>Magister Scientiae - MSc / Separation between the South American and African plate’s occurred along the present day Atlantic margin during the Middle to Late Jurassic leading to the formation of a passive margin along the west coast of Southern Africa. The margin then later developed into the large Orange Basin flanking the west coasts of South Africa and Namibia. The Orange Basin on the west coast of South Africa covers an area of roughly 130 000 square kilometers relevant to the 200 m isobath and has roughly one well drilled for every 4000 square kilometers. The basin has proven hydrocarbon reserves and potential for further discoveries. The study area is located within South African exploration licencing blocks 3A/4A and 3B/4B and covers a region of roughly 97 km by 150 km. The study aims at understanding the geological processes responsible for the formation of the Orange Basin with a focus on the evolution of source rock maturity. The methodology involved utilizing the Petrel software for seismic interpretation and well correlation utilising twodimensional seismic data and all the relevant well data including geological well logs, petrophysical well logs, well top data, check-shot data, borehole temperature data and geochemical well data such as Rock Eval and vitrinite reflectance data. PetroMod (IES, Version 10) was utilized to simulate the Orange Basin evolution and the affect on source rock maturity. Seismic interpretation of the Post-Hauterivian succession shows a relative thickening of the sedimentary sequence westward as the basin evolves from the early drift to complete drift phase. Results from the petroleum system modeling indicate that the Barremian - Early Aptian source rock is at present overmature and producing mostly gas in the shelf areas whereas the potential for oil are most likely present in the deep water area of the basin where Tertiary progradation has resulted in renewed petroleum generation. Petroleum system modeling results indicate that the younger Cenomanian - Turonian source rock is less mature than the older Barremian - Early Aptian source rock as indicated by a lower transformation ratio and is mainly producing oil.

Laboratory studies were conducted on fine-grained soils from the Mackenzie valley, N.W.T., Canada, to study the transient layer. Two laboratory models simulating repeated freeze-thaw cycles were placed in a walk-in freezer. Temperatures and pore water pressures were monitored along the soil columns during eleven freeze-thaw cycles. At the end of the testing program, soil moisture conditions and cryostructures were examined. Temperature and pore water pressure data were compared to computed results and the thaw consolidation theory, respectively. In both laboratory models, an ice-rich zone developed at the active layer and permafrost interface as a result of moisture migration to the freezing front. The high ice content zone was altered under extreme air temperature conditions. Distinct cryostructures were created after repeated freeze-thaw processes. The formation and shifting of the ice-rich zone provide useful information on moisture conditions and the cryostructures for further understanding the transient layer.

An intensive survey of the high angle asymmetric gravel-bed confluence of the Fraser River Main Channel with Minto Side Channel, downstream of a mid-channel island, was conducted using an acoustic Doppler current profiler (aDcp) during the freshet in June, 2008 at a combined discharge of 7 500 m 3/s. The confluence was characterized by a vertical mixing interface, with the Minto high velocity core being advected downwards in the upstream part of the scour zone; weaker helical flow is evident in the main channel flow as it confines the strongly helical left bank flow. Apparent bed velocity generally followed the thalweg, with the highest values near 0.15 m/s occurring at the edges of the scour zone and along the elongated bed step. In plotted spatial distributions, the areas of high primary bed velocity matched areas of high shear velocity and/or strongly upward vertical flow velocity.

