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1
Booth, Peter William King. "Pan-African imprint on the early mid-proterozoic Richtersveld and Bushmanland sub-provinces near Eksteenfontein, Namaqualand, Republic of South Africa." Doctoral thesis, University of Cape Town, 1990. http://hdl.handle.net/11427/26232.
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The present investigation examines the relationship between the Proterozoic Richtersveld and Bushmanland Subprovinces in the westernmost part of the Namaqua Province, near Eksteenfontein, Republic of South Africa. There is a controversy about this relationship because isotopic data contrast with field evidence. On a regional scale the Richtersveld Subprovince is separated from the Bushmanland Subprovince by the northward-dipping Groothoek Thrust. North of the thrust the Richtersveld Subprovince is comprised of low grade volcano/ plutonic rocks of the Vioolsdrif Terrane and medium grade volcano sedimentary sequences of the Pella Terrane. Medium grade rocks of the Steinkopf Terrane (Bushmanland Subprovince) lie immediately south of the thrust. Late Proterozoic strata of the Stinkfontein Formation (Gariep Group) overlie the Namaqua Province in the west; Cambrian Nama Group outliers occur east of the Stinkfontein Formation. Isotopic data show that lithologies of the Richtersveld Subprovince formed between 2000 - 1730 Ma, whereas those of the Bushmanland Subprovince are younger. It is not clear whether the Namaqua metamorphic imprint (at 1200 - 1100 Ma), which is manifest in terranes south of the Groothoek Thrust, extended as far as the Vioolsdrif Terrane in the north. Early Proterozoic structural and metamorphic imprints are inferred to have been obliterated during this event. The westernmost part of the Namaqua Province was overprinted for a distance of 100 km from the coast, during the Pan-African event at 700 Ma and 500 Ma. An area measuring nearly 500 km2 , traversing the western extremity of the boundary between the Richtersveld and Bushmanland Subprovinces was mapped on a scale of 1:36,000. Field mapping was carried out with the aid of aerial photographs, whereas laboratory techniques included map compilation, structural analysis, X-ray diffractometry, geochemical (XRF) and electron microprobe analyses. Supracrustal units of the Richtersveld Subprovince are composed of quartzo-feldspathic gneisses, schists, and minor meta-pelites. Supracrustals of the Bushmanland Subprovince are less diverse than those of the Richtersveld Subprovince and have a disconformable relationship with them. Most intrusive rock-types are thick granitic sheets, except the Early Proterozoic Vioolsdrif Granodiorite which forms part of a batholithic pluton in the north. The Sabieboomrante adamellite gneiss, Kouefontein granite gneiss and Dabbieputs granite gneiss could not be correlated with lithologies commonly occurring in the Richtersveld and Bushmanland Subprovinces. They have been given the new rock names. Mafic and ultramafic rocks of the Klipbok complex occur along the strike of the Groothoek Thrust. They form part of the Richtersveld Subprovince.
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Cawthra, Hayley Candice. "The marine geology of Mossel Bay, South Africa." Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/8697.
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Includes bibliographical references.This thesis presents work undertaken to better understand the complex evolution of the terrestrial landscape now submerged by high sea levels offshore of Mossel Bay along the South Coast of South Africa. Three marine geophysical surveys and scuba diving were used to examine evidence of past sea-level fluctuations and interpret geological deposits on the seafloor. Additional geological mapping of coastal outcrops was carried out to link land and sea features and rock samples were dated using Optically Stimulated Luminescence (OSL). Geophysical investigations include a regional seismic survey extending from Still Bay in the west to Buffels Bay in the east out to a maximum water depth of 110 m; a high-resolution investigation of the Mossel Bay shelf using multibeam bathymetry, side-scan sonar and sub-bottom profiling; and a shallow seismic pinger survey of Swartvlei, the most prominent coastal lake in the Wilderness Embayment. This study presents 9 discrete seismic sequences, and describes major offshore geomorphic features such as submerged sea cliffs, palaeo-coastal zones and fluvial systems. Oscillation in sea level between ca. 2.7 and 0.9 Ma likely resulted in the formation of the prominent -45 m terrace, which separates a relatively steep inner from a low-gradient mid shelf. Beach and dune deposits span from Marine Isotope Stage 15 (MIS 15) (582 ka) to Recent based on an age model that integrates OSL ages and the established eustatic sea-level record. The most prominent deposits date from the MIS 6 glacial to MIS 5 interglacial periods and include incised lowstand river channels and regressive aeolianites that extended at least 10 km inland from their associated palaeoshorelines. The MIS 5 deposits include transgressive beachrock, an extensive foreshore unit which prograded on the MIS 5e highstand, and regressive beach and dune deposits on the shelf associated with the subsequent fall in sea level. MIS 4 lowstand incised river channels were infilled with sediment truncated during rapid landward shoreface migration at the MIS 4 termination. Lowenergy, back-barrier MIS 4/3 sediments are preserved as a result of overstepping associated with meltwater pulses of the MIS 2 termination. The MIS 1 sediment wedge comprises reworked sediment and is best developed on the inner shelf. Holocene highstand sedimentation continues to prograde. Accommodation space for coastal deposits is controlled by antecedent drainage pathways and the gradient of the adjacent inner continental shelf. The geological deposits on the emergent shelf indicate a greatly expanded glacial coastal plain that potentially received more rain feeding low-gradient meandering rivers and wetland lakes. These extensive wetland environments provided a rich source of diverse food types which along with abundant marine resources on the shoreline made the Southern Coastal Plain an ideal habitat for our ancestors.
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Howarth, Geoffrey H. "Geology of the Kroonstad kimberlite cluster, South Africa." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1005573.
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The Cretaceous (133Ma) Kroonstad Group II Kimberlite Cluster is located approximately 200km south west of Johannesburg on the Kaapvaal Craton. The cluster is made up of six kimberlite pipes and numerous other intrusive dike/sill bodies. Three of the pipes are analysed in this study, which includes the: Voorspoed, Lace (Crown) and Besterskraal North pipes. These pipes were emplaced at surface into the Karoo Supergroup, which is comprised of older sedimentary rocks (300-185Ma) overlain by flood basalts (185Ma). At depth the pipes have intruded the Transvaal (2100-2600Ma) and Ventersdorp (2700Ma) Supergroups, which are comprised dominantly of carbonates and various volcanic units respectively. The pipes have typical morphology of South African pipes with circular to sub-circular plan views and steep 82o pipe margins. The Voorspoed pipe is 12ha in size and is characterised by the presence of a large block of Karoo basalt approximately 6ha in size at the current land surface. This large basalt block extends to a maximum of 300m below the current land surface. The main Lace pipe is 2ha is size with a smaller (<0.5ha) satellite pipe approximately 50m to the west. No information is available on the morphology of the Besterskraal North pipe as it is sub-economic and no mining has occurred. Samples from the Besterskraal North pipe were collected from the De Beers archives. The Kroonstad Cluster has been subjected to approximately 1750m of erosion post-emplacement, which has been calculated by the analysis of the crustal xenoliths with the pipe infill. The hypabyssal kimberlite from the three pipes shows a gradational evolution in magma compositions, indicated by the mineralogy and geochemistry. The Lace pipe is the least evolved and has characteristics more similar to Group I kimberlites. The Voorspoed and Besterskraal North kimberlite are intermediately and highly evolved respectively. The gradational evolution is marked by an increase in SiO2 and Na2O contents. Furthermore the occurrence of abundant primary diopside, aegirine, sanidine, K-richterite and leucite indicates evolution of the magma. The root zones of the pipes are characterised by globular segregationary transitional kimberlite, which is interpreted to be hypabyssal and not the result of pyroclastic welding/agglutination. The hypabyssal transitional kimberlite (HKt) is characterised by incipient globular segregationary textures only and the typical tuffisitic transitional kimberlite (TKt) end member (Hetman et al. 2004) is not observed. The HKt contact with the overlying volcaniclastic kimberlite (VK) infill is sharp and not gradational. The presence of HKt in the satellite blind pipe at Lace further indicates that the distinct kimberlite rock type must be forming sub-volcanically. The HKt is distinctly different at the Voorspoed and Lace pipes, which is likely a result of differing compositions of the late stage magmatic liquid. Microlitic clinopyroxene is only observed at the Lace HKt and is interpreted to form as a result of both crustal xenolith contamination and CO2 degassing. Furthermore the HKt is intimately associated with contact breccias in the sidewall. The root zones of the Kroonstad pipes are interpreted to form through the development of a sub-volcanic embryonic pipe. The volcaniclastic kimberlite (VK) infill of the Kroonstad pipes is not typical of South African tuffisitic Class 1 kimberlite pipes. The VK at Voorspoed is characterised by numerous horizontally layered massive volcaniclastic kimberlite (MVK) units, which are interpreted to have formed in a deep open vent through primary pyroclastic deposition. MVK is the dominant rock type infilling the Voorspoed pipe, however numerous other minor units occur. Normally graded units are interpreted to form through gravitational collapse of the tuff ring. MVK units rich in Karoo basalt and/or Karoo sandstone are interpreted to form through gravitational sidewall failure deep within an open vent. Magmaclasts are interpreted to form in the HKt during the development of an embryonic pipe and therefore the term autolith or nucleated autolith may be applied. Debate on the validity of the term nucleated autolith is beyond this study and therefore the term nucleated magmaclast is used to refer to spherical magmaclasts in the VK. The emplacement of the Kroonstad pipes is particularly complex and is not similar to typical Class 1 tuffisitic kimberlites. However the initial stage of pipe emplacement is similar to typical South African kimberlites and is interpreted to be through the development of an embryonic pipe as described by Clement (1982). The vent clearing eruption is interpreted to be from the bottom up through the exsolution of juvenile volatiles and the pipe shape is controlled by the depth of the eruption (+/-2km) (Skinner, 2008). The initial embryonic pipe development and explosive eruption is similar to other South African kimberlites, however the vent is cleared and left open, which is typical of Class 2 Prairies type and Class 3 Lac de Gras type pipes. The latter vent infilling processes are similar to Class 3 kimberlites from Lac de Gras and are dominated at the current level by primary pyroclastic deposition.
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Berhe, Seife Michael. "The geologic and tectonic evolution of the Pan-African/Mozambique Belt in East Africa." Thesis, Open University, 1988. http://oro.open.ac.uk/57038/.
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The presence of ophiolite complexes in NE and E Africa has been documented using Landsat, field and geochemical studies. This has led to the recognition of five ophiolite belts. These ophiolite belts represent sutures marking the position of island arcs and could be traced to Saudi Arabia on a pre-Red Sea drift reconstruction. Most of the ophiolites are dismembered, their mode of occurrence varies widely resulting in different structural relationships. The Yubdo complex in Western Ethiopia is formed of harzburgite which grades into dunites and pyroxenitic units, a cumulate sequence of ultramafic and gabbroic rocks and sheeted dykes. The Baragoi complex in Kenya is formed of tectonised ultramafics with dunite and chromite pods, a cumulate sequence of ultramatic and gabbroic units and a dyke unit. Trace element data of the Baragoi complex shows a transitional MORB to IAT affinity, and the presence of boninites suggest a supra- subduction setting, while data from the Adola- Moyale belt (S Ethiopia- NE Kenya) indicate an island-arc and MORB geochemistry, which developed in a back-arc setting. The chromites of Baragoi and Moyale have high Cr2O3 which follow an ophiolitic trend. Major and trace element data for granitoids from W Ethiopia, S Ethiopia- NE Kenya and central Kenya indicate three geochemically distinct granitoid groups: volcanic are granitoids, crustal melt granitoids and within-plate granitoids. Calc-alkaline rocks predominate in W Ethiopia, whereas the proportion of crustal melts appear to increase going further south in S Ethiopia/ NE Kenya and central Kenya. Diorites form about 10 percent of Precambrian outcrop in NE Sudan, while further south diorites are almost insignificant. Only in NE Sudan, W Ethiopia and Saudi Arabia do diorites feature prominently. However the lack of extensive cats-alkaline volcanic rocks, could simply reflect relatively narrow oceans and insufficient subduction of oceanic crust to produce large quantities of calc-alkaline melts, while the increase in the proportion of crustal melt granitoids in the southern part of the Mozambique belt indicates crustal thickening due to continent-continent collision. This study shows that the major lineaments identified in the Horn of Africa trend 010 ± 100, 055-065° and 145-165°. The 010 ± 10° and 145-165° trending lineaments form conjugate sets, while a later deformation episode reactivated 145-165° (NW-SE) trending lineaments and caused 055-0650 (NE-SW) lineaments. Two deformation mechanisms most likely controlled the growth of the major fault zones. Structural and metamorphic evidence suggests that crustal shortening was severe in S Sudan, Kenya and SE Ethiopia as compared to Saudi Arabia, NE Sudan and N and W Ethiopia due to oblique collision from the southeast causing stacking of crustal blocks along NW trending faults. Regional geologic, tectonic and geochemical studies suggest rifting c. 1200 Ma which subsequently led to the development of intraoceanic arcs and associated marginal basins in the north and narrow basins within the sialic basement gneisses further south in Kenya and Tanzania. This was followed by continent- continent collision which led to accretion of island arcs by mild collision from the northeast in Saudi Arabia and NE Sudan and severe crustal shortening In S Sudan, Kenya and SE Ethiopia as compared to Saudi Arabia, NE Sudan and N and W Ethiopia due to oblique collision from the southeast.
