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An inorganic geochemical investigation of mudrocks and sandstone from the southern Bredasdorp Basin, off the south coast of South Africa was carried out to unravel the provenance, paleoweathering, and tectonic setting of the basin. Seventy-seven representative samples from exploration wells E-AH1, E-AJ1, E-BA1, E-BB1, and E-D3 underwent geochemical analysis involving major and trace elements. The major oxide compositions show that the sandstones could be classified as sub-arkose and sub-lithic arenite. The provenance discrimination diagrams based on major oxide geochemistry revealed that the sandstones are mainly of quartzose sedimentary provenance, while the mudrocks are of quartzose sedimentary and intermediate igneous provenances. The discrimination diagrams indicate that the Bredasdorp sediments were mostly derived from a cratonic interior or recycled orogen. The bivariate plots of TiO2 versus Ni, TiO2 against Zr, and La/Th versus Hf as well as the ternary diagrams of V–Ni–Th∗10 suggest that the mudrocks and sandstones were derived from felsic igneous rocks. The tectonic setting discrimination diagrams support passive-active continental margin setting of the provenance. Also, the closely similar compositions of the analysed samples and recent sedimentary rocks of the East African Rift System perhaps suggest a rifted basin tectonic setting for the Bredasdorp Basin. Chemical index of alteration (CIA) indices observed in the sandstones suggest that their source area underwent low to moderate degree of chemical weathering. However, the mudrocks have high CIA indices suggesting that the source area underwent more intense chemical weathering, possibly due to climatic and/or tectonic variations.

A total of 92 representative sandstone samples of the Bredasdorp Basin in boreholes E-AH1, E-AJ1, E-BA1, E-BB1 and E-D3 have been investigated for their grain size characteristics. Grain size textural parameters and their cross plots, linear discriminate functions (LDFs), C–M (C = first percentile and M = median) diagram and log–probability plots were calculated and interpreted to understand the mode of transportation and hydrodynamic conditions and also to unravel the depositional environments of the sediments. The grain size textural parameters revealed that the Bredasdorp sandstones are unimodal, predominantly fine-grained, moderately well-sorted, mesokurtic and near symmetrical. The bivariate plots of grain size textural parameters indicate that the depositional environments had been influenced mainly by river/beach/coastal dune conditions. The LDF plots show that the sediments are turbidity current deposits in a shallow marine environment. The C–M diagram revealed that the studied sandstones were mainly deposited by traction currents and beach process. In addition, the grain size log–probability curves and C–M diagram show the predominance of suspension and saltation modes of sediment transportation. Based on the inter-relationship of the various statistical parameters, it is deduced that the Bredasdorp Basin are mainly shallow marine deposits with signature of beach and coastal river processes.

The Algoa Basin is a hydrocarbon potential basin which lies off the southern continental margin of South Africa, along the coastal region of Port Elizabeth area with both onshore and offshore components. Despite the continued consensus on the basin’s hydrocarbon potential, both its structural and stratigraphic geodynamics are still not well documented. In this study, gravity data constrained by borehole data was modelled to reveal onshore subsurface geology whereas the seismic sections were used for offshore. In addition, magnetic data was used to delineate magnetic zones and lineaments. The onshore magnetic results show the localised occurrence of large-scale geologic bodies, with high and positive anomalies forming bounding rims coincidental with the edges of the basin. The average depths to the top of the shallowest and deepest magnetic sources were estimated from the power spectrum to be approximately 0.4–0.6 km and 9.5 km, respectively. The onshore Bouguer gravity map is characterised by a gravity low zone over the basin’s sediment where it attains its lowest value over the depocentre. 2¾ D gravity modelling results along five profiles show that the basin comprises of two to three ‘“V” shaped’ sub-basins of shallow crustal depth with sediment thickness of up to 4.6 km. The models also revealed discontinuity in sediment units, confirming the diachronous nature of the Uitenhage Group. Analyses of offshore seven seismic sections show that the stratigraphic sequence consists of diachronous geological units, which are characterised by displacements, forming a series of minor and major faults. Complementary to onshore gravity models, seismic sections also shows relatively shallow vertical extension to the Paleozoic crustal basement between 1.3 and 5.3 km.

Electrical resistivity imaging (ERI) surveys and physico-chemical analysis were carried out on a solid waste landfill (SWL) in Eastern Cape, South Africa to assess the impact of leachate pollution on groundwater quality. 2-D resistivity imaging was done across three profile lines (A, C and E) on the landfill. Physico-chemical properties of water samples from the leachate pond and boreholes (BH1 and BH2), located between 80 m to 200 m from the edge of the landfill were analysed. The results revealed groundwater contamination to a depth of about 75 m,well within the aquiferous zone. High electrical conductivity (EC) and total dissolve solid (TDS) values observed in the groundwater samples indicate a downward transfer of leachate into the groundwater. The difference in EC and TDS values for BH2 and BH1 (9892 μS/cm/ 4939 mg/L and 6988 μS/cm/ 3497 mg/L respectively), indicated that concentration of contaminants increased towards the centre of the landfill The direction of flow of the leachate is towards the southwestern part of the landfill. In the absence of a leachate recovery system, the uncontrolled accumulation of leachate over time at the landfill will pose a threat to the groundwater quality, hence the need to improve waste management practices in the study area to mitigate the effects of pollution

