Geology

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The mineralogy and related geology of the Albert Silver Mine, Bronkhorstspruit, Transvaal
(1970) Champion, Alfred Timothy.
The Albert Silver mine is situated on the farm Roodepoortjie, 32 kilometres north of Brorikhorstspruit in the Transvaal. The deposit forms the largest of a number of sub-parallel quartzhematite lodes accompanied by sulphide mineralization and is accompanied by an extensive alteration zone along its northern flank.
The late cenozoic carnivora of the south-western Cape Province.
(1972) Hendey, Quinton Brett.; King, Lester Charles.
Abstract available in PDF file.
The hydrogeology of Botswana.
(1974) Jennings, Christopher Mark Hubert.
Botswana covers an area of 570 000 km and has a population of about 600 000. It is estimated that three-quarters of the human and livestock populations are dependent on ground water, with an estimated 26 x 10 m of water from this source being used annually. Details of the physiography, climate, denudational and depositional surfaces and geology are given: Ground water occurs in both primary and secondary aquifers under both water-table and artesian conditions at varying depths from less than 1m to over 300m. The water-bearing properties of the various aquifers are described with the basalt/Cave sandstone contact providing the greatest number of successful boreholes and the sedimentary rocks of the Pretoria Group providing the highest yields (208,45 litres/minute). The shallowest water is found in the Kalahari Beds and the deepest in the Ecca Group. Detailed descriptions are given of the hydrogeology of the Central Kalahari, Lobatse, Orapa and Serowe. In the Lobatse area, estimates of the average monthly recharge rate have been made as well as estimates of the total storage capacity of the various ground-water basins. The percentage of annual rainfall contributing to ground water has also been calculated. An annual recharge rate has also been calculated for Serowe while the total amount of water in storage in the important Cave sandstone aquifer has been estimated. Hydrogeological details of the Kalahari Beds, basalt/Cave sandstone aquifer and Middle Ecca aquifers are given following core drilling programmes. ERTS photography was used to assist in obtaining a figure of 56 x 10 m of extractable water present in storage in the "sand rivers" of eastern Botswana. Detailed aquifer tests on a variety of aquifers are described and show that the secondary aquifers generally present often behave in a similar fashion to primary aquifer. Approximately 5 000 boreholes are presumed to be present in Botswana. It is estimated that 17% of the successful boreholes have yields in excess of 150 1/min. The siting of boreholes using geological/geophysical aids has resulted in an increase in the success rate of nearly 25%. New geophysical techniques for the location of ground water have been investigated and ground geophysical methods used include electrical resistivity, inductive and conductive electromagnetic, Afmag, self-potential and seismic reflection and refraction methods. The well-tried resistivity method remains the most successful technique but self-potential, Afmag and seismic methods have given encouraging results. Extremely detailed studies using environmental isotopes are described. These have enabled quantitative estimates of ground-water storage and turnover times to be made; have given round-water flow rates; have outlined areas of recharge; have enabled permeabilities to be calculated; have enabled a clearer picture of recharge mechanisms through the unsaturated zone to be built-up; and have provided important evidence of areas in which recent recharge has contributed to ground-water supplies. The studies have shown that measurable amounts of tritium are present over far wider areas than originally anticipated and thus more recharge is taking place than thought earlier from laboratory tests and hydrogeological considerations. In Lobatse a water balance model is proposed and calculations based on this model indicate that some leakage, hitherto unsuspected, between several of the ground-water basins, take place. The carbon-14 method has, in addition, helped outline areas of recharge (Central Basin, Lobatse) which tritium had failed to do and has shown by using combined 3H and l4C data that mixing of young and old waters takes place. In the Kalahari, radiocarbon has been used to calculate ground-water flow rates, permeability and transmissivity. The oldest ground water in Botswana has an age of 33 700 years. Isotopic studies in the unsaturated zone have shown that water moves given rates downward at a rate of between 31 and 41 cm per year. Studies of water levels in boreholes have shown that nearly all boreholes show responses which can be directly correlated with seasonal recharge and hence the nature and frequency of recharge can be estimated. In addition, storage capacity and safe yield have been estimated using long term water level changes and knowing the amount abstracted from the basin. The rapid responses shown in some boreholes indicates surprisingly rapid recharge. Two boreholes in Botswana showed effects of the Tulbagh earthquake on 29th September 1969. The disturbance of semi-diurnal fluctuations in boreholes could possibly be used as an early warning device to predict catastrophic earthquakes. A prelimlinary annual safe yield for ground-water supplies in Botswana is estimated to be 4 x 10 9 m3 per annum. Tree roots have been found in boreholes at depths greater than 68m. This emphasises the role vegetation can have in causing transpirational losses from ground-water supplies. Irrigation from boreholes is unlikely to be profitable unless exceptionally large supplies are obtained or water be present at very shallow depth. Underutilised boreholes, e.g. boreholes drilled specifically for cattle ranching, could also be profitably used for irrigation. Details of ground-water chemistry and examples of fresh water overlying saline, saline water overlying fresh, chemical stratification with depth and changes in quality with time are given. The distribution of fluoride rich waters in Botswana is also given. This thesis has therefore attempted to outline the current status of hydrogeological research in Botswana and it is hoped that this will lay the foundation for later, more detailed and quantitative, studies. These will become even more vital than at present, as it is estimated that all readily available surface water resources in eastern Botswana will be fully utilised by the late 1980's and the country will rely even more heavily on ground water than at present.
Aspects of Karroo vulcanicity in the Komatipoort area Lebombo.
(1979) Logan, C. T.
