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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.


Pretorius, Huibrecht Catharina Florina 14 June 2013 (has links)
Vaalputs, the South African radioactive waste disposal facility, is currently licensed to dispose only low and intermediate level radioactive waste. The repository has been disposing radioactive waste since 1986; however, up until May 2011 no long-lived uranium containing waste has been delivered to Vaalputs. The Nuclear Energy Corporation of South Africa (Necsa) has foreseen this disposal and so ordered this study to establish a baseline for the behaviour of naturally occurring radionuclides from the uranium and thorium decay chains in the groundwater of Vaalputs. This baseline will be used to monitor the groundwater below Vaalputs for possible anthropogenic additions to the environmental radioactivity. This baseline was established by studying a unique dataset of 25 years of analysis of activities of man-made and naturally occurring radionuclides as well as cation and anion concentrations in the groundwater at Vaalputs. This database is the result of annual monitoring of the groundwater from a confined set of boreholes on and around the facility as part of the regulatory requirements of radioactive disposal. The analytical results of radionuclides in groundwater from 13 annually and 3 quarterly sampled boreholes have been evaluated during this study. Cation and anion concentrations were measured respectively by inductively coupled plasma optical emission spectrometry and ion chromatography. In routine analyses the activities of the long-lived radionuclides 238U and 232Th were measured by instrumental neutron activation analysis, while the short-lived radionuclide 226Ra was detected by γ-ray spectrometry. The overall radioactivity hazard from total α and β radiation levels were measured by gas flow proportional counting. On occasion groundwater samples have been analysed by α-spectrometry to determine the activities of α-emitting radionuclides from the decay chains of 238U, 235U and 232Th. These analytical results have been integrated in order to evaluate trends in activities of radionuclides, the relative contributions of individual radionuclides to total radiation levels and how these are influenced by groundwater conditions. 238U levels show a natural anomaly in the near-field of the disposal site, attributed to basement rocks anomalously enriched in uranium located close to the disposal trenches. This should be taken into consideration when monitoring the groundwater for possible additions of uranium. One set of duplicate samples from 2009 has been analysed by alpha spectrometry, determining an average activity ratio of 234U/238U in the groundwater of Vaalputs as 4.1. This average ratio has been used in the rest of the study for comparison of the contribution of 234U to total α radiation with the contribution of the other α-emitting radionuclides. However, it is suggested that a more extensive experiment should be carried out to determine a statistically representative activity ratio for the different areas at Vaalputs. High levels of 226Ra, unsupported by 238U, have been found in groundwater from certain boreholes, mostly boreholes lying closely together on the western side of the property. This groundwater also yielded low activity ratios for 234U/238U, lower pH and stronger oxidizing conditions than that of the rest of the area. The distinct host of Namaqualand rocks with the absence of overlaying sedimentary rocks has been suggested as the key to the different geochemical conditions of the groundwater of these boreholes. 232Th and its daughter radionuclides yielded levels far below the guideline of 1 Bq.l-1 given by the World Health Organisation, as is expected from the known low mobility of thorium. A peak in total α radiation levels was seen in 2000 in the near-field area. Assessing the cumulative contributions of the various radionuclides it was very clear that the greatest factor in producing α radiation is 234U. However, no data is available for the levels of 234U in 2000. It is suggested that future occurrences of elevated total α radiation levels should be investigated either by performing alpha spectrometry on a duplicate sample or on a sample collected as soon as possible after the original sampling. Analysis of total β radiation levels were found to be unreliable up to 2005, and since the analysis of β-emitting radionuclides was not part of the scope of this study, no conclusions with regard to the contributors to total β radiation could be made. It is suggested that the elevation of total β radiation levels of specific beta-emitting radionuclides, especially 40K, should be determined.


Wildau, Antje 23 July 2013 (has links)
Not available

Evidence of fault movement during the Holocene in Southern Louisiana: integrating 3-D seismic data with shallow high resolution seismic data

Frank, Joseph P 19 May 2017 (has links)
The Baton Rouge fault system of Louisiana is a well-known recently active system consisting of en echelon, east trending, down-to-the-south normal faults across the northeast periphery of the Mississippi River delta plain. Two, industry-donated, 3-D seismic surveys across 860 km2 image deep-seated faults below Lake Borgne, along an east strike that parallels previously well mapped segments of the Baton Rouge system. Four major faults (> 6 km fault trace) are imaged within the seismic surveys across the Lake. The industry seismic data were not processed for reliable imaging at depths (m). To bridge the depth gap in seismic, high resolution, shallow seismic data has been acquired in areas where faults are projected to intercept the surface. Integration of high resolution data with industry 3-D seismic data is fundamental to evaluating whether these faults are recently active (Holocene) and if they are strike aligned to nearby, linear wetland loss patterns.