An integrated geological assessment of groundwater contamination was carried out to determine the nature of the subsurface as well as establish linkages between groundwater and contaminants in the vicinity of the Roundhill landfill, South Africa. Quantitative analysis involved measurement of physico-chemical properties of groundwater samples from two boreholes and a leachate pond within the landfill. Qualitative assessment involved combined measurements of electrical resistivity and time domain induced polarization (IP) across three profiles, using the double-dipole array. The physico-chemical analysis results show the presence of heavy metals (i.e.mercury, lead and arsenic) in groundwater samples in concentrations above the general acceptable limits. Perhaps, the high concentration of these metals could be due to the dumping of toxic and hazardous waste substances on the landfill, contrary to the landfill design and classification. Resistivity and IP pseudo-sections revealed a 4-layered earth structure and anomalous zones of resistivity (≤112 Ω-m) and low chargeability (≤1.25 ms) in the top layers. This is indicative of percolating leachate plume in the unsaturated zone. Despite the fact that layer lithologies and stratigraphy pose low risk to groundwater contamination, structural controls such as fractures in the bedrock are favourably disposed to the percolation of contaminants into the groundwater over time. Proper waste classification and inspection should be carried out on the landfill prior to waste disposal., Environmental science, Geology, Geophysics, Earth sciences, Hydrology, Geochemistry, Environmental assessment, Environmental pollution, Contaminants, Eastern Cape, Landfill, Leachate, Electrical resistivity, Chemical analysis.

The southern Bredasdorp Basin, off the south coast of South Africa, is only partly understood in terms of its hydrocarbon potential when compared to the central and northern parts of the basin. Hydrocarbon potential assessments in this part of the basin have been limited, perhaps because the few drilled exploration wells were unproductive for hydrocarbons, yielding trivial oil and gas. The partial integration of data in the southern Bredasdorp Basin provides another reason for the unsuccessful oil and gas exploration. In this study, selected Cretaceous mudrocks and sandstones (wacke) from exploration wells E-AH1, E-AJ1, E-BA1, E-BB1 and E-D3 drilled in the southern part of the Bredasdorp Basin were examined to assess their total organic carbon (TOC), thermal maturity, organic matter type and hydrocarbon generation potential. The organic geochemical results show that these rocks have TOC contents ranging from 0.14 to 7.03 wt.%. The hydrogen index (HI), oxygen index (OI), and hydrocarbon index (S2/S3) values vary between 24&ndash, 263 mg HC/g TOC, 4&ndash, 78 mg CO2/g TOC, and 0.01&ndash, 18 mgHC/mgCO2 TOC, respectively, indicating predominantly Type III and IV kerogen with a minor amount of mixed Type II/III kerogen. The mean vitrinite reflectance values vary from 0.60&ndash, 1.20%, indicating that the samples are in the oil-generation window. The Tmax and PI values are consistent with the mean vitrinite reflectance values, indicating that the Bredasdorp source rocks have entered the oil window and are considered as effective source rocks in the Bredasdorp Basin. The hydrocarbon genetic potential (SP), normalized oil content (NOC) and production index (PI) values all indicate poor to fair hydrocarbon generative potential. Based on the geochemical data, it can be inferred that most of the mudrocks and sandstones (wackes) in the southern part of the Bredasdorp Basin have attained sufficient burial depth and thermal maturity for oil and gas generation potential.

The Late Triassic - Early Jurassic non marine clastic sediments of the Molteno, Elliot and Clarens Formations were studied to deduce their mineralogy and tectonic provenance. The study is based on road-cut exposures of the formations in the Eastern Cape Province of South Africa. Petrographic studies based on quantitative analysis of the detrital minerals shows that the clastic sediments (mostly sandstones) are predominantly made up of quartz, feldspars, and metamorphic and igneous rock fragments. Among the main detrital framework grains, quartz constitutes about 62-91%, feldspar 6-24% and 3-19% of lithic fragments. The sandstones can be classified as both sublitharenite and subarkose. Although, most of the sandstones (> 70 %) plotted in the sub-litharenite field. Petrographic and XRD analyses revealed that the sandstones originated from granitic and metamorphic rock sources. The QFL (Quartz-feldspar-lithic fragments) ternary diagrams indicate that the sandstones were derived from recycled or quartzose source rocks reflecting a craton interior or transitional continental setting which probably came from the Cape Fold Belt. This possibly revealed that most of the sandstones might have been derived as a result of weathering and erosion of igneous and metamorphic rocks in the Cape Supergroup. The study has revealed the depositional environments, and provide a basis for the description and interpretation of the sedimentology of the Molteno, Elliot and Clarens Formations.

