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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

The geochemistry of recent oxic and anoxic sediments of Oslo Fjord, Norway

Doff, David H. January 1969 (has links)
No description available.
2

Primary biological controls on UK lower namurian shale gas prospectivity : a step towards understanding a major potential UK unconventional gas resource

Koenitzer, Sven Fred January 2014 (has links)
Deep-water mudstones from ancient epicontinental settings are significant repositories for organic matter, but the primary controls underpinning the amount and type of organic matter preserved in these basins have not been examined. Comprehensive analysis of late Mississippian mudstones from the Widmerpool Gulf, UK, was undertaken using thin section analysis, bulk rock geochemistry (total organic carbon (TOC), δ[superscript 13]C[subscript org], Rock-Eval), palynofacies typing, sporomorph counts, δ[superscript 13]C of isolated organic matter fractions and gas-chromatography of extracted n-alkanes and kerogen pyrolysates. Late Mississippian mudstones, deposited across central and northern England, are known oil and gas source rocks but also represent important onshore exploration targets for shale gas. Using these data, the processes that delivered and buried organic matter during glacio-eustatic sea-level cycles are interpreted. During sea-level lowstands, thin-bedded silt-bearing clay-rich mudstones with up to 4.1% TOC (average=2.3±0.8%; mean δ[superscript 13]C[subscript org]=–28.2±1.0‰) are intercalated with graded silt-bearing mudstones and sand-bearing silt-rich mudstones (average TOC=1.7±0.6%; mean δ[superscript 13]C[subscript org]=–26.2±0.7‰). The clay-rich mudstones contain significant proportions of a granular translucent type of amorphous organic matter (AOMGr), comprising algal material and bacteria, and were deposited via dilute turbidity flows and hemipelagic settling of flocculated organo-mineralic material. The intervening coarser facies contain significant land plant-material deposited via intermittent sediment density currents. Kerogen composition varies between type II and III. During sea-level highstands, thin-bedded carbonate-bearing mudstones are the dominant facies, with up to 6.6% TOC (average=4.6±1.3%; mean δ[superscript 13]C[subscript org]=–28.5±0.9‰). Hemipelagic suspension settling was the main depositional process. These mudstones are rich in AOM[subscript Gr] which was abundant due to high bioproductivity in the water column; kerogen is consistently of type II. Mudstones accumulated during sea-level highstands represent the best potential targets for thermogenic shale gas. This study explains the systematic biological and sedimentary mechanisms for the delivery and preservation of organic matter in such prospective intervals.
3

A computer analysis of the geochemistry and mineralogy together with the petrology of the Upper Pennsylvanian and Lower Permian shales of Kansas, U.S.A

Cubitt, John M. January 1975 (has links)
The objectives of this thesis are twofold; firstly, to conduct a detailed geochemical, mineralogical and petrological survey of the Upper Pennsylvanian and Lower Permian Shales of Kansas, U.S.A., and to relate the variation observed in the stratigraphic and tectonic framework of the Mid-Continent during this period. Secondly, it was necessary to study the instrumental techniques applied to fine-sprained rocks, to develop standardized procedures and where appropriate to implement new techniques. Six facies are developed in Kansas Shales - a sand and siltstone facies and a brown clayey shale facies, corresponding to deltaic sands and silts and prodeltaic marine muds respectively, a, calcareous grey shale facies and a black shale facies, deposited in normal marine and restricted marine environments respectively, and two minor facies, a purple and red shale facies and shale parting's in Limestones. The first two facies normally constitute the thick shale Formations (outside shales) separating Limestone Formations in which the second facies pair develop (inside shales). The facies distributions subdivide the stratigraphic section into five zones - the Pleasanton and Lower Kansas City Groups (with cycles of marine and deltaic shales) the Upper Kansas City, Lansing end Douglas Groups, the Shawnee Group (containing cycles), the Wabaunsee Group and the Admire, Clia.se and Council Grove Groups. A combined standards regression technique was implemented for quantitative X-ray diffraction analysis of shale mineralogy. The smear technique of ZRD sample preparation was shown to be superior for distinguishing between shale samples although the pressed pellet and membrane filter techniques (developed in this thesis) were considered more appropriate to this study. Major oxide and trace element concentrations were determined by emission spectroscopy. Structural sites of ions in shales were estimated by electron spin resonance. Fabrics of shales were examined by scanning electron microscopy and micro morphological techniques.
4