The petrology, mineralogy and geochemistry of the Karroo-age basaltic and rhyodacitic volcanics present in the Lebombo Belt near Komatipoort, Eastern Transvaal, Republic of South Africa are described. The volcanics comprise a succession of extrusives within the Komatipoort area, consisting of: (3) Rhyodacitic lavas and tuffs (2) Basalts (1) Olivine Basalts. These volcanics dip eastwards at angles between 10° and 40°, with dips increasing as the Eastern boundary of the area, the Mozambique border, is approached. Further Karroo-age volcanics, constituting the upper part of this succession, lie across the border in neighbouring Mozambique. Various intrusives, similar in composition to the extrusives, are also present in the area, commonly as north-south trending dykes forming part of a large dyke-swarm. These, as else\Olhere in the Lebombo, are considered to be feeders to the extrusives. Three relatively major intrusions occur in the area, the largest being the Komatipoort Intrusion, here interpreted as a 700m thick, sub-concordant, composite sheet-like body, ~onsisting of five major lithological units. From the base upwards these are:- . unit 1 - olivine gabbro, unit 2 - igneously laminated gabbro, unit 3- granophyric gabbro, unit 4 - granophyre, unit 5 - feldspathic gabbro. The olivine gabbro, the granophyre and the feldspathic gabbro appear to form separate intrusive bodies, but the igneously laminated gabbro and the granophyric gabbro, could represent the products of in situ differentiation. If so, the granophyric gabbro has suffered subsequent disturbance as shown by evidence including a homogeneous composition, reaction and corrosion textures and the presence of deformed pyroxene grains, which are described in detail. Another major intrusive of probable Karroo age is the Crocodile River Intrusion, which occurs to the north-east of the main mapped, and represents the southern- most end of a northsouth trending line of mafic intrusives, which parallel the Lebombo for approximately 200 km. The intrusion here has a dykelike form, and shows evidence of fractionation by crystal settling. A smaller, obviously composite intrusion occurs near the base of the basaltic sequence in the Komatipoort area, (the Basal Intrusion). Representative samples of a variety of extrusive and intrusive rock types have been analysed. These analyses include major and trace element determinations of a series of samples of the major units of the Komatipoort Intrusion. In 'addition, analyses of a number of minerals from several different rock types occurring in the Komatipoort Intrusion, are presented. The analytical data available for the Komatipoort volcanics confirms the previously known southward variation in the geochemistry of the basalts and the presence of bath a high and a low-Ng basalt series in the Komatipoort area. The majority of the basic rocks in the Komatipoort area belong to the low-Mg series. Compositional variation in this series may be explained largely by low-pressure fractionation of olivine and pyroxene only, despite the presence of abundant plagioclase phenocrysts. Some of the variation in the high-Mg series , basalts can be explained by the fractionation of olivine, and what appear to be relatively highly fractionated rocks formed in this manner occur in the area. The Lebombo volcanics ln general display a bimodal silica distribution and rocks with an intermediate silica content are rare. In the Komatipoort area intermediate rocks do occur in the, form of two classes of granophyre, (high and low silica varieties), present in the granophyre unit of the Komatipoort Intrusion. Liquid immiscibility is a possible mechanism for the formation of the two types of granophyre, and a widespread development of this process in intermediate magmatic liquids could provide an explanation for the ,scarcity of rocks of this composition in the Lebombo belt. Relatively few analyses of the rhyolitic volcanics are presented in this study, but it appears possible that those available could be representative of two processes, firstly, partial melting of the lower crust or upper mantle, and secondly, fractionation by crystallisation of the commonly observed phenocryst phases,(feldspar, pyroxene, quartz, magnetite), or addition of these phases to the magma.
Stratigraphy and sedimentology of the Molteno formation in the Elliot and Indwe area, Cape Province.
(1981) Christie, Angus David Mackay.; Tavener-Smith, Ronald.
Abstract in PDF file.
The lithostratigraphy and petrogenesis of the Nsuze group northwest of Nkandla, Natal.
(1984) Groenewald, Peter Bruce.
The volcanic and sedimentary Nsuze Group constitutes the lower part of the
The geology of the Ngoye granite gneiss formation.
(1985) Scogings, Andrew John.
The Ngoye Granite Gneiss Formation is located in the Natal sector of the Proterozoic Namaqua-Natal Mobile Belt, about 10 km southwest of Empangeni. It forms a prominent east-west trending elongate whalebacked massif some 30 km in length, within amphibolitic gneisses and schists of the Tugela Group. A suite of twelve different, gneissic granitoids has been-recognised within the Ngoye Formation on the basis of field relationships, mineralogy and supportive geochemistry. They range in composition from peraluminous syenite to peralkaline granite. Peraluminous varieties are typically muscovite and garnet-bearing whereas metaluminous granites in the formation contain olivegreen biotite and/or hornblende and sphene. Riebeckite, aegerine and yellow-brown biotite, with accessory fluorite and zircon are characteristic of the peralkaline granites. Geochemically, the samples analysed display a range in SiO₂ from 63,79 - 78,47∞, are extremely depleted in CaO and MgO, while being enriched in Na₂O and K₂O. Depletion of CaO relative to alkalis is shown by an alkali-lime index of only 36, suggestive of an alkalic character. The agpaitic index (A. I. = mole Na₂O + K₂O/AL₂O₃) of the peralkaline samples ranges between 1,02 and 1,16; which classifies them as granites of comenditic affinity. Various chemical classification schemes have been tested and evaluated, of which the RI - R2 multicationic diagram provides results most similar to modally-derived terminology. Accordingly, the Ngoye granitoids are shown to range from minor syenites and alkali granites to predominant monzo - and syeno-granites. Trace element data indicate that the peralkaline granites are enriched in Nb, Zr and Zn relative to the other, non-peralkaline, granites in the formation. In addition, radioactive, magnetite-bearing quartz-rich rocks associated with the peralkaline granites, have extremely enhanced contents of Nb, Zr, Y, Zn, U, Th and to a lesser extent Sn and W. Peraluminous and near-peraluminous granites have the highst Rb/Sr and Rb/Ba ratios of all samples analysed, as well as enhanced Sn, U and Th contents while Zr is notably depleted. Small, muscovite-rich pods associated with muscovite-bearing granites are highly enriched in Sn. The application of certain discriminants based on modal and geochemical parameters has shown the Ngoye Formation to comprise typical "A" - type granites. "A" - type granites are characteristically intruded as ring complexes into anorogenic or post-orogenic tectonic settings in attenuated or epiorogenically-domed continental crust. Comparison of the Ngoye Formation wi th the well-known "younger granite" complexes of Nigeria and Saudi Arabia reveals marked similarities. The inference is therefore that the Ngoye Formation represents a metamorphosed "postorogenic" granite complex with most of the hallmarks of "A" type or "within-plate" magmatism. Four phases of deformation (D₁ to D₄) are recognised within the area mapped. Evidence of D₁ deformation is rare, but rootless folds within the transposed layering in the amphibolitic country rocks reflect the intensity of this prograde metamorphic event, M₁, during which upper amphibolite grades were achieved. Field evidence shows that the Ngoye granites were intruded after the D₁ event and prior to D₂. This latter event caused widespread folding about east-west F₂ axes, with the development of a pervasive S₂ planar fabric within the antiformally folded Ngoye Formation. S₂ is locally developed in the amphibolitic country rocks. The D₂ event culminated in the development of northward-directed overthrusting and retrogressive ,M₂, metamorphism of mylonitic thrust planes. Lateral shearing characterizes D₃, with development of macroscopic mylonites and mesoscopic conjugate shear zones. This was in response to a sinistral sense of movement, as indicated by prominent sub-horizontal extension lineations (L₃) and microscopic asymmetric augen structures. D₄ is deduced from stereograms and is indicated as cross-folding of F₃ fold axes.
