Browsing by Subject "Geology"
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- ItemOpen AccessA 3D fault seal analysis study conducted in the Ibhubesi Gas Field Offshore the West Coast of South Africa(2018) Ntombela, Nondumiso; Kahle, BethA three dimensional fault seal analysis study of the AK fault situated offshore of the West Coast of South Africa is presented. This study is aimed at informing the development plan of the Ibhubesi gas field with regards to the compartmentalization of the reservoirs, by understanding whether a key fault, the AK fault facilitates hydrocarbon migration to the Ibhubesi field reservoirs or whether it provides a seal. In order to address this research aim, a seismic interpretation of the area was carried out and combined with an interpretation of well data to construct a 3D structural model from which the fault seal analysis was carried out. Juxtaposition analysis was used to determine the lithologies that had been juxtaposed across the fault. Fault clay was determined using the Shale Gouge Ratio (SGR) algorithm and permeability and threshold pressure were also used to quantify the fault seal capacity. The results from the SGR were correlated to the across fault pressure difference and plotted on a reference diagram which is a comparison of sealing faults vs. leaking faults. This diagram indicates that faults with an SGR greater than 25% and threshold pressures greater than 8bars, have a high potential to seal. The AK fault SGR results range between 25 and 55 % with a threshold pressure of up to 20bars. These results indicate that the AK fault is likely to be a sealing fault.
- ItemOpen Access4D seismic analysis: discriminating between saturation and pressure changes form a data acquired Offshore Equatorial Guinea(2017) Msolo, Andile Lucky; Kahle, Beth; Gidlow, Maurice; Kahle, Richard4D seismic analysis is used to understand the performance of a producing oil field in order to increase production and mitigate risk. This is done by interpreting changes in water saturation and changes in effective pressure in the reservoir, which allows production to be maximized safely. In this project, I determined saturation and pressure changes in an oil field offshore Equatorial Guinea. I used Landrø's technique as a basis for the analysis, however Landrø's technique requires the presence of reservoir samples. For this project, rock samples of the reservoir were not available; this led me to modify Landrø's methodology using approximations based on well-accepted rock physics relationships. I tested this new methodology on a synthetic model, which gave encouraging results, after which it was applied to real seismic data. Pressure and saturation changes estimated in the reservoir indicate that the northern part of the reservoir experienced a decrease in pore pressure. The saturation changes over the northern part of the reservoir are not prominent. The central and southern parts of the reservoir show an increase in water saturation accompanied by an increase in pore pressure. The results are consistent with the production and injection history of this area. A comparison between saturation before production, saturation changes after production and pressure changes after production indicates an area (on the northern part of the reservoir) which shows fluid anomalies before production and does not show any production (or 4D) effects. New production wells could potentially be drilled in this area to increase production.
- ItemOpen AccessA contribution to the study of older granites in the Nigerian Precambrian with special reference to the Tegina granite(1960) Truswell, J F; Truswell, John FrancisRocks of the Older Granite suite occur throughout the Nigerian Precambrian. In part 1 of this thesis an example, the Tegina granite, is examined in detail. In part II the suite as a whole is described and discussed. The granite is an elongate mass covering an area of 49 square miles. Structural analysis indicates its vertical emplacement under internal pressure. The pressure was maintained during the formation of joints and secondary structures. Three petrological units are recognised in the granite. (1) The Main granite, a porphyritic biotite granite. Granodiorite and quartz-diorite in it represent local or marginal contamination. (2) Similar rocks are developed in the zone of banded foliation. In addition, there are remnant bands of granodiorite providing evidence that the 'granite' was formed as granodiorite subsequently 'granitised' with the formation of late phenocrysts of microcline microperthite. (3) The later biotite-muscovite microgranite at Karaya.