Diagenesis is one of the factors that affect reservoir quality in sandstones. Knowledge of diagenetic transformation and how it impacts the development of porosity in reservoirs rocks is thus key to successful mineral exploration. To date, little is known about the diagenesis of the uranium-hosted sandstones of the Stormberg Group, Karoo Basin, South Africa. Petrographic study, scanning electron microscopy (SEM) aided with energy dispersive X-ray (EDX), and X-ray diffraction (XRD) analyses were employed for the diagenetic study of the sandstones. This study aims to provide an account of the diagenesis of these rock units and how it impacts their reservoir quality. The diagenetic processes that have affected the sandstones are cementation, compaction, recrystallization, replacement, mineral overgrowth and dissolution. These processes have passed through early, late and uplift-related diagenesis. Formation of authigenic minerals and precipitation of the mineral cements occurred during different diagenetic phase but mostly during the early diagenetic stage. This stage was followed by lithification, which resulted in increased in grain packing, loss of pore spaces and thinning of bedding. Quartz and feldspar overgrowths, chloritization, muscovitization, concave-convex contacts, recrystallization, albitization and suture contacts are present in the late diagenetic stage. The uplift-related diagenetic stage was affected by calcitization, grain deformation and fracturing, dissolution and saussuritization. All these diagenetic processes largely affected the porosity and permeability of the sandstones. Primary and secondary porosities were both observed in the sandstones. In general, there is no single diagenetic process that is controlling the pattern of porosity evolution in the sandstones. On the other hand, the presence of fractured and dissolution pores tend to increase the porosity, thus enhancing the reservoir quality. This study shows that diagenesis has significantly altered the original petrologic characteristics of the sandstones which have induced considerable deterioration and heterogeneity in the reservoir quality of the Stormberg Group sandstones in the Main Karoo Basin of South Africa.

Geophysical surveys utilising magnetic and electromagnetic techniques were carried out at the Siloam hot spring. The spring is in the Soutpansberg Basin in the northern part of South Africa. The research was to investigate groundwater bearing structures at the hot spring. Magnetic survey results showed that the spring occurs between two north dipping dykes. The two dykes could be faulted segments of a single dyke or sill. Magnetic susceptibility results highlighted the presence of metamorphic and volcanic rocks. Electromagnetic survey results showed that the hot spring was within a roughly east to west trending, zone with high electrical conductivity values. Based on the survey results, water is exploiting fractures in the dyke or sill.

Grain size analysis is a vital sedimentological tool used to unravel the hydrodynamic conditions, mode of transportation and deposition of detrital sediments. In this study, detailed grain-size analysis was carried out on thirty-five sandstone samples from the Ecca Group in the Eastern Cape Province of South Africa. Grain-size statistical parameters, bivariate analysis, linear discriminate functions, Passega diagrams and log-probability curves were used to reveal the depositional processes, sedimentation mechanisms, hydrodynamic energy conditions and to discriminate different depositional environments. The grain-size parameters show that most of the sandstones are very fine to fine grained, moderately well sorted, mostly near-symmetrical and mesokurtic in nature. The abundance of very fine to fine grained sandstones indicate the dominance of low energy environment. The bivariate plots show that the samples are mostly grouped, except for the Prince Albert samples that show scattered trend, which is due to the either mixture of two modes in equal proportion in bimodal sediments or good sorting in unimodal sediments. The linear discriminant function analysis is dominantly indicative of turbidity current deposits under shallow marine environments for samples from the Prince Albert, Collingham and Ripon Formations, while those samples from the Fort Brown Formation are lacustrine or deltaic deposits. The C-M plots indicated that the sediments were deposited mainly by suspension and saltation, and graded suspension. Visher diagrams show that saltation is the major process of transportation, followed by suspension.

The southeastern Karoo Basin is considered to be one of the most prospective areas for shale gas exploration in South Africa. An interesting magnetic anomaly, the Beattie magnetic anomaly (BMA), and geologic intrusions are seen on the magnetic map. To date, the source of the BMA and interconnectivity of the igneous intrusions are not well understood. In this study, we investigate the interconnectivity of the igneous intrusions and possible location of the source of the BMA using gravity and magnetic methods. The gravity model results showed that igneous intrusions are interconnected at depth, which probably pose threat by increasing the risk of fracking the Karoo for shale gas exploration. The magnetic results revealed that the BMA becomes stronger with depth. The average depths to the top of the shallow and deep magnetic sources were estimated to be approximately 0.6 and 15 km, respectively.

