Cape Fold Belt Research Articles

Mineralisation controls for the diverse Cape manganese occurrences, South Africa

Abstract The Cape Fold Belt, comprising folded sedimentary sequences from predominantly the Palaeozoic Cape Supergroup, hosts a multitude of manganese occurrences and mineral deposits, many of which were subject to historical mining activity. Although size, grade and quality issues negate their modern-day exploitation for the steel-making process, the mechanisms by which Mn has enriched at these sites holds scientific value for our understanding of low-temperature Mn (bio-)geochemical cycling. Deposits located within the Cape Fold Belt comprise structure-hosted Mn deposits and a little described class of Mn mound deposits associated with chalybeate thermal springs (temperature = 41 to 48°C). Although the relationships between the two remain tenuous, detailed study of both classes provides insight into the conditions that favour Mn accumulation in the near-surface and sub-aerial environments. Comparisons between the physicochemistry of manganiferous- and non-manganiferous thermal springs suggest that manganese solubility is favoured by warm, acidic and slightly reducing fluids with elevated salinity. Transport, and associated fluid focusing typically within highly permeable sandstone units, serves to locate Mn mineralisation in near-surface structurally-complex trap sites that provide both accommodation space and conditions that are sufficiently oxidising. Where manganiferous spring waters spill out at surface, oxidation is caused by contact with atmospheric O2 to form Mn mound deposits, and ambient Mn-oxidising microbiota (e.g., genus Ramlibacter, and members of Burkholderiales, Rhodocyclaceae, and Oxalobacteraceae) are likely to play a role in enhancing the kinetics of this process. Relative to the structure-hosted deposits, these Mn mound deposits are typically lower grade (higher iron content) and relatively friable (high porosity and fine grain sizes). Supergene and diagenetic processes can lead to localised upgrade of the Mn mound material, although typically not to ore grade.

U-Pb detrital zircon age determination and provenance of the lower Karoo succession from the Karoo Research Initiative (KARIN) borehole KWV-1, Eastern Cape Province, South Africa

Abstract In recent years, the maximum age of sedimentation and possible sources of detritus to the sedimentary successions of the Karoo Supergroup has received a lot of interest, with various authors presenting age data from across the main Karoo Basin (MKB). Our paper aims to contribute to this ever-growing geochronological database as we report weighted mean ages for the youngest zircons as well as detrital zircon age distributions for the lower Karoo Supergroup succession sampled from the Centre of Excellence for Integrated Mineral and Energy Resource Analysis (CIMERA)-Karoo Research Initiative (KARIN) drill core KWV-1. A total of 880 near concordant zircon ages were determined using Laser Ablation Quadrupole Inductively Coupled Plasma Mass Spectrometry (LA-Q-ICP-MS) from fifteen samples representing the Dwyka Group, the Collingham-, Ripon-, Fort Brown- and Waterford formations of the Ecca Group and the Koonap Formation of the Beaufort Group as intersected by this ~2 352 m deep research borehole drilled in the southeastern sector of the basin. The weighted mean ages for the youngest zircons calculated for the formations of the Ecca- and Beaufort groups compares with findings reported by other authors and with the ages reported for tuffaceous layers associated with these units. The weighted mean ages for the youngest zircons of the Dwyka Group reflect the age of the youngest source area and do not aid in constraining the maximum age of deposition. A significant change in detrital zircon age distribution was noted between the Dwyka Group and the overlying formations of the Ecca and Beaufort groups, which we interpret as a change in provenance. The major Meso-to Neoproterozoic detrital zircon age fractions present in the Dwyka Group are attributed to source areas located towards the north and northeast of the MKB, in line with regional ice flow directions. A significant late Carboniferous to Permian detrital zircon age fraction is however observed throughout the formations of the Ecca- and Beaufort groups, with a lesser fraction of older zircon ages. The prevailing youngest age fraction reflects ages associated with magmatic source areas in the Gondwanide Orogeny located towards the south of the MKB at the time of deposition, while the recycling of deformed sedimentary strata of the Cape Supergroup contained in the Cape Fold Belt is considered the source of older detritus. The source of detritus to the MKB remained unchanged during the deposition of the respective formations of the Ecca- and Beaufort groups, despite changes in the depositional environment brough on by regional tectonics.