- ItemOpen AccessAlkaline igneous rocks of the coastal belt, south of Luderitz, South West Africa : a petrological study(1973) Marsh, Julian SavilleThe Luderitz Alkaline Province, as it is at present known, comprises the subvolcanic central complexes of Drachenberg, Pomona, and Granitberg. An attendant dyke swarm strikes NE-SW and crops out between the latitudes of 27°00' and 27°30' S. Stratigraphic indications (now confirmed by a K/Ar age from Granitberg) are that the Luderitz Province is early-Cretaceous in age and therefore older than the Klinghardt phonolites (Eocene) as well as the smaller melilitite and nephelinite intrusions. Granitberg is a circular foyaite complex, in the centre of which is preserved a large fragment of sedimentary rocks that originally formed the roof of the intrusion. The foyaites have been emplaced into the feldspathic sandstones and dolomites of the Bogenfels Formation, and three major intrusive phases can be recognised. The first phase produced chilled nepheline syenites beneath the roof of the intrusion. These chilled rocks grade downwards into coarse-grained foyaites. The second phase was the emplacement of the Inner Foyaite which crystallized as a cylindrically zoned plug, capped by a zone of layered, laminated, and xenolithrich foyaites. The third phase was the emplacement of the Outer Foyaite, into which the Roof Zone and the Inner Foyaite foundered. The Outer Foyaite is zoned with a miaskitic core, and an agpaitic outer zone.
- ItemOpen AccessAspects of the geology of the mountain ore body, Rosh Pinah mine, Namibia(1990) Siegfried, P R; Moore, J MDirectly underlying the ore bodies are zones of stockwork alteration as well as extensive brecciation. The aim of this thesis is to determine the cause of brecciation and its relationship to the ore body and mineralization. Methods of identification include field observations, transmitted and reflected light microscopy, staining and quantitative electron-microprobe analyses, carbonate isotope determination and an extensive literature survey.
- ItemOpen AccessAspects of the structure, tectonic evolution and sedimentation of the Tygerberg terrane, southwestern Cape Province(1982) Von Veh, Mark Wolter; Hartnady, C JA structural, deformational and sedimentalogical analysis of the Sea Point, Signal Hill and Bloubergstrand exposures of the Tygerberg Formation, Malmesbury Group, has been undertaken, through the application of developed geomathematical, digital and graphical computer-based techniques, encompassing the fields of tectonic strain determination, fold shape classification, cross-sectional profile preparation and sedimentary data representation. Emplacement of the Cape Peninsula granite pluton led to significant tectonic shortening of the sediments, tightening of the pre-existing synclinal fold at Sea Point, and overprinting of the structure by a regional foliation. Strain determinations from deformed metamorphic spotting in the sediments yielded a mean, undirected λ₁ : λ₂: λ₃ value of 1.57:1.24:0.52. This strain increment increases slightly towards the contact and it is proposed that it is non-coaxial to, and late relative to the ca 600Ma orogenic episode. The oblate nature of the strain ellipsoid lends support to the mechanism of radial distension as a means of pluton emplacement. An insight into the effect of the deformation on the structural configuration of the fold can be gained through a reconstruction of the 'pre-granite emplacement' down-plunge projection. In a reconstructed section, the matching of lithological units along strike was poor. Through detailed sedimentary logging of both limbs of the fold distinct lithological zones and facies, commonly displaying turbiditic characteristics, were recognised. Significant down-current changes in sedimentary structures, identified from a matching of the zones in the two limbs, are indicative of a small-sized depositional basin. The stratigraphic sequence thickens and coarsens upward and is consequently assigned to the lower and mid fan parts of a prograding submarine fan model.
- ItemOpen AccessAtomic absorption spectrometry and its application in geochemistry(1968) Butler, Louis Robert Patrick; Ahrens, L HThe atomic absorption method of analysis is reviewed. The theory describing the various phenomena such as atomic population, spectral line shapes, factors influencing absorption, analytical graph curvature, etc.are deduced. The practical aspects of atomic absorption are discussed with respect to: Instrumentation: flame studies and an attempt to develop "a universal" flame; contamination; sources of errors, etc. The method is applied to the analysis of silicate materials. Problems of sample dissolution and standards preparation are discussed. Applications have been made on the determination of the alkali metals (including lithium isotope determination), magnesium and calcium, copper, zinc, iron, manganese, molybdenum and aluminium. Although certain geochemical aspects of these elements are discussed, the analytical problems are stressed. The interference effects by other elements were tested and techniques developed to enable interferences to be overcome. It is concluded that atomic absorption spectrometry has significant uses for the geochemist, especially for the estimation of elements of the trace and minor concentration levels.