The subsurface geometry of five representative late Archaean ‘Chilimanzi and Razi’ suite plutons in the Zimbabwe craton (ZC) has been investigated by gravity modelling constrained in part by surface geology, density measurements and seismic information, to determine their 3D configuration and infer tectonic context of emplacement. The generally K-rich, massive, homogeneous monzogranites are characterised by large Bouguer gravity lows (up to − 30 mGal amplitude) whose gradients outline their spatial extent well. The southernmost plutons and their anomalies have general trends paralleling the North Marginal Zone (NMZ) of the Limpopo orogenic belt (LB). Predictive gravity models indicate that the density contrast of the Chivi batholith (CB) adjacent to the ‘volcanic arc-like’ Belingwe greenstone belt extends to a depth of about 13 km. The nearby Razi pluton (RP) which intrudes the ZC-LB boundary appears to have been emplaced at shallower depths/levels. The gravity model suggests a thickness of about 5–6 km, and a moderate to shallow dip to the southeast under the NMZ, compatible with syn-kinematic intrusion during overthrust of the LB over the ZC. The smallest Nalatale granite (Ng) is on average 2.5 km thick under the Fort Rixon greenstone belt but includes a root up to 4.5 km thick under the anomaly peak, and a steep contact with the tonalite/gneiss to the east. These granites follow the general power-law for pluton dimension and are similar in this respect to the classical wedge-shaped plutons, extending largely in one direction, with large aspect ratios (Length (L)/Thickness (T) > 7). However, the overall shape of the RP is typical of a diapir (Width (W) 5; L/T > 15). Overall, the CB and the ZG are interpreted as massive, deep-rooted batholithic intrusions (L/T ≅ 10), contrary to some geological interpretations of these late, post-kinematic intrusions as sheet-like bodies emplaced at relatively shallow levels in the crust. On the other hand, the ChB appears to be a tabular intrusion, probably fed by dykes; it exhibits a lateral extent much greater than the vertical one, outlining a sheeted geometry (W/T > 7; L/T > 18). The geophysical evidence, together with geological and fabric data, support and/or confirm the two main granite configurations: sheets and batholith; and thus also confirm the two main modes of emplacement: dyke and diapirism or ballooning plutonism. This is consistent with other known batholiths on the ZC but considered unusual for plutons of the same age and spatially close when compared to other Archaean cratons.

Finding productive boreholes in the Karoo fractured aquifers has never been an easy task. Fractured Karoo aquifers in the neotectonic zones in the Eastern Cape Province can be targeted for groundwater exploration. The Polile Tshisa hot spring is located in a seismo-tectonic region beset by neotectonics. Hot springs are indicative of circulation of groundwater at great depths along fault zones, and accordingly of neotectonics. The characterisation of hot springs by means of magnetic and electromagnetic methods can help infer the occurrence of structures which are favourable for groundwater potential. The Polile Tshisa hot spring is characterised by faults, fractures, and dolerite dykes. All these structures make the hot spring a good case study for groundwater exploration.

Potentiality for groundwater in the Ndlambe Municipality, comprising of rocks of the Witteberg Group, Cape Supergroup, was investigated using a combination of different approaches. Distribution of lineaments extracted from a satellite image is hardly homogenous; their density varies with different localities. Areas around the western and southwestern parts of the study area have relatively high-density values (≥39) while the northern, eastern and northeastern parts of the area of study are dominated by low-density values (0-39). Boreholes located in the northeastern part appear to be away from the zones of dense lineaments, have dried up, and were found not to be productive. In the northwest parts of the study area, there are several locations displaying intersections of lineaments, these zones of high lineament intersection can be targeted for groundwater exploration. Most of the lineaments in the study area trend in a northeast-southwest direction; this trend would be identical to the orientation of the preferential flow path. Quartz veins and normal faults seen in the field are good indicators for groundwater potential as they are a structural expression of extensional environmentsThe same applies to quartz grains affected by extensional micro-fractures, which resulted from brittle deformation as seen under the microscope. Subsurface geology investigation from borehole logging has depicted fractures in quartzitic sandstones; thus, micro-fractures in quartz grains and quartzitic sandstones enhance secondary porosity and groundwater flow. Low resistivities from the geophysical investigation in the study area were inferred to be weathered moist sandstone. The low resistivities at depth also indicate an overlying zone of fractured sandstone and quartzite, hence possibility of hosting some groundwater. Low resistivity zones between two large bodies suggest that the massive rock bodies are being weathered and fractured, and fractures act as conduits for groundwater.

The Cretaceous sandstone in the Bredasdorp Basin is an essential potential hydrocarbon reservoir. In spite of its importance as a reservoir, the impact of diagenesis on the reservoir quality of the sandstones is almost unknown. This study is undertaken to investigate the impact of digenesis on reservoir quality as it pertains to oil and gas production in the basin. The diagenetic characterization of the reservoir is based on XRF, XRD SEM + EDX, and petrographic studies of 106 thin sections of sandstones from exploration wells E-AH1, E-AJ1, E-BA1, E-BB1 and E-D3 in the basin. The main diagenetic processes that have affected the reservoir quality of the sandstones are cementation by authigenic clay, carbonate and silica, growth of authigenic glauconite, dissolution of minerals and load compaction. Based on the framework grain&ndash, cement relationships, precipitation of the early calcite cement was either accompanied or followed up by the development of partial pore-lining and pore-filling clay cements, particularly illite. This clay acts as pore choking cement, which reduces porosity and permeability of the reservoir rocks. The scattered plots of porosity and permeability versus cement + clays show good inverse correlations, suggesting that the reservoir quality is mainly controlled by cementation and authigenic clays.

