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The Karoo Basin of South Africa covers an area of 700 000 km2 and has been identified as a possible shale gas reserve. Any evaluation of the shale gas potential of the basin must consider the widespread dolerite dykes and sills. These intrusions were emplaced into the Karoo Supergroup and are well dated at around 183 Ma. Their intrusion triggered the explosive releases of gas in the basin, marked on surface by breccia pipes and hydrothermal vents. This outpouring of gas has been proposed as a significant contributor to global climate change. Research into the three-dimensional interconnected structure of these dolerite sills and dykes and their interaction with the hydrocarbon rich layers in the lower part of the Karoo Supergroup has been limited to localized observations of outcrop, magnetic data, legacy seismic data (from the 1970s) and well core. Here we present an interpreted 65 km long higher-resolution 2D seismic reflection profile across the Karoo Basin, approximately 100 km southeast of Trompsburg. These data were collected in the 1990s and at the time deeper structures along the line interpreted. In this study we focus on the top 0.6 to 2 seconds TWT of the data. The seismic line images the interconnected and cross cutting nature of the dolerite dykes and sills along the profile. We also report possible evidence of a gas escape structure (approximately 2.5 km in diameter at surface) emerging near the edge of a dolerite sill in close proximity to the Whitehill Formation, which is the main target for shale gas exploration. This suggests that gas vents in the eastern Karoo Basin close to Lesotho are due to the release of gas from the carbonaceous shales of the Ecca Group. This is similar to breccia pipes mapped on surface in the western part of the Karoo Basin. This seismic section highlights why dolerite sills and dykes must be considered when evaluating the shale gas potential of the Karoo Basin. We propose that better characterization of the Karoo Basin subsurface by seismic and magnetic studies is necessary prior to any efforts to calculate shale gas reserves. [ABSTRACT FROM AUTHOR]

To provide guidelines for future seismic surveys in the Bushveld Complex, we have conducted laboratory experiments to measure P-wave and S-wave velocities at ultrasonic frequencies on drill-core samples as a function of stress and bulk density. The rock samples include gabbroic, anorthositic, troctolitic and magnetite-olivine rich horizons, as well as granitic sills. Ultrasonic measurements of P- and S-wave velocities were conducted at both atmospheric pressure, and at elevated uniaxial stresses up to 65 MPa (equivalent to depths of 2 km), using 0.5 MHz P- and S-wave transducers. The results show that the seismic velocities tend to increase with increasing olivine or pyroxene content (e.g., Vp ~6.00 km/s for olivine ferrodiorite), and decrease with increasing plagioclase content (e.g., Vp ~4.70 km/s for troctolite). The bulk density and ultrasonic measurements suggest that significant reflection coefficients (RC) occur at some stratigraphic contacts that are readily identifiable in surface exposures (e.g., RC~0.09 for granite-olivine ferrodiorite contact), implying that these horizons, at least in terms of acoustic impedance contrasts, are favourable targets for surface reflection seismic surveys. Our results also suggest that with increasing stress (0 to 20 MPa), seismic wave velocities increase slightly for both anorthosite (Vp~5.5 to 6.0 km/s) and troctolite (Vp~4.80 to 7.20 km/s). The velocities are constant at higher stresses (20 to 65 MPa), which can be attributed to closure of macro- and microcracks at depths of 1.0 to 1.5 km. The observed relationship between seismic velocities, modal mineralogy and stress has particularly important implications (e.g., velocity analysis for seismic processing and time-to-depth conversion of the seismic data) for the design of future long, deep seismic profiles that can be used to constrain the deep structure and connectivity of the western and eastern limbs of the Bushveld Complex at depths. [ABSTRACT FROM AUTHOR]

Here we present a comprehensive depth and thickness map of the main Karoo and Cape Basins using borehole and reflection seismic data. The depth to the Whitehill Formation, which is the focus of current shale gas interest within the Karoo, is also mapped. Change: The deepest part of the basin is in the south, along the northern boundary of the Cape Fold Belt (~4000 m in the southwest Karoo and ~5000 m in the southeast; ~5500 to 6000 m sediment thickness). The Whitehill Formation along this boundary reaches a depth of ~3000 m in the southwest and ~4000 m in the southeast. Limited borehole data in the southeastern Karoo show a broad deepening of the basin here compared to the southwestern Karoo. In the southeast near East London faulting has resulted in deepening of the basin close to the coast, with the Whitehill Formation deepening to over ~5000 km. Seismic and borehole data show that the Cape Supergroup pinches out below the Karoo Basin around Beaufort West and Graaff-Reinet in the southern Karoo (32.6°S for the Bokkeveld and 32.4°S for the Table Mountain Group). The Cape Supergroup reaches thicknesses of around 4 km in the south. The gravity effect of these sediments does not account for the Cape Isostatic Anomaly (CIA) in the southern part of the Karoo Basin near Willowmore and Steytlerville, i.e., an ~45 mGal Bouguer gravity low. A refraction seismic profile over the anomaly shows this region is associated with a large volume of low velocity/density shallow sediments (4.5 m/s2, 2500 kg/m3), as well as a low velocity/density anomaly associated with a normal fault and the Klein Winterhoek Thrust Fault (5.5 m/s2, 2650 kg/m3). These low density shallow sediments are explained by uplift of Karoo and Cape sediments of ~2 km or greater that is evident on Soekor reflection seismic data. This deformation has brought lower density shales (1800 to 2650 kg/m3) of the Ecca Group closer to the surface. These shallower features along with a deeper lower crust in this region (6.5 m/s2, 2900 kg/m3) are interpreted to account for the CIA. [ABSTRACT FROM AUTHOR]