The petrology and geochemistry of intrusions at selected nunataks in the Ahlmannryggen and Giaeverryggen, western Dronning Maud Land, Antarctica.
(1986) Krynauw, Johannes Reynhardt.; Hunter, Donald Raymond.; Wilson, Allan H.
The mid-Proterozoic Borgmassivet intrusions of western Dronning Maud Land intrude Archaean granites and a volcano-sedimentary sequence, the Ritscherflya Supergroup. They are SiO2-rich ultramafic to mafic tholeiitic rocks which occur as layered bodies of unknown dimensions and sills up to 400 m thick. This thesis records detailed field, petrographic and whole rock geochemical studies on Borgmassivet intrusions at three widely-spaced localities within an area of approximately 20 000 km in the Ahlmannryggen and Giaeverryggen. Annandagstoppane-Juletoppane-Forstefjell area: The Annandagstoppane intrusions form part of a layered body or bodies, of which only a small part is exposed. They consist of a medium-grained 'main suite ' of gabbronorites and minor anorthosites, and a Iyounger suite ' of quartz diorite pegmatites, basaltic dykes, fine- to medium-grained gabbroic sills and minor albitite veins. The main suite rocks are ortho-cumulates in which plagioclase, orthopyroxene and clinopyroxene were primocrysts which crystallized in situ. The dykes and sills show typical basaltic and doleritic textures. Geochemical evidence suggests that the main and younger suites may be consanguineous. Robertskollen-Krylen area: The layered complex at Robertskollen comprises a lower, rhythmically layered ultramafic unit, overlain by a mafic unit. Olivine, orthopyroxene and clinopyroxene are the dominant cumulus phases in the ultramafic rocks, whereas plagioclase, orthopyroxene and clinopyroxene fractionation occurred during crystallization of the mafic rocks. Metastable co-existence of quartz with olivine and anomalous incompatible trace element characteristics of the Robertskollen complex suggest contamination of the magma(s) by crustal material. The Krylen intrusions show petrographic and geochemical characteristics similar to those of the main suite at Juletoppane. A felsic dyke at Krylen may represent a rheomorphic product derived from Ritscherflya sediments. (iii) Grunehogna-Jekselen area: The Grunehogna sill is a medium-grained diorite of unknown thickness, characterized by varying amounts of plagioclase and amphibole and a high Fe-Ti oxide content. It is overlain by a 50 m-thick quartz diorite pegmatite. The overlying 400 m-thick Kullen sill varies in composition from gabbronorite to gabbro and diorite and shows evidence for contamination by crustal material. Vugs, evidence for fusion, destruction of sedimentary structures and deformation in sedimentary contact zones and xenoliths and the abundance of pegmatites suggest that the sills intruded wet, unconsolidated or partially lithified sediments. The Jekselen complex consists of quartz diorites intruding Ritscherflya sediments. Amygdales in the upper zones of the complex indicate the subvolcanic nature of the intrusion. Major, trace and rare earth element data of the Borgmassivet intrusions and the Straumsnutane basalts (Watters, 1969a, 1969b, 1972, pers. comm., 1985) show a strong regional coherence, indicating that the rocks may be consanguineous. Abundance ratio patterns ('spidergrams') of the intrusions and basalts are identical. They are consistent with crustal contamination, possibly leucotonalite, of the magmas during ascent. The present distribution of the Borgmassivet. intrusions and Straumsnutane basalts reflects emplacement at stratigraphically higher levels within the Ritscherflya Supergroup from west to east. Previous radiometric isotope studies suggested that the intrusions are approximately 1700 to 1800 Ma in age, but recent investigations show that the isotopic data are poorly understood and have to be re-evaluated. Some of the isotope characteristics may result from crustal contamination and alteration effects during intrusion into water-saturated sediments.
Geochemistry and structure of the archaean granitoid-supracrustal terrane, southeastern Transvaal and northern Natal.
(1987) Smith, Roric Gerard.; Wilson, Allan H.; Hunter, Donald Raymond.
Sedimentary models for coal formation in the Klip River coalfield.
(1988) Christie, Angus David Mackay.; Tavener-Smith, Ronald.
The primary objective of this study was to establish sedimentary models for peat formation in the southern part of the Klip River coalfield during Ecca (Permian) times and to assess palaeoenvironmental controls on coal seam behaviour and distribution. In order to achieve this approximately 2 400 borehole logs and 25 field sections were collected. The coal-bearing Vryheid Formation records early to late Permian fluvio-deltaic sedimentation within the northeastern main Karoo basin. Three informal lithostratigraphic subdivisions, based on the investigations of Blignaut and Furter (1940, 1952), are proposed: the Lower zone, Coal zone and Upper zone. An examination of the structural framework and history of the northeastern Karoo basin reveals that the southern and western boundaries of the Klip River coalfield are defined by zones of rapid basement subsidence : the Tugela and Oannhauser Troughs respectively. There is some doubt as to the locality of the source area to the rivers emptying into the Ecca sea. Ryan (1967) postulated the "Eastern Highlands" situated off the present southeast African coast, but it is contended that the Swaziland area, situated no more than 200 to 300 km to the northeast of the Klip River coalfield, constituted a more plausible source area. The Lower zone represents sedimentation along a westerly to southeasterly prograding coastline dominated by high-constructive lobate or braid deltas, but also showing significant influence by wave processes. The Coal zone, which varies in thickness from 35 to 60 m, represents a major phase of coastal progradation and braided-river deposition on extensive alluvial plains. Significant coal seams formed only during periods of fluvial inactivity, the duration of which was dependent on source-area processes. Coal seam geometry and behaviour in the Klip River coalfield were not influenced by the depositional environments of associated clastic sediments. The following factors were found to have of profound influence in determining the extent, distribution and rate of peat accumulation: 1. Platform stability and temporal and spatial variations therein. 2. The absence or presence of penecontemporaneous clastic sedimentation. 3. Duration of periods of peat formation. 4. Lithology and topographic expression of clastic sediments underlying peat-forming swamps. The peat-forming phase of the Vryheid Formation was terminated by an extensive transgression brought about by an eustatic rise in basin water-level and/or an increased rate of platform subsidence.
The petrology, geochemistry and classification of the Bien Venue massive sulphide deposit, Barberton mountain land.
(1990) Murphy, Philip William.; Harwood, Anthony.; Kerr, Alan.