A combination of electrical resistivity and induced polarization methods were applied to a solid waste landfill in Alice, Eastern Cape, South Africa to delineate the lithologic layers and locate possible leachate plumes. Resistivity and IP data were collected along six profiles; VES on two and the dipole-dipole configuration was used in the rest four. The result shows a 4-layered earth system with a shallow depth to the top of the bedrock (

Petrography of the sandstones of Ecca Group, Karoo Supergroup in the Eastern Cape Province of South Africa have been investigated on composition, provenance and influence of weathering conditions. Petrographic studies based on quantitative analysis of the detrital minerals revealed that the sandstones are composed mostly of quartz, feldspar and lithic fragments of metamorphic and sedimentary rocks. The sandstones have an average framework composition of 24.3% quartz, 19.3% feldspar, 26.1% rock fragments, and 81.33% of the quartz grains are monocrystalline. These sandstones are generally very fine to fine grained, moderate to well sorted, and subangular to subrounded in shape. In addition, they are compositionally immature and can be classified as feldspathic wacke and lithic wacke. The provenance characteristics suggest the influence of plutonic and metamorphic terrains (meta-magmatic arc) as the main source rock with minor debris derived from recycled sedimentary rocks. The latter revealed that the compositional immaturity of the sandstones is a result of weathering or recycling and short transport distance. The weathering diagrams and semi-quantitative weathering index indicate that the Ecca sandstones are mostly from a plutonic source area, with climatic conditions ranging from arid to humid. The detrital modal compositions of these sandstones are related to back arc to island and continental margin arc. These results, therefore, support previous studies that infer foreland basin setting for the Karoo Basin.

Geochemical compositions of twenty-four sandstone and shale samples from the Ecca Group were analysed to decipher their provenance, paleoweathering conditions and tectonic setting. The shales have high Fe2O3, K2O, TiO2, Ce, Cu, Ga, La, Nb, Nd, Rb, Sc, Sr, Th and Y content more than the sandstones, whereas, sandstones are higher in SiO2, Hf and Zr than the shales. The positive correlations of Al2O3 with other elements as well as the abundance of Ba, Ce, Th, Rb, Zn and Zr suggest that these elements are primarily controlled by the dominant clay minerals. Tectonic discrimination diagrams revealed that the sandstones and shales are mostly of quartzose sedimentary provenance, suggesting that they were derived from a cratonic interior or recycled orogen. The binary plots of TiO2 versus Ni, TiO2 against Zr and La/Th versus Hf as well as the ternary diagrams of V-Ni-Th*10 indicate that the shales and sandstones were derived from felsic igneous rocks. A-CN-K (Al2O3-CaO-K2O) ternary diagram and indices of weathering (CIA, CIW and PIS) suggest that the granitic source rocks underwent moderate to high degree of chemical weathering. The CIA values range between 24.41% and 83.76%, indicating low to high weathering conditions. The CIW values for the studied sandstones and shales range from 25.90 to 96.25%, suggesting moderate to high intensive chemical weathering. ICV values for the sandstones and shales vary from 0.71 to 3.6 (averaging 1.20) and 0.41 to 1.05 (averaging 0.82), respectively. The k2O/Na2O ratios for the studied samples vary from 0.71 to 8.29, which reveal moderate to high maturity. The plot of CIA against ICV shows that most of the shales are geochemically mature and were derived from both weak and intensively weathered source rocks. The tectonic setting discrimination diagrams support passive-active continental margin setting of the provenance.

Diagenesis is one of the most important factors that affects reservoir rock property. Despite the fact that published data gives a vast amount of information on the geology, sedimentology, and lithostratigraphy of the Ecca Group in the Karoo Basin of South Africa, little is known about the diagenesis of the potentially feasible or economically viable sandstones and mudrocks of the Ecca Group. This study aims to provide an account of the diagenesis of sandstones and mudstones from the Ecca Group. Twenty-five diagenetic textures and structures were identified and grouped into three stages that include early diagenesis, burial diagenesis and uplift-related diagenesis. Clay minerals are the most common cementing materials in the sandstones. Smectite, kaolinite, and illite are the major clay minerals that act as pore lining rims and pore-filling materials. A part of the clay minerals and detrital grains was strongly replaced by calcite. Calcite precipitates locally in the pore spaces and partially or completely replaced clay matrix, feldspar, and quartz grains at or around their margins. Precipitation of cements and formation of pyrite and authigenic minerals occurred during the early diagenetic stage. This process was followed by lithification and compaction which brought about an increase in tightness of grain packing, loss of pore spaces, and thinning of bedding thickness due to overloading of sediments and selective dissolution of the framework grains. Mineral overgrowths, mineral replacement, clay-mineral transformation, dissolution, deformation, and pressure solution occurred during burial diagenetic stage. After rocks were uplifted, weathered and unroofed by erosion, this resulted in decementation and oxidation of iron-rich minerals. The rocks of the Ecca Group were subjected to moderate-intense mechanical and chemical compaction during their progressive burial. Intergranular pores, secondary dissolution, and fractured pores are well developed in the sediments of the Ecca Group. The presence of fractured and dissolution pores tend to enhance reservoir quality. However, the isolated nature of the pore linkage makes them unfavorable producers of hydrocarbons, which at best would require stimulation. The understanding of the space and time distribution of diagenetic processes in these rocks will allow the development of predictive models of their reservoir quality, which may contribute to the reduction of risks involved in hydrocarbon (oil and gas) exploration.