Geochemistry of Drilled (DSDP) Sediments from the Southern Indian Ocean

Fleet, A. J. January 1977 (has links)
No description available.
5

The gaseous exchange of ozone at terrestrial surfaces : non-stomatal deposition to grassland

Coyle, Mhairi January 2005 (has links)
It is important to understand how O<sub>3</sub> is generated and processed in the atmosphere. New critical levels that use accumulated stomatal uptake rather than atmospheric concentration have recently been set by the UNECE to quantify the effect of O<sub>3</sub> on vegetation. There are models available that can estimate the stomatal flux but the non-stomatal component is not well described. The total flux of O<sub>3</sub> was measured over grassland in central Scotland during 2001 to 2004 using micrometeorological methods and the uptake by stomata estimated by similarity with the water-vapour flux. The non-stomatal component is estimated using R<sub>ns </sub>=(R<sub>c</sub><sup>-1</sup> - R<sub>s</sub><sup>-1</sup>)<sup>-1 </sup>where R<sub>ns </sub>= non-stomatal surface resistance to ozone deposition, R<sub>c</sub> = total canopy resistance, R<sub>S</sub> = stomatal resistance. The dataset is used to examine the processes controlling deposition at this site with a view to providing a suitable parameterisation for the stomatal and non-stomatal components. There are two forms of model commonly used to estimate stomatal resistance: Jarvis type multiplicative models, and Ball-Berry photosynthesis based approaches. Measurements of plant physiology where made during 2001 and 2002 to parameterise a Ball-Berry type model; a standard parameterisation from EMEP is used for the Jarvis type then tuned to fit the measured data. The non-stomatal component is also important if O<sub>3</sub> concentrations are to be accurately modelled. Parameterisations based on the variation of R<sub>ns </sub>with surface temperature and wetness are developed. These “new” stomatal and non-stomatal formulae are implemented in a total-deposition model and the results compared to the measured data. Finally estimates of current and future critical levels for vegetation are calculated and their implications for effects examined.
6

The geochemical palaeo-oceanography and mineralogy of marine sediments from the Peruvian Continental Margin

McNeill, Gavin William January 1993 (has links)
A comprehensive study of marine sediments collected during the <i>R.R.S. Charles Darwin</i> Leg 38 cruise from the Peruvian continental margin, has been carried out using a wide range of geochemical analysis technqiues. The prime objective of the study has been to determine the strength and down-core variation of many oceanographic processes during the glacial/interglacial stages of the Late Quaternary by means of geochemical palaeo-environmental indicators. Coastal upwelling is a physical movement of cold, nutrient-rich water to replace surface water which has been blown off-shore by Ekman transport, as a result of along-shore winds. This results in high marine productivity levels within the Peruvian coastal upwelling zone, and is recorded by enrichments of organic carbon and other biogenic-remains in the sediments accumulating below. Particular metals, which have a capacity to be scavenged from sea-water as organic matter falls through it, are also enriched in the sedimentary record. Organic matter and fish-remains supply a continuous source of phosphorus to the surface sediment. Upon bacterial decomposition of this biogenic debris, phosphate can become enriched in the pore-waters until precipitation of carbonate fluorapatite occurs to form the diagenetic mineral known as phosphorite. Within the Peru margin cores, the presence of disseminated phosphorite pellets and zones of nodular hardgrounds has been determined using pore-water modelling and geochemical partitioning equations. Many trace elements can be incorported into the phosphorite mineral structure. Quantitative analysis of the uranium, strontium and yttrium concentrations within phosphorite zones has allowed for the partitioning of these elements into the organic, carbonate and terrigenous phases respectively. Y-series radiochemical age dating of a phosphorite nodule yielded a 'maximum' age of about 114,000 years for the phosphatic material. This age corresponds to an initial pellet growth on the continental margin during an interglacial period and supports the hypothesis of nodule diagenesis during the last glacial period as a result of heavy mineral concentration by bottom-water currents during a eustatic drop in sea-level.
7

Estimation of landscape carbon budgets : combining geostatistical and data assimilation approaches

