Ph.D. (Geology) / The Paleoproterozoic (i.e. 2500 Ma to 1600 Ma) apparent polar wander path (APWP) for the Kaapvaal craton (KC) is not well constrained, due to the lack of reliable paleopoles and absence of numerical ages for existing poles. In addition, the duration of emplacement, and timing of remanence acquisition of the Rustenburg Layered Suite (RLS) and other units of the Bushveld Large Igneous Province (LIP) are still unclear. During the present paleomagnetic study, samples were collected from the small intrusions that occur around the RLS and that are believed to be related to the Bushveld LIP for the establishment of new paleomagnetic and virtual geomagnetic poles. In addition, samples from post-Transvaal sills and dykes were targeted for U-Pb dating and geochemical analyses. Geochronological and geochemical data helped to constrain the timing of the newly defined paleopoles. These paleopoles were used in conjunction with previously published ones from KC to evaluate the APWP for this craton during the Paleoproterozoic. Two of the studied post-Transvaal sills in the eastern KC revealed U-Pb ages that are identical to the age recently reported from the Marginal Zone of the RLS. Geochemical signatures of sill samples were in very good agreement with the newly obtained ages. New ages and geochemical data provided constraints on the magnetic components recorded by the sills. The results confirm the existence of B1 Bushveld magma-related sills on KC as well as pre and post-Bushveld sills as previously suggested. Particularly, dataset from the B1 Bushveld magma-related sills allowed for understanding the magnetic history of the RLS at the early stages (Marginal Zone) of its formation. Paleomagnetic sampling of the Uitkomst Complex provided constraints on the remanence acquisition of this complex and also helped to understand the timing of the Bushveld magmatism outside of the main complex. Paleomagnetic data from a post-Transvaal dolerite dyke swarm near Lydenburg revealed a complex magnetic history. Characteristic magnetic components constrained by geochemical analyses were not similar to the RLS, but indicate probable relationship to other units of the Bushveld LIP. The new ages generated in this study coupled to those previously obtained from the upper layers of the RLS suggested that this suite emplaced within a time period of at least 4 million years. Paleomagnetic results from the B1 Bushveld magma-related sills and available data from the upper layers of the RLS reveal that during the RLS emplacement, the Earth’s magnetic field reversed at least eight times. These results, together with data from the Lydenburg dykes, further indicate a minimum of nine changes in polarity of the Earth’s magnetic field during the formation of the Bushveld LIP. During the present study, new pole positions of different reliability were added to the existing paleomagnetic database for the KC. Paleopoles from the Paleoproterozoic database of the KC (including those generated in the present study) were used to propose a new APWP for this craton from ~2200 Ma to ~1800 Ma. Particularly, poles from the B1 Bushveld magma-related sills and Uitkomst Complex provide the information to identify striking features in the APWP of the Paleoproterozoic KC.

Thesis (M. Sc. (Geology)) -- University of Limpopo, 2021 / The Glentig, Alma and Swaershoek Formations were deposited after the emplacement of the Bushveld igneous complex (BIC). The sediments accumulated in what is termed as the proto-basin of the Waterberg Group. The Glentig Formation is an unconformity-bounded formation that is overlain by the Swaershoek and Alma Formations of the Waterberg Group. This study revisited the stratigraphy and put perception on the petrography, lithofacies, provenance, paleoweathering, tectonic setting and source rock characteristics of the lower parts of Waterberg Group (Swaershoek and Alma Formations) and Glentig Formation. The methodologies employed in achieving the aforementioned goals include stratigraphical analysis, petrographical and modal composition analyses, lithofacies analysis and geochemical analysis. In the study area (northeast of Modimolle town), the Glentig Formation lies or bounded between the Swaershoek Formation and Schrikkloof Formation of the Rooiberg Group. The Glentig, Swaershoek and Alma Formations attained a maximum thickness of about 400 m, 300 m and 190 m, respectively. Based on the stratigraphical analysis, the Swaershoek, Alma and Glentig Formations can be correlated. The basis for the correlation rests solemnly on the similarities in the lithological characteristics that can be found in the three formations. Six facies were identified based on lithofacies analysis. The lithofacies are grouped into 2 facies association (FA1 and FA2). The two facies associations are FA1: Conglomerate and massive sandstone, and FA2: Cross-bedded sandstone, and planar cross-bedded sandstone. Sedimentological characteristics of the identified facies associations are interpreted as debris flow, and longitudinal and transverse bars (fluvial channel deposits). Petrography and modal composition analyses indicate that the detrital components of the sandstones are dominated by monocrystalline quartz, feldspar and lithic fragments. The sandstones of the Swaershoek, Alma and Glentig Formations can be classified as subarkosic arenite and lithic arkosic arenite. Also, provenance analysis indicates that the sandstones are derived from both felsic igneous provenance and intermediate igneous provenance. The modal composition analysis and geochemical tectonic setting discrimination diagrams show that the sediments are from both the passive and active continental margin tectonic settings. Also, the geochemical data of major and trace elements suggested that the studied formations have been derived from the same provenance source area. The indices of weathering indicated that the studied rocks have been subjected to moderate to the high degree of chemical weathering. Keywords: Geology, geochemistry, Glentig, Swaershoek, Alma, Waterberg Group, South Africa / Mining Qualification Authority (MQA)