- ItemOpen AccessThe Auborus Formation of the Bethanie district, South West Africa(1969) Miller, R McG; Martin, H; De Villiers, JohnA study of the southerly occurrence of Auborus sediments revealed a basal conglomerate varying in thickness from 100 ft. to 3300 ft. and lying unconformably on an undulating base of lavas and sediments of the Sinclair Formation. This is overlain by variable thicknesses of sandstone which contain a few interbedded conglomerate bands, most of which are wedge-shaped. Intercalated grit is present in both the sandstone and the conglomerate zones. Shale occurs in the north-west where the sediments reach a thickness of 8500 ft. Nama sediments overlie the formation unconformably. Deposition, after rapid erosion and decay, took place under warm humid conditions into a shallow, slowly subsiding, intracratonic basin. Inward dipping edges were produced by contemporaneous subsidence. Vertical post-depositional movements in the central section folded the beds of the whole succession in the west into vertical and overturned positions. Block faulting that followed had a meridional trend and elevated this central section. Roughly north-trending faulting has displaced the contact in the south-east, and two later sets of east-west faults occur in the north-east. Diagonal, release and tension joints were revealed by measurement. Fracture planes in conglomerate pebbles apparently show no relationship to nearby faults. Pebble, cobble and boulder conglomerates contain a great variety of rock types, which have mostly been identified as coming from nearby southerly sources. A matrix is always present. The sandstone is a uniform red colour, very fine-grained, well sorted, very well compacted and is felspathic and arkosic in character. Rock fragments are ubiquitous. The colouring matter is intergranular, crystalline hematite. Felspars and biotite show various stages of alteration. A little recrystallization of quartz has taken place. The main heavy minerals are ore (largely specularite), garnet, epidote, zoisite, clinozoisite, mica, monazite, zircon and tourmaline. Zircon has been classified on colour, roundness, inclusions and zoning; tourmaline on colour, roundness and inclusions. Bedding in the sands tone is from thin to laminated. The commonest sedimentary structures are cross-beds, mud cracks and clay-pellet impressions. Other features are ripple marks, parting lineations, flute casts and rain prints. The red colour was probably produced in the source area. Diagenetic processes have produced spots of decoloration; and some joints show decoloration. Chemical analyses have been made of the red beds and a decolored spot.
- ItemOpen AccessBenthic foraminifera from the Orange-Luderitz shelf, southern African continental margin(1981) Martin, Ruth AnnAn investigation of the benthic foraminifera in the surficial sediments of the continental shelf and upper slope off the Orange River mouth and the Namib Desert was undertaken as an adjunct to sedimentological and geophysical investigations being conducted by members of the Joint Geological Survey/University of Cape Town Marine Geoscience Group. 117 species in 65 genera of benthic foraminifera are described and illustrated, and five bathymetric zones are distinguished on the basis of faunal differences. A cluster analysis yielded clusters which correlated well with the three deeper bathymetric zones, but were ambiguous in the two shallower zones. Fauna interpreted as relict or reworked were present at a number of stations and were distinguished on the basis of glauconite or phosphorite infillings, anomalous, distributions, and tests which are worn, battered, and partially dissolved. Bibliography: p. 62-65.