Backstripping analysis has been carried out on five boreholes and one outcrop section of the Ecca Group in the Main Karoo Basin of South Africa to determine the sedimentation rate and subsidence history of the basin. The result shows that the rate of sedimentation in the Prince Albert, Whitehill, Collingham, Ripon and Fort Brown Formations range between 0.003–0.03, 0.02–0.05, 0.01–0.05, 0.03–0.22, and 0.15–0.025 mm year−1, respectively. The backstripped subsidence curves that are constructed by removing the effects of decompaction to the water column and sediment loads show subsidence rates decreasing with time, resembling the typical thermal subsidence curves of passive continental margins. Three major subsidence episodes characterized the Ecca Group, namely, (1) rapid subsidence in an extensional regime, (2) slow subsidence in the middle of basin development and (3) another rapid subsidence in a compressional regime. The aforementioned subsidence episodes show that the southeastern Karoo Basin was located on a passive continental margin, suggesting that the subsidence was initiated and mainly controlled by mechanical (gravitational loading) or tectonic events, with little contribution of thermal events. The average rate of tectonic subsidence in the Prince Albert, Whitehill, Collingham, Ripon and Fort Brown Formations are 63, 28, 25, 215 and 180 m Ma−1, respectively. It is also inferred that the southeastern Karoo Basin evolved from a passive continental margin into an Andean-type continental foreland basin; thus, portraying a completely evolved post-rift setting along the southeastern Gondwana margin.

Gamma ray measurements were carried out along two parallel lines close to each of the hot springs using a RS 125 spectrometer to find the concentration (ppm) of U, Th, and K at Polile Tshisa, Aliwal North, and Badfontein hot springs. The RS 125 spectrometer is auto-stabilized on the naturally occurring U, Th, and K, and provides concentrations (ppm) of the radioelements. The results show that the concentration of thorium is higher, and is below the world average hazardous threshold of 7.4 ppm. Thorium is related to the occurrence of monazite seen at the scanning electron microscope. Higher ratios of U/K are indicative of an increase of uranium relative to potassium. Binary diagrams (Th–U, K–U, and K–Th) do not show a clear best fit except at Polile Tshisa hot spring where thorium shows a quasi positive correlation to potassium. In general, it can be concluded that the concentrations of these three radioelements are quite low, acceptable for groundwater, and could be hazardous to the health of humans and animals if exposed to long time radiations.

Electrical resistivity tomography (ERT) was used to delineate subsurface structures at Siloam hot spring in the Soutpansberg Basin of South Africa. The spring water was reported to be hottest in South Africa. Groundwater with temperature ranging between 63.3 °C and 67.5°C was observed flowing from the spring. Relatively wet areas were noted to the south and north of the spring. Electrical resistivity arrays with Dipole-dipole and Wenner-Schlumberger configurations were used. Current injection and potential dipole separations of 5 m and 10 m were applied across the spring. Inversion results for arrays with the shorter dipole separation of 5 m had better resolution. Resistivity sections were generated from inversion of ERT data. The resistivity values for the low and high resistive zones were ρa < 10 and ρa > 70 Ωm respectively. Sub-horizontal resistivity zones were obtained from the inversion of Wenner-Schlumberger array survey data. High resistivity zones associated with dykes or sills were delineated on Dipole-dipole derived depth sections. Near vertical structures associated with water bearing faults or fractures were delineated at the Siloam hot spring.

The fractal-based approach was used for computing magnetic depths and temperatures for the Soutpansberg Basin in South Africa. The average depth to the top Zt and basement depth Zo for the Soutpansberg Basin were 4.36 ± 0.28 km, 10.43 ± 0.65 km, respectively. The average temperature at depth Zt was 184.69 ± 7.66 ºC. Magnetic source depths and basal temperatures that were in the Curie point range were determined, to be within 20.35 km to 21.68 km and 549.34 ºC to 585.24 ºC, respectively. Increasing the value of the fractal parameter β from 0 to 4, had an effect of retaining deeper depths and higher temperatures. The fractal parameter values of β > 3 retained Curie point depths and temperatures that indicated basal rock types with an igneous predisposition. The fractal-based approach proved to be an improved technique as compared to the conventional centroid method.

Teleseismic data recorded by twenty two northern stations of the Southern Africa Seismic Experiment (SASE) have been analysed to map the crustal and uppermost mantle structure of the Zimbabwe Craton and the Limpopo Belt. The results show that the crustal thickness of the Limpopo Belt ranges from 42 to 53 km with a complex Moho, while that of the Zimbabwe Craton ranges from 36 to 39 km, with a relatively sharp and simple Moho and no apparent mid-crustal discontinuities. Poisson’s ratio estimates show the crust under the Limpopo Belt to be of a relatively more mafic composition (σ > 0.26) than under the Zimbabwe Craton (σ ≤ 0.26), which is of intermediate composition.