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Paul, Jonathan David. "Dynamic topography and drainage of Africa and Madagascar." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708248.
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Lenhoff, Louis. "The marine geology of Walker Bay, off Hermanus, SW Cape, South Africa." Master's thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/22397.
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Bibliography: pages 55-58.The seafloor geology of Walker Bay on the southern Cape coastline is described by making use of geophysical information obtained over a period of 4 years, between 1986 and 1990. The data include side-scan sonar images, seismic profiles, seabed samples and observations by a Remotely Operated underwater Vehicle (ROV). Four sonograph facies were identified, based on their distinctly different reflectivity patterns. Using the seabed samples and R.O.V. observations, the physical characteristics of these facies are determined and presented in map format. Facies 1 consists of Bokkeveld Group rock outcrops with relatively high relief, occupying approximately 45 percent of the study area. Facies 2 represents similar outcrops but with low relief and partially covered by a thin veneer of unconsolidated sediment, including localized occurrences of loose cobbles and boulders. Facies 3 and 4 relate to sediment-covered areas displaying different bedform types. Facies 3 is dominated by well-defined patches of megarippled gravelly sand, whereas Facies 4 consists of small-scale rippled sand. The characteristics of the Facies 3 megarippled patches are discussed in detail and their relationships with the local wave pattern and nearby Facies 1 and 2 rock outcrops are investigated.
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Clarke, Lee Brian. "The geology of the Kruidfontein Volcanic Complex, Transvaal, S. Africa." Thesis, University of Leicester, 1989. http://hdl.handle.net/2381/27558.
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The Proterozoic Kruidfontein Volcanic Complex (KVC) is a collapsed carbonatitic caldera structure, preserved as a high-level feature within Transvaal Sequence sediments. An outer ring of hills contains silicate pyroclastic rocks composed of lithic and pumice fragments, crystals and recrystallized matrix. These rocks are the products of co-ignimbrite lithic breccias and partially welded ignimbrite flows. An inner caldera was filled with recrystallized carbonatitic bedded volcaniclastic rocks. Relic pyroclastic carbonate fragments, such as droplet and armoured lapilli, containing juvenile calcite laths, are present. Well preserved primary structure sequences indicate emplacement by pyroclastic flow, surge and air-fall. Together with some reworking and debris flow deposits. The volcanism spans from early eruption of phonolitic material, from ring vents associated with caldera collapse, to smaller volume carbonatitic eruptions, producing intracaldera deposits. The processes operating during emplacement of carbonatitic pyroclastic material are essentially the same as those of silicate tuffs. As well as numerous fragments of phonolitic pumice in the silicate tuffs, there are unusual banded fragments composed of alternating silicate and carbonate compositions which appear to have been originally magmas separated by liquid immiscibility. The fragments show replacement of Al by Fe, and have also been K-feldspathized. Sovite and alvikite carbonatite dykes show that variation between CaO, MgO and FeO is consistant with fractionation from sovite to Fe-rich alvikites. All the carbonatites are strongly enriched in REE. The alvikites are enriched in the incompatible elements La, Ce, Nd, Y, Th, compared with the sovites, but are depleted in Sr, P, Ti, because of early fractionation of Sr-rich calcite, apatite and Ti-Fe oxides. The alvikites also have more positive δ18O and less negative δl3C compositions compared with the sovites, with values trending away from "mantle" compositions. This interpretation is consistant with a carbonatite magma chamber beneath the KVC which fractionated to produce the carbonatites seen at the present day surface. The few, highly altered, KVC nephelinitic rocks have trace-element distributions suggesting that they are parental to the phonolites. Fractionation from nephelinites, to phonolites, to trachytes satisfactorilly accounts for the incompatible trace element distributions. Some of the rocks have suffered secondary alteration, but have retained their trace element signatures. Zr and Nd are residual, whilst crystal fractionation involving feldspar, magnetite, and apatite have depleted some rocks in P, REE, and Sr. The fractionation from phonolite to trachyte, which is the reverse of normally observed trends, is ascribed to increasingly high F contents in the fractionating KVC magma. Three types of fluorite mineralization are recognised at KVC: 1) Replacement and disseminated deposits, 2) Fluorite veins and fracture fillings, 3) Fluorite-rich carbonatite and related dykes. Only Type 1) deposits are of economic importance at Kruidfontein. Fluorite selectively replaces calcite rather than ankerite in the KVC rocks, with ankeritization preceeding and inhibiting fluorite mineralization. Shallow dipping ankeritic tuffs form the host rock for a large (Tilde with hyphen below 5xl06 tonnes) sub-economic horizontal stratiform fluorite orebody, emplaced after inward sag of the bedding.
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Scott, Mari. "Lead isotopes as a palaeodietary tracer in southwestern South Africa." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29428.
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This thesis evaluates the utility of lead (Pb) isotopes, in combination with strontium (Sr) isotopes, as a geochemical tracer for studying the palaeodiets and palaeo-landscape usage in southwestern South Africa. Isotopes of light elements, carbon (C), nitrogen (N), oxygen (O), and sulphur (S), are widely used as (palaeo) environmental tracers, but do not yield information on the geological substrates on which individuals have lived. Sr isotopes in bones and teeth are useful in distinguishing between areas of distinct bedrock geology, however, the efficiency of Sr is limited at near-coastal areas, which forms a major part of this study area. This is because Sr has a relatively high concentration and long residence time in seawater. In addition, coastal soils contain not only aerosol-derived marine Sr, but frequently also include fragments of shells and other marine carbonates, so their 87Sr/86Sr is like the ocean. This study analysed Pb and Sr concentrations and isotopic compositions of animals and plants derived from the various geological substrates of southwestern South Africa. In order to do this, a detailed Sr-Pb separation scheme was developed, involving the separation and pre-concentration of Sr and Pb from a single digested sample by means of ion-exchange chromatography. Elemental concentrations were measured with a Thermo X-series II quadrupole ICP-MS instrument. Sr concentrations ranged between 111 ppm and 1862 ppm, while Pb concentrations were lower, ranging between 0.012 ppm and 2.30 ppm. Isotopic ratios were determined by means of a Nu Instruments high resolution multi-collector inductively-coupled plasma mass spectrometry (HR-MC-ICP-MS). Samples were introduced into the system as solutions, producing an order of magnitude more precise results than laser ablation analysis on the same material. Sr isotopes are useful for distinguishing between individuals living in near-coastal environments and those living further inland, while Pb isotopes could differentiate between granites and shales/sandstones. Pb isotopes proved to be a valuable palaeodietary tracer and can be used in combination with Sr isotopes to extent our knowledge of palaeo-landscape usage at coastal-marine environments.
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Kleynhans, Ilse. "A critical appraisal of regional geotechnical mapping in South Africa." Pretoria : [S.n.], 2005. http://upetd.up.ac.za/thesis/available/etd-08122005-111838.
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Belcher, Richard William. "Tectonostratigraphic evolution of the Swartland region and aspects of orogenic lode-gold mineralisation in the Pan-African Saldania Belt, Western Cape, South Africa." Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/49789.
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Thesis (PhD)--Stellenbosch University, 2003.ENGLISH ABSTRACT: The Swartland region in the western Cape, South Africa, covers approximately 5000 km2 and forms part of the Pan-African Saldania Belt that represents the southernmost extremity of the Pan-African orogenic belts in southern Africa. Regional mapping of the Swartland area shows that lithologies can be classified using predominantly structural and to a lesser extent lithological criteria. This led to the proposal of a new classification, were rocks of the previous classification of the Malmesbury Group are divided into two new groups, namely the Swartland and Malmesbury groups. The Swartland group can be divided into the Berg River and Moorreesburg formations, a series of quartz-chlorite-muscovite-feldspar schists, quartz schists, graphitic schists and limestones; and the Bridgetown formation, a series of metavolcanic rocks with WPB-MORB affinities that possibly represent seafloor. Deposition of the sediments is suggested to have occurred concurrently with deformation in an accretionary prism/fore-arc and was initiated with the opening of the lapetus Ocean at ca. 600 Ma. This early deformation event, Dt (ca. 575 Ma), only affected the Swartland group and exhibits pervasive bedding transposition, thrusting and imbrication of units creating a tectonostratigraphic sequence. Where identified, kinematic indicators and fold vergence indicate a top-to-the-west transport direction during the early, low-angle Di deformation. The Malmesbury group overlies the Swartland group, being locally separated by an unconformity. The Malmesbury group is a succession of conglomerates, grits and shales (Piketberg Formation), grading into greywackes, shales, siltstones, sandstones and minor limestones of the Tygerberg and Porterville formations. Sedimentation probably commenced after ca. 575 Ma and lasted until shortly after 560 Ma. Both the Swartland and Malmesbury groups were then deformed by the deformation event, D2 (ca. 552-545 Ma), and were intruded by the 552 to 510 Ma Cape Granite Suite. The Franschhoek Formation, formally part of the Malmesbury Group is now classified, along with the inferred ca. 535-510 Ma Magrug and Populierbos Formations of the previous Klipheuwel Group. The redefined Klipheuwel group documents a change in depositional environment from the continental slope/ocean trench, marine and flyschoid deposits of the Malmesbury group to continental, fluvial half-graben and graben deposits. Exhumation, extensive erosion and the formation of a peneplain, was followed by the deposition of the Table Mountain Sandstone Group around 550-510 Ma. The Spitskop gold prospect, located 10 km south of Piketberg, represents the first identified occurrence of mesothermal gold mineralisation in the Saldania Belt. Metamorphic devolatilisation of the Swartland group during Di led to the scavenging and transportation of gold along shallow-dipping shear zones that are contained within the early, sub-horizontal So/Si tectonic fabric. Pervasive fluid movement in the Spitskop area led to elevated gold values compared to background values throughout the lithologies at Spitskop. The lack of any economic-grade gold mineralisation is probably related to the absence of suitably orientated structures, such as high-angle faults, that are commonly believed to represent the prerequisite for large fluid throughputs that could result in economic-grade gold deposits. The mineralisation at Spitskop, however, provides a genetic model for further exploration of gold in the Swartland group.
AFRIKAANSE OPSOMMING: Die Swartland streek in die Wes-Kaap, Suid-Afrika, beslaan ongeveer 5000 km2 en vorm deel van die Pan-Afrikaanse Saldania-gordel wat die mees suidelike deel van die Pan-Afrikaanse orogene gordels in suidelike Afrika verteenwoordig. Regionale kartering van die Swartland streek dui aan dat die gesteentes geklassifiseer kan word deur oorwegend strukturele, en tot 'n mindere mate litologiese kriteria te gebruik. Gevolglik word ‘n nuwe klassifikasie voorgestel, waar gesteentes volgens die vorige klassifikasie van die Malmesbury groep verdeel word in twee groepe, naamlik die Swartland en Malmesbury groepe. Die Swartland groep kan verdeel word in die Bergrivier en Moorreesburg formasies, ‘n reeks kwarts-chloriet-muskoviet-veldspaat skis, kwarts skis, grafitiese skis en kalksteen; en die Bridgetown formasie, ‘n reeks metavulkaniese gesteentes met WPB-MORB affiniteite wat moontlik oseaanvloer verteenwoordig. Daar word voorgestel dat afsetting van die sedimente gelyktydig plaasgevind het saam met vervorming in ‘n akkresionere prisma/voorboog, geinisieer deur die opening van die lapetus Oseaan (ca. 600 Ma). Hierdie vroee vervorming, Di (ca. 575 Ma), het slegs die Swartland groep geaffekteer en vertoon deurdringende verplasing van gelaagdheid, oorskuiwing en imbrikasie van eenhede en het ‘n tektonostratigrafiese opeenvolging gevorm. Waar identifiseer, dui kinematiese aanwysers en plooi kanteling op ‘n bokant-na-wes beweging gedurende die vroee, lae hoek Di vervorming. Die Malmesbury groep oordek die Swartland groep, plaaslik geskei deur ‘n diskordansie. The Malmesbury groep bestaan uit ‘n opeenvolging konglomeraat, grintsteen en skalie (Piketberg formasie), wat gradeer in grouwak, skalie, sliksteen, sandsteen en ondergeskikte kalksteen van die Tygerberg en Porterville formasies. Sedimentasie het waarskynlik begin na ca. 575 Ma en het voortgeduur tot kort na 560 Ma. Beide die Swartland en Malmesbury groepe is hierna vervorm deur D2, (ca. 552-545 Ma) en daaropvolgend ingedring deur die 552 tot 510 Ma Kaap Graniet Suite. Die Franschhoek Formasie, voorheen deel van die Malmesbury Groep, word nou geklassifiseer tesame met die afgeleide ca. 535-510 Ma Magrug en Populierbos formasies as deel van die voorheen geklassifiseerde Klipheuwel groep. Die hergedefinieerde Klipheuwel groep dui op 'n verandering in afsettingsomgewing vanaf die kontinentale glooiing/oseaantrog, mariene en flyschoiede afsettings van die Malmesbury groep na kontinentale, fluviale half-graben en graben afsettings. Herblootstelling, omvattende erosie en die vorming van ‘n skiervlakte is gevolg deur die afsetting van die Tafelberg Sandsteen Groep random 520-510 Ma. Die Spitskop goudvoorkoms, 10 km suid van Piketberg, verteenwoordig die eerste identifiseerde voorkoms van mesotermale goudmineralisasie in die Saldania Gordel. Metamorfe ontvlugtiging van die Swartland groep gedurende Dt het aanleiding gegee tot die roofuitruiling en vervoer van goud langs laaghellende skuifskeursones in die vroee, subhorisontale S0/Si tektoniese maaksel. Deurdringende vloeistofbeweging in die Spitskop omgewing het aanleiding gegee tot verhoogde goudwaardes in vergelyking met agtergrond waardes dwarsdeur die litologiee by Spitskop. Die gebrek aan ekonomiese graad goud mineralisasie is waarskynlik verwant aan die afwesigheid van geskikte georienteerde strukture, soos hoe hoek verskuiwings, wat oor die algemeen beskou word as ‘n voorvereiste vir die toevoer van groot hoeveelhede vloeistof wat kon aanleiding gegee het tot ekonomiese graad goudafsettings. Die mineralisasie by Spitskop verskaf egter 'n model vir verdere goud eksplorasie in die Swartland groep.
