The Lower Ecca Group of the Karoo Basin potentially contains significant unconventional gas, hosted in gas shales, of which the most significant sequence is the organic rich shales of the Whitehill Formation. The Whitehill Formation is directly overlain by clastic and volcaniclastic rocks of the Collingham Formation. Due to the potential for the upward migration of hydrocarbons from the gas-shales it is important to establish the integrity of the overlying formation. Here we report on the mineralogical, geochemical and physical properties of the Collingham Formation to test its ability to act as a cap rock to the underlying carbon-rich, potentially gas-bearing shales of the Whitehill Formation.Fresh core samples from a borehole drilled through the Lower Ecca Group near Jansenville, in the Eastern Cape, South Africa, were analysed for their mineralogical and geochemical content, using thin-section microscopy, XRD, XRF, TOC and SEM. The main rock types of the Collingham Formation contain three pore types (intrapore, interpore and microfractures) that are predominantly nanopores (<1 micron). The small size of pores, low permeability values, and their mineral content suggest that the Collingham Formation formed in a marine environment, subsequently modified through burial and regional metamorphism. Physical properties, determined through mercury porosimetry include porosity, permeability and density. Results show that the large proportion of clay minerals, a low TOC, the fine-grained nature of lithologies, a low porosity, a lack of permeability, a moderate fracturability, average density values, and the laminate nature of the formation, favour it as a suitable cap rock.We conclude that, although the characteristics of the formation favour it as a caprock, and therefore a sealing sequence to the Whitehill Formation, our results apply only to the Collingham Formation affected by the Cape Fold Belt. Further work is needed farther into the basin, to reveal its potential as a regional cap rock.

Who would have thought that the southern part of 'stable, old South Africa' was in fact 'not-so-stable', and that there has been spectacular tectonic activity in the Cape Fold Belt as recent as the early Holocene, about 10,327 +/- 755 years ago?Large-scale surface rupture, with at least 2 m of vertical geomorphic offset, has been recorded along the Kango Fault over a lateral distance of at least 84 km, from near the town of De Rust, east of Oudtshoorn, towards the western end of the Baviaanskloof in the Eastern Cape. Although the Kango Fault scarp was reported in the mid 1970's and late-1980's, detailed palaeoseismic investigation was not undertaken until recently, when the chief energy supplier for South Africa, Eskom, rekindled investigations to establish a number of nuclear power plants along the South African coastline. This paper reports the results of the first palaeoseismic trench excavated across the Kango Fault during the initial phase of the nations' current New Build programme.The location and date of the most recent event (MRE) is reported, as well as the style of faulting and local stress direction. These palaeoseismic data are derived from carefully-mapped logs of an 82 m long, 5 m deep trench, supported by 12 optically-stimulated luminescence (OSL) dates of stratigraphic horizons exposed in the trench. Various features of the stratigraphy, pedology and structure in the trench sidewall are described in detail, particularly those leading to the interpretation of the MRE. Development of a shear fabric in the cobble-to small boulder-sized alluvium at the main fault zone indicates that interpretation of local neotectonic fault style and stress direction should be made at least 4 to 5 m below the free face of the fault scarp. Retro-deformation of the trench log clearly defines the MRE and distinguishes apparent vertical displacement from the actual displacement of 2.0 +/- 0.06 m. It also reveals that 1.9 m of surface extension occurred during the rupture, as well as the depositional processes that subsequently buried the 32 m wide graben formed at the site.