- ItemOpen AccessCMB7 receptor modelling of airborne particulate matter in the Vaal Triangle(1995) Reddy, Visvanathan Subba; Willis, J. P.; Annegarn, H. AThe primary aim of the Vaal Air Monitoring (YAM) programme was to do a one year source apportionment study of airborne particulate matter in the Vaal Triangle. The V AM programme was undertaken by Mintek, in South Africa. Three receptor sites were set up, oneea.ch in the Central Business District (CBD) of Vereeniging, Vanderbijlpark and Sasolburg. For this thesis, CMB7 receptor modelling was performed on fifteen samples from the V AM study representing the pre-, mid-, and post-winter periods. Five samples from each receptor site were modelled following the United States Environmental Protection Agency (US-EPA)PM10 protocol. PM10 size selected particulates were collected on 47 mm Teflon and quartz fibre filter substrates over one week sampling periods. Thirty three chemical species were analysed for use in the Chemical Mass Balance receptor model. Teflon filters were used for inorganic elemental analysis. Inorganic elements were determined by energy dispersive X-Ray Fluorescence (EDXRFS), inductively coupled plasma mass spectrometry (ICP-MS) and Atomic Absorption Spectrometry (AAS). The quartz fibre filters were used for the determination of water soluble ions and carbon by Ion Chromatography (IC), and Thermal Optical Reflectance (TOR) respectively. Elemental and ion analyses were done at Mintek. Carbon analyses by TOR were done at the Desert Research Institute (ORI) in Reno Nevada, USA. Generally sample preparation and analysis of filter substrates followed ORI guidelines Where required, in-house methods developed at Mintek were successfully applied.
- ItemOpen AccessA comparative geological study of some major kimberlite pipes in the Northern Cape and Orange Free State(1982) Clement, Cameron Roger; Reid, A MIn the first part of this thesis the petrological status of 'kimberlite' is defined and mineralogical and textural classifications which allow systematic documentation and collation of these complex rocks are evaluated. Quantitative mineralogical classification based on the modal abundances of the matrix minerals is advocated. A textural classification is adopted within which different textures are related to different modes and conditions of kimberlite emplacement. In the subsequent and major part of the thesis the results of a comparative geological study of six diamondiferous kimberlite pipes are reported. The pipes concerned are the De Beers, Wesselton, Dutoitspan, Bultfontein, Finsch and Koffiefontein occurrences (collectively termed the KIMFIK pipes).
- ItemOpen AccessA comparative study of the geohydrology of archaean formations and associated rocks in the North-Western Transvaal and the North-Western Cape Province(1974) Schumann, Francois WilhelmAn area of 4 400 km² in the North-western Transvaal is compared to an area of 75 000 km² in the North-western Cape Province with regard to geology, physiography, and hydrology. In the Transvaal the Archaean Formations range from the Swaziland System to the Dominion Reef System, with younger intrusives and a cover of Tertiary to Recent ferricrete, calcrete and soil. In the Cape Province the comparable formations are the Kheis System to the Soetlief Formation, younger intrusives and a Tertiary to Recent cover of wind-blown sand, calcrete and soil. The available literature on the geological formations and structure is reviewed. Outcrops are scarce in the Transvaal in an almost featureless tree-covered plain with ill-defined drainage, except for the two perennial rivers. In the Cape Province relief is higher and drainage better developed towards the perennial Orange River. Large portions of the Bushmanland Plateau are nevertheless, covered by sand and calcrete, without well-developed drainage. The rain falls during summer in both areas, and the average annual rainfall is 526 mm in the Transvaal, and 176 mm in the Cape Province. In both areas the farms and villages are almost entirely dependant on ground-water supplies. The importance of geophysical methods in the selection of borehole sites is stressed, and a summary is given of the more important geological and geophysical procedures and methods in both areas. This included magnetic, electromagnetic, and electrical resistivity methods. A summary is given of previous hydrological investigations in both areas. It was fragmentary, and only a few reports from the Cape Province could be traced. The results of a total of nearly 1 500 boreholes drilled in Archaean Formations in the Transvaal, and nearly 3 800 boreholes drilled in these formations in the Cape Province are analysed with respect to different parameters. Boreholes are classified according to the geological formation in which they occur, and the physiographical conditions ruling in the area. In the different formations in the Transvaal, the (percentage of successful boreholes ranged from 30 per cent in the Dominion Reef System to 38 per cent in the Archaean Granite. In the Cape Province it ranged from 29 per cent in the Grey Gneiss to 45 per cent in the Kheis System, except for the adamellite with 6 per cent and the Soetlief lava with 90 per cent successful boreholes. In both areas certain geological and physiographical controls were determined by means of which borehole results can be improved. Analyses of geophysical data, especially apparent resistivity at the rest level, sometimes gave positive results. Depths at which water was struck, rest levels, depth of weathering, and other parameters are compared for different formations and areas.