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Jones, Michael G. "The geology of the Mt. Mare area, Pietersburg Greenstone Belt, South Africa." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/7329.
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Sargeant, Fiona. "The seismic stratigraphy of the Bushveld Igneous Complex, South Africa." Thesis, University of Liverpool, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250322.
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Gilchrist, Alan Robert. "Morphotectonics of passive continental margins : application to south-western Africa." Thesis, University of Liverpool, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316915.
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Stankiewicz, Jacek Maciej. "Receiver function analysis of crustal and upper mantle structure beneath Southern Africa." Master's thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/4226.
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Thamm, A. G. "Contributions to the geology of the Table Mountain Group." Master's thesis, University of Cape Town, 1988. http://hdl.handle.net/11427/21891.
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Modern analysis of Table Mountain Group sediments began with I. C. Rust's D.Sc. thesis "On the sedimentation of the Table Mountain Group in the western Cape Province" in 1967. Rust defined the stratigraphy of the Table Mountain Group, produced computer generated isopach and palaeocurrent maps for each formation and attempted palaeoenvironmental analyses based on what data he had available. For work dated prior to 1967 the reader is directed to Rust's excellent review in Chapter 2 of his thesis. The thesis served as a basis for Rust's later published work on the Cape Supergroup. Current published palaeoenvironmental models of the lower Table Mountain Group (the Piekenierskloof, Graafwater and Peninsula Formations) are based on a transgressive fluvial - littoral - shallow shelf model (Tankard et al., 1982) following earlier facies and palaeoenvironmental analyses (Tankard and Hobday, 1977: Rust, 1977; Hobday and Tankard, 1978: Vos and Tankard, 1981). The validity of this model has recently been questioned (Turner, 1986; 1987) although no comprehensive alternative has been proposed to date. The sedimentology of the upper Table Mountain Group i.e. the Pakhuis, Cedarberg, Rietvlei, Skurweberg and Goudini Formations (the latter three the newly named Nardouw Subgroup) has not been studied systematically. Good progress has recently been made on the fossil content of the Cedarberg Formation (Gray et al., 1986; Cocks and Fortey, 1986) and palaeoenvironmental analyses initiated in the Nardouw Formation. This thesis documents contributions to the geology of the Table Mountain Group. It is not the intention of the author to present an extensive overview and treatise on the lower Table Mountain Group, but rather to concentrate on three topics that can provide some insight into Table Mountain Group geology. The following three topics were selected 1) Petrology and Diagenesis of lower Palaeozoic sandstones in the s.w. Cape Sandveldt (Clanwilliam and Piketberg Discricts). 2) Palaeoenvironmental indicators in the Faroo Member, (Graafwater Formation) at Carstensberg Pass, R364. 3) Facies analysis of conglomerates and sandstones in the Piekenierskloof Formation: Processes and implications for pre-Devonian braid-plain sedimentology. These topics form the basis of the thesis.
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Jones, Rhian Eleri. "Petrological and geochemical study of Platreef chromitites, northern Bushveld, South Africa." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/53836/.
Full textAbstract:
The Platreef, located in the northern limb of the Bushveld Complex in South Africa, is a world-class Ni-Cu-PGE deposit. The complexity of the deposit has meant that despite the numerous studies, developing an accepted genetic model to account for the variations observed has been difficult. While some authors have suggested that it is part of the Upper Critical Zone, correlating it to the Merensky Reef, others have suggested that the Platreef is unrelated to mineralisation found elsewhere in the Bushveld Complex. The model tested is the multiple staging chamber model developed by McDonald and Holwell, that proposes that the parental magma was upgraded in PGE (plus Ni and Cu) prior to emplacement. Key to testing this model has been the analysis of immiscible sulphide inclusions trapped within chromite grains, believed to represent the early parental magma. Analysis has shown that they contain high PGE tenors, significant semi-metal (Bi, Te and As) content and the low S/Se ratios of the inclusions suggest a mantle source. Interaction of the sulphide liquid with multiple batches of magma in the staging chamber is proposed to have enabled enrichment to occur prior to emplacement through a process known as multi-stage dissolution upgrading. The analysis of chromite grains from the three study farms has shown that the variation in chromite composition is dependent on host lithology and the location of the sample along strike of the Platreef. Some correlation can be made with chromites from the UG2 but Platreef chromites cannot be directly correlated to those from the Merensky Reef. Investigation of PGE concentrations within the BMS from Zwartfontein has shown a strong association between PGE and BMS and that the distribution of PGE is consistent with fractional crystallisation of a sulphide liquid. The PGM study has shown that variation along strike and down dip of the Platreef is not strictly controlled by footwall lithologies as previously proposed. Variation is suggested to be the result of differing temperatures and ƒO2 conditions due to the proximity around proposed feeder zones. In order to further test the staging chamber model, S isotope analysis should be carried out on the sulphide inclusions to ascertain if a magmatic signature is present. In addition, further support to the model may be achieved by examining other Lower Zone bodies for chalcophile element depletion.
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Diarra, Pobanou Hughes. "The geology and genesis of the Syama gold deposit, Mali, West Africa." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362528.
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Bartman, R. D. (Reynard Dirk). "Geology of the Palaeoproterozoic Daspoort Formation (Pretoria Group, Transvaal Supergroup), South Africa." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/42447.
Full textAbstract:
This thesis examines the geology of the Daspoort Formation (Pretoria Group, Transvaal Supergroup) of
South Africa, with the accent on describing and interpreting its sedimentology. The Palaeoproterozoic
Daspoort Formation (c. 2.1‐2.2 Ga) forms part of the Pretoria Group on the Kaapvaal craton. This
sandstone‐ and quartzite‐dominated lithological formation covers an elliptical geographical area
stretching from the Botswana border in the west to the Drakensberg escarpment in the east, with its
northern limit in the Mokopane (Potgietersrus) area and Pretoria in the south; altered outliers are also
found in the overturned units of the Vredefort dome in the Potchefstroom area. Deposition of the
Daspoort Formation was in a postulated intracratonic basin which applies equally to the entire
Transvaal Supergroup succession in the Transvaal depository. Various characteristics from the
formation, such as sedimentary architectural elements (e.g., channel–fills etc.), maturity trends and
distribution of lithofacies assemblages across the preserved basin give insight into the developing
conditions during deposition and genesis of the Daspoort Formation. Subordinate evidence from basic
geochemistry, ripple mark data and optical microscope petrology studies support the sedimentary
setting inferred for this Palaeoproterozoic deposit. Fluvial and epeiric marine conditions prevailed
during the deposition of the Daspoort clastic sediments into the intracratonic basin. This shallow
epeiric sea was fed by fluvial influx, predominantly from the west when a transgressive regional
systems tract led to the filling of the basin, evolving into the deeper marine Silverton Formation
setting, laid down above the Daspoort. Transgression from the east (marine facies predominate) to the
west (fluvial facies) is supported by cyclical trends, palaeoenvironmental and palaeogeographical
interpretations. Accompanying poorly preserved microbial mat features contribute to the postulated
shallow marine environment envisaged for the eastern part of the basin whereas ripple marks and
grain size distribution support a fluvial setting for the west, with lithofacies assemblages accounting for
both areas’ depositional interpretation.Dissertation (MSc)--University of Pretoria, 2013.
tm2014
Geology
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Surtees, Grant Bradley. "The evolution of the Brosterlea Volcanic Complex, Eastern Cape, South Africa." Thesis, Rhodes University, 2000. http://hdl.handle.net/10962/d1005556.
Full textAbstract:
Detailed field mapping (Map, Appendix B) has been conducted in and around the boundaries of a 14x18km, volcanic complex 35km northeast of Molteno in the Eastern Cape Province, South Africa. The structure is interpreted as a subsidence structure, and is filled with two volcaniclastic breccias, numerous lava flows, a number of sedimentary facies, and lies on a base of Clarens Formation overlying Elliot Formation rocks. This is an important study because 'widespread, voluminous fields of basaltic breccias are very rare (see Hanson and Elliot, 1996) and this is the first time that this type of volcanic complex and its deposits have been described. Detailed analyses of the two volcaniclastic breccias revealed changes in colour, clast types, clast sizes, and degree of alteration over relatively short distances both vertically and laterally within a single breccia unit. The variation in clast sizes implies a lack of sorting of the breccias. The lower of the two volcaniclastic breccias fills the subsidence structure, and outcrops between the Stormberg sedimentary sequence and the overlying Drakensberg basalts and was produced from phreatomagmatic eruptions signalling the start of the break-up of Gondwanaland in the mid-Jurassic. The upper volcaniclastic breccia is interbedded with the flood basalts and is separated from the lower breccia by up to 100m of lava flows in places, it is finer-grained than the lower volcaniclastic breccia, and it extends over 10km south, and over 100km north from the volcanic complex. The upper breccia is inferred to have been transported from outside the study area, from a source presumably similar to the subsidence structure in the volcanic complex. The pyroclastic material forming the upper breccia was transported to the subsidence structure as a laharic debris flow, based on its poorly sorted, unwelded and matrix-supported appearance. However, both breccias are unlikely to have been derived from epiclastic reworking of lava flows as they contain glass shards which are atypical of those derived from the autoclastic component of lava flows. The breccias are therefore not "secondary" lahars. There is also no evidence of any palaeotopographic highs from which the breccias could have been derived as gravity-driven flows. Based on the occurrence of three, 1m thick lacustrine deposits, localised peperite, fluvial reworking of sandstone and breccia in an outcrop to the south of the subsidence structure, and channel-lags encountered only in the upper units of the Clarens Formation and only within the subsidence structure, the palaeoenvironment inferred for the subsidence structure is one of wet sediment, possibly a shallow lake, in a topographic depression fed by small streams. Magmatic intrusions below the subsidence structure heated the water-laden, partly consolidated Clarens Formation sandstones, causing the circulation of pore fluid which resulted in the precipitation of minerals forming pisoliths in the sandstones. Intruding magma mixed, nonexplosively, with the wet, unconsolidated sediments near the base of the Clarens Formation (at approximately 100m below the surface), forming fluidal peperite by a process of sediment fluidisation where magma replaces wet sediment and cools slowly enough to prevent the magma fracturing brittly. Formation of fluidal peperite may have been a precursor to the development of FCIs (Fuel Coolant Interactions) (Busby-Spera and White, 1987). The breccias may represent the products of FCIs and may be the erupted equivalents of the peperites, suggesting a possible genetic link between the two. The peperites may have given way to FCI eruptions due to a number of factors including the drying out of the sediments and/or an increase in the volume of intruded magma below the subsidence structure which may have resulted in a more explosive interaction between sediment and magma. Phreatic activity fragmented and erupted the Clarens Formation sandstone, and stream flows reworked the angular sandstone fragments, pisoliths and sand grains into channelised deposits. With an increase in magmatic activity below the subsidence structure, phreatic activity became phreatomagmatic. The wet, partly consolidated Clarens Formation, and underlying, fully consolidated Elliot Formation sediments were erupted and fragmented. Clasts and individual grains of these sediments were redeposited with juvenile and non-juvenile basaltic material probably by a combination of back fall, where clasts erupted into the air fell directly back into the structure, and backflow where material was erupted out of the structure, but immediately flowed back in as lahars. This material formed the lower volcaniclastic breccia. A fault plane is identified along the southwestern margin of the subsidence structure, and is believed to continue up the western margin to the northwestern corner. A large dolerite body has intruded along the inferred fault plane on the western margin of the structure, and may be related to the formation of the lower volcaniclastic breccia, either directly through fluidisation of wet sediment during its intrusion, or as a dyke extending upwards from a network of sill-like intrusions below the subsidence structure. Geochemical analysis of the Drakensberg basalt lava flows by Mitchell (1980) and Masokwane (1997) revealed four distinct basalt types; the Moshesh's Ford, the Tafelkop, the Roodehoek, and the Vaalkop basalts. Basalt clasts sampled from the lower volcaniclastic breccia were shown to belong to the Moshesh's Ford basalt type which does not outcrop in situ within the subsidence structure. This implies that the Moshesh's Ford basalts were emplaced prior to the formation of the lower volcaniclastic breccia, and may have acted as a "cap-rock" over the system, allowing pressure from the vaporised fluids, heated by intruding basalt, to build up. The Moshesh's Ford basalt type was erupted prior to the resultant phreatomagmatic events forming the lower volcaniclastic breccia.