Research Article| March 01, 2016 Iphakade is Earth Stewardship Science M.J. de Wit; M.J. de Wit AEON-ESSRI, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa e-mail: Maarten.deWit@nmmu.ac.za Search for other works by this author on: GSW Google Scholar P. Booth P. Booth AEON-ESSRI, and Department of Geosciences, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa e-mail: Peter. Booth@nmmu.ac.za Search for other works by this author on: GSW Google Scholar Author and Article Information M.J. de Wit AEON-ESSRI, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa P. Booth AEON-ESSRI, and Department of Geosciences, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa e-mail: Maarten.deWit@nmmu.ac.za e-mail: Peter. Booth@nmmu.ac.za Publisher: Geological Society of South Africa First Online: 20 Nov 2017 Online Issn: 1996-8590 Print Issn: 1012-0750 © 2016 March Geological Society of South AfricaGeological Society of South Africa South African Journal of Geology (2016) 119 (1): 3–14. https://doi.org/10.2113/gssajg.119.1.3 Article history First Online: 20 Nov 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M.J. de Wit, P. Booth; Iphakade is Earth Stewardship Science. South African Journal of Geology 2016;; 119 (1): 3–14. doi: https://doi.org/10.2113/gssajg.119.1.3 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search © 2016 March Geological Society of South Africa Two collaborative bilateral Earth System Science Programmes - Inkaba yeAfrica and !Khure Africa - have been active for 12 and 6 years with Germany and France, respectively, and have been generously supported by DST and NRF throughout this time (see www.inkaba.org). More recently the two programmes merged into one as the bilateral spirits of these programmes started to fade. It is therefore timely to move on and establish a South African Programme that can stand on its own, and attract international collaborations on the basis of its indigenous research excellence in... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The location and estimated magnitude of a recent surface rupturing earthquake along the eastern part of the Kango Fault traversing the southern Cape Fold Belt, South Africa, is reported here, as well as the minimum recurrence interval and maximum slip rate. These palaeoseismic data are derived from analysis of the mapped logs of an 82 m long, 5 m deep trench excavated across the fault, supported by 12 optically stimulated luminescence (OSL) dates.The tectonic event that formed the observed 2.0 +/- 0.06 m free-standing fault scarp at the trench site had a moment magnitude estimated between 6.97 +/- 0.01 M and 7.18 +/- 0.01 M. According to the recently established Environmental Scale of Intensity, the rupture was devastating (ESI I-o = XI). It would have been accompanied by strong ground shaking felt across most of South Africa by the ancestors of the indigenous people groups who experienced the well-known 6.3 M Ceres-Tulbagh event of 29 September 1969 (currently South Africa's largest and most damaging earthquake). This latter strike-slip event occurred along the western end of the same Ceres-KangoBaviaanskloof-Coega (CKBC) fault system, but was not accompanied by significant surface deformation. In contrast, the Kango 'Toorwater' earthquake reported here displaced the land surface vertically, by over 2 m in places. While the fault scarp extends laterally for at least 84 km, from near the town of De Rust, east of Oudtshoorn, towards the start of the Baviaanskloof in the Eastern Cape, it is unlikely the entire surface rupture length originated during only the most recent event.The palaeoseismic data reported here have contributed to a seismic source characterization model used to update the existing seismotectonic model for South Africa, first established in the mid-1990's, and revised at various intervals since. The presence of a potentially active, capable, seismogenic structure within a low-seismicity intraplate stable cratonic region suggests that the current 5.3 to 6.3 M m(max) for the south and south eastern Cape must be reviewed, should these data be included in a revised ProbabilisticSesimic Hazard Assessment (PSHA) for critical structures in the region.