Expansive soils are considered to be a nightmare to the geotechnical engineers. As the losses to the infrastructure constructed on expansive soils is estimated to be in billions of dollars world wide annually, several researchers and practitioners from various regions of the world have made significant contributions to better our present understanding of these problematic soils. One of the topics that attracted interest is related to the 1-D heave prediction or estimation methods for expansive soils. Early research studies on this topic were focused on developing empirical relationships which are not universally valid. Current techniques use soil suction methods and oedometer test methods to predict or estimate the 1-D heave; however, the various soil parameters required in these techniques can only be obtained from time consuming laboratory or in-situ tests that are expensive and difficult to be performed by conventional geotechnical engineers. In the present study, a simple technique is proposed to estimate the 1-D heave in expansive soils which requires only the information of plasticity index, Ip and variation in water content with respect to depth in the active zone. This technique is developed using the results of 5 case studies published in the literature. In addition to these case studies, 8 other case studies results of 1-D heave in expansive soils are summarized. The data of 13 of the case studies is collected from various regions of the world which include Australia, Canada, Chile, Saudi Arabia, Sudan, United States and Yugoslavia. Comparisons are provided between the measured and estimated 1-D heave for all the case studies have been using the proposed simple technique. There is a reasonably good comparison between the measured heave and the estimated heave for 8 of the 13 case studies results (i.e., less than 30%). The estimated heave is more than the measured heave for all the case studies; which is conservative from an engineering practice perspective. The reasons associated with the discrepancies between the measured and predicted 1-D heave values for the remainder of the five case studies are also discussed. The proposed simple technique is encouraging for the practicing geotechnical engineers in the estimation of 1-D heave in expansive soils.

Distributions of future extreme hydrologic events represent a major concern in the context of climate change and its potential impacts. The accurate inference of their probability distribution for a given period (present or future) is crucial for the safe and economic design of a range of engineering works, from hydraulic structures such as dam spillways and bridges, to flow routing infrastructure such as culverts, stormwater ponds and channels. These distributions are likely to evolve with climate change and the development of methods to estimate possible impacts on extreme event distributions has become a key area of study. In this study the impact of climate change on flood frequency distributions is ascertained through a combination of physical modeling and statistical analysis. This approach utilizes two of the most valuable tools in the field; general circulation models (GCMs) and non-stationary extreme value analysis, and seeks to capitalize on the strengths of established methods while limiting the number of unnecessary assumptions.

<p> The characterization of silty soils is usually designated by the percentage of silt contained within the soil matrix, along with the soil&rsquo;s void ratio, which is used to describe the soil&rsquo;s current state. The use of these parameters to assess a soil&rsquo;s strength and undrained behavior is limited when finer material is contained within the soil. Therefore, additional parameters must be considered in order to correctly assess the strength and liquefaction potential of silty soils. These additional parameters include the skeleton void ratio, equivalent void ratio and granulometric factors. The current research investigates the influence of granulometric parameters, specifically the Median Grain Size Ratio (<i>D</i>₅₀/<i> d</i>₅₀), denoted as &mu;_DR (or MDR within graphs and charts), on the strength and liquefaction potential of loose silty sands. A series of undrained monotonic triaxial compression tests (&sigma;3&rsquo;= 69, 83, and 103 kPa) are performed on reconstituted soil samples, using three different base sand samples and a constant silt material. As a result, three distinct median grain size ratios (&mu;_DR = 4.2, 6.75, and 9) were tested with fines content ranging from 0-30% for each &mu;_DR. The undrained shear strength at all confining pressures tends to increase with in &mu;_DR; beyond 10% fines content there was no noticeable influence of &mu;_DR. At any &mu;_DR the excess PWP is higher than that of clean sand, when fines content is larger than 5% fines content. The slope of the instability line and phase transformation line are directly affected by the &mu;_DR and fines content, with an increase in the instability line and decrease in the phase transformation line with a growing &mu;_DR. The results indicate loose granular fills can be designed to be stronger and more resilient under extreme conditions by careful choice of materials in which the &mu;_DR>6.75 and the fines content does not exceed 10%.</p>

The combined use of cation exchange enrichment and spectrochemical analysis has been investigated for determining trace constituents (particularly caesium and the rare earths) in common igneous rocks and chondritos. Cation exchange chromatography with hydrochloric acid elution was employed to resolve the complex mixtures obtained from rocks and meteorites into a number of fractions in which the concentration of various trace constituents were above their spectrochemical detection limits; the trace constituents are not required in a highly concentrated form. These elements may then be determined spectrochemically. Before developing suitable column procedures for the enrichment of trace constituents, the sequence with which both major and trace constituents of common igneous rooks and chondrites moved through cation exchange columns on elution with various concentrations of HCl were established. Perchloric acid was also investigated as an eluant. The spectrograph was used to monitor the effluent fractions obtained from the cation exchange columns. Suitable column conditions were then developed for concentrating several trace elements for spectrochemical analysis.

