshaw Fm.
2

Palaeoclimatic Records from Speleothems in the Eastern Mediterranean

Mason, Jennifer January 2009 (has links)
Speleothems are key archives of palaeoclimatic information, chronologies for which can be precisely derived by Uranium Series methods. This investigation uses stable isotopes, trace elements and petrography in speleothems from the Eastern Mediterranean to reconstruct palaeoclimatic parameters in the area over the last -100 ka. Speleothems were collected along a transect from North-East to South West Turkey to Greece. Five stalagmite samples were selected for detailed geochemical analysis which was anchored by - 30 Uranium-Series dates. Most notably, oxygen isotope ratios in a stalagmite from Karaca cave, northeast Turkey exhibit similar temporal patterns to the Greenland ice core oxygen isotope records and to Chinese speleothem records of East Asian Monsoon (EAM) fluctuations over the period 77 ka to 6 ka. Winter rainfall maxima in north-east Turkey coincide with periods of intensified EAM. The isotope curve is interpreted as an insolation (precession) forced record of rainfall seasonality on glacialinterglacial timescales, with periods of high Northern Hemisphere insolation giving rise to cool wet winters and hot dry summers. Millennial-scale variability is caused by shorter-term changes in seasonality of precipitation and/or switching of moisture source areas in response to the stadial-interstadial climatic oscillations originating in the North Atlantic Basin and widely recorded in both marine and terrestrial climate records. Oxygen isotope rations in a 21 ka to7 ka stalagmite from southern Greece are interpreted similarly to Karaca. Shifts in S13C values in the record are related to soil biogenic activity. An isotopic event at 21 ka is interpreted as a short term increase in winter rainfall in response to increased seasonality due to increased insolation (precession). In south-west Turkey the 110 ka to 68 ka KE- I record is characterised by several large shifts in &180 and 613C corresponding to MIS 4,5a, 5b and 5c. These variations are again related to changes in seasonality of rainfall and are correlative with the Hulu speleothem record and Greenland ice core oxygen isotope records.
3

Applications of mass spectrometry to organic geochemistry

Haug, Patricia Ann January 1967 (has links)
No description available.
4

Geochemical analysis by inductively-coupled plasma optical emission spectroscopy using slurry atomization

Gray, Alison Ruth January 1985 (has links)
No description available.
5

Flow Field Formation and Compositional Variations of Flood Basalt Eruptions

Vye, Charlotte January 2009 (has links)
Characterisation of three lava flow fields from the Columbia River Basalt Group (CRBG), USA, reveals compositional heterogeneity on all scales, from adjacent lava lobes to the intra-crystal scale. Simple flow fields can be traced from vent areas to distal reaches, but those with multiple-layered lobes present a degree of complexity that make lava pathways and eruption sequences difficult to identify. A 3-D model based on field investigation of a single flow field establishes a volcanological context for geochemical sampling. Compositional v.ariation within each flow field suggests that small-scale geochemical heterogeneity is common within and between lobes of these flood basalt lavas. Lobe cores emplaced during the latter stages of an eruption have less evolved compositions and more enriched incompatible elements, suggesting progressive variation of magma composition caused by either recharge or sequential tapping of compositionally zoned magma. Progressive crustal contamination of magma during a single eruption is indicated by Re-Os isotope ratios. Initial 1870s/1880s ratios range from 1.405 in the earlier emplaced lava crust to 0.128 in the latter emplaced lava core. These values are more radiogenic than any known enriched sources (normative mantle -0.127, HIMU -0.15) consistent with previous data that indicate that neither an enriched source nor sub-continental lithospheric mantle can be the source of CRBG magma. Os isotope signatures can be explained by different degrees' of contamination of two isotopically distinct lithologies represented by the North American craton and Jurassic accreted terranes underlying the province. Intra-crystal Sr isotope analyses within a flow field record variable histories in an open magmatic system. Results suggest crystal residences in an increasingly contaminated melt within the crust with several recharge events of less-contaminated more primitive basaltic melt. Assembly of melt and crystal cargo occurred immediately prior to eruption without significant residence times in the final host magma. The combined compositional evidence suggests that an extensive shallow-crustal network of dykes and sills supplied magma to the CRBG eruptions.
6

The application of cosmogenic 3He surface exposure dating within the dry valleys of East Antarctica