We report on geochemical and petrophysical properties of shales from the Prince Albert, Whitehill and Collingham Formations of the Lower Karoo Supergroup, near Jansenville in the Eastern Cape, close to the tectonic front of the Cape Fold Belt. Results are based on two boreholes sited on a southerly dipping limb of a shallowly plunging syncline. Structural, sedimentological, lithological, mineralogical, geochemical and petrophysical analyses provide detailed characteristics that have become the focus of interest for potential shale gas occurrences.The black shales of the Whitehill Formation are composed of quartz, illite, muscovite and chlorite, with lesser plagioclase and accessary pyrite. The Collingham Formation rocks have the largest proportion of quartz, which gives this formation a higher brittleness factor than that of the Prince Albert and Whitehill formations. Mercury porosimetry analyses yield average meso- and macroporosity values of 0.83% for black shales of the Whitehill Formation, confirming that these sediments are tightly packed. Layers of dolomite within the shales have porosities of 2.9%, and pores measuring 1.5 mu m wide.The black shales of the Whitehill Formation have an average total organic carbon (TOC) content of 4.5 weight % whereas the TOC content of shales in the Collingham and Prince Albert Formations is <1 weight %. The elemental composition and relatively higher delta C-13 and delta N-15 stable isotope values suggest that the Whitehill Formation was deposited under anoxic conditions, which led to the preservation of the mixed marine and terrestrial organic matter, whereas the Prince Albert and the Collingham Formations were deposited under oxidizing conditions.High maximum temperature values (Tmax average: 528 degrees C), low overall hydrogen and oxygen index values (all from Rock Eval analyses) and high reflectance measurements on bitumen (BRo= 4%) characterise these sedimentary rocks as over mature. As a consequence, they display few hydrocarbon yields in pyrolysis and thermovaporization experiments, and offer a minor late-gas potential.The main characteristics of black shales in the study area indicate that their overmaturity with respect to hosting gas deposits is attributed to the tectono-metamorphic overprinting during the Cape Orogeny (ca. 250 Ma, Halbich, 1993; Hansma et al., 2013).Rocks of the lower Karoo Supergroup outcropping within the area flanking the northern tectonic margin of the Cape Fold Belt therefore have limited potential for hosting shale gas deposits. This finding has implications for estimates of potential shale gas resources of the Karoo Basin.

Geological structures at two localities, some 20 km apart, along the R67 National Road between Grahamstown and Fort Beaufort, show that thrust faulting and folding have affected rocks of the Karoo Supergroup at both localities. At the northern locality, which is only 10 km south of Fort Beaufort, a prominent backthrust displaces shales and mudstones in hanging wall strata southwards over footwall rocks containing a series of forethrusts with a ramp/flat configuration, as well as imbricate faults, all dipping south. The backthrust developed in response to southward movement of hanging wall rocks, creating a gentle fold above a proposed footwall ramp. At the southern locality, a complex arrangement of fore and backthrusts in a structural triangle zone, composed mainly of sandstone beds, formed as a result of duplexing. The duplex is truncated by a backthrust on its northern side, the latter forming part of a series of backthrusts into the foreland. The development of structures at both localities is interpreted as coeval because the fold axial planes and strike orientation of thrusts have the same structural orientations. A compressional model is invoked to explain the structural harmony displayed by the thrust faulting and folding. Structures at the study sites are linked to a proposed sole thrust/detachment fault rooted in Cape Supergroup rocks farther south, where thrust faulting is known to be present in these rocks. The presence of backthrusts just south of Fort Beaufort suggests that the deformation front for the Cape Fold Belt, including further fore-thrusting, occurs to the north of the northern locality studied.

A study of Late Palaeozoic Witteberg Group rocks (Cape Supergroup) near Kirkwood, Eastern Cape was carried out to determine the viability of extracting silica for solar cell production. Mineralogical, geochemical and structural analyses of selected outcrops of quartz-arenites showed that source rocks in the study area do not possess the appropriate chemical attributes to warrant extraction of silica. Despite this finding the study presents valuable information on strata composition and structural data which are compared and interpreted with known regional structural patterns of the Cape Fold Belt in the Eastern Cape.Samples from the Witpoort Formation were analyzed using petrographic light microscopy, scanning electron microscopy and X-ray fluorescent spectroscopy. Analyses indicate that samples are composed almost entirely of quartz, with accessory biotite, muscovite, sericite, baryte, apatite, nitile and monazite. Haematite occurs most frequently along fractures, and is more prevalent in the Rooirand Member than the Perdepoort Member, giving the former a reddish brown colour on outcrop. The presence of chemical impurities is thought to be paaly controlled by the original depositional environment, namely, near-shore and beach environments.Strata in the study area display a range of fold styles, mostly showing northward vergence. Low angle thrust faults clip south and some thrusts dip north. In general, the orientation of fore-thrusts and folds in the study area indicate a northward-directed compression event during the Late Palaeozoic. This pattern conforms to the structural development in other parts of the Cape Fold Belt in the Eastern Cape. South-clipping normal faults and strike-slip faults post-date thrust faulting, and formed during the breakup of Gondwana, during the Mesozoic, transecting all other structures in the study area.