Petrographic characterization of Late Jurassic to Early Cretaceous sandstones in the offshore Bredasdorp Sub-basin, South Africa: An example of a dynamic recycled provenance interpretation

The Mesozoic syn-rift sediments of the Bredasdorp Sub-basin were deposited during the structural inversion of the orogenic Cape Fold Belt (CFB), a crucial time during the break-up of Gondwana. The Late Jurassic to Early Cretaceous non-marine to marine sediments of the Bredasdorp Sub-basin were studied to infer their composition, parent-rock lithologies, tectonic settings and their dynamic response to tectonic perturbations. The knowledge on the provenance terrains in the Bredasdorp Sub-basin is poorly understood and therefore this research shed light on these provenance terrains. Petrographic quantitative analysis revealed that the mineralogical composition of the sediments comprises mainly of litho-quartzose and feldspatho-litho-quartzose sediments. Modal petrographic data indicates a recycled orogen provenance on QFL plots suggesting the occurrence of a collisional provenance terrain. This setting can be interpreted as the reactivation of the CFB structures eroding the Bokkeveld Group (and younger Karoo Supergroup) and the Table Mountain Group metasediments (and Pre-Cape sediments). The shedding of these sediments in the Bredasdorp Sub-basin were coeval with the deposition of the D-V, V-BUSM and BUSM-1AT1 ‘informal’ sequences. Furthermore, an evolving recycled provenance from sedimentaclastic (un-dissected) to basementaclastic (dissected) sediments are proposed and could be a defining characteristic to the enigmatic offshore Jurassic-Cretaceous stratigraphic nomenclature.During the deposition of the D-V Sequence, a spatial variation in provenance due to intrabasinal uplifted fault blocks (possibly reactivated shear zones) occurred between the erosion of the Bokkeveld Group (and Karoo Supergroup) and the Table Mountain Group (TMG) metasediments. The deposition of the V-BUSM Sequence showed a similar compositional trend within their provenance terrain but showed a stronger correlation to an increased quartz and feldspar content. This is possibly due to the erosion of the dominant TMG, which was further supported by the occurrence of distinct type 3 polycrystalline quartz. The deposition of the BUSM-1AT1 sequence saw an increase in plutonic lithic fragments and feldspar content, indicative of an igneous source, which was attributed to the erosion of the proximal Cape Granite Suite. This distinction is crucial in creating a unifying stratigraphic nomenclature for the Jurassic-Cretaceous sequences of South Africa. A dynamic recycled orogen is envisaged for the Bredasdorp Sub-basin and therefore the use of these type of dynamic models should be incorporated in provenance models especially if there is a well-documented geological setting.

Braided-river architecture of the Triassic Swartberg member, Katberg Formation, South Africa: assessing age, fluvial style, and paleoclimate after the end-Permian extinction

ABSTRACT The Triassic Katberg Formation has played a central role in interpreting the end-Permian ecosystem crisis, as part of a hypothesis of aridification, vegetation loss, and sediment release in continental settings. We use drone images of an inaccessible cliff near Bethulie to investigate the Swartberg member, a braided-fluvial body 45 m thick, describing remote outcrop facies to identify geomorphic units and using spatial analysis to estimate their proportions in 2-D sections. Here the Swartberg member comprises three channel belts within shallow valleys, the lowermost of which is ∼500 m wide and incised into lacustrine deposits. The component channel bodies consist mainly of trough cross-bedded sand sheets (48%) and channel-scour fills (28%). Recognizable bars (15%) comprise unit bars with high-angle slipfaces and mounded bar cores (components of mid-channel compound bars), bars built around vegetation, and bank-attached bars in discrete, probably low-sinuosity conduits. Abandoned channels constitute 8% and 16% of flow-parallel and -transverse sections, respectively. When corrected for compaction, the average thalweg depth of the larger channels is 3.9 m, with an average bankfull width of 84 m, scaling broadly with the relief of the bars and comparable in scale to the Platte and South Saskatchewan rivers of North America. The fluvial style implies perennial but seasonably variable flow in a vegetated landscape with a humid paleoclimate. The northward paleoflow accords with regional paleoflow patterns and deposition on a megafan sourced in the Cape Fold Belt, where the Swartberg member represents the avulsion of a major transverse-flowing river. U-Pb dating of in situ and reworked pedogenic carbonate nodules from below the base of the Swartberg member yielded Anisian to Ladinian ages (Middle Triassic), younger than the previously assumed Early Triassic age and implying that considerable gaps in time exist in the succession. An assessment of the interval spanning the lower to mid Katberg Formation is needed to reevaluate the inferred unidirectional trend in fluvial style, aridification, and fossil distributions in this condensed, disjunct succession.