A multi-electrode resistivity survey, carried out over metasedimentary strata and metavolcanics in the Harare greenstone belt in northeastern Zimbabwe as part of a groundwater resources investigation, illustrates the ability of this technique to produce high-resolution images of the subsurface, which are useful for groundwater resources assessment. The resistivity results provide a clear view of the thickness of the weathered regolith and of the distribution of the various lithological units. Using a combination of apparent formation resistivity and inferred depth of weathering, it is possible to characterize the various lithologies on the geophysical profiles. These assigned lithologies show excellent correlation with the mapped geology, and the main lithologies, metabasalt, meta-arenite, granodiorite and banded iron formation can be clearly identified. The banded iron formation is characterized by low resistivity values, while a combination of the depth of weathering and resistivity values are used to distinguish between the meta-arenite on one hand and the metabasalt and granodiorite on the other. The multi-electrode method is successful in identifying potentially favourable zones for obtaining groundwater, such as areas with a maximum depth of weathered regolith, zones of fracturing and faulting, and high porosity and permeability zones associated with lithological contacts.

The formation of Archean crust appears to in- volve processes unique to early earth history. Initial results from receiver function analysis of crustal structure beneath 81 broadband stations deployed across southern Africa re- vealsignicantdierences inthenatureof thecrustandthe crust-mantle boundary between Archean and post-Archean geologic terranes. With the notable exception of the colli- sional Limpopo belt, where the crust is thick and the Moho complex, the crust beneath undisturbed Archean craton is typically thin ( 35{40 km), unlayered, and characterized byastrongvelocitycontrastacrossarelativelysharpMoho. Thiscrustalstructurecontrastsmarkedlywiththatbeneath post-ArcheanterranesandbeneathArcheanregionsaected bylarge-scaleProterozoicevents(theBushveldcomplexand the Okwa/Magondi belts), where the crust tends to be rel- atively thick (45{50 km) and the Moho is complex.

The Cabora Bassa Basin in northern Zimbabwe is an Upper Paleozoic karoo basin trending almost east-west. It has clearly recognisable gravity and magnetic signatures from which its dimensions are estimated to be approximately 150 km long and at least 62 km wide. Its southern boundary is marked by a north dipping, listric, master fault of possibly a ramp-flat-ramp geometry. Within the basin there is erosional truncation of over 2 km of sediment at the top of the stratigraphy and an absence of a post-rift thermal subsidence phase. Modern and major river channels are characteristically narrow, deep and without considerable amounts of silt on the river beds, whilst their valley sides are marked by multiple terraces. These ongoing erosional processes are evidence for sustained and possibly episodic uplift of the basin since the end of rifting in the Late Cretaceous/Early Tertiary. An evaluation of possible uplift mechanisms for the basin and its surroundings lends support to lithospheric thickening as the most likely mechanism. Compression and magmatic underplating and/or intrusion are two common ways of thickening the lithosphere. The absence of major compressional structures within the basin suggests that magmatic underplating and intrusion may have played a major role in lithospheric thickening. Major element data for the mantle-derived Jerama basalts indicate substantial hidden cumulates, which possibly thickened the lithospheric column. Modelling of gravity data, constrained by both seismic reflection results, and the densities of the surface rocks, show that the crustal thickness beneath the basin is in the range 19–23 km. The stretching factors from seismic and gravity models range from 1.6 to 1.9. There is up to 5 km difference between the expected and modelled crustal thicknesses beneath the basin, which could be explained by magmatic underplating.

SUMMARY The Bouguer gravity anomaly map of the Zimbabwe and Kaapvaal cratons, the Limpopo Belt and the Mozambique basin shows a regional gravity high in the southeast. Superimposed on this gravity high is a line of elongate gravity highs that is coincident with the Lebombo-Nuanetsi-Sabi volcanics. Gwavava et al. ( 1992) argue that the regional anomaly over this region is the effect of Mesozoic crustal thinning and igneous activity during the breakup of Gondwana. Lithospheric extension resulted in crustal thinning by at least 4 km beneath the central Limpopo Belt. 2-D Fourier transforms of Bouguer gravity and topography data have been used to obtain the admittance and coherence throughout the region. Assuming a regionally compensated isostatic model comprising two layers with statistically independent surface and subsurface loading, the predicted coherence was compared to the observed coherence to obtain the best estimate of the effective elastic thickness of the lithospheric plate. This coherence analysis reveals that the Archaean cratons have a minimum effective elastic thickness of about 56 km, whereas that of the area beneath the Mozambique basin is only about 22 km, a value similar to that obtained in other East African rift basins. Hence, the stable cratonic areas are more rigid than the area beneath the Mozambique basin, which was subjected to Mesozoic crustal extension and thinning. An isostatic anomaly map has been computed by filtering the Bouguer gravity in the wavenumber domain with the square root of the predicted coherence function of the whole area generated from the best-fitting two-layer model with an effective elastic thickness of 52 km. The isostatic anomaly map is characterized by (1) a zone of positive isostatic anomalies over the Lebombo-Nuanetsi-Sabi area, which are partly due to crustal thinning and partly to basic plutons emplaced in the upper crust, both resulting from an extensional episode associated with Gondwana breakup, (2) positive isostatic anomalies over the Southern Marginal Zone of the Limpopo Belt, which we interpret as being due to dense granulites within the upper crust, (3) negative isostatic anomalies over the Northern Marginal Zone of the Limpopo Belt, which may have resulted from recent rapid erosion, and (4) negative isostatic anomalies over the Mozambique basin, which are due to the gravity effect of low-density Cretaceous and Tertiary sediments.