The Cape Fold Belt has been a topic of investigation for over 100 years, and with each renewed surge of interest, new ideas on the origin of the fold belt as a whole have come to the fore. During the last two decades researchers who have focused on the structural geology of the Cape Supergroup, in particular, have provided greater insight into local characteristics of the fold belt, but a broader understanding of the tectonic development of the fold belt is not without controversy. Research focus has been on documentation and interpretation of mainly thin skinned structural characteristics in the central and eastern part of the main “arm” of the fold belt. Identification of thrust sheets, particularly in lower units of the Cape Supergroup coincident with the thickest accumulations of sediment, led researchers to propose a thrust stacking mechanism to account for the abnormal thickness of quartzitic units, rather than previously accepted models. The significance of thrust stacking and the disruptive effect it has had on sediments of the entire Cape Supergroup is emphasized. The stratigraphic order of Cape Supergroup rocks, as currently accepted, is therefore called into question, especially in areas of pervasive thrusting, and needs revision. Some tectonic models proposed to date account only for local characteristics of the fold belt, whereas other models do take into account the entire fold belt. Examples of the latter include the Andean type model which adequately explains the general northward vergence of structures, but thickness estimates of stratigraphic packages of Cape and Karoo Supergroup cover rocks revealed through recent seismic surveys across the central part of the fold belt do not corroborate this model. Proponents of the Transpression model, on the other hand, advocate that right-lateral strike-slip motion produced en-echelon folds and flower structures in some parts of the fold belt. The latter model lacks refinement in that it does not explain the presence of structures interpreted to have formed through left-lateral movement, especially in the western part of the fold belt. This paper outlines unanswered questions relating to the stratigraphy, structural geology and proposed tectonic models that remain enigmas, and these need resolving before the tectono-thermal history of the fold belt can be fully understood.

This review focuses on our understanding of the structural and tectonic setting of the Cape Fold Belt (CFB) based on contributions made by academics and professional geologists, mainly during the last two decades. Most of the research concentrated on the identification and mapping of thrust faults in the southern arm of the CFB, as well as seismic surveys which provided data for putting forward tectonic models to account for structural and stratigraphic features of the fold belt. Thrust stacking is a common characteristic in all three stratigraphic sequences of Palaeozoic Cape Supergroup rocks. A complex pattern of ductile and brittle deformation occurs in the Table Mountain Group whereas in the overlying Bokkeveld and Witteberg Groups there is a close association of folding with development of thrust faults. Thin-skinned characteristics are prevalent in the southern arm of the CFB, but give way to thick-skinned features in the southernmost central part of the fold belt where basement rocks have been thrusted northwards towards the foreland. A variety of tectonic models proposed for the CFB have generated some controversy among researchers. Currently popular are the Andean and the strike-slip (transpression) models. The former accounts for the northward vergence of structures in the southern arm of the fold belt, but thicknesses of crustal substrate obtained from recently carried out deep sounding seismic surveys across the fold belt do not entirely corroborate this model. Structural characteristics in cover rocks that favour the transpression model are en echelon folds and faults as well as flower structures which are commonly associated with strike-slip regimes.

The current seismo-tectonic model for South Africa depicts the south-eastern Cape Fold Belt as a tectonically stable intraplate-type environment, where earthquakes are relatively infrequent to rare, particularly large surfacerupturing events. The closest surface rupture recorded by the SANSN, which underpins the model, is the extensional Mozambique 7.2M event on 22 February 2006, related to southward propagation of the East African Rift. A similar 84km-long extensional surface rupture has been found along the Kango fault within the southern Cape Fold Belt, 50km east of Oudtshoorn. Optically stimulated luminescence dating indicates it occurred around 10,620 ± 509, at the start of the Holocene. This fault, together with the adjoining Baviaanskloof and Coega faults, and other nearby adjacent faults, is the subject of a palaeoseismic investigation to determine the Quaternary tectonic history of the south-eastern continental margin. This region of South Africa has little seismic information, and the record is too short to include the long recurrence intervals of large, surface damaging earthquakes typical of intraplate regions. The data reported includes the location and extent of the surface rupture, the local stress direction, the date and magnitude of the most recent event, the minimum recurrence interval, and maximum slip rate. The earthquake environmental effects are also evaluated according to the new Environmental Seismic Intensity Scale (ESI 2007), to provide an independent assessment of seismic intensity. A potential local tectonic driver, the Cape Isostatic Anomaly (CIA) is also discussed, as well as a possible trigger mechanism leading to the rupture. Results should facilitate PSHA of several new critical facilities planned for the province.