The Bien Venue massive sulphide deposit is associated with a felsic volcanic succession developed in the north-eastern part of the Barberton Greenstone Belt, Eastern Transvaal. The deposit is situated 8km east-north-east of Louw's Creek between the Lily Syncline to the south and the Stentor Pluton to the north. The stratigraphy of the Onverwacht, Fig Tree and Moodies Groups in the vicinity of the deposit is poorly documented, and the exact stratigraphic position of the host felsic volcanics is not known. They are tentatively correlated with the felsic volcanics from the Theespruit Formation, Onverwacht Group. The felsic volcanics have undergone low-grade greenschist facies metamorphism and occur as quartz-sericite schists. Detailed petrography enables sub-division of the volcanic succession into distinct units. A lapilli metatuff unit hosts the base metal and precious metal mineralisation. The sulphides are best developed in the upper part of this unit, together with intercalated barite-rich horizons and cherts. A series of structural events have modified the attitude of the lithological units and disrupted the continuity of the orebody. The orebody comprises stratabound lenses of massive to semi-massive and often banded sulphides, as well as disseminated sulphide mineralisation. The dominant base metal mineralogy consists of pyrite, sphalerite, chalcopyrite, galena and tennantite. Native silver and various copper-silver sulphides are also associated with the base metal sulphides. A vertical zonation of the mineralisation exists, from pyrite-chalcopyrite-rich ore in the footwall, to pyrite - chalcopyrite-sphalerite-galena-barite-rich ore towards the hanging wall. Geochemical studies indicate that the Bien Venue lithologies are rhyolitic to rhyodacitic in composition and show a calc-alkaline affinity. The mobility of some elements at Bien Venue has been clearly demonstrated. This is believed to be associated with hydrothermal alteration that has led to SiO2 and MgO enrichment, as well as K2O depletion, in the wall rocks of the deposit. The geological setting and nature of the mineralisation at Bien Venue suggest that it is an example of a volcanogenic exhalative sulphide deposit. In terms of the classification scheme suggested by Hutchinson (1973, 1980), Bien Venue would best be described as a Primitive type deposit that contains barite.
Alkaline intrusives from the Tugela terrane, Natal metamorphic province.
(1991) Scogings, Andrew John.; Cooper, Mike.; Dunlevey, John N.
Three gneissose alkaline granitoid intrusives at Ngoye, Bulls Run and Wangu are described. They are located within the Nkomo Nappe of the Tugela Terrane, near the northern margin of the Natal Metamorphic Province. The Ngoye Complex comprises alkaline granites, with minor syenite and monzodiorite phases. According to modal am geochemical criteria the Ngoye granites range from peraluminous (muscovite-bearing), through metaluminous (biotite- and/or hornblende-bearing), to peralkaline (riebeckite-, aegirine- and magnetite-bearing). The granites are A-types according to their modal and geochemical characteristics. Rb-Sr isotopic data for the hornblende granites indicate an age of 1063 ± 17 Ma and the initial ratio (R๐ = 0.7025) provides evidence for derivation from a mantle source. Plotting of the Ngoye geochemistry on tectonic-discrimination diagrams suggests intrusion into rifted continental crust. It is concluded that the gneissose Ngoye granites constitute a deformed central complex, similar to anorogenic complexes in Nigeria and the Sudan. The Bulls Run Complex is situated 30 km west of the Ngoye Complex. A concentric outcrop pattern has been mapped, according to which an envelope of silica-saturated biotite-muscovite syenite surrounds a core of nepheline-bearing syenites. Minor intrusive phases include biotite-rich dykes, sovite carbonatite sheets, silica-oversaturated microsyenite dykes and feldspathic ijolite. The outer envelope of muscovite-rich syenite is interpreted as fenitised pelitic country rock. An alkali-lamprophyre origin is suggested for the biotite-rich dykes. Geochemically the syenites are predominantly miaskitic, apart from the microsyenite dykes which are mildly peralkaline. Rb-Sr isotopic data for the nepheline syenites indicate an age of 1138 ± 45 Ma (Ro = 0.70322). Carbonate separates from the carbonatites provide a similar low initial ratio (Ra = 0.70319) which supports a comagmatic mantle origin. A comparison is drawn between the Bulls Run Complex and miaskitic nepheline syenite gneisses in the mid-Proterozoic Grenville Province of canada. From this, it is suggested that the Bulls Run Complex is pretectonic and was intruded into the rifted passive margin of a continent. The Wangu Granite Gneiss is situated 3 km southwest of the Bulls Run Complex. The granites are fine grained and contain aegirine-augite and/or magnetite, and classify as alkali-feldspar granite. Peralkaline chemistry is characteristic of the Wangu granites, with trace-elenent contents indicating a distinct A-type signature. Biotite-rich mafic dykes intrude the southern part of the Wangu outcrop and, on the basis of major- and trace-element signatures, are suggested to be metamorphosed volatile-rich alkaline lamprophyres similar to those at Bulls Run. Geochemical similarities between the Wangu granites and certain comendites from the Kenya Rift are noted. It is suggested that the Wangu granites were emplaced as high-level dykes, within rifted continental crust. It is proposed that the Ngoye, Bulls Run and Wangu intrusives be united as the Nkwaleni Suite. Comparison of the Tugela Terrane with the Grenville Province reveals many similarities, particularly their mid- to late-Proterozoic age and the occurrence of pre-tectonic anorogenic continental magmatism. It is concluded that, unlike the current model which would have the Tugela Terrane as obducted ophiolite, these new data indicate that the Tugela Terrane is a metamorphosed continental rift system.
Sedimentology, coral reef zonation, and late Pleistocene coastline models of the Sodwana Bay continental shelf, Northern Zululand
(1991) Ramsay, Peter John.; Mason, Tom R.