A scientific drilling project in the Bushveld Igneous Complex in South Africa has been proposed to contribute to the following scientific topics of the International Continental Drilling Program (ICDP): large igneous provinces and mantle plumes, natural resources, volcanic systems and thermal regimes, and deep life. An interdisciplinary team of researchers from eight countries met in Johannesburg to exchange ideas about the scientific objectives and a drilling strategy to achieve them. The workshop identified drilling targets in each of the three main lobes of the Bushveld Complex, which will integrate existing drill cores with new boreholes to establish permanently curated and accessible reference profiles of the Bushveld Complex. Coordinated studies of this material will address fundamental questions related to the origin and evolution of parental Bushveld magma(s), the magma chamber processes that caused layering and ore formation, and the role of crust vs. mantle in the genesis of Bushveld granites and felsic volcanic units. Other objectives are to study geophysical and geodynamic aspects of the Bushveld intrusion, including crustal stresses and thermal gradient, and to determine the nature of deep groundwater systems and the biology of subsurface microbial communities. [ABSTRACT FROM AUTHOR]

We report palaeomagnetic and 40Ar/39Ar age data for dykes that intrude the ∼2 Ga eastern Bushveld Igneous Complex (BIC). The dykes were previously assumed to be of Karroo age (Jurassic ∼ 180 Ma) based on their NE–SW orientation. Palaeomagnetic data (pole position ), however, clearly demonstrate that these dykes are Precambrian in age, either ∼1.9 Ga and close to the Early Proterozoic Bushveld age, or 1649 ± 10 Ma based on 40Ar/39Ar plagioclase laser fusion ages from one of the dykes. Both normal and reverse polarity dykes are identified, and a positive reversal test together with a semi-conclusive contact test attests to a primary magnetization. If the 40Ar/39Ar age represents a primary cooling age then palaeomagnetic poles from South Africa (Kalahari) at ∼1.9 to ∼2 Ga and ∼1650 Ma are virtually identical, and suggest an apparent polar wander loop; alternatively, the Kalahari Craton drifted from high southerly (>50°) to high northerly latitudes (or vice versa) during this interval. Conversely, if we assign a ∼1.9 Ga age for dyke emplacement as suggested from a comparison with Kalahari palaeomagnetic poles (e.g. Waterberg–Soutpansberg pole), the ∼1650 Ma 40Ar/39Ar age must relate to a thermal disturbance that did not erase the primary magnetic signature. [ABSTRACT FROM AUTHOR]

Tumor necrosis factor-α (TNF-α) stimulates osteoblast production of interleukin-6 (IL-6), an inflammatory cytokine implicated in osteoclastic bone resorption. Therefore, we tested the hypothesis that TNF-α-induced IL-6 production in MG-63 osteosarcoma cells occurs via the p38 mitogen-activated protein kinase (MAPK) pathway. TNF-α activated p38 MAPK and stimulated IL-6 secretion by MG-63 cells, and pre-incubation of cells with the p38 MAPK inhibitor abrogated TNF-α-dependent IL-6 secretion. Transfection of IL-6 full-length and 5'- deletion gene promoter reporter constructs indicated that p38 MAPK activation by TNF-α enhanced IL-6 gene expression, and that the p38 MAPK-responsive region resided in the proximal 260-bp segment. Transfection of NFκB and C/EBPβ-sensitive reporter promoter constructs demonstrated that NFκB activity was enhanced and that constitutive C/EBPβ was inhibited by TNF-α, with both effects being p38 MAPK-dependent. In conclusion, although p38 MAPK activation by TNF-α stimulates IL-6 secretion by MG-63 cells, it has opposing effects on c/EBPβ and NFκB activity. [ABSTRACT FROM AUTHOR]