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Leinster, Robin Christian. "Shear zones and tectonics of the Northern Barberton Mountain Land, South Africa." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261755.
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Latorre-Muzzio, Gina. "The influence of geological, genetic and economic factors on the ore reserve estimation of Kwaggashoek east iron ore deposit." Thesis, Rhodes University, 1993. http://hdl.handle.net/10962/d1005584.
Full textAbstract:
Tectonics plays an important role in the genesis and subsequent mlnlng development of the Kwaggashoek East ore body. Lithological key units control the effectiveness of the ore forming processes, affecting the in situ ore reserve, The Kwaggashoek East deposit is the product of primary and secondary processes. A genetic model focussed on the source, migration and deposition of iron suggests a possible original source of iron as the product of very dilute hydrothermal input into deep ocean waters, with subsequent migration through structural conduits. Supergene processes account for the upgrading of the ore and the phosphorus redistribution. A good correlation between samples in a preliminary geostatistical study reflects the effectiveness of this process in the high grade ore zone. A broad overview of the economic issues which affect the commercialization of iron, indicates a balanced supply-demand situation for the five next years. The reserve estimation procedure requires accurate scientific terminology and appropriate methodology. Documentation is essential and should be detailed enough to allow for future reassessment. The results of three estimation methods in Kwaggashoek East differ by less than 5%. The accuracy of the final results depends more on geological interpretation and assumptions than on the method applied. Although optimization of grade and tonnage in the Kwaggashoek East deposit seems to be met with the actual cut-off grade used in the Thabazimbi mine district, the grade-quality concept introduced in this thesis indicates a decrease in the estimated reserves for the deposit
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Pether, John. "The sedimentology, palaeontology and stratigraphy of coastal-plain deposits at Hondeklip Bay, Namaqualand, South Africa." Master's thesis, University of Cape Town, 1994. http://hdl.handle.net/11427/22469.
Full textAbstract:
Bibliography: pages 295-307.The exposures in diamond mines on the Namaqualand west coast of South Africa provide a rare opportunity to examine a record that is normally inaccessible beneath a thick cover of aeolian sands. This study presents the main results of fieldwork in mine excavations on the farms Hondeklip and Avontuur-A, near Hondeklip Bay. Sections in the deposits were described in detail and the vertebrate and invertebrate faunas were sampled. The buried topography of the gneiss bedrock, obtained by prospecting, is complex, with the main feature consisting of a coast-parallel ridge flanking a wide palaeochannel on its landward side. Advanced kaolinitic weathering affected both the bedrock and a diamondiferous, basal kaolinitic sediment patchily preserved in the channel. The incision of the channel is related to the Oligocene regression and the basal kaolinitic sediment is interpreted as a fluvial arkose deposited in the channel. Both the bedrock and the deposit in the channel were then kaolinized during humid climatic conditions in the late Oligocene and early Miocene. Weathering-profile silcrete also developed in the basal kaolinitic sediment. It is tentatively proposed that this weathering period may be represented in the Namib Desert by the thick laterite capping Eocene sediments at Kakaoberg. Subsequently, the palaeochannel was exhumed and was ultimately filled by late Tertiary marine deposits. The marine deposits were laid down in shallowing-upwards sequences of the shore face environment. Two regressive, progradational packages (alloformations) are recognized. The older extends seawards from at least -50 m asl. and is the "45-50 m Complex" of Carrington and Kensley (1969), now called the 50 m Package. East of the channel, on the exposed coast, high-wave-energy storm-deposition in the lower shoreface dominates the preserved record. With lowering of sea-level, the bedrock ridge emerged to the seaward of the prograding palaeoshoreline, reduced the level of incident wave energy and profoundly influenced the development of sub-environments within the progradational regime. Ultimately, low-energy bay deposits filled the palaeochannel in the bedrock. On the basis of vertebrate evidence and correlation with global sea-level trends, the age of the 50 m Package is middle Pliocene. The upper facies of the 50 m Package (foreshore and upper shoreface) have been extensively removed by later subaerial erosion. The subsequent transgression truncated the seaward extent of the 50 m Package, reached ~30 m asl. and prograded seaward from that elevation. It is called the 30 m Package and combines the "29-34 m Beach" and "17-21 m Complex" of Carrington and Kensley (1969). A late Pliocene age is envisaged. The upper-shoreface facies of the 30 m Package is usually preserved, but may be disguised by pedogenesis. The diamondiferous marine gravels mined in the area are mainly lower-shoreface storm deposits and pre-existing transgressive lags and shelf deposits have generally been reworked during regression. Enigmatic, muddy and/or phosphatic units, previously called "E-stage," are patchily preserved in the base of the 50 m Package and are revealed to be distal storm deposits laid down in the transitional shoreface to offshore environment. They are part of the overlying regressive sequence, but may include a fragmentary , petrified, mixed, vertebrate remanie. Nevertheless, eroded remnants of older deposits must also occur in places.
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Wynn, Timothy James. "Proterozoic analogues of mid crustal deformation from NW Scotland and Namaqualand, South Africa." Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320409.
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McMillan, I. K. "Late Quaternary foraminifera from the southern part of offshore south west Africa/Namibia." Thesis, Aberystwyth University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239620.
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Van, Zyl Frederik Wilhelm. "Geological mapping of the inner shelf off Cape Town's Atlantic Seaboard, South Africa." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29676.
Full textAbstract:
The Atlantic Seaboard is an 18 km stretch of coastline located on the Cape Peninsula, South Africa, roughly between the Cape Town suburbs of Mouille Point in the north and Hout Bay in the south. It borders heavy shipping traffic and contains a mix of urban and natural environments including up-market seaside neighbourhoods and is part of the Table Mountain National Park. The predominantly rocky coastline has a northeast–southwest orientation with interspersed sandy pocket beaches. A narrow, low-lying coastal plain (marine terrace) in the north merges with coastal cliffs further south. The geomorphology and sedimentology of the coast are closely linked to the underlying geology, influencing the shape of coastal embayments and promontories, as well as the composition and distribution of sediment. Hydrographic, geophysical and sedimentological techniques were used to collect high-resolution bathymetry, seafloor geology and sediment distribution data to better understand modern coastal processes. The results indicate a low-relief seafloor consisting of Malmesbury Group rocks in the north. To the south the seafloor consists of high-relief Cape Granite reefs interspersed with fine to medium grain sand and bioclastic (shelly) gravel. Sediment transport is generally northward by longshore drift. In the south, the high-relief granite reef and headlands form sediment traps resulting in several large pocket beaches and offshore sediment deposits. In the north, the low-relief Malmesbury bedrock is largely free of sediment, except within narrow erosional gullies. Most sediment rapidly passes through to the north resulting in a sediment-starved rocky seafloor. The three principal sources of beach sand are aeolian fine sand transported by the Karbonkelberg headlands bypass dune entering the sea at Sandy Bay, biogenic carbonate production along the coast, and weathering of Table Mountain Group sandstone and granite bedrock. A fourth source is sediment entering the system via longshore drift from the south of Duiker Point. The water depth around the Duiker Point headland is presently too deep for sediment to be transported easily through longshore drift, other than during large storm events, but during past sea-level low stands this would have played an important part in supplying sediment to the coast. Changes in sea level play an important part in shaping the geomorphology of the coastline. Beach deposits, both sandy and boulder beaches have been left at various elevations along the coast, both offshore and onshore. Although today the Sea Point area is protected by sea walls and man-made structures, a higher sea level was responsible for shaping the narrow coastal plain. Increasing rates of global sea-level change are becoming an important issue all over the world and the Atlantic Seaboard coast is not immune to the effects of sea-level rise. The frequency and magnitude of storm events that breach the sea defences erode beaches and sea cliffs and cause damage to private and public property are likely to increase in the future
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Chukwuma, Kenneth. "Spatial and temporal variations in the geometry and composition of the Permian Whitehill Formation South Africa." Doctoral thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25057.
Full textAbstract:
The Lower Permian Whitehill Formation (WHF) is an important hydrocarbon resource unit in the main Karoo Basin where it occurs in outcrops and up to 4 400 m in the subsurface and thus it is distributed over an area in excess of 260 000 km² in the southern half of South Africa. Although the formation is composed predominantly of black laminated carbonaceous shales, earlier studies detected significant spatiotemporal variability in its stratigraphy and composition, particularly the distribution of its organic carbon content across the basin. Because these stratigraphic variations and compositional heterogeneities remained largely uninvestigated, there are conflicting interpretations of not only the hydrocarbon potential of this resource unit but also the paleoenvironmental conditions that prevailed in the Karoo Basin during its accumulation. Following the recent global proliferation of unconventional hydrocarbon resources originating in organic-rich shale successions, the WHF is seriously being considered for gas shale exploitation in South Africa. Consequently, re-characterizing and explaining the spatiotemporal variations in its geometry and composition would be invaluable to the energy industry as well as the larger scientific community. With this aim, this study applied a combination of field descriptions, vintage borehole data, micro- to nano-scale petrographic observations, and multiple geochemical data so that a more critical understanding of the sedimentological controls responsible for the variability can be established. Using this integrated approach, five primary sedimentary facies (F1-F5, i.e., stratigraphic subunits in the WHF) were identified, which show specific and systematic variations in nature and content of organic carbon, stable isotopic composition (of δ¹³Corg and δ¹⁵N), C/N ratio, major and trace elemental enrichment, nature and content of iron sulfides, quartz texture, and CIA across the basin. The lower dark grey to black thinly laminated pyritic, carbonaceous fine shales (facies F1 and F2) contain up to 16.5 % TOC, δ¹³Corg of -15.57‰, δ¹⁵N of 12.49‰, C/N ratio of 1.50, average CIA of 68.11, Rb/K (x10⁻³) and Sr/Ba ratios of 6.56 and 0.67, respectively. Relative to average shale, this unit is up to 6.27 and 3.11 times richer in Mo and Fe, respectively. The organic materials in this facies comprise Tasmanites cysts, colonial algae cells, and amorphous macerals and occur in well-defined laminae (lamalginites) as well as in discrete organic domains loosely associated with mineral grains (organo-minerallic aggregates). At least 25% of the silicate in this facies is of early diagenetic origin, possibly derived from alteration of air-fall volcanic ash. Iron sulfides occur dominantly in form of framboidal aggregates of pyrite. Marcasite in form of lags cement and nodules is also reported. A binary mixture of organic matter and phosphorites with botryoidal textures is also abundant. The upper medium to light grey calcareous-siliceous silty lenticular shale (F3-F5) contain up to 2.04% TOC, δ¹³Corg of -24.71‰, δ¹⁵N of 4.93‰, C/N ratio of 17.62, average CIA of 74.33, Rb/K (x10⁻³) and Sr/Ba ratios of 3.83 and 0.36, respectively. Relative to average shale, this unit was up to 2.65 and 0.43 times richer in Mo and Fe, respectively. Their organic macerals comprise disarticulated plant remains in disseminations with few amorphous macerals. At least 85% of the quartz content is of detrital origin likely sourced from the basin margins and transported to the basin by the action of bottom-hugging currents. Few iron sulfides occur dominantly in form of octa- and euhedral pyrite grains. The data presented in this thesis suggest that the lower WHF (subunits F1 and F2) may have accumulated in a marine setting with high bioproductivity of organic carbon delivered in form of flocculated organo-minerallic aggregates (pelagic snow) onto an anoxic seabed overlain by dysoxic to oxic waters. Reduced terrigenous input, presence of phosphorites, increasing CIA and increasing δ¹³Corg values with higher TOC point to a depositional setting that resulted from an interplay of sea-level highstand and climatic warm-ups. In contrast, the upper WHF (subunits F3-F5) was deposited largely under non-marine conditions with OM in the company of great detrital debris sourced from terrestrial settings, transported into the basin mainly in form of fluid mud flows and deposited above storm wave base. The presence various body and trace fossils, as well as the variations in bioturbation styles and intensities in subunits F3-F5, indicate that colonisation of the basin by invertebrate and vertebrate organisms is related to the different stages in the oxygenation of the sediment-water interface in an increasingly oxygenated setting.
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Dinis, Yambi Renato Daniel. "Sedimentology of the lower Uitenhage Group in the Middle to Late Mesozoic Oudtshoorn Basin, South Africa." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29618.
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The Oudtshoorn Basin is the largest onshore Mesozoic depocentre along the southern margin of South Africa, and is among the sedimentary basins that have been linked to the break-up of southern Gondwana. Filled by the continental lower Uitenhage Group, which for the most part is sparsely fossiliferous, difficult to correlate on a regional scale and void of non-renewable natural resources, the Oudtshoorn Basin is relatively poorly studied. This project aims at carrying out an in depth, field- and lab-based investigation of the sediment supply processes and directions, location of sediment sources and palaeoclimate during the deposition of the lower Uitenhage Group in the Oudtshoorn Basin. In addition to the sediment transit patterns from source to sink via palaeocurrent measurements and petrographic studies, the sedimentary architecture was assessed via modern facies analysis techniques, which also permitted the investigation of the reason, the nature and the mode of sediment transport (traction currents vs. mass movements) in the early stages of Gondwana fragmentation. The study identified nine facies associations, the composition, clast size and orientation of which suggest steep vs. gentle gradients along the northern and southern basin margins, respectively, and very gentle gradients in the basin centre. Furthermore, the common mass movement-deposits in the north contrast the sediments laid down by traction current and in turbid waters in the south, southwest, west and centre of the basin. Sediments were sourced from the northern and southern margins in alluvial fans, and moved toward the centre, where axial fluvial system dominated. Sedimentary facies distribution, grain size, and petrological composition collectively indicate sediment transport distances that were shorter and more rigorous in the north than in the south. Geochemical proxies and mineralogy indicate moderate weathering and deposition under an arid palaeoclimate. The lack of clear lithostratigraphic markers and the sparse distribution of isolated outcrops in the basin prevent the relative age assessment of the facies associations. This study highlights the need for systematic high-precision geochronological studies, if possible from drill core samples, of the facies associations identified herein to constrain the stratigraphic relationships in the Oudtshoorn Basin. Until these reconstructed palaeoenvironments are in temporal isolation, the history of the Oudtshoorn Basin and its relationship to the other Mesozoic grabens and half grabens of the southern Cape remain elusive.