- ItemOpen AccessA comparison of melt depletion, thermal structure and metasomatism of proterozoic mantle lithosphere in the Namaqua-Natal and Rehoboth Provinces of Southern Africa(2017) Shiimi, Ellwin Taleni; Janney, Philip EdwardMajor and trace element mineral data are presented for garnet and spinel bearing peridotite xenolith suites from four Late Cretaceous kimberlites to the west of the Kaapvaal craton in two Proterozoic terranes: Hoedkop and Pofadder in the north-western Namaqua-Natal Province and Rietfontein and Louwrensia (Gibeon) in the Rehoboth Province. These are used to constrain and compare the thermal structure, the extents of melt extraction and metasomatism of the two mantle terranes with each other and with the Archaean Kaapvaal craton. Xenoliths from the Rietfontein and Pofadder localities have never previously been studied in detail. The information from this study is crucial for understanding the thermal and chemical evolution of Southern Africa's off-craton lithospheric mantle and the various processes (e.g., kimberlite and other magmatism, continental breakup) that have affected it. Mineral thermobarometry from a variety of independent thermobarometers indicates that, at pressures less than about 4 GPa, xenoliths from the Rehoboth Province (Louwrensia and Rietfontein) lie on or very near the Kaapvaal geotherm and between the 40mWm⁻² and 45mWm⁻² conductive geotherms, demonstrating that the lithospheric mantle in the Rehoboth Province was thermally similar to that of the Kaapvaal craton during the Late Cretaceous. In contrast, peridotites from the Namaqua-Natal Province (Hoedkop and Pofadder) in this pressure range fall at temperatures approximately 100°C - 200°C warmer than the Kaapvaal geotherm at any given depth and lie between the 45mWm⁻² and 50 mWm⁻² conduction geotherms, suggesting a Phanerozoic thermal disturbance in these regions. At higher pressures, samples from both terranes (represented only by Louwrensia and Hoedkop) fall above the Kaapvaal geotherm. However, these deeper, higher temperature peridotites are mostly sheared and indicate localised melt-rock interaction, therefore are not likely representative of the general thermal state of the lithosphere. Peridotites from the four suites have similar mineral major element compositions and their compositional variations fall well within the range of other southern Africa off-craton xenolith localities. Most garnets have smooth REE patterns with LREE depletions and relatively enriched, flat MREE - HREE abundances and patterns, while most clinopyroxenes have negatively sloping REE patterns with maximum enrichments in Nd and Sm. The average extents of melting beneath both Proterozoic provinces are moderate, and the samples are more fertile, on average, than cratonic lithospheric mantle. Peridotites from Louwrensia (Gibeon) appear to have experienced the greatest extents of melt extraction, as garnets from this locality extend to the lowest Y contents and some display strongly sinusoidal REE patterns similar to cratonic subcalcic garnets, suggesting that all of the REE were initially strongly depleted prior to metasomatism. A notable difference between the two terranes is that peridotites from Gibeon and Rietfontein (Rehoboth Province) show well developed trace element equilibrium between clinopyroxene and garnet, whereas those from Hoedkop and Pofadder (NW Namaqua-Natal Province) display significant disequilibrium. Although all peridotites show evidence for metasomatic incompatible element enrichments, some peridotites from Hoedkop show strong disequilibrium in Rb, Ba, Th and Nb (with clinopyroxene being overly enriched in these elements) and all Pofadder peridotites show major disequilibrium, with clinopyroxene being overly enriched in Ba and Nb and overly depleted in the middle and heavy REE relative to garnet. Further, clinopyroxenes from Pofadder peridotites are unique in that they have linear REE patterns, with maximum enrichment in La, in contrast to clinopyroxenes from all other localities in this study, which show concave-down patterns in the light to middle REE. Differences in the likely nature of the metasomatising agents affecting the lithosphere of the two off-craton terranes are discussed, as well as implications for the region's geological evolution.