Margerison, H. R. January 2005 (has links)
<i>In situ </i>produced cosmogenic <sup>3</sup>He provides independent support for the existence of a stable hyper-arid polar climate within East Antarctica since the mid-Miocene. Cosmogenic <sup>3</sup>He concentrations have been measured in over sixty boulders from glacial deposits in the Dry Valleys providing both age constraints for glacial events and quantitative erosion rate estimates for the region. Through these analyses, the processes that control cosmogenic <sup>3</sup>He concentrations in moraine boulders are assessed. The interpretation of cosmogenic <sup>3</sup>He exposure ages has been improved through, (a) the incorporation of erosion rate estimates, and (b) quantitative correction for non-cosmogenic <sup>3</sup>He in Ferrar dolerite pyroxenes. Sub-glacial flood deposits in the northern Dry Valleys were exposed as the overriding ice retreated over the Transantarctic Mountains and out of the Dry Valleys, at approximately 15 Ma. The cosmogenic <sup>3</sup>He concentrations suggest exposure ages of between 8.6 and 10.4 Ma approximately 25% lower than <sup>40</sup>Ar/<sup>39</sup>Ar age estimates that have been used to constrain the retreat of the ice sheet. Applying an erosion rate correction of between 0.03 and 0.04 m Ma<sup>-1</sup> implies these samples were deposited 15 Ma as the ice retreated from the Dry Valleys. Nearby Ferrar dolerite bedrock surfaces confirm the occurrence of very low rates of erosion in the region, with surfaces eroding at an average rate of 0.17 m Ma<sup>-1</sup>. Non-cosmogenic <sup>3</sup>He, both derived from mantle and nucleogenic sources, can cause cosmogenic <sup>3</sup>He analyses to overestimate the surface exposure age of magnetic rocks > 1 Ma. Ferrar dolerite from a mining drill core at a depth of over 600 m has never been exposed to cosmic rays. The 8.46 x 10<sup>6</sup> at g<sup>-1</sup> measured in pyroxene from this sample is close to the theoretical production of nucleogenic <sup>3</sup>He in the mineral based on measured U, Th and Li concentrations. This makes less than 1% difference to the majority of samples analysed within this work but becomes more important in Quaternary surfaces. Constraining erosion rates and estimating levels of non-cosmogenic <sup>3</sup>He increases the accuracy with which cosmogenic <sup>3</sup>He dating techniques can be applied to the glacial history the Dry Valleys. The existence of mid-Miocene aged flood deposits from the northern Dry Valleys confirm the antiquity of the landscape and support the existence of a stable hyper-arid polar climate and consequent limited geomorphic landscape evolution since this time. There must however be some flexibility within the stability model.
7

The behaviour of radionuclides in the Ribble Estuary, NW England

Brown, Justin January 1997 (has links)
The main aim of this project was to consider the geochemical behaviour of a suite of radionuclides (137Cs, 241 Am, isotopes of Pu, Th and U and 234mpa)in the Ribble estuarine environment. Controls on the vertical distribution of radionuclides in sediment deposits were considered and the fluxes of sediment and radionuclides at sites close to the river channel were investigated. Vertical activity distributions were studied by taking cores from various intertidal sediment deposits. Sediment/activity fluxes were studied by installing sediment traps. All samples were analysed by gamma spectrometry. Selected samples were analysed for total organic carbon, mineralogy (XRD), major and trace-metals (XRF), grainsize distribution (laser granulometry) and alpha-emitting radionuclides (alpha spectrometry). The geochemical phase associations of radionuclides were investigated using sequential extraction experiments. Sellafield-derived radionuclides exhibited distinct subsurface maxima (up to 4 785 ± 42 Bq kg" 137Cs, 618 ± 14 Bq kg" 239,240pUand 868 ± Bq kg" 241Am) in mature saltmarsh sediment deposits. Thorium-230 exhibited more complex depth profiles (maximum = 2383 ± 36 Bq kg"). Variations in grain-size were low and therefore not important in controlling the specific activity variation with depth at these sites. The effects of early diagenesis on the specific activity profiles of 137Cs, 241 Am, 239,240pU and 230Th were small. The vertical distribution of Sellafield-derived radionuclides reflected the cumulative discharge pattern from Sellafield implicating a sediment transport mechanism that has involved the integration of contamination from previous discharge events. The vertical distribution of 230Th reflected the annual discharge pattern from BNFL Springfields implicating a transport pathway that involves little mixing of sediment. Levels of Springfields-derived 234mpaand 234Th were highly variable in time and space «0.5 - 495 kBq kg' recorded at Penwortham over the course of the study). The antecedent river discharge regime appears to be the dominant influence on the specific activity of these radionuclides at upstream sites.
8

Effects of ecosystem disturbance on fluvial carbon losses from tropical peat swamp forests