Mixed silicilcastic-siliceous succession, Miocene Monterey formation, Point Dume to Paradise Cove, Malibu, California

Njuguna, Wanjiru Margaret 24 January 2017 (has links)
<p> The 752 meter section of the Miocene Monterey exposures between Point Dume and Paradise Cove is described in detail using meter-by-meter Spectral Gamma Ray data, lithologic descriptions, sandstone analysis (percent sandstone and thin section petrography) and X-ray diffraction data. Samples were analyzed to determine total organic carbon (% TOC) and diatom assemblages. The stratigraphic section is subdivided into four distinct members and is portrayed in a new stratigraphic column. In stratigraphic order, the members are the Dolomitic Phosphatic Shale Member, the Porcelanite and Shale Member, the Mixed Clastics Member and the Cherty Diatomite Member. High TOC values in the Dolomitic Phosphatic Shale range between 4.2 and 7.5%. Opal-CT phase silica occurs in cherts and porcelanite and biogenic Opal-A phase silica occurred in the diatomites. Rocks showing a complete diagenesis to Quartz phase silica are not in the section. Bedding confined fractures and joint sets between different siliceous rocks are abundant in the Porcelanite and Shale Member. The base of the Mixed Clastics member has high energy deposits indicating down-slope movement with major sandstones and conglomerates. The top of the section contains the Cherty Diatomite member and consists of rhythmically bedded pure diatomite, &ldquo;speckled&rdquo; beds, muddy diatomites, siliceous/calcareous mudrocks and Opal-CT chert. Dolostone forms a significant component of the rock type throughout the section. The Monterey Formation is found throughout Coastal California and in most of the Neogene sedimentary basins in the State. It is highly petroliferous, forming both the source and reservoir rock. Understanding the exposures in Malibu, CA contributes to the understanding of this economically important formation.</p>

Pore structure of opal-CT and quartz porcelanites, Monterey Formation, California

Kassa, Tesfalidet Ghirmay 08 November 2016 (has links)
<p> Secondary and backscattered electron scanning electron microscopy of argon-ion polished or focused-ion beams&rsquo; cut surfaces reveal significant differences in pore size, shape and complexity between opal-CT and quartz-phase porcelanites, but also between rocks of the same silica phase with distinct silica content or sedimentary fabric. Previous studies of these important petroleum reservoir rocks measured an order-of-magnitude lower permeability in opal-CT than quartz-phase porcelanites. Detrital-poor quartz-phase porcelanite (> 80% silica) has massive or laminated microfabrics. The massive type consists of low-porosity matrix and high-porosity lenticular patches with 17-20% bulk porosity. In contrast, a laminated detrital-poor porcelanite (26% bulk porosity) has &sim;100 &micro;m-thick layers that alternate between well connected, highly porous (35% and low-porosity layers (19%) with isolated pores. Massive detrital-rich porcelanites have porosity of 10% with and poor connectivity. </p><p> Opal-CT porcelanites also have two detrital-poor (>75% silica) and one detrital-rich (&lt;60% silica) microfabrics. One detrital-poor porcelanite with 30% bulk porosity has a pervasive lepispheric fabric in which lepispheric cores and interlepisphere porosity each comprise &sim;1/2 of the total porosity (3-138 nm size). Lepisphere core are mostly isolated by a surrounding, virtually pore-free, impermeable mantle. The larger and better-connected interlepisphere pores are formed by larger, crosscutting and radiating bladed crystals. The detrital-poor, opal-CT porcelanite is characterized by extraordinarily large and connected vuggy pores with bulk porosity of 60%. This unique pore structure is associated with silica mobility during stalled burial or tectonic uplift of the opal-CT to quartz transition zone. The third fabric is in detrital-rich opal-CT porcelanite that has 18% bulk porosity with poorly connected pores. </p>

Stratigraphy, sedimentology and petroleum potential of the Upper Devonian Duperow Formation, southwest Manitoba

Bates, Kerry 16 September 2016 (has links)
The Upper Devonian (Frasnian) Duperow Formation in the Williston Basin consists of cyclical deposits of carbonate rocks and evaporites deposited in the semi-restricted Duperow Embayment. The formation can be divided, in ascending order, into the Saskatoon, Wymark and Seward members. Three lithofacies associations (subtidal, intertidal and supratidal/sabkha) comprised of nine lithofacies, representing a semi-restricted interior platform setting, are recognized in this study. These lithofacies include diagenetic features representing alteration in marine, burial and meteoric environments. Thin organic-rich laminae throughout the Wymark Member have good generative potential for oil and/or gas but are thermally immature. Dolomitized units of the Saskatoon and Wymark Members have good reservoir potential. The best potential for conventional petroleum plays exists in possible structural traps related to salt dissolution in the Prairie Evaporite and block faulting along the Birdtail-Waskada Zone, as well as stratigraphic traps related to laterally and vertically variable dolomitization. / October 2016

Mapping Sweetness of the Second White Speckled Shale S Member| Ricinus Area, Alberta, Canada