This geostrophic current-controlled Zululand/Natal shelf displays a unique assemblage of interesting physical, sedimentological and biological phenomena. The shelf in this area is extremely narrow compared to the global average of 75km, and is characterised by submarine canyons, coral reefs, and steep gradients on the continental slope. A shelf break occurs 2.1km to 4.1km offshore and the shelf can be divided into a northern region and a southern region based on the presence or absence of a defined shelf break. The southern shelf has a poorly-defined shelf break whilst the northern shelf has a well-defined break at -65m. The poor definition of the shelf break on the southern shelf can possibly be attributed to the presence of giant, climbing sand dunes offshore of Jesser Point at depths of -37m to -60m. The northern shelf has a series of coast-parallel oriented patch coral reefs which have colonised carbonate-cemented, coastal-facies sequences. The northern shelf can be divided into three distinct zones: inner-, mid-, and outer-shelf zones. The inner-shelf is defined as the area landward of the general coral reef trend, with depths varying from 0m to -I5m and having an average gradient of 1.1. The mid-shelf is defined by the general coral reef trend, varying from -9m over the shallow central axis of the reefs to -35m along the deep reef-front environments. The outer-shelf is seaward of the coral reefs and occurs at a depth range of -35m to - 65m. Gradients vary from 1° in the south to 2.5° in the northern part of the study area, and are steep compared to world average shelf gradient of 0.116°. Four submarine canyons occur in the study area and are classified as mature- or youthful-phase canyons depending on the degree to which they breach the shelf. The origin of these canyons is not related to the position of modern river mouths but can probably be linked to palaeo-outlets of the Pongola and Mkuze River systems. It is suggested that the canyons are mass-wasting features which were exploited by palaeo-drainage during regressions. The youthful-phase canyons appear to be mass-wasting features associated with an unstable, rapidly-deposited, progradational late Pliocene sequence and a steep upper continental slope. The mature-phase canyons were probably initiated by mass-wasting but have advanced shoreward, breaching the shelf, due to their link with the palaeo-outlets of the Pongola and Mkuze Rivers during late Pleistocene regressions. Evidence of modem canyon growth has been noted on numerous SCUBA diving surveys carried out on the canyon heads. These take the form of minor wall slumps and small-scale debris flows. The canyons are also supplied with large quantities of sand in the form of large-scale shelf subaqueous dunes generated and transported by the Agulhas Current. As these bedforms meet the canyons the sediment cascades down the canyon thalweg and causes erosion and downcutting of the canyon walls and floor thereby increasing the canyon dimensions. Late Pleistocene beachrock and aeolianite outcrops with or without an Indo-Pacific coral reef veneer are the dominant consolidated lithology on the shelf. These submerged, coast-parallel, carbonate cemented, coastal facies extend semi-continuously from -5m to -95m, and delineate late Pleistocene palaeocoastline events. The rock fabric of these high primary porosity lithologies shows grains floating in a carbonate cement with occasional point-contacts. Grains are mostly quartz (80-90%), minor K-feldspar and plagioclase (5-10%), and various lithic fragments. The rocks contain conspicuous organic grains including foraminifera, bivalve, echinoid, bryozoan, red algal, and occasional sponge spicule fragments; these commonly display replacement fabrics or iron-stained rims. The dominant sedimentary structures found in these sandstone outcrops include high-angle planar cross-bedding and primary depositional dip bedding. Palaeocurrent directions sngest a palaeoenvironment dominated by a combination of longitudinal and transverse dunes with wind directions similar to those observed forming the modem dune systems. Erosional features evident on the submerged beachrocks and aeolianites include gullies trending in two different directions and sea-level planation surfaces with or without the presence of potholes. The unconsolidated sediment on the shelf is either shelf sand, composed mainly of terrigenous quartz grains; or bioclastic sediment which is partially derived from biogenic sources. The quartzose sand from the inner-shelf is generally fine-grained, moderately- to well-sorted, and coarsely- to near symmetrically-skewed. Carbonate content is low, and varies between 4-13%. Quartzose sand from the outer-shelf is fine-grained, moderately- to well-sorted, and coarsely- to very coarsely-skewed. The inner-shelf quartzose sand is better sorted than the outer-shelf sand due to increased reworking of this sediment by the high-energy swell regime. Sediment from the shallower areas of the outer-shelf (< -50m) is better sorted than sediment from depths of greater than -50m. Generally wave-reworking of quartzose shelf sand from the Sodwana Bay shelf results in greater sediment maturity than that observed from geostrophic current effects or a combination of geostrophic and wave-reworking. This sediment was derived by reworking of aeolian and beach sediments, deposited on the shelf during the period leading up to the Last Glacial Maximum (15 000 - 18 000 years B.P.) when sea-level was -130m, during the Holocene (Flandrian) transgression. Bioclastic sediment on the Sodwana Bay shelf is defined as having a CaC03 content of greater than 20% and is a mixture of biogeoically-derived debris and quartzose sand. The distribution of bioclastic sediment in the study area is widespread, with reef-derived and outer-shelf-derived populations being evident. This sediment consists of skeletal detritus originating from the mechanical and biological destruction of carbonate-secreting organisms such as molluscs, foraminifera, alcyonaria, scleractinia, cirripedia, echinodermata, bryozoa, porifera. The reef-derived bioclastic population is confined to depths less than -40m in close proximity to reef areas, whereas the shelf-derived bioclastic population occurs at depths greater than -40m and is derived from carbonate-producing organisms on deep water reefs and soft-substrate environments on the shelf. Large-scale subaqueous dunes form in the unconsolidated sediment on the outer-shelf due to the Agulhas flow acting as a sediment conveyor. These dunes are a common feature on the Sodwana Bay shelf occurring as two distinct fields at depths of -35m to -70m, the major sediment transport direction being towards the south. The two dune fields, the inner- and outer subaqueous dune fields, are physically divided by Late Pleistocene beachrock and aeolianites ledges. A bedform hierarchy has been recognised. The larger, outer dune field appears to have originated as a system of climbing bedforms with three generations of bedforms being superimposed to form a giant bedform, while the inner dune field has a less complex construction. The largest bedforms are those of the outer dune field off Jesser Point, being up to 12 m high, 4 km long and 1.2 km wide. A major slip face, with a slope of 8° is present. Bedload parting zones exist where the bedform migration direction changes from south to north. Three bedload parting zones occur in the study area at depths of -60m, -47m and -45m; two in the inner dune field and one in the outer dune field. These zones are invariably located at the southern limits of large clockwise eddy systems. Such eddies appear to be the result of topographically induced vorticity changes in the geostrophic flow and/or the response to atmospheric forcing caused by coastal low-pressure system moving up the coastline. It has been demonstrated that the inner subaqueous dune sediment conveyor is not active all the time but only during periods . of increased current strength