Charles Darwin's discovery of Devonian fossils in the Falkland Islands, 1833, and its controversial consequences

Abstract In March 1833 Charles Darwin discovered Devonian fossils in the Falkland Islands. He was excited by his find but could have had little premonition of the long-running geological controversy that he was initiating. Darwin's fossils matched a coeval South African fauna and, as further collections were made, the association was apparently strengthened. A particularly important contribution arose around 1910 through collaborations between a local collector, Constance Allardyce, and professional palaeontologists: Ernest Schwarz in South Africa and John Clarke in the USA. The accumulating evidence was seized upon by the early proponents of ‘displacement theory’ – continental drift – notably Alexander Du Toit, who relocated the Falkland Islands northward for his 1927 South Atlantic reconstruction. A more radical, but geologically sounder proposal arose in 1952 when Ray Adie suggested that the Falkland Islands, rotated through 180°, had originated as the eastward culmination of the Cape Fold Belt and Karoo Basin. In effect, Adie had presciently described a rotated microplate, perhaps the first on record. An opposing view saw the Falkland Islands as part of a fixed, South American promontory, and argument around these two contrasting interpretations of South Atlantic geology continues to the present day.

Braided-river architecture of the Triassic Swartberg Member, Katberg Formation, South Africa: assessing age, fluvial style, and paleoclimate after the End-Permian Extinction

The Triassic Katberg Formation has played a central role in interpreting the end-Permian ecosystem crisis, as part of a hypothesis of aridification, vegetation loss, and sediment release in continental settings. We use drone images of an inaccessible cliff near Bethulie to investigate the Swartberg member, a 45 m thick braided-fluvial body, describing remote outcrop facies to identify geomorphic units and using spatial analysis to estimate their proportions in 2D sections. Here the Swartberg member comprises three channel belts within shallow valleys, the lowermost of which is ~500 m wide and incised into lacustrine deposits. The component channel bodies consist mainly of trough cross-bedded sand sheets (48%) and channel-scour fills (28%). Recognizable bars (15%) comprise unit bars with high-angle slipfaces and mounded bar cores (components of mid-channel compound bars), bars built around vegetation, and bank-attached bars in discrete, probably low-sinuosity conduits. Abandoned channels constitute 8% and 16% of flow-parallel and -transverse sections, respectively. When corrected for compaction, the average thalweg depth of the larger channels is 3.9 m, with an average bankfull width of 84 m, scaling broadly with the relief of the bars and comparable in scale to the Platte and South Saskatchewan rivers of North America. The fluvial style implies perennial but seasonably variable flow in a vegetated landscape with a humid paleoclimate. The northward paleoflow accords with regional paleoflow patterns and deposition on a megafan sourced in the Cape Fold Belt, where the Swartberg member represents the avulsion of a major transverse-flowing river. U-Pb dating of in situ and reworked pedogenic carbonate nodules from below the base of the Swartberg member yielded Anisian to Ladinian ages (Middle Triassic), younger than the previously assumed Early Triassic age and implying that considerable gaps in time exist within the succession. An assessment of the interval spanning the lower to mid Katberg Formation is needed to reevaluate the inferred unidirectional trend in fluvial style, aridification, and fossil distributions in this condensed, disjunct succession.

