• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 186
  • 135
  • 45
  • 19
  • 5
  • 3
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 471
  • 134
  • 106
  • 99
  • 88
  • 81
  • 58
  • 49
  • 47
  • 43
  • 42
  • 41
  • 41
  • 40
  • 36
  • 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.
91

FLUID EVOLUTION AND STRUCTURAL CONTROL ON URANIUM DEPOSITS IN SUCCESSOR BASINS IN NORTHERN CANADA AND NORTHERN AUSTRALIA

Dieng, SERIGNE 14 August 2012 (has links)
Uranium deposits associated with Paleoproterozoic successor basins were investigated using structural, petrographic, geochronological and geochemical relationships to understand the character and timing of ore-forming fluids and the structural control on uranium mineralization. The work focused on two successor basins that share similar geological characteristics: the Martin Lake Basin in the Beaverlodge area in Canada, and the El Sherana Basin in the South Alligator River area in Australia. The Beaverlodge area records six temporally distinct stages of U mineralization spatially associated with the Martin Lake successor basin. Early minor stages are hosted in cataclasite and veins at ca. 2.29 Ga and in albitized granite in the Gunnar deposit between ca. 2.3 Ga and 1.9 Ga, which predates the main stage of U mineralization of hydrothermal breccias that formed at ca. 1.85 Ga. Later stages of mineralization are related to minor veins at ca. 1.82 Ga linked to alkaline mafic dikes associated with the Martin Lake Basin and to minor veins at ca. 1.62 Ga corresponding to the timing of unconformity-type U mineralization in the overlying Athabasca Basin. The main breccia-type U mineralizing event that affected all deposits in the Beaverlodge area formed at ca. 1.85 Ma from metamorphic fluids at ca. 330oC linked to metasomatism during regional metamorphism of the Trans-Hudson Orogen. The ore-forming fluids were likely derived from metamorphic remobilization of pre-existing U-rich basement rocks, and ascended upward along deep fracture systems that resulted from brittle reactivation of early ductile shear zones. The main event of U mineralization in the South Alligator River area formed at ca. 1.82 Ma, subsequent to deposition of the El Sherana Group at 1.84-1.83 Ma. The formation of these deposits is related to fluids derived from diagenetic processes in sandstone of the El Sherana Group. Mineralization formed when a 250oC, low latitude, oxidizing, U-bearing basinal brine from diagenetic aquifers in the Coronation sandstone descended downward into the unconformity along fracture systems created by brittle reactivation of the El Sherana-Palette fault system. Uranium deposits associated with successor basins in the Beaverlodge and South Alligator River area are older than those in the U-rich Athabasca and Kombolgie basins. Rocks that host these deposits have been folded, and then exhumed during subsequent tectonic events. These older U deposits can be considered as a potential source for detrital uraninite that fed sediments of the Athabasca and Kombolgie basins and therefore contributed to the inventory of uranium that formed unconformity-related U mineralization in the younger basins. Therefore, the occurrence of older U mineralization associated with successor basins can be considered as positive criterion for exploration of unconformity-related U mineralization in younger Paleoproterozoic basins. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2012-08-13 18:54:41.141
92

The sequence stratigraphy of the Lower Jurassic of Western Europe

Parkinson, D. Neil January 1994 (has links)
The Lower Jurassic stratigraphy of seven contrasting areas in western Europe is compared in order to seek evidence for a pan-Western European stratigraphic forcing mechanism. Sequencestratigraphic models are discussed and emphasis is placed upon the differing response of sedimentary systems in "accommodation space-dominated" and "supply-dominated" settings. Spectral gamma-ray data from clastic successions in the Wessex and Cleveland basins (England) are used to elucidate vertical trends. A proximal-distal model for control of Th/K ratios is advanced. Stage-frequency regressive-transgressive cycles in the two areas are shown to be closely correlative. Sedimentolgical logs and spectral gamma-ray data are presented for the carbonate ramp into turbidite sequence of Peniche (Portugal) and for a new exposure of the Pliensbachian-Toarcian in southern Germany. Systematic variation in clay mineralogy across Europe is suggested. Cycles in the Lower Jurassic of the North Viking Graben (Norwegian North Sea) are examined using wireline log correlation and the stratigraphic evolution of the Tethyan Rift in the Western and Southern Alps is reviewed. X-ray diffraction studies of the Pliensbachian-Toarcian interval in the Southern Alps are presented in order to elucidate sediment supply to the pelagic realm. The cycles observed in the English sections appear to be manifest widely across western Europe in a variety of tectonic and sedimentary settings. Sharp basinward facies shifts (candidate sequence boundaries) do not appear to be synchronous between basins. <sup>87</sup>SR/<sup>86</sup>SR analysis of belemnites from the Portuguese and German sections confirms the regional applicability of the results of Jones (1992) and the utility of this technique in long range correlation. Carbon and oxygen analysis of the same material supplements the data of other workers and a direct relationship is suggested between relative sea level and organic carbon burial in the Early Jurassic.
93

Impact of Reservoir Evaporation and Evaporation Suppression on Water Supply Capabilities

Ayala, Rolando A 03 October 2013 (has links)
Reservoir storage is essential for developing dependable water supplies and is a major component of the river system water budget. The storage contents of reservoirs fluctuate greatly with variations in water use and climatic conditions that range from severe multiple-year droughts to floods. Water surface evaporation typically represents a major component of the reservoir water budget. This thesis investigates the effects of evaporation and potential reductions in this evaporation on the water supply capabilities of reservoirs in Texas. As part of this research, a literature review based assessment of capabilities for reducing reservoir evaporation using monolayer films and other methods was performed. The literature review assessment provides an overview of past evaporation suppression studies performed using monolayer films and other evaporation suppression technologies including water shades and covers. The overview provides a summary on monolayer film application techniques, environmental impacts, operational and material costs, evaluation methods, and achievable evaporation reduction rates. This research project quantifies the impact of reservoir evaporation on water supply availability/reliability by using the Texas Water Availability Modeling (WAM) System which consists of the Water Rights Analysis Package (WRAP) and 21 sets of WRAP input files covering the 23 river basins of the state, a geographic information system (GIS), and contains over 8,000 water rights permits, which include 3,435 reservoirs. The impact of evaporation on water supply availability/reliability was evaluated by performing several analyses in which evaporation rates are reduced by specified percentages starting when storage levels drop below certain trigger percentages of reservoir storage capacity.
94