when the Agulhas Current meanders inshore. The smaller bedforms in the outer dune field undergo continuous transport due to the current velocity on the shelf edge outer dune field being higher than the velocity experienced on the inner dune field. The very large 2·D dune which forms the outer dune field is probably not active at present: this is inferred due to the shallow angle of the mega-crest lee slope (8°). The very large Sodwana Bay subaqueous dune fields may be compared with the very large, reconstructed, subaqueous dunes which occur in Lower Permian sediments of the Vryheid Formation, northern Natal. These Permian dunes are represented, in section, as a fine- to medium-grained distal facies sandstone with giant crossbeds. These large-scale bedforms are unidirectional, but rare directionally-reversed, climbing bedforms do occur, this directional reversal may be related to bedload parting zones. On the evidence presented in this thesis, it is proposed that these Permian subaqueous dunes may be ancient analogues of the modem subaqueous dune field on the Sodwana Bay shelf. Positive-relief hummocks and negative-relief swale structures are fairly common in the fine-grained, quartzose shelf sand at depths of -30m to -60m. These appear to be transitional bedforms related to the reworking by storms of medium 2-D subaqueous dunes. These hummocky structures may be the modem equivalent of hummocky cross-stratification noted in the geological record, and if so, they are probably the first to have ever been observed underwater. The occurrences of ladderback ripples on the Sodwana Bay shelf at depths of -4m to -17m, suggest that subtidal ladderback ripples may be more common than previously thought. Ladderback ripples are common features of tidal flats and beaches where they form by late-stage emergence run-off during the ebb tide. They are generally considered diagnostic of clastic intertidal environments. The mode of formation on the Sodwana Bay shelf is different from the classic late-stage emergence run-off model of intertidal occurrences, being a subtidal setting. Subaqueous observations indicate that ladderback ripples are not environment-specific, and that additional evidence of emergence is therefore necessary to support an intertidal setting in the rock record: ladderback ripples alone are insufficient to prove an intertidal environment. The coral patch reefs of the northern Natal coast are unique, being the most southerly reefs in Africa, and totally unspoilt. The Zululand reefs are formed by a thin veneer of Indo-Pacific type corals which have colonised submerged, late Pleistocene beachrocks and aeolianites. Two-Mile Reef at Sodwana Bay has been used to develop a physiograpbic and biological zoning model for Zululand coral reefs, which has been applied to other reefs in the region. Eight distinct zones can be recognised and differentiated on the basis of physiographic and biological characteristics. The reef fauna is dominated by an abundance of alcyonarian (soft) corals, which constitute 60-70% of the total coral fauna. The Two-Mile Reef zoning model has been successfully applied to larger reefs such as Red Sands Reef, and smaller patch reefs (Four-Mile and Seven-Mile Reefs) in the same general area. In this thesis extensive use has been made of Hutton's uniformitarian principles. Hutton's doctrine is particularly relevant to the study of depositional processes and relict shorelines. Coastal processes and weather patterns during the late Pleistocene were broadly similar to modem conditions enabling direct comparisons to be made. A computer-aided facies analysis model has been developed based on textural statistics and compositional features of carbonate-cemented coastal sandstones. Many attempts have been made to distinguish different ancient sedimentary depositional environments, most workers in this field having little success. The new method of facies reconstruction is based on: (1) underwater observations of sedimentary structures and general reef morphology; (2) a petrographic study of the reef-base enabling flve facies: aeolianite, backbeach, forebeach, swash, and welded bar facies to be recognised, which control the geomorphology of Two-Mile Reef; (3) cluster and discriminant analysis comparing graphic settling statistics of acid-leached reef-base samples with those of modem unconsolidated dune/beach environments. The results of this analysis demonstrated that the beachrocks and aeolianites on the shelf formed during a regression and that late Pleistocene coastal facies are similar to modem northern Zululand coastal environments, which have been differentiated into aeolian, backbeach, forebeach, swash, & welded bar. A late Pleistocene and Holocene history of the shelf shows that during the late Pleistocene, post Eemian regressions resulted in deposition and cementation of coast-parallel beachrocks and aeolianites, which define a series of four distinct palaeocoastline episodes with possible ages between 117 000 and 22 000 years B.P. The beachrock/aeolianites formed on the shelf during stillstands and slow regressions, and the gaps between these strandline episodes represent periods of accelerated sealevel regression or a minor transgressive phase which hindered deposition and cementation. The formation of these lithologies generated a considerable sediment sink in the nearshore zone. This reduced sediment supply and grain transport in the littoral zone during the Holocene, and probably enhanced landward movement of the shoreline during the Flandrian transgression. Prior to the Last Glacial Maximum, the beachrock/aeolianite sedimentary sequence was emergent and blanketed by shifting aeolian sands. The Pongola River, which flowed into Lake Sibaya, reworked the unconsolidated sediments on the shelf, and exploited the route of least resistance: along White Sands and Wright Canyon axes. The erosion resulting from fluvial denudation in Wright Canyon has caused this canyon to erode some of the beachrock/aeolianite outcrops which form palaeocoastline episode 2 and entrench the canyon to a deeper level; this eroded the shelf to a distance of 2km offshore. During the Flandrian transgression the unconsolidated sediment cover was eroded, exposing and submerging the beachrock/aeolianite sequence. Flandrian stillstands caused erosional features such as wave-planed terraces, potholes, and gullies to be incised into beachrock and aeolianite outcrops; these are seen at present depths of -47m, -32m, .26m, -22m, -17m to -15m, and -12m. High energy sediment transfers, in an onshore direction, resulted in the deposition of sand bars across the outlet of Lake Slbaya's estuary and the development of a 130m + coastal dune barrier on a pre-existlng, remnant Plelstocene dune stub. Sea-level stabilised at its present level 7 000-6 000 years B.P. and coral reef growth on the beachrock/aeolianite outcrops probably started at 5 000 years B.P. A minimum age for the formation of the northern Zululand coral reefs has been established at 3780 ± 60 years B.P. A mid Holocene transgression relating to the Climatic Optimum deposited a + 2m raised beach rock sequence. This transgression eroded the coastal dune barrier and caused a landward shoreline translation of approximately 40m. A minor transgression such as this can be used as a model for coastal erosion which will result from the predicted 1.5m rise in sea-level over the next century. This rise in sea-level could result in a 30m landward coastline translation of the present coastline, ignoring the influence that storms and cyclones will have on the coastline configuration.
Sedimentary models and geomorphological classification of river-mouths on a subtropical, wave-dominated coast, Natal, South Africa.
(1991) Cooper, James Andrew Graham.; Mason, Tom R.
Abstract available in PDF.
The petrology and geochemistry of the karoo sequence basaltic rocks in the Natal Drakensberg at Sani Pass.
(1992) Ramluckan, Vijay Rajlal.; Dunlevey, John N.; Mitchell, A. A.