The thesis presented is a compilation of both published and unpublished work carried out during the past ten years. The arguments and conclusions are based largely on field observations together with a study of the chemical composition of the rocks involved. Part I of the paper deals with the structure, petrography and economic geology of the Sukulu Complex. Structural Geology: The mapping of the Sukulu-Tororo complex provided the first detailed examination of the structure of an African carbonatite. The most important result of this survey was the demonstration that the carbonatites were emplaced in a plastic condition, in the form of "collars", dykes and ring-dykes, into and around an earlier calcitic plug which occupied the conduit. This concept is diametrically opposed to that previously accepted. (Strauss & Truter, Spitskop. von Eckermann, Alno Island). Later work in other areas (Chilwa Island, Ondurakarume, Homa Mountain) has confirmed the author's interpretation. The regional and surface structure connected with alkaline complexes is discussed and the definite genetic relationship of carbonatites with Elgon type volcanoes is stressed. Petrography: Owing to the deep weathering of the complex at Sukulu the associated alkaline rocks are poorly exposed but the examination of borehole cores shows that the rock types found in many other African carbonatites are also present here. Economic Geology: The economic soil deposit discovered by the author in 1949 is described. This deposit consists of an easily worked, deep eluvial soil containing the tour economic minerals apatite, magnetite, pyrochlore and baddeleyite. The soil covers the perimeter of the carbonatite and tills the wide valley embayments running into the centre of the complex. The description given constitutes the first detailed discussion of the economic geology of a new type of deposit. A brief classification of economic mineral deposits associated with the carbonatite complexes is included. PART II. The Origin of the African Carbonatites. A review is given of the rock types and structures found in alkaline ring complexes and volcanoes of Elgon type. The formation of undersaturated magma is attributed to the segregation of pyroxenes and to some extent plagioclase from a parent basaltic magma. Nephelinite is the type most commonly produced and constitutes the main lava flows of these volcanoes. The development of rocks containing melilite, melanite and primary calcite from nephelinitic magma is shown to be the result of the relative increase in lime, together with desilication of the residual liquid during the crystallisation and segregation of nepheline. Chemical variation diagrams are presented in support of these contentions. Chemical and arithmetical evidence is given to show that the removal of beforsitic carbonatite from nephelinitic magma leaves a phonolitic residual liquid, while the removal of iron-rich, alvikitic carbonatite leaves a trachytic residuum. The mechanism of carbonatite formation is thought to be the exsolution and upward migration of bubbles of carbondioxide during paroxysmal eruptions, the ascending gas chilling the magma and reacting with the dissolved oxides of calcium, magnesium, iron, manganese, barium and strontium to form carbonates. The rising gas streams serve to concentrate the carbonates by agitation and flotation with the establishment of a specific gravity gradient. Revival of pressure from below caused the typical intrusion pattern observed. The hypothesis presented reconciles all the recorded field and chemical data on African carbonatites. Should the hypothesis gain general acceptance, it would be possible to reduce greatly the unwieldy nomenclature in this branch of petrography. It is of interest to note that confirmatory laboratory evidence has recently appeared (O. Tuttle, "Nature", March, 1959) which demonstrates the feasibility of the existence of magmatic carbonates as a separate phase.