Recent volcanic and tectonic evolution of the Southern Mariana arc

Becker, Nathan C January 2005 (has links)
Thesis (Ph. D.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 150-166). / Also available by subscription via World Wide Web / xv, 166 leaves, bound col. ill., col. maps (1 fold.) 29 cm
95

Mariana forearc basin evolution from 14°N to 18°N : a seismic stratigraphic analysis

Chapp, Emily January 2006 (has links)
Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 78-83). / ix, 83 leaves, bound ill., map 29 cm
96

Petrographic characterization of sandstones in borehole E-BA1, Block 9, Bredasdorp Basin, Off-Shore South Africa.

Van Bloemenstein, Chantell Berenice January 2006 (has links)
<p>The reservoir quality (RQ) of well E-BA1 was characterized using thin sections and core samples in a petrographic study. Well E-BA1 is situated in the Bredasdorp Basin, which forms part of the Outeniqua Basin situated in the Southern Afircan offshore region. Rifting as a result of the break up of Gondwanaland formed the Outeniqua Basin. The Bredasorp Basin is characterized by half-graben structures comprised of Upper Jurassic, Lower Cretaceous and Cenozoic rift to drift strata. The current research within the thesis has indicated that well E-BA1 is one of moderate to good quality having a gas-condensate component.</p>
97

Porosity and permeability distribution in the deep marine play of the central Bredasdorp Basin, Block 9, offshore South Africa.

Ojongokpoko, Hanson Mbi January 2006 (has links)
<p>This study described porosity and permeability distribution in the deep marine play of the central Bredasdorp Basin, Block 9, offshore South Africa using methods that include thin section petrography, X-ray diffraction, and scanning electron microscopy, in order to characterize their porosity and permeability distributions, cementation and clay types that affect the porosity and permeability distribution. The study included core samples from nine wells taken from selected depths within the Basin.</p>
98

An investigation of appropriate technology on-site water conservation, roof runoff supply and water reuse systems for application within the Adelaide Metropolitan Area /

Allen, Martin Unknown Date (has links)
Thesis (M Eng) -- University of South Australia, 1993
99

Environmental economic aspects of river basins and their catchment. Identification and quantification of flood related land use externalities

Dorner, Wolfgang January 2009 (has links)
[Abstract]This thesis investigates a common problem of land use impacts on flood damage costs on a catchment scale. It does this through a particular case study, to quantify the technical upstream-downstream dependencies and highlights the externalities through hydroeconomicanalysis of flood damages and mitigation costs. The substantive content of the project is cross disciplinary.Peak and volume of river flows are functions of the catchment surface characteristics. This means that any impacts to the run-off regime (for example surface sealing or river training) could affect people and land users in the lower catchment. Thus, upstream activities cancause higher flood peaks, and also entail higher damages downstream. These damages are either borne by the affected parties or they are mitigated by state financed flood defence works or offset with financial compensation. These costs are usually not included in the economic considerations of the upstream land user who is partially causing them. In economic terms, these effects are referred to as unidirectional externalities. This means that a producer can export parts of his production costs to third parties and these are not included in the price of the product.The Herzogbach is a small tributary of the Danube River in Lower Bavaria. It is located in a rural area, dominated by intensive farming practices. Two villages (Bachling and Buchhofen) in the headwaters and middle section of the catchment and one city (Osterhofen) in the lowercatchment were analysed to determine the impact of upstream land use practices on the flood situation.A combination of hydrological and hydraulic modelling provided the core data to allow the interpretation of economic data, using methods of cost damage estimation. A hydrological model of the catchment provided hydrograph simulations based on (a) a regionalisation approach,(b) hydrologic flood routing and (c) hydrologic reservoir routing. A two dimensional stream flow model was then used to convert the hydrographs into flood levels, to simulatethe run-off in settled areas and determine the flood affected areas, flood levels and flow velocities. Estimates for flood damages or mitigation costs resulting from different hydrological scenarios were compared. The scenarios are based on different land uses and alloweconomic externalities to be estimated.It was found that intensive farming and river training increase the peaks, shape and volume of flood waves in comparison to extensive land use, grassland or forest. In the study area, especially river training reduced the detention effect of the river bed and the natural floodplain. These significant changes to the natural run-off regime directly affect land use in the lower catchment through flood damages and increased flood risk, and by reducing the effectiveness of planned or existing flood protection works.The thesis concludes with linked technical and economic findings which indicate a rich potential new area for research - “hydroeconomics”. The published literature shows few people have worked in this cross disciplinary area. The technical finding is that changes to land use, especially in agriculture, can increase the flood damages in downstream settlements or increase the cost of flood mitigation works significantly. From an economic point ofview, this is a unidirectional externality which should be considered in catchment and flood management. Possible solutions could include the control of land use and instruments such as separate waste water fees for rainwater and sewage or run-off certificates.
100

An investigation of appropriate technology on-site water conservation, roof runoff supply and water reuse systems for application within the Adelaide Metropolitan Area /

Allen, Martin Unknown Date (has links)
Thesis (M Eng) -- University of South Australia, 1993

Page generated in 0.0266 seconds