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.

Nodules within the lower Bokkeveld shales often contain well-preserved invertebrate fossil material. The aim of this study was to describe some characteristics seen at various scales (macro-, micro- and ultra -) within nodules that might contribute to an understanding of aspects of nodule formation and the reasons for the excellent preservation of the fossil material within these nodules. Detailed, high quality macro-photographs were taken of sliced and whole nodule surfaces and a catalogue was produced to tentatively identify fossils present and illustrate the variations seen within nodules. Selected nodules were then subjected to petrographic, ultra-structural (SEM) and some chemical (EDS, XRD & XRF) analysis to investigate the possible reasons for these variations. The chemical results have indicated that nodules are enriched with quartz compared to the surrounding shale. Quartz is also the dominant mineral replacing trilobite carapace material within nodules, while trilobite material within shales is replaced with equal proportions of hematite, biotite and quartz. It appears that the higher resistance of quartz to weathering is the dominant factor leading to the preservation of both nodules within the shales and trilobite material within the nodules examined. A comparison with some Western Cape nodules highlighted possible variations in overall nodule chemical composition along strike. Western Cape nodules are predominantly composed of apatite whereas the Cockscomb nodules are mainly composed of quartz. This quartz-apatite compositional variation in nodules occurring within a single formation has been reported from nodules found in the Armorican Massif of France which are very similar in a number of respects to the Bokkeveld nodules described in this study. Based on various features of the fossils present and the structure of nodules they were probably formed during early diagenesis within an epeiric marine deposit greatly affected by sea level fluctuations.

The research examines the sedimentary environments and provenance of the Balfour Formation of the Beaufort Group (Karoo Supergroup) in the Eastern Cape Province, South Africa. This Formation occurs in the southeastern part of the Karoo Basin. It consists of sedimentary rocks, which are an alternating siltstone, shale and mudstone succession with subordinate interbedded sandstone and subsequently intruded by Karoo dolerite in the form of sills and dykes. ithostratigraphically, the Balfour Formation is subdivided into five units namely, from the base to the top, the Oudeberg, Daggaboersnek, Barberskrans, Elandsberg and Palingkloof Members. The Balfour Formation is overlain by the Katberg Formation. This study involved field investigations in the vicinity of the towns of Bedford and Adelaide with integrated stratigraphical, sedimentological and petrological studies. A geological map was constructed after field investigations. Lithofacies of the Balfour Formation that were studied are characterised by sandstone facies (Sh, Sm, St, Sr, Sp) and fine-grained sediments (Fl or Fsm) which reflect point-bar, cut-bank, channel and floodplain deposits. Lithologically, the Oudeberg Member consists of sandstone of which some units are internally massive alternating with thin laminated siltstone and mudstone. The Daggaboersnek Member is characterised by regular, generally non-lenticular, overall stratification, in the Barberkrans Member consists of sandstone lithosomes, while the Elandsberg Member is an argillaceous unit, similar to the Daggaboersnek Member. The Palingkloof Member is composed predominantly of red mudstone that can be used to distinguish the Balfour Formation from the overlying Katberg Formation, which consists predominantly of sandstone. The stratigraphic sequence displays two fining upward megacycles of sedimentary deposits with change in the sediment supply pattern from low-sinuosity to high-sinuosity river systems which reflect both braid and meandering deposits, respectively. Sedimentary structures in the sandstone units and the provenance of the Balfour Formation indicate that these deposits were produced by rivers flowing from the southeast with minor drift towards the northwest. According to the composition of the sediments and their sequence of deposition the Formation represents a fluvial environment. Mineralogical and grain size data from the sandstones of the various members of the Balfour Formation indicate the same source area of granitic, metamorphic and older sedimentary rocks and show no significant petrographic differences. The petrographic and geochemical investigations confirmed the sandstone to be feldspathic litharenite and ultralithofeldspathic sandstone. The palaeocurrent investigation indicates the main provenance to have been situated to the southeast of the Karoo basin. Heavy-mineral concentrations within the sandstones also give an indication that the source had a transitional arc plate tectonic setting.