The amalgamation of Gondwana: calcite twinning and finite strains from the early–late Paleozoic Buzios, Ross, Kurgiakh and Gondwanide orogens

Abstract Orientated carbonate (calcite twinning strains; n = 78 with 2414 twin measurements) and quartzites (finite strains; n = 15) were collected around Gondwana to study the deformational history associated with the amalgamation of the supercontinent. The Buzios orogen (545–500 Ma), within interior Gondwana, records the high-grade collisional orogen between the São Francisco Craton (Brazil) and the Congo–Angola Craton (Angola and Namibia), and twinning strains in calc-silicates record a SE–NW shortening fabric parallel to the thrust transport. Along Gondwana's southern margin, the Saldanian–Ross–Delamerian orogen (590–480 Ma) is marked by a regional unconformity that cuts into deformed Neoproterozoic–Ordovician sedimentary rocks and associated intrusions. Cambrian carbonate is preserved in the central part of the southern Gondwana margin, namely in the Kango Inlier of the Cape Fold Belt and the Ellsworth, Pensacola and Transantarctic mountains. Paleozoic carbonate is not preserved in the Ventana Mountains in Argentina, in the Falkland Islands/Islas Malvinas or in Tasmania. Twinning strains in these Cambrian carbonate strata and synorogenic veins record a complex, overprinted deformation history with no stable foreland strain reference. The Kurgiakh orogen (490 Ma) along Gondwana's northern margin is also defined by a regional Ordovician unconformity throughout the Himalaya; these rocks record a mix of layer-parallel and layer-normal twinning strains with a likely Himalayan (40 Ma) strain overprint and no autochthonous foreland strain site. Conversely, the Gondwanide orogen (250 Ma) along Gondwana's southern margin has three foreland (autochthonous) sites for comparison with 59 allochthonous thrust-belt strain analyses. From west to east, these include: finite strains from Devonian quartzite preserve a layer-parallel shortening (LPS) strain rotated clockwise in the Ventana Mountains of Argentina; frontal (calcite twins) and internal (quartzite strains) samples in the Cape Fold Belt preserve a LPS fabric that is rotated clockwise from the autochthonous north–south horizontal shortening in the foreland strain site; Falkland Devonian quartzite shows the same clockwise rotation of the LPS fabric; and Permian limestone and veins in Tasmania record a thrust transport-parallel LPS fabric. Early amalgamation of Gondwana (Ordovician) is preserved by local layer-parallel and layer-normal strain without evidence of far-field deformation, whereas the Gondwanide orogen (Permian) is dominated by layer-parallel shortening, locally rotated by dextral shear along the margin, that propagated across the supercontinent.

The Ordovician System of South Africa: a review

AbstractOutcrops of the Ordovician System in South Africa are extensive; they cover significant portions of the Northern, Western and Eastern Cape provinces as part of the Cape Fold Belt as well as the KwaZulu-Natal Province as supracrustal cover overlying the Natal sector of the Paleoproterozoic Namaqua-Natal metamorphic province. Within the Cape Fold Belt, Ordovician rocks of the Table Mountain Group (Piekenierskloof, Graafwater, Peninsula, Pakhuis and Cedarberg formations as well as the enigmatic Sardinia Bay Formation) outcrop extensively whilst pre-Cape rocks of the Kansa Group (Vaartwell, Uitvlug, Gezwinds Kraal and Schoongezigt formations) and Schoemanspoort Formation are present within the Kango Inlier encapsulated by the fold belt. The Natal Group (Durban and Mariannhill formations) is entirely located within KwaZulu-Natal. For the most part, these metasiliciclastic rocks are markedly unfossiliferous except for the world class fossil deposits of the Cedarberg Formation and important trace fossil sites in the Graafwater, Peninsula and Pakhuis formations. The lack of palaeontological material and other accurate geochronological proxies in these successions (as well as those of the Kansa and Natal groups and Schoemanspoort Formation) makes estimations of relative age constraints tenuous at best and difficult to correlate with global Ordovician chronostratigraphic frameworks. Regardless of the challenges faced in correlating these rocks within global frameworks, these rocks provide a unique low latitude glimpse into Earth surface processes and the feedback loops that ensued within the biological realm along the southern margin of Gondwana.