- ItemOpen AccessDenudation rates and geomorphic evolution of the Cape Mountains, determined by the analysis of the in situ-produced cosmogenic 10BE(2012) Scharf, Taryn E; De Wit, Maarten; Codilean, Alexandru TSouthern Africa is host to a unique mountain system, the Cape Mountains, which includes the coastal Cape Fold Belt (CFB) and an inland Escarpment. Apatite fission track analysis has shown that this mountain system is an erosion feature, exhumed from beneath 2-7 km of overburden by large-scale denudation processes affecting the subcontinent during Gondwana break-up (ca. 140 – 65 Ma). Despite its antiquity and location on a passive continental margin, the ruggedness of the present-day topography of the Cape Mountains compares to that of the world’s active orogens. The coastal Cape Mountains are traversed by deeply-incised, meandering rivers that cut canyons through the most resistant quartzite ridges of these mountains, perpendicular to their structural grain inherited from the CFB. The evolution of this landscape is poorly understood, because little quantitative data exists on the denudation history of the Cape Mountains. This study presents the first in situ-produced cosmogenic 10Be inventories determined for quartz from catchment sediments and bedrock surfaces within the coastal Cape Mountains, with which to quantify denudation rates, exposure ages and the recent geomorphic evolution of these Cape Mountains. River sediments sampled from catchments within the Langeberg and Swartberg Ranges of the Western Cape, as well as bedrock from the Tradouw River traversing the Langeberg Range, were analysed. In addition, charcoal from alluvial material was collected for radiocarbon dating. Catchment-averaged denudation rates reported from these mountains range between 2.1 ± 0.3 and 6.9 ± 1.9 m·Myr-1. These are amongst the lowest reported rates globally, despite the rugged terrain of the mountain system. The spatial consistency between the low denudation rates suggests a landscape approaching geomorphic steady-state. This finding is best attributed to lithological control on denudation rates in a tectonically quiescent environment, and a relatively dry climate.
- ItemOpen AccessDrivers and uncertainties of future global marine primary production in marine ecosystem models(2015) Laufkötter, C; Vogt, M; Gruber, N; Aita-Noguchi, M; Aumont, O; Bopp, L; Buitenhuis, E; Doney, S C; Dunne, J; Hashioka, T; Hauck, J; Hirata, T; John, J; Le Quéré, C; Lima, D I; Nakano, H; Seferian, R; Totterdell, I; Vichi, M; Völker, CPast model studies have projected a global decrease in marine net primary production (NPP) over the 21st century, but these studies focused on the multi-model mean and mostly ignored the large inter-model differences. Here, we analyze model simulated changes of NPP for the 21st century under IPCC's high emission scenario RCP8.5 using a suite of nine coupled carbon–climate Earth System Models with embedded marine ecosystem models with a focus on the spread between the different models and the underlying reasons. Globally, five out of the nine models show a decrease in NPP over the course of the 21st century, while three show no significant trend and one even simulates an increase. The largest model spread occurs in the low latitudes (between 30° S and 30° N), with individual models simulating relative changes between −25 and +40%. In this region, the inter-quartile range of the differences between the 2012–2031 average and the 2081–2100 average is up to 3 mol C m-2 yr-1. These large differences in future change mirror large differences in present day NPP. Of the seven models diagnosing a net decrease in NPP in the low latitudes, only three simulate this to be a consequence of the classical interpretation, i.e., a stronger nutrient limitation due to increased stratification and reduced upwelling. In the other four, warming-induced increases in phytoplankton growth outbalance the stronger nutrient limitation. However, temperature-driven increases in grazing and other loss processes cause a net decrease in phytoplankton biomass and reduces NPP despite higher growth rates. One model projects a strong increase in NPP in the low latitudes, caused by an intensification of the microbial loop, while the remaining model simulates changes of less than 0.5%. While there is more consistency in the modeled increase in NPP in the Southern Ocean, the regional inter-model range is also very substantial. In most models, this increase in NPP is driven by temperature, but is also modulated by changes in light, macronutrients and iron as well as grazing. Overall, current projections of future changes in global marine NPP are subject to large uncertainties and necessitate a dedicated and sustained effort to improve the models and the concepts and data that guide their development.