A 100 metre section of quarry face in the Moregrove quarry in Port Elizabeth was mapped with the purpose of carrying out a detailed structural analysis of Peninsula Formation rocks. Along the quarry face primary sedimentary structures and deformation structures (faults, cleavages, joints) were measured in detail with a Brunton compass, and results plotted on an accurately constructed section, with accompanying stereogram data. Rock types are predominantly quartzites with lesser phyllite horizons. The latter occur as lense-shaped pods along faults zones and are highly sheared. Several thrust faults dipping shallowly towards the southwest have in places imbricate faults ramping up to join thrust planes, thus forming duplex structures. Normal faults are also present showing displacements of the order of only a few metres. A fracture cleavage, probably related to thrust development, is prominent in hangingwall blocks. At least two open joint sets are present in the quartzites which enhance the close-spaced fracture patterns in these rocks. In addition there are en echelon quartz filled fractures, which relate to the normal fault development probably during a post- thrusting episode. Structures formed as a result of compressional tectonism are interpreted as having developed during the Cape Orogeny, during the Late Palaeozoic, whereas normal faulting is probably related to the breakup of Gondwana, during the Mesozoic.

This study of Late Palaeozoic Witteberg Group rocks (Cape Supergroup) near Kirkwood, Eastern Cape, focused mainly on quartzitic rocks because these rock types crop out in mountainous terrain where lithological and structural data collection was possible. A detailed structural analysis has been carried out and the results compared to the regional structural pattern of the Cape Fold Belt in the Eastern Cape. Field methods include air photo interpretation of lithological and structural features, and the measurement of structural elements with the aid of a Brunton compass. Thin sections of the main rock types analysed by microscopic and SEM techniques show that arenaceous rocks are composed predominantly of quartz, whereas argillaceous rocks contain mainly micaceous minerals with lesser quartz, feldspar and iron oxides. Strata are folded into open anticlines and synclines that plunge at shallow angles to the east-southeast as well as in the opposite direction and show northward vergence. The general east–west orientation of thrust faults, and their southward dips indicate that they formed during a northward-directed stress field that was present during the Late Palaeozoic. Predominantly south-dipping normal faults formed during the Mesozoic, as part of the process of the break-up of Gondwana.

A field study of the lowermost stratigraphic unit of the Witteberg Group (Cape Supergroup, Steytlerville area, Eastern Cape), has shown that rocks of the Weltevrede Formation are composed predominantly of folded argillaceous rocks intercalated with lesser thinly-bedded arenaceous beds. The purpose of this study is to document and provide detailed lithological and structural data, and interpret these in relation to regional geological and structural patterns in the area. Rocks of the Weltevrede Formation show colour variations in both shales and quartzites as a result of variable quantities of iron oxide minerals in the rock. Sedimentary structures are plentiful, especially in quartzites and are useful in the interpretation of facing direction of strata. Trace fossils characteristic of the Witteberg Group, especially Zoophycos and Monocraterion are frequently present in all rock types. Strata are folded into open anticlines and synclines that plunge at shallow angles towards the eastsoutheast. Folds all verge northwards, indicating deformation forces originated from the south. One set of faults have an east-west strike orientation, whereas a second set strike approximately north-south. The former are interpreted as products mainly of flexure-slip folding, whereas the latter are probably related to a prominent strike-slip fault in close proximity to the study area. From the orientation of structures in the study area we conclude that all structures in the study area conform with the regional structural pattern, and therefore have an integral relationship with deforming forces that were present during the Cape Orogeny, during the Late Palaeozoic.