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Curl, Edward Alexander 1972. "Parental magmas of the Bushveld Complex, South Africa." Monash University, Dept. of Earth Sciences, 2001. http://arrow.monash.edu.au/hdl/1959.1/9080.
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Boast, Robert. "The hydrology and geomorphology of Dambos in southern central Africa using remotely sensed data." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316799.
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Muedi, Thomas Tshifhiwa. "Cretaceous dyke swarms and brittle deformation structures in the upper continental crust flanking the Atlantic and Indian margins of Southern Africa, and their relationship to Gondwana break-up." Thesis, Nelson Mandela Metropolitan University, 2013. http://hdl.handle.net/10948/d1020896.
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Permanent brittle deformation of rocks of the upper crust is often manifested in the growth of fractures, or sliding along fractures, which may subsequently be intruded by magma and other fluids. The brittle deformation structures described here include faults, joints and dykes. Brittle deformation structures along passive continental margins result from continental fragmentation and related uplift, as is seen around the southern African margins in response to Gondwana break-up. In many cases the fragmentation is accompanied by significant magmatic events, for example the Cretaceous mafic dyke swarms that form major components of the South Atlantic Large Igneous Province (LIP) and originated during the break-up of West Gondwana (Africa and South America). The magmatic events accompanying the break-up of Gondwana resulted in crustal extension and the formation of joint systems and dyke swarms that exhibit distinct geometric features that appear to display fractal patterns. This work analyses the relationship between the Henties Bay-Outjo Dyke Swarm (HOD) on the west coast of Namibia, and the Ponta Grossa Dyke Swarm (PG) on the coast of Brazil, both of which formed ca. ~130 Ma, to test for their co-linearity and fractal geometry before and during West Gondwana break-up. This was achieved by reconstructing Gondwana‘s plates that contained the PG and HOD swarms, using ArcGIS and Gplates software. The dyke analyses was complemented with a comparative study of joints of the Table Mountain Group quartzites (TMG, ca. 400 Ma) in the Western Cape Province and Golden Valley Sill (GVS, ca. 180 Ma) in the Eastern Cape Province, to compare their fractal patterns and possible relationship. Mapping of joints was carried out in the field with the use of a compass and GPS. The HOD trend is positioned largely NNE > NE, but a NW dyke trend is also common. The dominant joints in the TMG trend NNW > WSW and the GVS joints trend WNW > NNE and others. The GVS and HOD orientations appear strongly correlated, while TMG shows no simple orientation correlation with GVS and HOD. The lack of correlation is attributed to the TMG‘s formation in different host-rocks with variable anisotropy and/or the presence of different mechanical processes acting at a different time in geological history. All mapped dykes and joints were analysed to test for fractal geometry. The fractal dimension results of about 18605 HOD dykes from microscopic to mega scale (0.1 mm – 100 km) shows fractal patterns that range between Df = 1.1 to 1.9; and the fractal dimension of about 1716 joints in the TMG and about 1026 joints in the GVS at all scales range between ca. Df = 1.6 to 1.9. The similarity of the fractal patterns indicates that joints and dykes may have formed in response to similar tectonic stress events; and similar orientations may indicate that joints pre-dated the dyke intrusions. However, the data also indicate that dykes are not always related to pre-existing joints.
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Slabber, Nina. "The geology and geochemistry of the Bridgetown Formation of the Malmesbury Group, Western Cape Province." Thesis, Stellenbosch : Stellenbosch University, 1995. http://hdl.handle.net/10019.1/54889.
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Thesis (MSc) -- Stellenbosch University , 1995.ENGLISH ABSTRACT: A number of small greenstone bodies of the Bridgetown Formation are exposed as elongated lenses and dykes within metasediments of the Malmesbury Group in the Western Cape Province, South Africa. The Malmesbury Group is part of the Neoproterozoic to Cambrian (Namibian) Saldania Subprovince which is the southern continuation of a Pan-African mobile belt system. A detailed geological and geochemical study was conducted on the largest outcrop of the Bridgetown Formation, situated 20km east of the town Moorreesburg. The Bridgetown Formation consists of a meta-volcano-sedimentary sequence that experienced polyphase deformation and metamorphism up to the lower greenschist facies. Tectonically, the Bridgetown Formation is included in the Boland tectonic domain, east of the Piketberg-Wel lington fault zone that is suggested to run Skm west of Heuningberg and subparallel to the Berg River. This agrees with Rabie's (1974) original subdivision of the tectonic domains. The Bridgetown Formation consists of: i) A basal unit of poorly differentiated alkaline metabasalt with a within-plate tectonomagmatic fingerprint. ii) An intermediate unit of poorly differentiated tholeiitic metabasalt, intruded by a younger tholeiitic metabasite with a low degree of differentiation. Both members of the intermediate unit have ocean-floor basalt (P-type MORB) and island arc basalt fingerprints. iii) An upper unit of poorly differentiated as well as more evolved alkaline metabasalts, interlayered with metatuff with an alkaline basaltic composition, metasedimentary rocks with a marine origin, and graphitic schists and muscovitequartz schists, both with a continental crust provenance. iv) An overlying metasedimentary sequence including dolomite, massive and oolitic chert, jasper and jaspilite. The Bridgetown Formation probably also comprises a lower metamorphosed ultramafic unit, indicated by the association of Ni- and Cr-rich talc bodies, Ni-and errich banded chert, chlorite schist and small dolomite-talc-chlorite bodies at Spitskop, situated directly northwest of the main greenstone body. The sequence of eruptive stages and the geochemistry of the metavolcanics resemble Hawaiian volcanism , indicated by an initial deep water stage of alkaline magmatism, followed by main tholeiitic edifice and post-caldera alkaline magmatism. Post-caldera alkaline magmatism occurred contemporaneously with deposition . of sediments and chemical precipitates (carbonates and cherts). The Bridgetown metavolcanics have no magmatic association with either the Bloubergstrand volcanics or mafic and intermediate plutonic rocks in the Malmesbury Group. However, some physical and geochemical similarities exist between the Bridgetown Formation and the age related Grootderm Formation of the Marmora Terrane (Gariep Supergroup) which is considered to represent ophiolitic material. The Bridgetown Formation probably represents segments of oceanic crust, including seamounts of oceanic islands, which were tectonically emplaced in an accretionary prism zone during subduction of oceanic crust underneath the Kalahari Craton, 600 to 700 Ma ago. This resulted in the present spatial configuration of various small greenstone bodies in the Malmesbury Group. To date no exploitable mineral deposits have been found 1n the Bridgetown Formation. However, Au and As anomalies in stream sediment and soil samples, taken in the Spitskop area, require further attention. lt is suggested that the gold and arsenic is hosted in brittle deformed clear to milky quartz veins which developed at zones of competency contrasts in all the li tholog ies in the Spitskop area.
AFRIKAANSE OPSOMMING: 'n Aantal klein groenskisliggame van die Bridgetown Formasie is blootgestel as verlengde lense en gange binne metasedimente van die Malmesbury Groep in die Wes-Kaap Provinsie, Suid-Afrika. Die Malmesbury Groep is deel van die Neoproterozo·iese tot Kambriese (Namibiese) Saldania Subprovinsie wat die suidelike voortsetting is van 'n Pan-Afrikaanse mobiele gordel sisteem. 'n Gedetaileerde geologiese en geochemiese studie is gedoen op die grootste dagsoom van die Bridgetown Formasie, gelee 20km oos van die dorp Moorreesburg. Die Bridgetown Formasie bestaan uit 'n metavulkanies-sedimentere opeenvolging wat pol ifase vervorming en metamorfisme tot en met die laer groenskis fasies ondergaan het. Die Bridgetown Formasie word hier in die Boland tektoniese domein ingedeel deur die Piketberg-Wellington verskuiwingsone 5km wes van Heuningberg, subparallel a an die Bergrivier, te plaas. Dit stem ooreen met Rabie ( 197 4) se oorspronkl ike verdeling van die tektoniese domeine. Die Bridgetown Formasie bestaan uit: i) 'n Basale eenheid wat hoofsaaklik bestaan uit min gedifferens ieerde alkali-metabasalte met binneplaat tektonomagmatiese eienskappe. ii) 'n lntermediere eenheid wat bestaan uit min gedifferensieerde tholeiitiese metabasalt en 'n jonger intrusiewe tholeiitiese metabasiet wat 'n lae graad van differensias ie ondergaan het. Beide intermediere eenhede het oseaanvloer-basalt (P-t ipe MORB) en eilandboog basaltiese eienskappe. iii) 'n Boonste eenheid wat bestaan uit min gedifferensieerde asook meer gedifferensieerde alkal i-metabasalte, tussengelaagd met metatuf met 'n alka libasaltiese samestelling; metasedimentere gesteentes met 'n mariene oorsprong, en grafitiese ski ste en kwarts-muskoviet skiste, beide met 'n kontinentale kors oorsprong . iv) 'n Oorliggende metasedimentere opeenvolging wat dolomiet, massiewe en ooli tiese chert, jaspis en jaspiliet insluit. Die Bridgetown Formasie slu it moontlik ook 'n onderliggende gemetamorfiseerde ultramafiese eenheid in; aangedui deur die assosiasie van Ni- en Cr-ryke ta lkl iggame, Ni- en Cr-ryke gebande chert, chlorietskis en klein dolomiet-talk-chloriet liggame by Spitskop, gelee direk noordwes van die hoof groensteenliggaam. Die opeenvolg ing van magmatisme en die geochemie van die metavulkaniese gesteentes stem ooreen met Hawaiiese vulkanisme, naamlik 'n diepwater stadium, gekarakteriseer deur alkaliese magmatisme, gevolg deur 'n hoof tholeiitiese opbouing en post-kaldera alkaliese magmatisme. Die post-kaldera alkaliese magmatisme het gelyktydig plaasgevind met afsetting van sedimente en chemiese presipitate (karbonate en cherte ). Die Bridgetown metavulkaniese gesteentes het geen magmatiese assosiasie met 6f die Bloubergstrand vulkaniese gesteentes 6f mafiese en intermediere plutoniese gesteentes in die Malmesbury Groep nie. Fisiese en geochemiese ooreenkomste bestaan egter tussen die Bridgetown Formasie en die Grootderm Formasie van die Marmora Terrein (Gariep Supergroep) wat beskou word as ofiolitiese materiaal. Die Bridgetown Formasie verteenwoordig moontlik segmente van oseaankors, insluitende oseaan-eilande, wat tektonies in 'n melange sone ingeplaas is tydens subduksie van oseaankors onder die Kalahari Kraton in (600 tot 700 Mj gelede). Dit verklaar die huidige ruimte like verspreiding van verske ie klein groensteenliggame in die Malmesbury Groep. Tot en met hede is geen ontginbare mineraalafsettings in die Bridgetown Formasie ontdek nie. Au en As anomalie in stroomsediment- en grondmonsters, geneem in die Spitskop area, behoort egter verdere aandag te geniet. Daar is voorgestel dat die goud en arseen voorkom in brosvervormde helder tot melkerige kwartsare wat ontwikkel het in swak sones in al die litologie in die Spitskop area.
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Smildzins, V. (Viesturs). "Using mineral chemistry to constrain P-T conditions for mantle xenoliths from the Kaapvaal craton, South Africa." Master's thesis, University of Oulu, 2016. http://urn.fi/URN:NBN:fi:oulu-201611233107.
Full textAbstract:
Kimberlites are igneous rocks that originate by small degrees of melting of the mantle. Notably, kimberlites carry large variety of crustal and mantle xenoliths. Geochemical data on xenoliths can provide insights into the processes occurring in the subcontinental lithosphere (SCLM) and deeper.
The Kaapvaal craton in South Africa hosts one of the best-studied kimberlite populations on Earth. In this thesis, a total of 24 thin sections of peridotite xenoliths from Group I Letlhakane, Letseng, Premier and Frank Smith kimberlites were investigated to constrain the pressure, temperature and depth of these mantle xenoliths. To do so, olivine, orthopyroxene, clinopyroxene, garnet and spinel were analyzed for their major element chemistry using electron microprobe analysis (EPMA). P-T calculations were performed using the PTEXL3 spreadsheet program, which contains different geothermobarometers. Depth constraints were fitted to the characteristic Kaapvaal craton geotherm.