Moore, Sam January 2011 (has links)
Investigations into the effects of anthropogenic disturbance on greenhouse gas emissions from tropical peatlands are relatively well documented. However, the effects of such disturbance on fluvial carbon (C) losses has, thus far, been overlooked and remains unaccounted for in these ecosystem C budgets. Here, three land-cover classes in Central Kalimantan, Indonesia, were investigated in order to determine the effect of tropical peatland disturbance on fluvial organic C budgets. Intact peat swamp forest (IPSF), moderately disturbed and severely disturbed peat swamp forest (DPSF1 and 2) catchments were monitored for one year. Results demonstrate a trend of increasing annual total organic carbon (TOC) yields with increasing drainage severity, from 63 in IPSF to 105 and 131 g C m-2 y(1 in DPSF1 and 2, respectively. Including this routinely-ignored fluvial C loss component in the disturbed peatland ecosystem C budget increases the estimated total C loss by 30%. Radiocarbon analysis of dissolved organiC carbon (DOC) reveals that whilst DOC leaching from IPSF was derived from recent primary production, DOC leaching from the two disturbed sites was comprised of much older C, originating from deep within the peat column. The TOC flux from the Sebangau River basin was estimated to be 0.46 teragrams y(1, which upon regional extrapolation indicates that Indonesian rivers account for 10% of the global annual riverine DOC export to the ocean. There were no significant differences between sites in the quality of the organic C lost, but DOC lost from disturbed sites was generally less aromatic than from the intact site. It is recognized that a large portion of this labile C will be emitted to the atmosphere via biotic decomposition. Since 1990, peatland disturbance has resulted in a 53% increase in fluvial organic C export from Southeast Asia, an increase that alone approximates the entire annual fluvial organic C flux from European peatlands.
9

The timescales of andesite generation at Mount Ruapehu, New Zealand

Hughes, Robert January 1999 (has links)
Intermediate composition arc volcanoes present some of the most serious natural hazards because of their tendency towards violent, explosive eruptions. Very little is known about the long term processes which produce such magmas and the timescales over which they operate. U-series systematics have considerable potential for helping to understand these timescales, although very few studies to date have examined individual volcanoes in detail. A detailed series of <sup>230</sup>Th-<sup>238</sup>U and <sup>226</sup>Ra-<sup>230</sup>Th analyses are presented in conjunction with major and trace elements and Sr, Nd and Pb isotopes for lavas sampled from coherent stratigraphic sequences on Mount Ruapehu. This andesitic volcano lies at the southern end of the Taupo Volcanic Zone (TVZ) in the centre of North Island, New Zealand. Volcanic activity at Ruapehu is related to the subduction of the Pacifc Plate beneath the Indian Plate along the Hikurangi Trough. Major element trends are dominated by shallow level crystallisation and assimilation processes. Modelling of crystallisation trends suggests that the magmas were hydrous and may have elevated fO<sub>2</sub>. Trace element patterns show high LILE/HFSE ratios characteristic of arc lavas. AFC models of isotope data suggest that 50% crystallisation and 10-15% assimilation can explain the observed trends. The assimilant is likely to have been dominated by partial melts of local Torlesse basement. Major element extrapolations suggest that the mantle wedge beneath the TVZ was relatively fertile. Modelling of the trace element budgets in relatively primitive lavas suggests that a three component model is required for magma generation. Partial melts of sediments were added to the mantle wedge at a relatively shallow level, and the modified mantle was then fluxed by fluids derived from subducted oceanic crust at greater depth. 10-90% of many LILE and other elements are derived from fluids and sediments rather than the wedge. U-Th analyses show 1-14% U excess and (<sup>230</sup>Th/<sup>232</sup>Th) ratios in the range 0.75-0.85. Data for the coherent stratigraphic sequences fall on linear trends on an equiline diagram. Crystallisation and alteration are ruled out as causes of the observed U/Th variation and although the lavas have been affected by assimilation, links between U/Th and indices of assimilation are difficult to demonstrate. Crustal melts with similar U/Th ratios to the parental basalts and relatively low U and Th abundances are the most likely candidate for the assimilant. It is argued that the U-Th systematics reflect addition of hydrous fluids to the mantle wedge. Whole rock pseudo-isochron ages are derived for the different stratigraphic sequences, and compared with data on eruption ages to estimate combined transit and residence times (CTRTs). Rocks from older sequences dated at -80 ka and -130 ka have very short CïRTs << 40 ka, whereas younger sequences have longer CTRTs on the order of 40-80 ka. It is inferred that the magmas of the younger sequences spent a longer period of time ponded at the base of the crust and underwent limited chemical modification. A detailed model of the behaviour of U-Th-Ra systematics during crustal magmatic processes is also presented. This allows crystallisation, assimilation and replenishment processes to be combined with a time factor to predict magma evolution curves. Whilst detailed systematic studies of individual volcanic centres are required to test the model, the lack of age constraints and complex sub-volcanic history of Ruapehu magmas do not permit the detailed application of this model here.
10

Organic geochemistry, of the marl slate and other organic-rich sediments

Dungworth, G. January 1972 (has links)
No description available.

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