Thesis (DSc (Geology))--Stellenbosch University, 1948. / 375 leaves printed on single pages, preliminary pages and numbered pages1-312. Includes bibliography, figures and photos. / Digitized at 330 dpi color PDF format (OCR), using KODAK i 1220 PLUS scanner.

Thesis (PhD) -- Stellenbosch Univesrsity, 1972. / The Darling batholith is characterised by large scale hybridisation, but mainly consists of the coarsely porphyritic Darling granite. This granite changes gradationally into a biotite-rich variety which occupies a roughly elliptical area with a major, northwesterly trending axis of 30 km. The biotite granite envelops a large irregular body of hybrid granodiorite. Small intrusions of younger granite occur within the batholith namely the Klipberg and Contreberg granites and possibly the biotite-rich Dassenberg granite. Dassen Island is underlain by fine-grained granite which could be related to either the younger or coarsely porphyritic granites. A prominent northwesterly trending mylonite zone can be traced through Darling to Swartberg, and ultimately to Trekoskraal in the Saldanha batholith, but is not continuous since it occasionally changes into gneissic granite and is also interrupted by the younger intrusives. Quantitative mapping included measurement of matrix grain size, average maximum phenocryst length, xenolith distribution density, quartz nodule distribution density and average size, lineation, dark mineral index and gneissosity. On Dassen Island the distribution of tourmaline nodules was , determined. The results are displayed as small scale contour maps which show strong correlation between the various parameters. The average values of matrix grain size, average phenocryst length and xenolith distribution density are respectively 2-5mm, 20-60mm and 0-1,5 per m² for the Darling granite, and 1-2 mm, 5-20 mm and 1-9 per m² for the hybrid granodiorite. It was found that the matrix grain size decreases with increase in hybridisation. The spotty distribution pattern of tourmaline nodules on Dassen Island indicates addition of boron by assimilation of metamorphites and a late stage liquid immiscibility process. The granites :.have normal mineralogy and the K-feldspar of the phenocrysts is maximum microcline (Δ = 0,9 - 1,0). The hybrid granodiorite contains much pinitised cordierite and locally garnet. The deeply pleochroic bioti te is probably of the 2M1 polytype and has a higher Fe:Mg ratio in the hybrid granodiorite than in the granite (2,8 - 3,0 vs. 2,2 - 2,3). The intimately associated chlorite seems to be of the Ia polytype. The cordierite is of the normal and low temperature type with average intensity index of 2,7 , distortion index of 0,3 and 2 a of 63°. The xenoliths are predominantly quartzitic metagraywackes, but lime-rich types holding sphene and diopside were occasionally encountered. Thirteen new chemical analyses and thirty-one previously published analyses are used to calculate average composite analyses of the various rock types. The results of calculations employing Barth standard cell values indicate that the hybrid granodiorite could have originated by reaction between granite magma and Malmesbury quartzitic metagraywacke and pe-lite with a little limestone. A "granite differentiation index" based on weight percentages of (Ti02 + MgO + FeO + Fe2O3) and (Si02 + Na2O + K2O) shows a linear relationship between the granites in probable order of age. The magmatic differentiation trend is separated from the hybridisation trend on a 6alk - 2(al - alk) - (100 - 2al) diagram. Mesonorms and their cordierite variants are used to effect comparison with the experimental granitic system of von Platen (1965). The Darling and Contreberg granites plot near the relevant cotectic surfaces. A pilot experimental study of melting behaviour indicates that the Contreberg granite is closer to a minimum melt composition than the Darling granite. Comparison of alkali values with a M Na2O - M K2O Schreinemakers diagram of Korzhinskii (1959), shows that the alkali ratio of the older analyses may be incorrect, and indicates that the dark minerals have a greater effect on plagioclase composition than the amount of K-feldspar. The classification of granites by means of Harpum diagrams is shown to have little relevance to the reconstruction of the ancient thermodynamical variants. The Darling granite is correlated with the Hoedjies Point granite of the Saldanha batholith and on geochronological evidence probably corresponds in age (500- 600 m.y.) with the Cape Peninsula granite. The younger granites of Darling are tentatively correlated with the Cape Columbine granite of the Saldanha batholith. The northeastern boundary of the Darling batholith is a major fault, the Colenso fault, which is considered to extend as far as Northwest Bay, Saldanha. It is proposed that the Darling batholith occupies a down-faulted block within a graben and that the hybrid granodiorite represents a remnant synform of the roof rocks intruded by the granite. The younger granites constitute only four percent by volume of the batholith and may represent anatectic melts from a nearby subjacent source.