Coeval development of extensional and contractional features along transform margins: insights from the Diaz Marginal Ridge

Abstract The Diaz Marginal Ridge (DMR), on the southern transform margin of South Africa, is a bathymetric feature parallel to the Agulhas Falkland Fracture Zone (AFFZ) that has long been considered an archetype marginal ridge; and yet its origin and evolution remains unconstrained. Using recently acquired seismic data we present a new structural interpretation of the DMR and its association with the evolution of both the AFFZ and the Southern Outeniqua Basin. In contrast to previous scenarios invoking thermo-mechanical explanations for its evolution, we observe a more straightforward structural model in which the genesis of the DMR results from the structural inversion of a Jurassic rift basin. This inversion resulted in the progressive onlap of latest Valanginian–Hauterivian-aged stratigraphic units, important for the formation of stratigraphic plays of the recent Brulpadda discovery. Paradoxically, this contraction is contemporaneous with renewed extension observed in the inboard normal faults. The orientation of the DMR and inboard structures have been demonstrated to be controlled by the underlying Cape Fold Belt (CFB) fabric. The onset of motion across the AFFZ shear system led to east–west-orientated maximum stress and north–south-orientated minimum stress. We propose this stress re-orientation resulted in strain partitioning across existing structures whereby in addition to strike-slip on the AFFZ there was coeval extension and contraction, the nature of which was determined by fault orientation. The fault orientation in turn was controlled by a change in orientation of the underlying CFB. Our model provides new insights into the interplay of changes in regional stress orientation with basement fabric and localized magmatism along an evolving transform. The application of horizontal strain partitioning can provide an explanation of similar features observed on other transform margins.

The composition, geography, biology and assembly of the coastal flora of the Cape Floristic Region.

The Cape Floristic Region (CFR) is globally recognized as a hotspot of plant diversity and endemism. Much of this diversity stems from radiations associated with infertile acid sands derived from sandstones of the geologically ancient Cape Fold Belt. These ancient montane floras acted as the source for most subsequent radiations on the Cape lowlands during the Oligocene (on silcretes) and Mio–Pliocene (on shales). The geomorphic evolution of the CFR during the Plio–Pleistocene led to the first large-scale occurrence of calcareous substrata (coastal dunes and calcarenites) along the Cape coast, providing novel habitats for plant colonization and ensuing evolution of the Cape coastal flora—the most recent diversification event in the Cape. Few studies have investigated the CFR’s dune and calcarenite floras, and fewer still have done so in an evolutionary context. Here, we present a unified flora of these coastal calcareous habitats of the CFR and analyze the taxonomic, biological and geographical traits of its component species to gain insights into its assembly. The Cape coastal flora, comprising 1,365 species, is taxonomically dominated by the Asteraceae, Fabaceae and Iridaceae, with Erica, Aspalathus and Agathosma being the most speciose genera. In terms of growth-form mix, there is a roughly equal split between herbaceous and woody species, the former dominated by geophytes and forbs, the latter by dwarf and low shrubs. Species associated with the Fynbos biome constitute the bulk of the flora, while the Subtropical Thicket and Wetland biomes also house a substantial number of species. The Cape coastal flora is a distinctly southern African assemblage, with 61% of species belonging to southern African lineages (including 35% of species with Cape affinity) and 59% being endemic to the CFR. Unique among floras from the Cape and coastal Mediterranean-climate regions is the relatively high proportion of species associated with tropical lineages, several of which are restricted to calcareous substrata of the CFR. The endemic, calcicolous component of the flora, constituting 40% of species, represents 6% of the Cape’s regional plant diversity—high tallies compared to other biodiversity hotspots. Most coastal-flora endemics emerged during the Plio–Pleistocene as a product of ecological speciation upon the colonization of calcareous substrata, with the calcifugous fynbos floras of montane acid substrata being the most significant source of this diversification, especially on the typically shallow soils of calcarenite landscapes. On the other hand, renosterveld floras, associated with edaphically benign soils that are widespread on the CFR lowlands, have not been a major source of lineages to the coastal flora. Our findings suggest that, over and above the strong pH gradient that exists on calcareous substrata, soil depth and texture may act as important edaphic filters to incorporating lineages from floras on juxtaposed substrata in the CFR.