The 600-km-long by 250-km-wide Limpopo Belt forms a wedge-shaped structure between the Zimbabwe and Kaapvaal cratons in southern Africa. The results of a gravity survey which included the part of the Limpopo Belt within Zimbabwe are incorporated with other data and presented as a regional gravity map. Three gravity profiles crossing the Limpopo Belt and one within Mozambique have been interpreted in terms of lateral changes in crustal structure. These interpretations are controlled by density measurements and seismic refraction data across the northern and central parts of the Belt. The Zimbabwe craton appears from gravity modelling to be characterised by a horizontal Moho at 34 km depth. The Limpopo Belt is parallel to the ENE-trending gravity contours and in the east has a southwest-northeast line of gravity highs coincident with the Nuanetsi-Sabi volcanic rocks. This study has shown that the regional gravity high associated with these features is consistent with crustal thinning probably caused by the breakup of Gondwana. The crust thins in a south-southeast direction to about 30 km in the Central Limpopo Belt with a dip on the Moho which varies from about 4° to 7°. The short-wavelength positive gravity anomalies occurring on the Nuanetsi-Sabi regional gravity high are due to late Karoo igneous intrusions and volcanics. A north-south similar line of gravity highs exists along the Lebombo monocline on the Mozambique/South Africa border. Beyond the Lebombo monocline to the east the gravity anomaly suggests a thickness of 6 km or more of sediments that could represent a paleo-deltaic environment prograding over the continental margin. The Lebombo-Nuanetsi-Sabi gravity anomaly that dominates the gravity response in the eastern part of the study area is likely to be a failed-arm triple junction and could imply a much tighter fit of Gondwana than has been previously suggested. As such the geometry of such a margin may provide a major constraint on the geometric fit of East Antarctica with Africa.

Bulawayo is the second largest city in Zimbabwe with a population of about one million people and has been facing water problems since the beginning of the 1990s. A weIl field was drilled in the Nyamandhlovu aquifer in 1996 for immediate water supply for the city due to continued water crisis. However, the aquifer is also heavily exploited by the local farmers in the Nyamandhlovu area. Due to over-exploitation of the aquifer, research has been initiated both for management of the aquifer and to identify alternative aquifers. The research presented here is part of an on-going groundwater project between Universities of Zimbabwe, Lund (Sweden), Aarhus (Denmark), and Leeds (UK) funded by SIDAISAREC.

The Mana Pools sedimentary basin lies within the Zambezi mobile belt in northern Zimbabwe. New and preexisting magnetotelluric data and the available seismic reflection data are used to constrain the basin structure and the depth to the electrical basement. Long-period magnetotelluric (LMT) data were collected at five stations along a 60 km north-south profile across the Mana Pools basin and onto the southern escarpment. These data augment an existing audiofrequency (AMT) data set from 11 sites in the same area. The subsurface apparent resistivities measured at periods sampling the basin are very low (a few Ωm). After processing both data sets, the estimated impedance tensor is decomposed, showing that the resistivity structure of the Mana Pools basin can be modeled two dimensionally. The ρ+ algorithm is used to show that there is no systematic offset in magnitude between the AMT and LMT data sets before they are combined. Minimum structure resistivity models of the Mana Pools basin compare well with the information from reflection seismic data and support its previous description as a half graben basin of ∼7 km depth. The excellent conductor in the Mana Pools basin is quite different to those seen elsewhere in the orogenic belt in that it is a feature of the sedimentary fill rather than the basement. The resistivity of the basement is low but no localized good conductor is observed; these low resistivities may result from a high degree of either chemical or tectonic alteration to the underlying rocks due to metamorphic processes and tectonic disruption during rift formation.

The Parana-Etendeka province comprises one of the largest continental flood basalt provinces on earth. This magmatic province was associated with the opening of the South Atlantic Ocean during the Early Cretaceous. The Parana lava field covers an area of at least 1.2x106 km2 over southern Brazil, Uruguay, eastern Paraguay and northern Argentina, and its present extent is bounded by the margin of the underlying Palaeozoic-Mesozoic Parana basin. The Etendeka lavas, are scattered over an area of 0.8x105 km2 in northwestern Namibia. The basement beneath the Parana basin consists of several Archean to Early Proterozoic cratonic blocks surrounded by Brasiliano cycle (700-450 Ma.) mobile belts. The majority of analysed samples of the Parana-Etendeka magmatism give 40Ar-39Ar ages between 129 Ma and 134 Ma with northward younging, although there is evidence of earlier magmatism inland (135-138 Ma) and younger magmatism persisting along the coast (120-128 Ma).

The research was conducted to seek geothermal energy potential in the Soutpansberg Basin, located in the northern part of South Africa. The depths of the potential heat sources were computed from the radially averaged power spectrum of airborne magnetic data. Shallower magnetic sources were delineated using the Euler deconvolution method. An anticline at depths of 2.0–3.5 km was delineated in the central part of the basin. Potential magnetic and basement heat sources exist between depths of 4.8 and 11.1 km. Airborne magnetic data sets with larger window sizes are preferred for depth computations, as they preserve spectral signatures of deeper sources and reduce the contribution of shallower sources. The research clearly highlighted evidence for the existence of the Soutpansberg Basin Geothermal Field.