A structural study of Witteberg Group Rocks was conducted along the Soutkloof River, approximately 14 km east of Steytlerville, Eastern Cape Province of South Africa. Here a north to south geotraverse was studied in an attempt at unravelling the structural geology of the rocks belonging to the Upper Devonian to Lower Carboniferous Witteberg Group (Upper Cape Supergroup). These rocks are mostly arenaceous and include quartzite, sandstone, siltstone and shale which have been folded, faulted and metamorphosed. Thrust, normal and strike-slip faulting occur in the area. Shallow south dipping low-angle thrust fault planes are displaced by steep south-dipping thrust planes and subordinate north-dipping backthrusts. Displacement along thrust planes is predominantly northwards. Steeply dipping thrust fault planes are often reactivated by east-west striking normal faults. Strike-slip faulting post dates all structural features and displaces normal and thrust fault planes. Open to tight folds are present and are mostly north-vergent and often steepened or truncated by steep south-dipping thrust fault planes. South-vergent folds are related to backthrusting and post-fold faulting. The study has revealed that the current geologic map and the local stratigraphy were compiled without recognising major structural features such as thrust, normal and strike-slip faulting, and its validity is therefore questioned. Extensive faulting suggests that the conventional stratigraphic interpretation of the Witteberg Group strata should be revised.

The Weltevrede Formation (Witteberg Group, Cape Supergroup) at Steytlerville was mapped to elucidate the relationship between folding and thrusting in this formation. The Weltevrede Formation has an upper, mainly arenaceous unit and a lower, mainly argillaceous unit. Folds of variable style and wavelength are generally north vergent and plunge towards the west-northwest and east-southeast. Folds have an associated axial planar cleavage which dips steeply to the south-southwest, Numerous thrust faults transect the Weitevrede Formation, occurring in closely spaced zones in the lower unit of the formation. Where the boundary thrust in the study area changes its strike orientation and obliquely transects strata north of Steytlerville it is interpreted as having a ramp-flat-ramp geometry. In the eastern part of the study area individual thrusts locally have outcrop traces similar to the boundary thrust, with easterly plunging folds in the hanging-wall of thrusts. Fold orientation, style, and amount of plunge are determined by competency and thickness of beds, position above thrust planes, and the intensity of deformation. Characteristics of thrusting and associated folding are interpreted in the context of a large duplex structure that formed during a northward-directed compression event associated with the Cape Fold Belt. West-northwest-striking normal faults which transect all existing structures formed during the break-up of Gondwana.

Selected outcrops along the Baakens valley and coastal strip east of Sardinia Bay were used to determine the overall structure of the Table Mountain Group (TMG) close to Port Elizabeth. A large recumbent fold (nappe?) structure is interpreted to be the result of an early phase of shortening. Pelitic horizons were subsequently smeared out along thrusts in the TMG. This caused repeated stacking, resulting in an unusually thick sequence of quartzites. The last phase of tectonism was extensional. An 8 km broad graben formed between two prominent west-northwest-striking fault zones, the Moregrove and Chelsea-Noordhoek faults

North-south-striking Pan-African shear zones in the Gariep marginal zone southeast of Eksteenfontein, Namaqualand, segment basement rocks of the Namaqua Province into crustal blocks averaging 4 km in width. Most of the shear zones are rotational faults, and some show large strike-slip and dip-slip displacements. In the centre of the area the most prominent shear, the Steenbok Shear, for example, has a strike-slip component of 8,8 km and a dip-slip component of 6,3 km. Shears in the western part of the area have a more complex history than those east of the Kromnek, and Steenbok Shears

Rocks of pre-Cape age in the Gamtoos area are preserved in an elongate northwest-southeast-trending horst block bounded by the Elandsberg and Gamtoos Faults. The pre-Cape strata have been deformed into a series of recumbent isoclinal folds sliced by a number of southward-dipping imbricate thrusts. Subsequent Cape folding has further affected the pre-Cape rocks, but the pre-Cape and Cape folds are different in style and orientation