Late Devonian non-marine Naiadites devonicus nov. sp. (Bivalvia: Pteriomorphia) from the Waterloo Farm Lagerstätte in South Africa

This study defines a new bivalve species, Naiadites devonicus nov. sp., of Famennian (Late Devonian) age. The material was excavated from the non-marine deposits of the Waterloo Farm Lagerstätte in South Africa, which form part of the Witpoort Formation (Witteberg Group, Cape Supergroup) of the Cape Fold Belt region. The type material of Naiadites devonicus nov. sp. is preserved in metamorphosed, clayey to silty mudstones of a coastal estuarine to lagoonal facies, deposited along the shoreline of the Agulhas Sea, in a high-palaeolatitude Gondwanan setting. The new bivalve species is the stratigraphically oldest representative of the genus Naiadites Dawson. It is a faunal element of a high-latitude palaeoecosystem, immediately preceding the Hangenberg extinction event at the end of the Late Devonian.

Palaeo-environmental and provenance reconstruction of the Lower Permian mudstones (lower Ecca Group) in the main Karoo Basin, South Africa

Assessing the composition and origin of the organic matter-rich mudstones, which dominate the early basin fill of the main Karoo Basin of South Africa, are essential for reconstructing the palaeo-environment, palaeo-climate, and potential provenance areas in southern Gondwana during the Early Permian. This study investigates the sedimentary geochemistry and petrography (e.g., major oxides, trace elements, mineral compositions, sedimentary structures, textures) of the lower Ecca Group, which was sampled in newly drilled boreholes. Our results show that the rate of weathering decreased over time as the environment changed from an ice-house to a more hot-house setting (i.e., the Chemical Index Alteration is 72–85 in the Prince Albert Formation and 60–76 in the Collingham Formation). Comparisons of the V/Cr, V(V + Ni), and Ni/Co ratios and Fe–S-TOC ternary plot show oscillations between anoxic and oxic conditions during deposition. Furthermore, there is evidence, albeit somewhat equivocal, for changing palaeo-salinity levels, low sedimentation rates, and high bio-productivity. Trace-element Principal Component Analysis, the Index of Compositional Variability, and Discriminant Function Analysis of the older mudstones (Prince Albert and Whitehill formations) imply different provenance regions with felsic to intermediate signatures predominantly found in the western MKB and mafic signatures in the eastern MKB. The youngest unit, the Collingham Formation, has a more uniform composition across the region, and was mostly sourced from the quartz-arenites and granites most likely associated with the Cape Fold Belt.

Long-lived stable shelf deposition along Gondwana's southern margin during the Ordovician-Silurian: Inferences from U[sbnd]Pb detrital zircon ages of the Table Mountain Group (South Africa) and correlatives in Argentina and the Falklands/Malvinas Islands