Bibliography: pages 188-203. / The Jagersfontein kimberlite contains an abundance of both deformed high-temperature peridotites and Cr-poor megacrysts. The Cr-poor megacryst suite is represented by olivine, orthopyroxene, clinopyroxene and garnet. The megacrysts show features which are unique to Jagersfontein, a particularly notable feature being the absence of ilmenite and ilmenite-silicate intergrowths. Major element and REE compositions of the Cr-poor megacryst suite are consistent with a magmatic fractionation sequence. ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of the Cr-poor clinopyroxene megacrysts indicate a source similar to that of non-DUPAL ocean island basalts. Deformed peridotites at Jagersfontein have high calculated temperatures of equilibration (1132-1361°C), which are slightly lower but which overlap with those of the Cr-poor megacryst suite. Both the high-temperature peridotites and the Cr-poor megacrysts yield similar pressures of equilibration (51±2 kbar), indicating their association with a thermal perturbation and supporting a close spatial association between them. Olivine and pyroxenes in the high-temperature peridotites appear homogeneous, but compositional gradients were observed in several garnet porphyroclasts. These garnets show rim enrichments in TiO₂ and Na₂O. This zonation in the garnets is evidence for enrichment of the deformed peridotites shortly before kimberlite eruption. This enrichment is likely to be due to interaction with the megacryst magma. In addition, the high-temperature peridotites show a general enrichment in Fe, Ti, Na and Al with decreasing Ca/(Ca+Mg). Such features support a magmatic aureole model, in that temperature and degree of enrichment might be expected to increase with proximity to the megacryst magma body. ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of clinopyroxene separates from the high-temperature peridotites are similar to those from oceanic peridotites. Modal abundances and olivine forsterite contents of the high-temperature peridotites are consistent with an origin as residues of partial melting events involving basalt formation. It is suggested that partial melting events, in the upper mantle beneath Jagersfontein, resulted in the formation of a depleted protolith which underplated the base of the Archaean lithosphere. This depleted protolith was subsequently enriched by interaction with the Cr-poor megacryst magma just prior to kimberlite eruption. The high-temperature peridotites therefore represent samples from the base of the lithosphere rather than from the convecting asthenosphere.

A hydrocensus of all groundwater users in the Swartkops River Basin was conducted in 1992 and 1993 to assess the occurrence and quality of groundwater in the Basin, as well as the characteristics of the various aquifers in the Basin. The extent of pollution of the groundwater reserves was noted. This specialist study was carried out to assist the Department of Water Affairs and Forestry in formulating a water quality management plan for the river basin, and was prompted by concern regarding the deteriorating water quality of the region. It was determined that the only aquifer in the river basin which was severely polluted in places was the Swartkops River Alluvial Aquifer. Following recommendations arising from the initial survey, a groundwater monitoring network of shallow boreholes was installed in the alluvial aquifer in 1994 and groundwater sampling runs commenced in 1995. Groundwater occurs in the region in a shallow alluvial aquifer and a deeper fractured secondary aquifer. These aquifers are separated from one another by an impermeable, confining layer of Cretaceous sediments in the central and eastern parts of the study area, causing artesian conditions in places. The groundwater of the aquifers in the study area has a sodium-chloride character of low salinity in the western high-lying portion of the study area, with mineralisation increasing eastward, as aquifer lithology and distance from recharge sources change. The hydrochemical character of the groundwater is a function of the proximity of the basin to the sea, as well as connate conditions existing in the sediments of marine origin. It is shown that pollution of both the surface and shallow sub-surface water bodies is occurring, mainly in the industrial and residential areas of Uitenhage and Despatch. These polluted zones are not extensive when compared with the whole catchment area but have a definite effect on local conditions. Estimations of pollution load volumes are made based on hydraulic parameters derived from aquifer tests. This study represents an overview of the geohydrology of the Swartkops River Basin, thereby providing a reference tool for water-resource management purposes in the region. It includes a unique study on the geohydrology of the Swartkops River Alluvial Aquifer and the extent of pollution of this aquifer, as well as a detailed account and discussion on the historical and present factors affecting variations in groundwater flow and artesian conditions in the area. A summary of suggested aquifer management practices is given to ensure the long-term sustainability of the groundwater resources of the river basin.