- ItemOpen AccessDynamics of Indian Ocean slavery revealed through isotopic data from the colonial era Cobern Street Burial site, Cape Town, South Africa (1750-1827)(Public Library of Science, 2016) Kootker, Lisette M; Mbeki, Linda; Morris, Alan G; Kars, Henk; Davies, Gareth RThe Dutch East India Company (VOC) intended the Cape of Good Hope to be a refreshment stop for ships travelling between the Netherlands and its eastern colonies. The indigenous Khoisan, however, did not constitute an adequate workforce, therefore the VOC imported slaves from East Africa, Madagascar and Asia to expand the workforce. Cape Town became a cosmopolitan settlement with different categories of people, amongst them a non-European underclass that consisted of slaves, exiles, convicts and free-blacks. This study integrated new strontium isotope data with carbon and nitrogen isotope results from an 18 th -19 th century burial ground at Cobern Street, Cape Town, to identify non-European forced migrants to the Cape. The aim of the study was to elucidate individual mobility patterns, the age at which the forced migration took place and, if possible, geographical provenance. Using three proxies, 87 Sr/ 86 Sr, δ 13 C dentine and the presence of dental modifications, a majority (54.5%) of the individuals were found to be born non-locally. In addition, the 87 Sr/ 86 Sr data suggested that the non-locally born men came from more diverse geographic origins than the migrant women. Possible provenances were suggested for two individuals. These results contribute to an improved understanding of the dynamics of slave trading in the Indian Ocean world.
- ItemOpen AccessEconomic geology of the refractory clays in the Union of South Africa with particular reference to the Transvaal deposits(1949) Warde, John M; Warde, John M; Jacobs, HThe purpose of this thesis is to describe the occurrence, nature, properties, and utilization of the refractory clays in South Africa with particular reference to the Transvaal deposits, focusing on those characteristics which may be of direct value in the future development of this important mineral resource. Principal attention has been devoted to producing areas and-generally confined to those materials used in the production of fire-clay refractories; however, in many cases these identical clays are employed in the manufacture of "golden brown" building brick, sewer pipe, earthenware, etc. A fundamental study of the constitution of the commercial refractory clays was carried out on selected samples obtained from operating workings. The differential thermal method of analysis was featured in these studies, supple mented by X-ray examination and other recognized determinative procedures. The basic data so obtained were correlated, where possible, with the ceramic properties of the clays in order to lead to a better understanding of the relationship between the refractory clays and the ware made from them.
- ItemOpen AccessFluid evolution and mineralising potential in the outer margin of the southern Gariep Belt(1998) Board, Warwick Stuart; Frimmel, Hartwig EFluid inclusion analyses of quartz veins of various generations from the outer margin of the southern Gariep Belt reveal the presence of two chemically distinct fluid populations: the pre-orogenic, rift-related Rosh Pinah ore-forming fluid and the orogenic fluids. The oreforming fluid is more saline and chemically more complex than the orogenic fluids, probably representing hot, chemically evolved hypersaline brines induced by rift-related magmatism. Four generations (D₁/D₂, D₃, D₄ and D₅) of orogenic veins are recognised on the basis of their structural relationships. The orogenic fluids are chemically similar, dominantly aqueous and generally of moderate to low salinities (<10 wt% NaCleq), with the few higher salinity estimates (10-16 wt% NaCleq) being attributed to the interaction of some of the orogenic fluids with evaporitic horizons. A trend of decreasing temperature with a decrease in age (D₄> D₁/D₂>D₃>D₅) is developed within the orogenic fluids, with the exception of those fluids related to the emplacement of the Kuboos Pluton, which yielded the highest temperatures. The D₁/D₂ fluids from the northern and Vanrhynsdorp areas were hotter than the fluids from the central area, whereas the D₃ and D₅ fluids exhibit no apparent temperature variation as a function of area. D₄ fluids show a decrease in temperature further away from the pluton. Estimates of the maximum metamorphic pressure recorded in the outer margin of the belt have been further constrained, using microthermometry results in conjunction with mineral assemblages, to 2.9-3.6 kbar, 2.9-3.1 kbar and 1.8-3.1 kbar for the northern, central and Vanrhynsdorp areas, respectively. Field observations and fluid inclusion analyses suggest channeled fluid flow on a regional rather than on an intra-formational scale, even though a rock-buffered system is suggested by oxygen isotope results. A different, largely rock-dominated fluid system was developed within the relatively impermeable carbonate units compared with the fluid system developed within the rest of the outer margin of the belt. The D₁/D₂ fluids probably represent circulating formation and metamorphic waters that were advectively forced out of the orogen and into the foreland, whereas channeled meteoric fluid flow most likely dominated during the transtensive phase of the orogeny. The D₄ fluids probably contain a magmatic component, in addition to the meteoric component. Comparisons between the ore-forming fluid and the orogenic fluids indicate that the latter have neither the required salinities, nor the required chemistry necessary in order to transport sufficient metals to produce a massive sulphide deposit the size of Rosh Pinah. The chemistry of the orogenic fluids are, however, similar to those associated with gold remobilisation and as such the potential for gold mineralisation related to these orogenic fluids should not be ruled out. Base metal sulphide exploration within the outer margin of the belt should be confined to rocks of the Hilda Subgroup. The recognition of highly saline, chemically complex nonorogenic quartz vein-hosted fluid inclusions is considered critical from the point of view of base metal sulphide exploration.