The Sani Pass in the Natal Drakensberg is situated in the north-eastern sector of the Lesotho Highlands which forms a major Karoo-age basaltic massif in the Karoo Igneous Province. The volcanic section exposed in the pass is approximately 800m thick, and comprises a succession of regularly stratified, massive and amygdaloidallavas which were extruded mainly by fissure-type eruptions. Dolerite dykes, which now occupy thefissures,form a network ofpredominantly NE-SW and NW-SE trending topographic features. During post-eruption cooling hydrothermal solutions percolated through the volcanic succession and produced an amygdale zonation which was controlled predominantly by ambientpressure and temperature conditions. An original maximum thickness of 1 820m of the volcanic succession has therefore been estimated and an average fossil geothermal gradient of 111° C/km is conceived to have persisted during amygdale formation. New electron microprobe data are presented for the silicate phases in the Sani Pass basalts and dolerites. These data do not effectively separate the Sani Pass volcanic succession into different geochemical units. Microprobe analysesfor olivine, albeit limited, are in the forsterite range and indicate that a proportion of olivine in the high-MgO basalts is due to cumulus enrichment. The pyroxenes are predominantly augite and minor pigeonite, with some ofthe augites displaying a tholeiitic trend similar to that recognised at Skaergaard. Plagioclase is mainly in the labradorite to bytownite range, the phenocrysts being slightly enriched in anorthite compared to the groundmass. The use ofwhole-rock geochemistry for 67 basalts and 8 dolerites has permitted the recognition of five geochemically distinct magma types, namely, the Giant's Cup, Agate Vale, Sakeng, Mkhomazana and the Phinong. The Phinong basalts comprise the upper two-thirds ofthe volcanic succession and although are generally homogeneous, there is a slight tendency for the more evolved rocks to be found higher up in the stratigraphic sequence. The remaining magma types precede the Phinong succession and are generally enriched in silica and have higher Zr/Nb and lower PfZr ratios than the Phinong basalts. Within the pre-Phinong succession the Giant's Cup basalts are generally depleted in the compatible elements, while the overlying Agate Vale basalts are enriched in incompatible elements. Except for a marginally lower Na20 and Sr content, the chemistry ofthe Sakeng basalts is variable, generally overlapping with the other magma types. The Mkhomazana basalts are slightly enriched in MgO, Ni, Cr and Sc compared to all other pre-Phinong basalts. The dolerites in the area adjacent to the Sani Pass are geochemically similar to the Phinong basalts. The Phinong magma type is considered to be equivalent to the Lesotho magma type, based on their geochemical and stratigraphical similarities. In terms ofdiscriminant diagrams the Giant's Cup, Sakeng and Mkhomazana basalts generally show some compositional overlap with the Phinong, or plot in incoherentfields, but the Agate Vale basalts are distinctly different and might indicate a new magma type within the Karoo Central area. Broad compositional overlap between the Phinong basalts and those preserved at Kirwan and Heimefrontfjella, Antarctica, indicates juxtaposition of Antarctica along the southern African east coast in a reconstructed Gondwanaland. Petrogenesis of the Sani Pass basalts has been examined in terms of alteration, open and closed system fractional crystallization, partial melting procesess and a heterogeneous source. Although limited alteration and conduit contamination have occurred, the most feasible mechanism responsible for the geochemical variation lies in the existance ofinhomogeneities in the upper mantle at the time ofgeneration of the Sani Pass magmas.
Geological evolution of western H.U. Sverdrupfjella, Dronning Maud land, Antarctica.
(1992) Grantham, Geoffrey Hugo.; Hunter, Donald Raymond.
The oldest rocks of western H.U. Sverdrupfjella, the Jutulrora Formation, consist of interlayered mafic to felsic ortho- and paragneisses thought to represent calc-alkaline volcanic and clastic sedimentary rocks. These rocks are structurally overlain by the largely paragneissic, carbonate- dominated Fuglefjellet Formation which may represent a miogeosynclinal shelf facies. This sequence is structurally overlain by the dominantly para-gneissic Sveabreen Formation which may comprise a eugeosynclinal facies. Three granitic bodies, the Roerkulten, Jutulrora and Brekkerista Granites intrude the Jutulrora Formation. The trace element chemistry of these granites suggest that accessory minerals played significant roles during their generation and crystallization. Various mafic intrusions, now discordant amphibolites, and a phase of diorite veining are present. The Dalmatian Granite was emplaced syntectonically with the 470Ma Pan-African (or Ross) orogeny during D3. This granite was generated by crustal anatexis at >5kb. Jurassic age intrusions include alkaline complexes at Straumsvola and Tvora and numerous dolerite dykes, some of which postdate the alkali intrusions. Five episodes of deformation are recognised. The first two resulted in folds (F1 and F2) which are co-planar and coaxial resulting in type 3 interference structures. Low angle thrust faulting occurred during D2. Fold vergence and associated lineations suggest tectonic transport from the southeast during D1 and D2, D3 involved folding and reverse faulting. The orientations of the fault and axial planes of these structures suggest transport from the west and north-west. D4 involved open dome and basin folding. D6 involved normal faulting and jointing, adjacent and parallel to the Jutulstraumen Glacier in the west. The joints affect the Tvora Alkaline Complex. Three phases of metamorphism, related to the deformation, are recognised. The dominant mineral assemblages are typical of medium to high grade metamorphism and define S1 and S2 planar fabrics. Discordant mafic intrusions provide evidence of a long history of metamorphism. M3 mineral development, commonly represented by biotite, is oriented axial planar to D3 folds. Comparison of the geology of the area with that of southern Mozambique reveals many similarities. These support reconstructions based on geophysical data which juxtapose Dronning Maud Land and southern Africa prior to the break up of Gondwanaland.
Richards Bay zircon.
(1992) Pietersen, Kevin John.; Cornell, David H.
Zircon from the zircon concentrate of Richards Bay Minerals was investigated with a view to understanding the morphology and provenance. The obsevations were applied to the reduction of uranium, thorium and other trace elements in the heavy mineral placer deposits. It is evident from differences in morphology, optical characteristics, cathodoluminescence, inclusion types and trace element analyses that the zircon is derived from numerous parent rocks. Rare earth element modelling reveals several possible parent rocks including rhyolites, granites, syenites, pegmatites and carbonatites. Fission track U mapping of individual zircons indicated an enrichment of U in the rims and grain terminations. The U maps were used to devise and test several methods, including abrasion and partial dissolution, to reduce the combined U and Th concentration from 450-563ppm to below 400ppm. The effect of magnetic cleaning, density separation and size classification of the zircon concentrate on the U +Th concentration was found to be negligible. Air abrasion and HF acid dissolution successfully reduced the U +Th concentrations to between 332 and 383ppm. The contribution of trace elements from inclusions, surface pit fillings and coatings, and foreign minerals within the zircon concentrate were evaluated by by scanning electron microscope identification.