According to geochemical results and rough modal mineral estimations, the majority of the mantle xenoliths were identified as depleted harzburgites or lherzolites. Mineral major element compositions show trends of depletion, which correlate with the corresponding mantle xenolith sampling depth. Olivine and orthopyroxene have high average Mg# values of 92.1 and 93.0, respectively, at shallower depth ~70–160 Km. Below ~160 km, Mg# starts to drop rapidly and transition towards a more typical asthenospheric composition. The majority of garnet compositions fall into the G9 classification field. Titanium shows a distinct partition trend that correlates with depletion. Garnets have well developed alteration reaction rims, especially at shallower depths.
Geothermobarometric calculations for four-phase peridotites are comparable with the results from other studies. However, the temperature estimates obtained by T(BKN90) are slightly overestimated and, in contrast, the pressure estimates from P(BBG08) are slightly underestimated. Other assemblages have considerable calculated pressure and temperature conditions and were best fitted for the regional conductive geotherm. The mantle xenoliths show pressures ranging from 22 to 56 kb and temperatures from 753 to 1344 °C that characterize an extensive sampling depth range from 70 to 190 km. Three of the samples extend into the diamond stability field. The obtained P-T data for mantle xenoliths cluster along a 44.0±2.0 mWm⁻² conductive Kaapvaal craton continental geotherm, being slightly higher than that of the average thermal state estimate for the craton.
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Moodley, Adam. "The sedimentary petrology of carbonate nodules in the Elliot Formation, Karoo Supergroup, main Karoo Basin (South Africa)." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20345.
Full textAbstract:
In South Africa, fossils found in the upper part of the Elliot Formation (Stormberg Group, Karoo Supergroup) are often associated with genetically poorly-constrained carbonate nodules. The origin of carbonate nodules i.e., pedogenic versus diagenetic, is important as pedogenic carbonate nodules can be used as palaeoclimate indicators, while diagenetic nodules carry limited palaeoclimatic information on the depositional setting. This research aims to characterize the carbonate nodules of the Elliot Formation macroscopically, petrographically and geochemically and to establish a diagnostic set of criteria to enable the differentiation between pedogenic and diagenetic nodules and/or diagenetic overprint. The research techniques employed in this study range from a) macroscopic field observations of the stratigraphic relationships of the nodules to the sedimentary features of the host rocks; b) sedimentary petrography of the textural features in the nodules; and c) X-ray diffraction for the assessment of the clay composition trapped within the nodules as compared to host rocks. Macroscopic field observations have shown that carbonate nodules found in the UEF are strongly associated with host rocks that contain pedogenic features such as root traces, burrows, colour mottling, and desiccation cracks, and thus are suggestive of ancient soils. However, the microscopic analysis of the nodules reveal no evidence for biological activities but rather a range of abiotic features such as septarian cracks, circumgranular cracks, and micronodules which are more likely have resulted from physicochemical processes that may have occurred during diagenesis. Clay minerals identified by X-ray diffraction include illite, muscovite, and montmorillonite confirm the generation of the sediments under arid to semi-arid climatic conditions.
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Olajide, Oluseyi. "The petrophysical analysis and evaluation of hydrocarbon potential of sandstone units in the Bredasdorp Central Basin." Thesis, University of the Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_9559_1181561577.
Full textAbstract:
This research was aimed at employing the broad use of petrophysical analysis and reservoir modelling techniques to explore the petroleum resources in the sandstone units of deep marine play in the Bredasdorp Basin.
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Riganti, Angela. "The geology and geochemistry of the north-western portion of the Usushwana Complex, South-Eastern Transvaal." Thesis, Rhodes University, 1992. http://hdl.handle.net/10962/d1005570.
Full textAbstract:
The 2.9 Ga old Usushwana Complex in the Piet Retief-Amsterdam area (south-eastern Transvaal) represents an exposed segment of a layered intrusion. It has the form of a dyke-like body elongated in a northwesterly direction, and extends to an estimated depth of 3000 -5500 m. Lithologically, the Complex consists of a cumulate succession of mafic rocks capped by granitoids and has intruded along the contact between the basement and the supracrustal sequences of the Kaapvaal Craton. Differentiation of an already contaminated gabbroic magma resulted in an ordered stratigraphic sequence comprising progressively more evolved lithotypes, with at least two imperfect cyclic units developed over a stratigraphic thickness of about 700 metres (Hlelo River Section). Meso- to orthocumulate textured gabbros and quartz gabbros grade upwards into magnetite- and apatite-bearing quartz gabbros, interlayered with discontinuous magnetitite horizons. The gabbros in turn grade into hornblende-rich, granophyric granodiorites. The differentiation process is regarded as having been considerably enhanced by the assimilation of acidic material, derived by partial melting of the felsic country rocks at the roof of the magma chamber. Recrystallisation of these rocks gave rise to the microgranites that locally overlie the granodiorites. Mineralogical, textural and geochemical features indicate a relatively advanced fractionation stage, suggesting that the exposed sequence of the Usushwana Complex in the study area represents the upper portion of the intrusion. No significant mineralised occurrences were identified. However, on the basis of similarities between the Usushwana Complex and other mafic layered intrusions which host significant ore deposits, it is suggested that economic concentrations of base metal(Cu-Ni) sulphides, PGE and chromitites are likely to be developed at lower stratigraphic levels.
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Smithies, Robert Hugh. "The geology and alteration/mineralization of the Van Rooi's vley W/Sn deposit, Namaqua metamorphic complex, South Africa." Thesis, Rhodes University, 1987. http://hdl.handle.net/10962/d1004526.
Full textAbstract:
Scheelite, wolfram Ite and cassIterIte mIneralizat ion is hosted wIthin numerous quartz-tourmaline-feldspar-fluorite veins at Van Rooi's Vley, N.W. Cape Province . MineralizatIon and hydrothermal alteration within, and around, these veins is hIghly complex and reflects the intricate interaction of hydrotherma l activity upon a structurally deformed sequence of ProterozoIc med ium to high-grade gneisses. Four distinct stages of alteration and mineralization occurred, including a l ate 'epithermal stage'. Although the location of mineralization was strongly controlled by st ructure, the concentration of mineralizati on was controlled by physicochemical variables, of which host-rock geochemistry was particularly important . Further W/Sn mineralization occurs on a local scale, some of which is spatia lly related to minor leucogranite dykes. Leucogranite bodies are not uncommon within the region and some are enriched in Wand Sn. By comparing FIB ra tio s,W/Sn ratios, the alteration mineralogy, the ore mineralogy and the Fe-content of tourmaline, the deposits within the Van Rooi's Vley area can be placed into a 'proximal' to 'distal' classification, with respect to a common source of mineralizing hydrothermal fluids. The Van Rooi's Vley deposit, whilst affiliated to greisen-style deposits, represents a ' distal' quartz-vein lode deposit.KMBT_363
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Brunsdon, Gideon. "A structural study of Witteberg group rocks (Cape supergroup) in the Cape fold belt, Steytlerville district, Eastern Cape." Thesis, Nelson Mandela Metropolitan University, 2006. http://hdl.handle.net/10948/d1019682.
Full textAbstract:
A structural study of Witteberg Group Rocks was conducted along the Soutkloof River, approximately 14 km east of Steytlerville, Eastern Cape Province of South Africa. Here a north to south geotraverse was studied in an attempt at unravelling the structural geology of the rocks belonging to the Upper Devonian to Lower Carboniferous Witteberg Group (Upper Cape Supergroup). These rocks are mostly arenaceous and include quartzite, sandstone, siltstone and shale which have been folded, faulted and metamorphosed. Thrust, normal and strike-slip faulting occur in the area. Shallow south-dipping low-angle thrust fault planes are displaced by steep south-dipping thrust planes and subordinate north-dipping backthrusts. Displacement along thrust planes is predominantly northwards. Steeply dipping thrust fault planes are often reactivated as east-west striking normal faults. Strike-slip faulting postdates all observed structural features and displaces normal and thrust fault planes. Open to tight folds are present and are mostly northvergent and often steepened or truncated by steep south-dipping thrust fault planes. South-vergent folds are related to backthrusting and post-fold faulting. The study has revealed that the current geological map and the local stratigraphy were compiled without recognising major structural features such as thrust, normal and strike-slip faulting and their (the map and currently accepted stratigraphy) validity are therefore questioned. The presence of extensive faulting suggests that the conventional stratigraphic interpretation of the Witteberg Group should be revised.
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Goossens, Angelique Emily Maria. "A study of the structural geology of the Witteberg Group and lowermost Karoo Supergroup, Darlington Dam, Jansenville District, Eastern Cape." Thesis, University of Port Elizabeth, 2003. http://hdl.handle.net/10948/291.
Full textAbstract:
A number of outcrops of the Witteberg Group and lowermost Karoo Supergroup rocks were studied in the area south of the Darlington Dam, Jansenville District, with the aim of documenting structural characteristics of the area. All lithologies are folded with fold styles varying from gentle to near isoclinal (based on interlimb angle). Fold axes are either sub-horizontal or plunging at gentle to moderate angles whereas axial planes dip gently to vertically (predominantly steep to sub-vertical). Folds verge predominantly towards the north but where southward verging they are associated with faulting or strongly folded areas. Folds plunge gently to the east-southeast and west-northwest. The area consists of a large anticlinorium with both first and second order folds occurring. Eastwest striking faults occur in the study area and are classified as normal, reverse and thrust faults. A study of the joint sets shows that there are four dominant joint directions, namely 18o, 33o, 97o and 107o (in order from least to most important). An interpretation of the tectonic history is presented in which the relationships between faults and folds show that faults formed during and after folding. Folding, and reverse and thrust faulting, occurred during the compressional events that formed the Cape Fold Belt, whereas the normal faults formed during the relaxation of these compressional forces or during the break-up of Gondwana.
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Decker, John E. "Landscape evolution and equilibrium in Southern Africa : insights from cosmogenic noble gases in Karoo dolerites and geospatial analyses." Doctoral thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/11706.
Full textAbstract:
Includes abstract.Includes bibliographical references (p. 321-356).
Southern Africa’s landscape is characterised by a high plateau (elevation > 1,000 m) bound by escarpments and extensional continental margins, and the region has been influential in the development of geomorphological theory. However, the evolution of this landscape in response to tectonic and climatic forcing remains poorly understood, and is investigated here though an analysis of the topography and surface exposure history of early Jurassic (~183 Ma) Karoo dolerites.
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Reid, Mhairi. "Taphonomy, palaeoecology and taxonomy of an ophiuroid-stylophoran obrution deposit from the Lower Devonian Bokkeveld Group, South Africa." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25404.
Full textAbstract:
The Lower Devonian Voorstehoek Formation is a fossil-rich, siliciclastic unit (Ceres Subgroup, Bokkeveld Group, Cape Supergroup) in South Africa. This Emsian unit contains a highly endemic benthic fossil biota characteristic of the cool to cold water Malvinokaffric Realm of southwestern Gondwana. The palaeontological and sedimentological investigations of the Voorstehoek Formation suggest that deposition took place in a shallow marine environment within the storm influenced, proximal part of an offshore transition zone. A relatively diverse, ophiuroid–stylophoran assemblage, well-preserved in the Karbonaatjies obrution bed, was excavated at the study site in the Hex River Pass, Western Cape. In this study the taphonomy, taxonomy and the palaeoautecology of Palaeozoic ophiuroids and stylophorans was investigated using micro CT scans. Over 60 samples were scanned, manually segmented and stitched together to create a virtual 3D model of a portion of the Karbonaatjies obrution bed. This method allowed for the determination of the degree of fossil articulation, fossil orientation and faunal counts, without damaging the delicate echinoderm fossils. Furthermore, the ability to digitally analyse the fossil-rich bed has revealed an echinoderm assemblage composed of over 700 articulated ophiuroids dominated by a proposed new genus and species Gamiroaster tempestatis, over 145 articulated mitrate stylophorans Paranacystis cf. petrii Caster, 1954 and eight Placocystella africana (Reed, 1925). Taphonomic analysis of this ophiuroid–stylophoran assemblage indicates this obrution deposit formed due to rapid burial that smothered a potentially gregarious community during a single storm event. Additionally, the admixture of skeletal debris and intact echinoderms present in the Karbonaatjies obrution bed reflects a complex history with significant time-averaging. This unique assemblage provides a taphonomic window into the marine ecosystems of the Early Devonian, including the structure of an unusual, echinoderm-dominated benthic community that forms part of a much wider fossil biota from the Falkland Islands and Precordillera of Argentina, which formed part of SW Gondwana.
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Westerlund, Kalle. "A geochemical study of diamonds, diamond inclusion minerals and other mantle minerals from the Klipspringer kimberlites, South Africa." Master's thesis, University of Cape Town, 2000. http://hdl.handle.net/11427/4230.
Full textAbstract:
Summary in English.Bibliography: leaves 157-171.
The Klipspringer kimberlites occur in the north-eastern part of the Kaapvaal craton which is poorly represented in kimberlite and mantle studies. The kimberlites have been dated at 148+-4 Ma and the current study presents the geochemical characteristics of their diamonds, diamond inclusion and mantle macrocrysts/bimineralic nodules. The Klipspringer lithosphere is dominated by eclogite and Iherzolite with harzburgite and dunite present to a lesser extent.
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Steyn, Juan Greisch. "Structural geology and controls of gold mineralization in the Siguiri Mine, Guinea, West Africa." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/19933.