Thesis (DSc.)--Stellenbosch University, 1952. / ENGLISH ABSTRACT: The ideal geological column of the Kimberley-Elsburg Series in the East Rand Basin is described, with particular reference to the IQrnberley group of sediments. A system of nomenclature has been devised, and it is suggested that it could'also be used in other parts of the large structural basin, stretching from Johannesburg'in the north to near Theunissen in the south,. and from .Klerksdorp in the west to Greylingstad in the east. The stratigraphy of individual areas in the East Rand Basin is described in detail, and it is shown that certain stratigraphic.units display a remarkable regularity, maintaining their lithologica~ characteristics bver large areas, persisting also into the Greylingstad- Balfour district, the Central Rand, the West and Far West Rand, the Klerksdorp area, and into the Orange Free State goid field. In the East Rand Basin the May Reef is the principal gold carrier, and is of economic importance in certain mines. In the Orange Free State gold field the lowermost Kimberley reef is also of economic importance. Three regional unconformities have been recognised in the part of the column extending from below the Kimberley Shales to above the May Reef. The May Reef covers the upper one', and owes its existence to this period of erosion. The history of this reef could be traced back to its parent rock~ in this case, stratigraphically older auriferous gravels. The author believes that the unconformity below the May Reef developed as a result of sub-aqueous erosion. The. oldest erosion surface probably developed in the same way. The middle one developed largely on the land, but was subsequently submerged. It is concluded that the sediments of the Kimberley-Elsburg Series were deposited in the marine neritic environment, i.e. in a sea of substantial but not excessive depth. A few remarks have been added on the metamorphism of the System. An interesting feature in this connection is the occurrence of ubiquitous authigenic rutile in the form of minute needles and knee-shaped twins. It appears that the rutile developed as a stress mineral, ilmenite having been the original detrital constituent. / AFRIKAANSE OPSOMMING: geen opsomming

D.Phil. / This study which describes rocks of the Upper Critical Zone of the Bushveld Complex is subdivided into three parts. The main rock type of the Upper Critical Zone, the noriteanorthosite, is the subject of the first part. Inclusions in chromite and plagioclase were studied. The inclusions' in chromite were observed at different stages of their formation. The chromite crystals usually overgrow plagioclase, pyroxene and hydrous minerals (biotite, amphibole and clinozoisite) trapping them at grain boundaries or triple junctions of chromite host grains. With 'continuous growth of the host minerals the inclusion starts changing its shape from elongated to circular and the hydrous mineral proportion of the inclusion increases. Simultaneously amphibole changes its composition from pargasitic to tremolitic...