- ItemOpen AccessFluvial facies architecture and provenance history of the Abrahamskraal-Teekloof formation transition (lower Beaufort group) in the main Karoo Basin(2016) Paiva, Francisco; Bordy, Maria EmeseThe Middle Permian lower Beaufort Group in the southern main Karoo Basin comprises of the fluvio-lacustrine Abrahamskraal and the overlying Teekloof and correlative Middleton Formations. These units are mainly made up of mudrocks with subordinate fine-grained sandstone-rich intervals. The objective of this mainly qualitative facies analysis study is the evaluation of the vertical and lateral abundances of the facies associations in order to decouple the preserved tectonic and climatic signals in the formations. The results on the stratigraphic trends should aid paleo-environmental, paleontological, and basin analysis studies, and improve our understanding of reservoir dynamics (e.g., permeability, connectivity) when used as outcrop analogues for subsurface fluvial reservoirs. High resolution facies mapping showed that flat-topped, laterally continuous (for 10s of Kms) channel-belt complexes are the most common external architecture of the channel sandstones in all formations.
- ItemOpen AccessFluvial facies, vertebrate taphonomy and palaeosols of the Teekloof formation (Permian) near Beaufort West, Cape Province, South Africa(1989) Smith, Roger M H; Minter, Laurie; Cluver, MikeThe main Karoo Basin of South Africa contains a relatively continuous sequence of continental deposits that accumulated over a 100 million year period from Permo-Carboniferous (280 Ma) to early Jurassic (180 Ma). In the southwestern region of the basin the Karoo succession is approximately 4 000 m thick, the upper half of which consists of vertebrate fossil-bearing fluvial rocks of the Beaufort Group. This study deals with Lower Beaufort (Adelaide Subgroup) strata belonging to the Teekloof Formation which are exposed in the cast-west trending erosional escarpment between the towns of Beaufort West and Fraserburg in the central Cape Province. The 450-mctre succession consists mainly of vertically accreted floodplain mudrocks with interbedded continuous sheets of fine-grained sandstone that bear evidence of having accumulated by lateral accretion on the inner banks of meandering channels. The mudrocks contain numerous fossilized skeletons of therapsid "mammal-like" reptiles as well as more primitive cotylosaurs and a few amphibians. Rarely, impressions of Glossopteris leaves and equisetalcan stems are found although root moulds are relatively abundant. Several types of calcareous nodules and sheets occur in the mudrocks and arc interpreted as evidence of calcic palaeosols that formed under semi-arid climatic conditions. This is an interdisciplinary study that integrates a conventional sedimentary facies analysis with investigations of the taphonomy of in situ therapsid fossils and the nature and distribution of palaeosols. Such an approach has not previously been applied to any of the Karoo strata. The results contain descriptive and quantitative information on sedimentary processes, palaeohydrology, absolute time represented in the stratigraphic record and the topography, soils and habitats of the ancient landscape. These are summarized into a palaeoenvironmental synthesis of the Teckloof Formation.