Full textAbstract:
Thesis (MSc)--Stellenbosch University, 2012.ENGLISH ABSTRACT: This study presents results of a detailed geological mapping and structural analysis of auriferous quartz-vein sets of the nine current open-pit operations, of the Siguiri Mining Complex in the northeastern parts of Guinea. The Siguiri Mining Complex is hosted by a low-grade metamorphic, turbiditic succession within the larger Siguiri Basin, which forms part of the Palaeoproterozoic Birimian Supergroup of the Boualé-Mossi domain on the West African Craton. The Siguiri Mining Complex is located in a deeply weathered saprolite profile developed over the monotonous succession of interlayered metapelites and -psammites. In fresh bedrock and core samples, the host succession is mainly made up of quartz-muscovite schists, muscovite-chlorite schists and metagreywackes, with isolated occurrences of intraformational breccias. The main deformation to have affected the metasedimentary succession of the Siguiri Mining Complex can be assigned to a D2 deformational event. D2 structures comprise of north-south trending strike-slip and reverse faults anastomosing around and enveloping open- to tightly folded domains exposed over an area of 12 by 3 km. The geometry, orientation and kinematics of faults and folds suggest that D2 structures formed during progressive deformation in an overall dextral transpressive brittle-ductile shear zone. Structures within the D2 corridor record east-northeast subhorizontal shortening and north-northwest subhorizontal extension. An omnipresent carbonate alteration in form of carbonate-alteration spots testifies to the pervasive, syn-D2 hydrothermal fluid-flow within the sediments. A structurally- and fracture-controlled fluid-flow is evidenced by the abundance of auriferous quartz veins throughout the Siguiri Mining Complex. These quartz veins host the bulk of the gold mineralization. One main and, at least, three minor sets of auriferous quartz veins can be distinguished. The main quartz-vein set shows very consistent easterly to northeasterly trends and steep southerly dips throughout the Siguiri Mining Complex. This orientation is consistent with the dextral transpressive kinematics and strain within the D2 host structure and illustrates the significance of D2 strains for the mineralization. The volumetrically minor vein sets can be shown to be related to different stages of F2 folding and fold amplification. Zones of economic-grade mineralization occur in areas where competent, psammitic units are developed in structural sites of increased dilatancy. Areas of dilatancy are represented by either dilational jog geometries within the overall transpressive structure or zones of pronounced shear-zone subparallel stretch. Jog geometries could be identified in the larger Bidini-Toubani-Sanu Tinti Complex having formed as a result of the anastomosing geometry of the bounding D2 shear zones. In the large Kami Complex, F2 axial culminations and depressions correspond to zones of increased stretch within the D2 transpression zone, delineated by closer vein spacing and the formation of D2 normal faults parallel to the main vein set and normal to F2 fold hinges. The size and extent of the Siguiri Mining Complex suggests that the host D2 transpressive corridor must be assumed to have a significantly larger along-strike continuation, being part of a larger shear zone system related to the accretionary history of Palaeoproterozoic basins and arcs onto the Archaean Man Shield in West Africa.
AFRIKAANSE OPSOMMING: Hierdie studie lewer die resultate voor van 'n gedetailleerde geologiese kartering en strukturele analise van die gouddraende kwarts-aar stelle in die huidige nege oop-groef operasies van die Siguiri Myn Kompleks, in die noordoostelike deel van Guinea. Die Siguiri Myn Kompleks is geherberg deur 'n lae metamorfiese graad turbidiet suksessie in die groter Siguiri Kom, wat deel form van die Paleo-Proterosoïkum Birimian Supergroep van die Boualé-Mossi streek op die Wes Afrika Kraton. Die Siguiri Myn Kompleks is geleë in die diep veweerde saproliet profiel, wat onwikkel het oor die eentonige suksessie van metapeliete en -psammiete. In vars bodemrots en kern monsters is die herberg-gesteente opgemaak uit kwarts-muskoviet skiste, muskoviet-chloriet skiste en metagrouwakte, as ook afgesonderde voorvalle van intraformasie breksies. Die hoof deformasie fase wat die metasedimentêre suksessie van die Siguiri Myn Kompleks geaffekteer het, kan toegeken word aan 'n D2 deformasie gebeurtenis. D2 strukture bestaan uit noord-suid neigende strekkingwaartse verskuiwings en opskuiwings, wat anastomoserend oop- en steil geplooide gebiede omsluit en is oor 'n area van 12 by 3 km ontbloot. Die geometrie, oriëntasie en kinematika van verskuiwings en plooie stel voor dat D2 strukture gevorm het tydens progressiewe deformasie in 'n algemene regse transpressie skuifskeursone, onder brosheid-duktiliteit toestande. Strukture in die D2 gang wys 'n oos-noordoos subhorisontale verkorting en 'n noord-noordwes subhorisontale verlenging. Die alomteenwoordigheid van karbonaat alterasie, in die vorm van karbonaat-alterasie spikkels, getuig van die deurdringende, sin-D2 hidrotermiese vloeistof vloei in die sedimente. Die strukturele- en breuk-beheerde vloeistof vloei is ook duidelik, as gevolg van die oorvloed van gouddraende kwarts-are reg deur die Siguiri Myn Kompleks. Die kwarts-are bevat die grootmaat van die goud mineralisasie. Een hoof, en te minste drie minder belangrike stele van gouddraende kwarts-aar stelle kan uitgeken word. Die hoof kwarts-aar stel wys konstante oostelike to noordoostelike neigings en steil suidelike hellings, reg deur die Siguiri Myn Kompleks. Die oriëntasie is konstant met regse transpressie kinematika en vervorming in die D2 strukture en illustreer die belangrikheid van D2 vervorming vir mineralisasie. Die minder-belangrike aar stelle is verwant aan die verskillende staduims van F2 plooiing en plooi amplifikasie. Sones van ekonomiese graad mineralisasie kom voor in areas waar bevoegde eenhede van psammiete ontwikkel het in strukturele terreine van verhoogde dilatasie. Areas van dilatasie word verteenwoordig deur dilatasie uitwykings in die transpressie strukture of sones van skuifskeur subparalelle verlenging. Uitwykings geometrië kan geidentifiseer word in die groter Bidini-Toubani-Sanu Tinti Kompleks, waar dit gevorm het asgevolg van die anastomoserende geometrie van die D2 skuifskeur sones. In die groter Kami Kompleks kom F2 aksiale kulminerings en depressies voor in sones van verhoogde strekking binne-in die D2 transpressie sone en word uitgebeeld deur nader aar-spasiëring en die formasie van D2 afskuiwings, parallel aan die hoof kwarts-aar stel en normaal met betrekking tot die F2 plooi-skarniere. Die groote en omvang van die Siguiri Myn Kompleks stel voor dat die D2 transpressiewe gang nog n groter voorsetting het, en vorm deel van 'n groter skuifskeur sisteem en is verwant aan die anngroeings geskiedenis van die Paleo-Proterosoïese komme en boë aan die Argeïese Man Skild in Wes Afrika.
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Tsikos, Harilaos. "Petrographic and geochemical constraints on the origin and post-depositional history of the Hotazel iron-manganese deposits, Kalahari Manganese Field, South Africa." Thesis, Rhodes University, 2000. http://hdl.handle.net/10962/d1005599.
Full textAbstract:
The giant Palaeoproterozoic manganese deposits of the Kalahari manganese field (KMF), Northern Cape Province, South Mrica, have been a world renowned resource of manganese ore for many decades. In recent years, the mineralogical composition, geochemistry and genesis of these deposits have been the objects of many geological investigations, yet their origin remains contentious up to the present day. A characteristic feature of the Kalahari deposits is the intimate association of manganese ore and iron-formation of the Superior-type, in the form of three discrete sedimentary cycles constituting the Hotazel Formation. This striking lithological association is an almost unique feature on a global scale. From that point of view, the present study is effectively the first attempt to shed light on the origin and post-depositional history of the Hotazel succession, using as prime focus the petrographic and geochemical characteristics ofthe host iron-formation. Petrographic and whole-rock geochemical information of iron-formation from the southern parts of the KMF, suggests that the Hotazel iron-formation is almost identical to other iron-formations of the world of similar age and petrological character. The rock exhibits essentially no high-grade metamorphic or low-temperature alteration effects. Mineralogically, it contains abundant chert, magnetite, subordinate amounts of silicate minerals (greenalite, minnesotaite, stilpnomelane) and appreciable concentrations of carbonate constituents in the form of coexisting calcite and ankerite. Such mineralogical composition is indicative of processes occurring in a diagenetic" to burial (up to very low-greenschist facies) metamorphic environment. Bulk-rock geochemical data point towards a simple composition with Si02, total Fe-oxide and CaO being the chief major oxide components. Whole-rock rare-earth element data suggest that the iron-formation precipitated from a water column with chemical signatures comparable to modern, shallow oceanic seawater. The virtual absence of positive Eu anomalies is a feature that compares well with similar data from Neoproterozoic, glaciogenic iron-formations of the Rapitan type, and suggests but only a dilute hydrothermal signal, poten!ially derived from distal submarine volcanic activity. Carbon and oxygen isotope data from iron-formation and Mn-bearing carbonates as well as overlying ferriferous limestone of the Mooidraai Formation, compare well with the literature. The former exhibit variable depletion relative to seawater in terms of both BC and 180, while the latter have signatures comparable to normal marine bicarbonate. Isotopic variations appear to be related to fluctuations in the amount of co-precipitated marine carbonate, in conjunction with processes of coupled organic matter oxidation - FelMn reduction in the diagenetic environment. Oxygen isotope data from quartz-magnetite-calcite triplets suggest that crystallisation took place under open-system conditions, with magnetite being the most susceptible phase in terms of fluid-rock isotopic exchange. Data also suggest that the calcite-magnetite pair may constitute a more reliable geothermometer than the quartz-magnetite one, mainly due to the interlinked diagenetic histories between calcite and magnetite. Iron-formation from the northern parts of the KMF can by categorised into three main classes, namely pristine, altered and oxidised. Pristine iron-formation is identical to the one seen in the southernmost parts of the field. Altered iron-formation corresponds to a carbonate-free derivative of intense oxidation and leaching processes at the expense ofpristine iron-formation, and contains almost exclusively binary quartz-hematite mixtures. The rock appears to have lost essentially its entire pre-existing carbonate-related components (i.e., Ca, Mg, Sr, most Mn and Ba) and displays residual enrichments in elements such as Cr, Th, V, Ni and Pb, which would have behaved as immobile constituents during low-temperature alteration. The low temperature origin of altered iron-formation is supported by oxygen isotope data from quartz-hematite pairs which indicate that isotopically light hematite would have derived from oxidation of magneftte and other ferroussilicate compounds in the presence of a low-temperature meteoric fluid, while quartz would have remained isotopically unchanged. Occasional occurrences of acmite-hematite assemblages suggest localised metasomatic processes related to the action ofNaCI-rich fluids at the expense of altered iron-formation. The conditions of acmite genesis are very poorly constrained due to the very broad stability limits of the mineral in environments ranging from magmatic to surface-related. Oxidised iron-formation constitutes a distinct rock-type and shares common attributes with both the pristine and the altered iron-formation. The rock contains hematite as an important constituent while the amount of magnetite is substantially reduced. With regard to carbonate nlinerals, calcite contents are clearly very low or absent, having being replaced in most instances by a single, Mgenriched, dolomite/ankerite:type species. Oxidised iron-formation contains somewhat higher amounts of iron and reduced amounts of Sr and Ba relative to pristine iron-formation, whereas enrichments in elements such as Ni, Th, Pb, Cr, and V are seen, similar to altered iron-formation. Oxidised iron-formation appears to have originated from processes of dissolution-mobilisationreprecipitation of solutes derived primarily from leaching that produced altered iron-formation. It is proposed that the Hotazel iron-formation and associated manganese deposits were formed as a result of episodic sea-level fluctuations in a stratified depositional environment that gradually evolved into a shallow carbonate platform. A critical parameter in the development of manganese sediment may include regional climatic patterns related to a glacial event (Makganyene diamictite) prior to deposition of the Hotazel strata. This suggestion draws parallels with processes that are believed to have led to the formation of worldwide iron-formations and associated manganese deposits subsequent to Neoproterozoic episodes of glaciation. Submarine volcanism related to the underlying Ongeluk lavas appears to have had very little (if any) metallogenic significance, while evidence for a sudden rise in the oxygen contents of the atmosphere and ambient waters is lacking. With regard to later alteration processes, combination of geological and geochemical data point towards the potential influence of surface weathering prior to deposition of rocks of the unconformably overlying Olifantshoek Supergroup, possibly coupled with fault- and/or thrustcontrolled fluid-flow and leaching of the Hotazel succession during post-Olifantshoek times.
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Ntombela, Nondumiso. "A 3D fault seal analysis study conducted in the Ibhubesi Gas Field Offshore the West Coast of South Africa." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/27833.
Full textAbstract:
A 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.
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Neethling, J. M. "Stratigraphic evolution and characteristics of lobes : a high-resolution study of Fan 3, Tanqua Karoo, South Africa." Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/2249.