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg, August 2015 School of Geosciences, University of the Witwatersrand / The possibility of extensive shale gas resources in the main Karoo Basin has resulted in a renewed focus on the basin, and particularly the Whitehill Formation. The main Karoo Basin has been the subject of geological studies since before the 1920s, but geophysical data provides an opportunity to shed new light on the basin architecture and formation. In this thesis, I use regional gravity, magnetic and borehole data over the basin, as well as vintage seismic data in the southern part of the basin. Modern computational capacity allows for more information to be extracted from these seismic data, and for these data to be better integrated with potential field data. The integration of datasets in a three-dimensional model (3D) has allowed for a better understanding of the shape of the basin and its internal structure, in turn shedding light on basin formation. A new depth map of the basin constructed using this extensive database confirms that the basin deepens from on- to off-craton. The basin is deepest along the northern boundary of the Cape Fold Belt (CFB), with a depth of ~4000 m in the southwestern Karoo and ~5000 m in the southeastern part of the basin. Sediment thickness ranges from ~5500 to 6000 m. The Whitehill Formation along this boundary reaches a depth of ~ 3000 m in the southwest and ~4000 m in the southeast. Despite limited boreholes in this region, the basin appears to broadly deepen to the southeast. These seismic and borehole data also allow for mapping of the Cape Supergroup pinch-out below the Karoo basin (32.6°S for the Bokkeveld and 32.4°S for the Table Mountain Group), with the basin reaching a thickness of around 4 km just north of the CFB. The gravity effect of these sediments in the south is not sufficient to account for the low of the Cape Isostatic Anomaly near Willowmore and Steytlerville. This ~45 mGal Bouguer gravity low dominates the central region of the southern Karoo at the northern border of the CFB. The seismic data for the first time show uplift of lower-density shales of the Ecca Group (1800 – 2650 kg/m3) in this region, and structural and seismic data suggest that these lower density sediments continue to depth of 11 to 12 km along normal and thrust faults in this region. Two-dimensional density models show that these shallow crustal features, as well as deeper lower crust compared to surrounding regions, account for the anomaly. These seismic and borehole data also allow for constraints to be placed on the distribution and geometry of the dolerite intrusions that intruded the basin after its formation, and in some cases impacted on the shale layer, to be constrained. The highest concentrations of dolerites are found in the northwest and east of the basin, pointing towards two magma sources. The region of lowest concentration is in the south-central part of the basin. Here the intrusions are confined to the Beaufort Group, ~1000 m shallower than the shale reservoir, suggesting it should be the focus of exploration efforts. These dolerite sills are shown to be between 5 and 30 km wide and are saucer-shaped with ~ 800 m vertical extent, and dips of between 2° and 8° on the edges. The sheets in the south of the basin extend for over 150 km, dipping at between 3° and 13°, and are imaged down to ~ 5 km. This change in dip of the sheets is linked to deformation within the Cape Fold Belt, with greater dips closer to the belt, although these sheets do not appear to intrude strata dipping at more than 15 to 20°. In order to understand the shape of the Karoo basin and construct a 3D model of the basin, an understanding is needed of the underlying basement rocks. The Beattie Magnetic Anomaly (BMA) that stretches across the entire southern part of the basin forms part of the basement Namaqua-Natal Belt. Filtered magnetic data confirm that the Namaqua and Natal Belts are two separate regions with different magnetic characteristics, which is taken into account during modelling. The BMA is shown to be part of a group of linear magnetic anomalies making up the Natal Belt. The anomaly itself will therefore not have an individual effect on basin formation, and the effect of the Natal Belt as a whole will have to be investigated. An in-depth study of outcrops associated with one of these linear magnetic anomalies on the east coast of South Africa suggest the BMA can be attributed to regions of highly magnetic (10 to 100 x 10-3 SI) supracrustal rocks in Proterozoic shear zones. Along two-dimensional magnetic models in the southwestern Karoo constrained by seismic data, these magnetic zones are modelled as dipping slabs with horizontal extents of ~20-60 km and vertical extents of ~10-15 km. Body densities range from 2800- 2940 kg/m3 and magnetic susceptibilities from 10 to 100 x 10-3 SI. These, as well as other geophysical and geological constraints, are used to construct a 3D model of the basin down to 300 km. Relatively well-constrained crustal structure allows for inversion modelling of lithospheric mantle densities using GOCE satellite gravity data, with results in-line with xenolith data. These results confirm the existence of lower density mantle below the craton (~3270 kg/m3) that could contribute to the buoyancy of the craton, and an almost 50 kg/m3 density increase in the lithospheric mantle below the surrounding Proterozoic belts. It is this change in lithospheric density along with changes in Moho depths that isostatically compensate a large portion of South Africa’s high topography (<1200 m). The topography higher than 1200 m along the edge of the plateau, along the Great Escarpment, are shown to be accommodated by an asthenospheric buoyancy anomaly with a density contrast of around 40 kg/m3, while still mimicking the Bouguer gravity field. These findings are in line with recent tomographic studies below Africa suggesting an “African Superplume” or “Large Low Velocity Seismic Province” in the deep mantle. The basin sediment thickness maps were further used to investigate the formation of the main Karoo Basin. This was accomplished by studying the past flexure of the Whitehill Formation using north-south two-dimensional (2D) profiles. Deepening of the formation from ~3000 m in the southwest to ~4000 m in the southeast is explained using the concept of isostasy, i.e., an infinite elastic beam that is subjected to an increasing load size across the Cape Fold Belt. Load height values increase from 4 km in the southwest to 8 km in the southeast. This larger load is attributed here to “locking” along a subduction zone further to the south. The effective elastic thickness (Te) of the beam also increases from around 50 km over the Namaqua and Natal Belts in the southwest to 80 km over the Kaapvaal Craton and Natal Belt in the southeast. The changes in Te values do not correlate with changes in terrane, i.e., a north to south change, as previously though. The large extent and shape of the Karoo basin can therefore, in general, be explained as a flexural basin, with the strength of the basement increasing towards the southeast. Therefore, while factors such as mantle flow could have contributed towards basin formation, reducing the load size needed, it is no longer necessary in order to account for the large extent of the basin. This flexure model breaks down further to the southeast, most likely due to a very high Te value. This could be the reason for later plate break in this region during Gondwana breakup. It is inferred that this increase in Te is linked to the buoyancy anomaly in the asthenospheric mantle.