Spadavecchia, Luke January 2008 (has links)
Quantification of carbon (C) budgets at the landscape or catchment scale is generally achieved using process-based models as scaling tools. Such models require some metric of the exchange surface capability (e.g. Leaf Area Index, LAI) and a set of rate parameters for C processing. The net C exchange is then determined by driving the model with meteorological observations. Regional fields of parameters and drivers may be derived by upscaling site level measurements, constrained using Earth Observation data such as vegetation indices and digital elevation models (DEMs). I explore issues of error and uncertainty when upscaling C model parameters and drivers, and the effect of these uncertainties on the final analysis of the carbon budget. Two study areas focus the research: a region of tundra in Arctic Sweden and a ponderosa pine stand in Oregon. I use geostatistical techniques to develop fields of LAI and meteorology, complete with error statistics, whilst the distributions of rate parameters for a C model are derived via the Ensemble Kalman filter (EnKF). I report that the use of DEM data can provide LAI fields with an r<sup>2</sup> ~50% greater than those derived from EO data alone. In particular I find strong relationships between LAI, elevation and topographic exposure. I explore the use of spatio-temporal geostatistics to improve meteorological fields, but report a better interpolation skill when temporal autocorrelations are ignored. Variation in parameters has a much larger effect on the uncertainty of the carbon budge (~50%) than driver uncertainty (~10%). The combined uncertainty in parameterisation and meteorology may result in a 53% uncertainty in total C uptake.
8

Investigating the links between faunal activity and organic geochemistry in continental margin sediments : tracer studies across the Arabian Sea oxygen minimum zone

Woulds, Clare January 2005 (has links)
The objectives of this study were to investigate the role that fauna play in short-term OM processing, how this varies with OM supply and quality, oxygen availability and faunal community structure, and how faunal activity is linked to sediment organic geochemistry. This was achieved through experiments and organic geochemical sampling, at sites spanning the OMZ on the Pakistan margin. The steep gradients in OM quantity and quality, oxygen, and faunal communities, and seasonal changes in OM supply, provided an exceptional natural setting to assess these relationships. Incubation studies were conducted on intact sediments containing whole faunal communities, aboard ship and <i>in situ </i>and using a novel system to maintain ambient oxygen levels. <sup>13</sup>C-labelled algae were added to the sediments and traced into organisms, sediments, and respired pools. The resulting carbon budgets are some of the most complete to date, and allowed direct comparison among an unprecedented range of site conditions. Where macrofauna and higher-quality OM were present, OM uptake by fauna was greater; at one site macrofaunal uptake equalled total respiration, illustrating the key significance of fauna. Oxygen had a threshold effect on the faunal groups responsible for OM processing, with foraminifera and macrofauna dominating OM processing below and above the threshold, respectively. Notably, a new technique was developed for the quantitative tracing of labelled amino acids, which allowed the first molecular level tracing of OM in whole community and <i>in situ </i>experiments, and provided among the first direct links between faunal digestive activity and sediment OM composition. Compound-selective assimilation and OM alteration were observed, the patterns of which were taxon-specific.
9

Radon emissions to the atmosphere and their use as an atmospheric tracer

Robertson, Lynette B. January 2004 (has links)
The naturally-occurring radioactive gases <sup>222</sup>Rn and <sup>220</sup>Rn are widely used as atmospheric tracers in a variety of applications pertinent to climate and air quality studies, but their use in this context is currently limited by poor knowledge of the spatial and temporal pattern in emissions. The aim of this research was to improve knowledge of <sup>222</sup>Rn and <sup>220</sup>Rn emissions by investigating their spatial and temporal variation in emissions on various scales. Novel approaches to measuring <sup>222</sup>Rn and <sup>220</sup>Rn fluxes by the closed chamber method have been developed and compared with some existing methods, and studies of some controlling variables for which there is limited and conflicting information (water table depth, freezing of the soil and snow cover) have been carried out. Studies of the short-term variability in <sup>222</sup>Rn emissions made with an automatic chamber showed that outside periods of rain the <sup>222</sup>Rn flux was relatively constant (CV = ~ 25 %), but heavy rainfall may temporarily completely suppress the radon flux if the soil surface becomes saturated. On the seasonal time-scale, flux measurements made on a medium- moisture was found to be the most important factor controlling the variations in radon flux; air pressure and temperature were not important. Field measurements and a laboratory study using a soil monolith showed that water table depth was also an important factor for <sup>222</sup>Rn flux, but not for <sup>220</sup>Rn, due to its much shorter diffusion length. Freezing of the soil surface layer (~ 5cm depth) did not cause a significant reduction in <sup>222</sup>Rn or <sup>220</sup>Rn flux. Studies of the spatial variability of <sup>222</sup>Rn emissions at the local scale showed that <sup>222</sup>Rn flux is approximately normally distributed (CV = 55 %), and that soil moisture is an important factor. However, measurements made at 15 sites of different soil type and geology across North Britain showed <sup>222</sup>Rn emissions to be log-normally distributed at this larger scale and highly variable (CV = ~ 200%). The <sup>226</sup>Ra content of the soil, which ranged from <3 Bq kg<sup>-1</sup> to 55 Bq kg<sup>-1</sup> was found to account for a large proportion of the observed variability (~ 80 %). The median <sup>222</sup>Rn flux was 9.7 Bq m<sup>-2</sup> h<sup>-1</sup>, indicating that the average flux from this region is considerably lower than the global average, as would be expected given the large proportion of peat soils and generally high soil water content and shallow water tables. A <sup>222</sup>Rn flux map produced for North Britain using a GIS and empirical model based on soil and geology classifications was able to reproduce the main spatial pattern in emissions, but on the whole, significantly under- predicted the magnitude of fluxes.
10