Full textAbstract:
Thesis (MSc (Earth Sciences))--University of Stellenbosch, 2009.Fan 3 is one of four basin-floor fans that form part of the Tanqua Karoo Fan Complex in South Africa. It can be subdivided into several sandstone lobes, based on the presence of thin-bedded siltstone intervals above and below major sandstone packages. Six lobes are identified in the mid fan section, as well as two older groups of thin, low-volume turbidite deposits at the base. Some of the lobes are further divided into an upper and lower lobe-element based on depositional behaviour. The volumetrically and spatially larger lobes have a finger-like appearance in plan view, which is attributed to multiple lobe-scale axial zones. This is especially visible towards the eastern margins of Lobes 2, 4 and 5. The stratigraphy and facies distribution are presented on several 2D panels. Computer generated isopach maps are presented for each lobe, lobe-element and interlobe unit. Autogenic control on the depositional pattern of the Fan 3 lobe complex was inferred from the palaeoflow patterns of the composing lobes and lobe-elements. The majority of the lobes show a north-eastern palaeoflow direction in the south, with a gradual westward shift in the north. Inferred controls are basin-floor topography, the presence of pre-existing lobes, and characteristics of the depositional flow, such strength, density, sediment load, palaeoflow direction.
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Moore, John Michael. "A comparative study of metamorphosed supracrustal rocks from the western Namaqualand metamorphic complex." Doctoral thesis, University of Cape Town, 1986. http://hdl.handle.net/11427/22585.
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Bibliography: pages 346-370.A regional study of highly metamorphosed supracrustal rocks was undertaken in the western portions of the Namaqualand Metamorphic Complex. The study area was essentially restricted to a north-south section some 50 kilometres wide and 220 kilometres long. Eight east-west-trending belts of supracrustal rocks were examined, together with several smaller paragneiss remnants, in an area dominated by quartzo-feldspathic gneisses of granitic composition. The supracrustal rocks were classified into seven major lithological groups: quartzitic rocks, metapelitic and metapsammitic rocks, quartzo feldspathic rocks, metabasites, metacarbonate rocks, magnesium-rich cordierite rocks and iron formations. Further subdivision, based on variations in mineral constituents within each group, also occurred, as well as the presence of lithologies with compositions transitional between certain groups. The various supracrustal sequences were subdivided into formations containing minor distinctive members on an informal lithostratigraphic basis. Correlation between the major supracrustal belts was then undertaken. Four subgroups were identified across the study area, comprising a quartzo feldspathic gneiss subgroup and an overlying feldspathic quartzite/garnetcordierite gneiss subgroup that both predominate in the southern and central part of the area, a glassy quartzite/mica- sillimanite schist subgroup that predominates in the northern part, and a cordierite gneiss/metacarbonate subgroup that is restricted to the Geselskapbank synform. The supracrustal rocks appear to have been emplaced on a basement of augen gneisses. This relationship is, however, complicated by the intrusion of granit i c rocks within the contact zone.
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Fraser, Nicholas Tweedie. "A Metamorphic Study of Pretoria Group Sediments Found at the Dwarsrivier Pass, Bushveld Igneous Complex, South Africa." Diss., University of Pretoria, 2019. http://hdl.handle.net/2263/76009.
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The study takes place in the Dwarsrivier area which lies on the border between Mpumalanga and Limpopo, to the North-West of Lydenberg, at an exposed road cutting. Within the road cutting, there is a unique portion of exposed rock which is light in colour and identified as a calc-silicate. The calc-silicate material is present as a package of rock and is surrounded top and bottom by pyroxenite. The surrounding rock belongs to the Bushveld Igneous Complex (BIC), which is the largest known layered intrusion on the planet and is host to numerous mines. The sample area is within the Critical Zone of the BIC and the host rock consists of pyroxenite which is crystalline and mafic. The calc-silicate package originates from the Pretoria Group sediments, which hosts the BIC, and has undergone varying degrees of metamorphism and mineralisation. The metamorphism formed and allowed for the preservation of two rare minerals, namely wüstite and chlorospinel. Numerous tests were performed on the samples, including SEM point scans to identify these rare minerals and to better understand how the calc-silicate package was preserved in the BIC. A model was created to explain the occurrence of the calc-silicate slab and surrounding features. The previous model involved the slab rising up through the BIC, but the proposed model in this thesis is that the calc-silicate was part of the roof rock which then delaminated, and subducting into the ductile magma of the BIC.Dissertation (MSc)--University of Pretoria, 2019.
Geology
MSc
Unrestricted
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Tregoning, Trevor Denzil. "The tectono-metallogenesis during the irumide and pan-African events in South West Africa/Namibia." Thesis, Rhodes University, 1987. http://hdl.handle.net/10962/d1004490.
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A large portion of South west Africa/Namibia is underlain by 2 great orogens. They are the Irumide (Sinclair/Rehoboth) and Damara Orogenies. The L-shaped Irumide Province forms part of a belt which extends over the subcontinent from Namaqualand to as far as Zambia. The volcano-sedimentary sequences of the Irumide are believed to have formed in intracratonic rifts and pull-apart basins during the period 1400 to 900 Ma. The evolution of the NW trending Sinclair Group proceeded by means of 3 major cycles each beginning with the emplacement of basic to intermediate magmas followed by felsic ones. The cycle ended off with subsidence, deposition of immature clastic debris and final tilting of the volcano-clastic sequence. It was suggested that the extensive calc-alkaline lavas present, developed within a magmatic arc above a subduction zone, but this proposal has not been generally accepted. The NE trending Klein Aub-Witvlei Basins consist essentially of red bed alluvial fans and lacustrine sediments with minor volcanics near the base. The red beds and aeolian sediments were deposited in an arid climatic condition. The regional greenschist facies metamorphism and deformation is attributed to a major tectono-thermal event at 1100 Ma. The Damara Orogen (900 - 550 Ma) forms part of the Pan-African mobile belt system of global proportions. The NE trending intracontinental branch (aulacogen) and 2 coastal branches constitute a triple junction with its focal point near Swakopmund. The NE extension of the intracontinental belt has been linked with the Lufilian Arc hosting the renown Zambian Copper Belt deposits. In South West Africa/Namibia this belt hosts many different mineral occurrences which can be grouped into rift and collision related deposits. The tectonic history of the Damara Orogen supports a geodynamic-evolution-with-time hypothesis and represents a transitional phase in which limited Wilson Cycle Tectonics was active. The Theory of Mantle Advection is invoked to explain rifting, thinning and subsidence. Extensive ensialic rifting resulted in a relatively stable Northern Carbonate Platform and several deep troughs hosting turbiditic sequences. Crustal rupture in the Khomas Trough allowed for the emplacement of ocean floor tholeiites known as the Matchless Amphibolite Belt. Subsequent ocean closure and collision resulted in deformation, metamorphism and generation of predominantly S-type granites. The southern continental plate was partially overridden by the northern plate during final collision at 550 Ma. These low angle thrust faults allowed for the emplacement of the Naukluft Nappe Complex on top of younger Nama sediments. The break up of Gondwanaland during the Mesozoic with the splitting of the Atlantic Ocean was responsible for the intrusion of anorogenic alkaline ring complexes along the extension of the NE trending transform faults within the intracontinental branch of the Damara Orogen. A close relationship between the tectonic setting and mineral deposits has been recognized in both the Irumide and Damara Orogenies. In the Irumide, stratiform syngenetic copper deposits are hosted by alluvial fan, playa and lacustrine sediments. The uninterrupted sedimentation from the Irumide to Damara Orogen resulted in similar stratiform copper deposits during the early stages of rifting. In the Damara Orogen the rifting (extensional) phase is characterized by 4 main mineralizing systems: diagenetic/syngenetic (Kupferschiefer-type), epigenetic/hydrothermal Cu-Pb-Zn (Mississippi Valley-type), volcanogenic cupriferous pyrite (Besshi-type) and volcano-exhalative Pb-Zn (Red Sea-type). The collision (compressional) phase was accompanied by 4 main mineralizing processes: epigenetic/hydrothermal Cu-Pb-Zn, hydrotheral/metasomatic Sn-W-rare earth, metamorphogenic Au and U-bearing anatectic melts. The key to the selection of viable exploration targets lies in the understanding of the field evidence and the geodynamics modelling to explain the evolution of the orogen and its associated mineral deposits.
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Crous, Stephanus Philippus. "The geology, geochemistry and stratigraphic correlations of the farm Rietfontein 70 JS on the south -eastern flank of the Dennilton Dome, Transvaal, South Africa." Thesis, Rhodes University, 1996. http://hdl.handle.net/10962/d1005572.
Full textAbstract:
The study area is located between Loskop Dam and the town of Groblersdal, on the southeastern flank of the Dennilton dome, and is underlain by lithologies of the Pretoria Group, Bushveld Complex mafics and ultramafics and acid lavas that resort under the Rooiberg felsites. Field work comprised of geological mapping, soil-, hard-rock- and stream sediment geochemistry, various geophysical techniques and diamond drilling. The rocktypes that resembles the Rustenburg Layered Suite on the farm Rietfontein 70JS is subdivided into a Mixed Zone, Critical Zone and Main Zone, on grounds of geochemical and certain geophysical attributes. The Mixed Zone that overlies the Bushveld Complex floor-rocks, is furthermore separated into an i) Lower-, ii) Middle- and, iii) Upper Unit. The Lower Unit of the Mixed Zone consists primarily of magnetite-gabbros, iron-rich pegmatites, harzburgites and feldspathic pyroxenites. The Fe-rich constituents of this stratigraphic horizon generates a pronounced magnetic anomaly within the study area. On the basis of; amongst other parameters, Zr/Rb and Sr/Al₂0₃ ratios, the magnetite-gabbros are postulated to conform to lithotypes in the vicinity of magnetite layers 8 to 14 of Upper Zone Subzone B in a normal Bushveld Complex stratigraphical scenario. Similarly, it is argued that the feldspathic pyroxenites and norites that display elevated chromium values are analogues to normal Critical Zone rocktypes of the Rustenburg Layered Snite. A more elaborate and precise stratigraphic correlation for the Critical zone was, however, not possible. It is advocated that a volume imbalance was created by the hot, ascending mafic magmas of the intruding Bushveld Complex, resulting in the updoming of certain prevailing basement features such as the Dennilton Dome. In addition to this ideology, it is proposed that the Mineral Range Fragment is in fact a large xenolith underlain by mafics, after being detached from the Dennilton Dome during the intrusion event. Evidence generated by this study unequivocally indicate that the potential for viable PGE's, Ni, Cu and Au within a Merensky Reef- type configuration or a Plat Reef-type scenario under a relatively thin veneer of acid Bushveld Complex roof-rocks on the eastern flank of the Dennilton Dome, appears feasible.
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Van, Rensburg Tamsyn. "Identification of the physical controls on the deposition of Aptian and Albian deep water sands in the Bredasdorp Basin, South Africa." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/22886.
Full textAbstract:
In the petroleum industry, the location of a new well is selected based on several factors, one of which is the presence of reservoir-quality sands. To determine the lateral extent of these sands away from well control, the depositional environment and character of the deposit must be adequately identified. This study aims to explain the physical controls on the deposition of the 13A (Aptian) and 14A (Albian) sequence sands within the deep water region of the Central Bredasdorp Basin through identifying the mass transport facies and processes and relating these to tectono-eustatic factors. Since a primarily seismic-based approach was used to achieve the project objective, the results reflect findings based on 3D seismic data interpretations as well as seismic surface and volume attribute extraction supported by wireline well logs and well completion reports. This dataset contains information that enabled the identification of the structural and stratigraphic architecture of the 13A and 14A sequences as a whole, the location of the sediment provenances and possible triggers of the mass flows as well as the consequential sand distribution trends from the basin slopes to across the basin floor during the Aptian-Albian time. The onshore Tankwa Basin was studied as an analogue to the Bredasdorp Basin because it hosts world class outcrops of deep water lowstand fan deposits and therefore shows the finer-scale details of the associated depositional stratigraphy. The 13A and 14A sequence sands would have entered the Bredasdorp Basin in progradational pulses alternating with mud-rich successions associated with local sea level fluctuations that were on trend with the gradual global sea level rise from the Aptian to the Albian. These alternating successions are identified as lowstand, transgressive and highstand systems tracts in the seismic and wireline well log data used in this study. The presented depositional model of the 13A sequence sands is a system of northwest to southeast sediment transport across the Central Bredasdorp Basin with indications of a final swing in orientation towards the east. The sands were mainly sourced from the paleo shelf edge on the northwest margin, although additional sediment input may have come from the west too. The faults that were active before and during the deposition of the Aptian-aged (13A) sands appear to have been the main control on sand distribution across the basin, guiding the sands from slope channels into basin floor fans and from shelf edge slumps into base of slope fans in a basinwide northwestsoutheast trend. The model of deposition of the 14A sequence sands is based on a channelised flow of sediment from the Central Bredasdorp Basin paleo shelf edge, down the slope and onto the basin floor primarily from the onshore source on the western margin. Supplementary sediment input may have originated from the Agulhas basement high on the southern margin of the basin in the form of less confined channels and mass wasting deposits. Inherited topography of the sea floor at the Albian time appears to have been the primary control on 14A sand distribution, causing bypass zones and giving rise to narrow, confined channel complexes despite some of the active faults possibly redirecting some of the sands from their initial trend. Overall the pattern of deposition of the Aptian and Albian deep water sands in the Bredasdorp Basin appears to have been physically controlled by the regional paleo seabed topography and fault activity until the late Aptian.