Boucher, Ryan James 30 November 2016 (has links)
<p> The Second White Speckled Shale Formation, located in the Western Canadian Sedimentary Basin is Late Cretaceous (Cenomanian-Turonian) in age, and consists of finely interbedded siltstone and mudstone. Since the 1960s, the formation has produced oil and gas in unpredictable quantities. Understanding the lateral heterogeneity of the formation&rsquo;s characteristics such as thickness, hydrocarbon saturation, total porosity, brittleness, clay volume, and TOC could potentially help to uncover causes for production variations. In this study, well logs and core data from 25 different wells were used to map petrophysical characteristics for the S member. Once distribution of these properties was determined, two methods were used to identify potential &ldquo;sweet spots&rdquo; for further drilling. The first method involved suggesting appropriate cut-off values for each property and establishing which areas lie inside all of the cut-off values for all properties. The second method was more complex and involved assigning a weight to each characteristic, solving for their &ldquo;plot&rdquo; values, and then contouring the Sweetness Index (SI) to locate sweet spots. The first method resulted in identifying two potential sweet spots (&ldquo;A&rdquo; and &ldquo;B&rdquo;). The second method resulted in contoured values for the Sweetness Index with a somewhat different area of highest potential. After comparing these sweet spots with production, it was concluded that the S member is indeed very heterogeneous, and there is either not a direct correlation of high production to areas with the best petrophysical attributes, or the current wells might not be in the optimum location as suggested by these sweetness maps.</p>

Strain localization and exhumation of the lower crust: A study of the three-dimensional structure and flow kinematics of central Fiordland, New Zealand

Newman, Alice 01 January 2014 (has links)
In this thesis, I present structural and kinematic data on rock fabrics, shear zones and fault zones from the Cretaceous Malaspina orthogneiss and some of its satellite plutons in central Fiordland, New Zealand. Central Fiordland exposes a large tract of granulite- to eclogite-facies lower crust that was exhumed between late Mesozoic to Cenozoic times. The deformational structures of interest were formed and preserved during the lifecycle of a Cretaceous continental arc that involved thickening to over 60 km followed by collapse and rifting. As such, they provide an excellent opportunity to study strain localization in the deep crust and the process of exhumation. Detailed structural mapping, analysis, and the construction of a 45-kilometer cross section through the Malaspina orthogneiss and adjacent plutons reveal the spatial distribution, sequence, and kinematics of crosscutting deformational structures. The earliest structures record Cretaceous magmatism, high-grade metamorphism at the granulite and eclogite facies, and ductile flow that resulted in widespread (over 1200 km2), disorganized magmatic foliations. These events were followed by regional extension that resulted in the formation of multiple, ≤0.5 km-thick ductile, upper amphibolite facies shear zones that record cooling, hydration, and horizontal flow during the Late Cretaceous. Extension continued but changed obliquity in the early to middle Tertiary and resulted in sets of strike-slip and normal brittle to semi-brittle faults forming a sinistral transtensional system. These faults are distributed across central Fiordland and crosscut and transpose the ductile shear zones and magmatic foliations. Lastly, a change in relative plate motions resulted in the inception of the Alpine fault and the development of a late Tertiary transpressional fault system that crosscuts all previous structures. The dominant factors controlling strain localization in central Fiordland changed from magma, heat, and melting, to fluid activity, plate boundary reorganization, and reactivation of inherited structures. The succession of contrasting strain localization styles in response to changing tectonic and local conditions led to the development of multiple phases of deformation. These multiple phases of deformation allowed the deep crust to be exhumed in a heterogeneous and fragmented, or 'piecemeal', way. In particular, the inability of late Cretaceous ductile shear zones to fully exhume the lower crust was compensated by the ability of early Tertiary transtensional faults to simultaneously thin and further exhume the lower crust. Investigations of strain localization patterns in central Fiordland shed light on the causes and mechanisms of crustal exhumation, a phenomenon that is integral to the lifecycle of virtually all orogenic belts.

Geology and mineralization controls surrounding the Palmarejo mining district - A compilation of remote and hands on exploration techniques

Molina Sotelo, Castulo 22 February 2017 (has links)
<p> Exploration is the base of the mining industry, and it is often taken as synonymous with "finding a mine". In reality it is a more complex process; where the selection, evaluation, screening and testing of successively smaller areas lead to the discovery of an economic deposit. Once the deposit is found, the economic factors become more important than the geological ones, and then the exploration becomes a tool to give sustainability to the mining operation through time. </p><p> The silver and gold deposits of the world-class Palmarejo District are typical, intermediate sulfidation-style epithermal, precious metal occurrences, hosted in Cretaceous- to Tertiary-aged volcanic and intrusive rocks of the Lower Volcanic Complex (LVC), and host one of the newest and largest silver and gold producers in Mexico. </p><p> Using a series of five chapters, three of them focused on the mine, and two at regional level, this author will show the geology and mineralization controls at different scales within the study area. Once the mineralization controls at regional and mine scale are known, the combination of previous knowledge with the right tools, helps the explorer to decide where to, wisely and effectively, spend the resources.</p>

8 published articles on geology

Reynolds, Doris January 1937 (has links)
No description available.

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