The nature of the chemically enriched components of the Iceland mantle plume

Williams, Alice Josiane January 2005 (has links)
The main intentions of this research are to identify and characterise enriched components in the sub-Icelandic mantle and to determine their origins and relationships with other mantle components. Helium, strontium, neodymium and lead isotope data, in conjunction with major and trace element data, allow the characterisation of enriched mantle sources in the flank-zones. Postglacial olivine- and pyroxene-bearing basalt samples have been collected from each of three flank-zones. Pyroxene <sup>3</sup>He/<sup>4</sup>He may have been affected by pre- or post-eruptive addition of radiogenic <sup>4</sup>He, but olivine <sup>3</sup>He/<sup>4</sup>He represent the time-integrated <sup>3</sup>He/(U+Th) of the mantle source. Published oxygen isotope data indicate that the flank-zone basalts have not been affected by crustal contamination. Coherent trends in He-Sr-Nd-Pb isotope co-variation diagrams allow the identification of three distinct enriched components in the North Atlantic mantle. Each enriched component is characterised by lower <sup>3</sup>He/<sup>4</sup>He (< 6 R<sub>a</sub>)<sub> </sub>and <sup>143</sup>Nd<sup>/ 144</sup>Nd<sup> </sup>and more radiogenic Pb and Sr isotope ratios than the depleted mantle components sampled in the rift-zones and along the MAR. One enriched component, EI<sub>l</sub>, is most prevalent in the mantle beneath the SFZ. It is distinguished from the other enriched components by its extreme Pb isotope composition (<sup>206</sup>Pb/<sup>204</sup>Pb<sup> </sup>> 19.4). It is probably derived from recycled oceanic crust (a young-HIMU-like component). The second enriched component, EI<sub>2, </sub>is only sampled at Öræfajökull (EFZ), and is distinguished by its extreme <sup>87</sup>Sr/<sup>86</sup>Sr (> 0.7037) and positive D7/4. Its isotopic composition most likely has its origins in recycled pelagic or terrigenous sediments. The third enriched component, E13, dominates the Jan Mayen (North Atlantic) and Snæfell (EFZ) mantle sources. It has similar Sr, Nd and He isotopic compositions to EI<sub>l</sub>, but is characterised by less-radiogenic Pb isotope ratios ( <sup>206</sup>Pb/<sup>204</sup>Pb<sup> ~ </sup>18.6). It is also most likely derived from young recycled oceanic crust. Enriched mantle beneath Snæfellsnes appears to be derived from mixing of EI<sub>l</sub> and EI<sub>3</sub>. Two depleted components (DI<sub>1</sub> and DI<sub>2</sub>) are required to explain negative trends in He-Sr, He-Nd or He-Pb co-variation diagrams. They have similar Sr, N d and Pb isotopic compositions to each other, but can be distinguished on the basis of <sup>3</sup>He/<sup>4</sup>He. DI<sub>1</sub> is characterised by <sup>3</sup>He/<sup>4</sup>He ~45 R<sub>a </sub>and represents the depleted Iceland plume component. DI<sub>2</sub> is characterised by lower <sup>3</sup>He/<sup>4</sup>He (7-9 <i>R</i><sub>a</sub>)<sub> </sub>and represents the depleted component in the N-MORB mantle. Only a very small contribution of DI<sub>1</sub> can change the <sup>3</sup>He/<sup>4</sup>He of a source without affecting its Sr; Nd or Pb isotopic composition. A mixing model is presented which enables plume-derived enriched components to be distinguished from those present in the shallow asthenospheric mantle. Only EI<sub>l</sub> appears to be intrinsic to the plume, whereas EI<sub>2</sub> and EI<sub>3 </sub>are upper-mantle heterogeneities.

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