Zinc-lead mineralization at Pering Mine in the Griqualand West sub-basin : an isotopic study.
(1992) Turner, Audrey Michelle.; Duane, M. J.; Kruger, Frans J.
Detailed studies, both chemical and physical, have been performed on various dolomites and vug-filling carbonates, to determine the pathways and extent of the mineralizing fluids associated with the Pering Zn-Pb deposit within the Griqualand West sub-basin. Three carbonate phases were identified within the vugs using cathodoluminescence microscopy. The first phase formed a reaction rim on the host dolomites during the deposition of sphalerite and oscillatory zoned carbonate. Finally calcite was deposited, which is associated with post-mineralizing fluids. The vug-filling carbonates have very radiogenic 87Sr/86Sr values (0.72-0.76) compared with the host dolomites (0.70-0.73). The gangue carbonate minerals deposited within the vugs have similar radiogenic 87Sr/86Sr values to the gangue minerals of the main Pering orebody, indicating that the vugs formed part of the aquifer system through which the mineralizing fluids migrated. Radiogenic 87Sr was not acquired from the surrounding host dolomite. The mineralizing fluids may have picked up radiogenic 87Sr when migrating through porous rocks such as the Makwassie Quartz Porphyry of the Ventersdorp Supergroup or felsic rocks forming the Kaapvaal Craton. In addition, radiogenic Sr may have been acquired from dewatering of the Lokammona shales within the area, or expelled from amphibolite and granulite rocks involved in the Kheis or Namaqua Tectonic events. Two models are proposed to explain the genesis of the main Pering deposit and the occurrence of sphalerite in the vug-filling carbonates surrounding the deposit: 1) Mixing Model; and 2) Single Fluid Model. The Single Fluid Model is preferred which involves a single fluid migration and interaction with the carbonate host rock and/or pore fluid. The metals were probably transported as chloride complexes together with reduced sulphur at temperatures greater than 2000 C. Deposition of the ore minerals resulted from either a dilution of the fluid, a pH increase or a temperature decrease. Both dolomites and vug-filling carbonates have a model Pb age between 2.0 and 2.7. Secondary 1Ga model ages indicate a minor Namaqua tectonic influence. Carbon and oxygen isotopes indicate that the fluids originated in a deep burial environment. Future exploration work using cathodoluminescence microscopy and staining techniques will be both useful and cost-effective. Isotopic work should concentrate on the Rb-Sr system as radiogenic 87Sr/86Sr values are the best indicators of the path of the mineralizing fluid, and the proximity to ore concentrations.
A study of titanium-bearing oxides in heavy mineral deposits along the East Coast of South Africa.
(1993) Hugo, Victor Emmanuel.; Cornell, David H.
Heavy mineral deposits along the east coast of South Africa represent the world's largest demonstrated resource of beach placer ilmenite. This mineral occurs as homogeneous, subrounded grains, with chemical compositions close to pure FeTi03• Concentrates contain between 48 and 52 per cent Ti02, with minor impurities of MnO, MgO, and Cr203. Most coastal ilmenites are unaltered or display only incipient alteration, but the entire spectrum of alteration products from ilmenite to rutile or anatase, is observed. Transmission electron microscopy of weathered ilmenites reveals that ilmenite commonly alters to pseudorutile and then to rutile or anatase, as described by Teufer and Temple (1966) and Grey and Reid (1975). Ilmenite may also alter directly to rutile (or anatase) in a single-stage process. In addition, ilmenite altered by high temperature oxidation and hydrothermal processes is found in the deposits. There is good mineralogical evidence that the alteration of ilmenites found in the coastal sediments is best described by a multi stage model, in which some ilmenite grains were altered prior to final deposition. Other common iron-titanium oxides in the deposits include magnetite, rutile and hematite, which may occur as discrete grains or as composite grains of two or more oxides. Ilmenite and magnetite in the coastal sediments are derived from rocks of both the Karoo Igneous Province and the Natal Basement, while rutile is derived solely from the latter. Ilmenites from certain rock groups may be distinguished on the basis of their chemical composition. However, magnetite chemistry is a better indicator of provenance, and magnetites from the above two sources can be clearly distinguished. The petrography of the iron-titanium oxides may be used as a provenance indicator, but may be misleading, as the proportions of the oxide intergrowths change with transport and weathering. Variations in the proportions and chemical compositions of iron-titanium oxides and other heavy minerals within the coastal sediments are caused by provenance, selective sorting during deposition, age of the deposit, weathering, and the recent geological history of the area. A model is proposed in this study which describes the formation of the heavy mineral deposits in relationship to the above influences.
The geological evolution of a part of the Pongola basin, southeastern Kaapvaal Craton.
(1993) Gold, Digby James Comrie.; Strydom, Dawie.; Von Veh, Mark.; Hunter, Donald Raymond.
A stratigraphic and structural study of the Archaean Pongola Sequence on the southeastern Kaapvaal Craton centred on the area around the Klipwal Gold Mine is described. The lower predominantly volcanic Nsuze Group is overlain with a gradational transition by the upper clastic Mozaan Group in which six formations are recognized. The Sinqeni, Ntombe, Thalu, Hlashana, Odwaleni and the Kulphiso Formations. The Sinqeni and Hlashana Formations are predominantly arenaceous while the Ntombe and Kulphiso Formations are mainly argillaceous. The Odwaleni Formation contains a diamictite which is interpreted as a tillite, and is therefore the oldest glacial rock on record. The stratigraphic position of the Kulphiso Formation is problematic. The Mozaan Group was deposited in a deepening epeiric sea which was invaded periodically by storm generated deposits. Dolerite and ultramafic dykes and sills of various ages are represented. Three phases of deformation are recognized in the Klipwal area. Early compression from the south-southeast initiated a major zone of bedding-parallel shear, the Izermijn shear zone, along the Nsuze-Mozaan contact and an oblique ramp, the Klipwal shear zone, at a higher stratigraphic level. An extensional phase caused reactivation of the Klipwal shear zone and the development of a major low-angle normal fault, the Gu'nsteling fault, above the Sinqeni Formation. The main phase of deformation, related to northeast-southwest compression is the most complex and most widely developed. Early northwest-trending subhorizontal upright folds were disrupted by contemporaneous north-striking dextral or dextral reverse shearing and northwest-striking sinistral or sinistral normal shearing. The obtuse relationship of these shear zones to the compression direction is probably the result of reactivation of basement structures with similar orientations. Northwest-trending folding continued during and after the shearing. The structural styles and orientations observed in the Klipwal area are recognized regionally in the main Pongola basin, highlighting the need for further detailed studies before basin-wide correlations are made.

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