The Ordovician-Silurian siliciclastic units of the Table Mountain Group (TMG; Cape Supergroup) of the Cape Fold Belt (CFB) are classically considered to signify a period of long-lived sedimentation along the southern margin of southern Africa. Despite its vast, prominent outcrop, meaningful interpretations regarding the provenance of the TMG, based on a representative number of UPb detrital zircon age fractions, remains lacking. Within southern Gondwana, the TMG succession is considered broadly time-correlative to the Sierra del Volcan and Balcarce formations of the Sierras Tandilia and lowermost successions of the Ventana Group of the Sierras Australes in Argentina and the Port Stephens Formation of the West Falkland Group (WFG) in the Falkland/Malvinas Islands and Natal Group (South Africa). UPb detrital zircon ages have previously been reported for the Balcarce Formation and Ventana and West Falkland groups. However, their age fractions have not necessarily been compared to the broadly time –equivalent units of the TMG. In addition to the overall scarcity of detrital zircon age data on the TMG, the validity of using conventional, qualitative probability density diagrams to display and interpret such data sets have come into question, with some authors arguing for a quantitative approach for comparing detrital zircon age data sets. A total of 1521 concordant UPb detrital zircon ages and some 330 LuHf isotope analysis for the Peninsula- and Skurweberg formations (TMG) are therefore contributed, from samples obtained throughout the CFB, along with detrital zircon age fractions for the Balcarce, Providencia and Port Stephens formations. A qualitative as well as quantitative approach to compare the UPb detrital zircon age fractions measured for these units were adapted. Noticeable similarities among detrital zircon age fractions of the Peninsula- and Skurweberg formations throughout the western to south-eastern reaches of the CFB could be confirmed by quantitative pairwise comparisons. These point towards very little change in sediment source during the deposition of the lower to upper formations of the TMG during the Ordovician-Silurian. Pairwise comparisons of the TMG zircon age fractions to those of the Balcarce-, Providencia and Port Stephens formations revealed that they all have major late Neoproterozoic to Cambrian and a late Mesoproterozoic to early Neoproterozoic age fractions in common, with some minor contributions from Ordovician-Silurian sources. Due to the overlap in prevalent detrital zircon age fractions as well as Hf-isotope signature of these units, it is difficult to assign a specific provenance area for them with a fair amount of confidence, even if dominant palaeocurrent directions are considered. A quantitative pairwise comparison among data sets of the same or time-equivalent formation did not necessarily allow for age fractions from different source areas to be sufficiently distinguished from each other. In contrast to the classically inferred Namaqua-Natal Metamorphic Complex (NNMC) as source major proto-source for the TMG, it is argued that the sediment sources were located much further to the north such as the Damara and Mozambique belts, given that parts of the NNMC were likely denudated and covered by the sediments such as those of the Nama and Vanrhynsdorp Groups during the Ordovician-Silurian. Older sedimentary successions such as the Nama Group, were likely recycled during the deposition of the TMG: a scenario which also provides a feasible explanation for the noticeable lack of Archean ages among the detrital zircon age fractions. The ages of the youngest detrital zircon fraction conforms to the maximum age of deposition as proposed in literature, although the newly reported ages does not allow for more stringent cross-basin correlations. Regions within Patagonia, considered to have been in relatively close proximity to the relevant depositories, and possibly the Famatinian Belt (Argentina), are considered the source of the youngest Ordovician-Silurian detrital zircons.

Variations in isochore thickness and depositional surface of the Dwyka, Ecca and Beaufort Groups in the Western Cape Province of South Africa as deduced from 2.5D gravity profile models

A 2.5D gravity modelling along seven selected profiles that covers the Western Cape Province of South Africa was carried out to deduce the depositional surface and isochore (true vertical) thickness of the Dwyka, Ecca and Beaufort Group sediments. The results revealed that the Karoo Basin deepens to a depth of about 4600 m in the south-western region, near the front of the Cape Fold Belt. Also, the model gives indication that the Karoo dolerite intrusions are interconnected at depth and are mostly concentrated at the centre of the basin. The isochore thickness maps show that the Beaufort Group is the thickest group in the Karoo Supergroup, with a maximum thickness of about 6046±277 m, followed by the Ecca and Dwyka Groups with thicknesses of around 3720±183 m and765±69 m, respectively. The maximum depositional surface (elevation) for the Dwyka, Ecca and Beaufort sediments are approximately 1696 m, 1247 m and 1491 m, respectively, whereas the maximum depth below sea level are around 3668 m, 3209 m and 480 m, respectively. Furthermore, the isochore thickness maps indicate that the Ecca Group, which is the main target for hydrocarbon exploration in the Karoo, thickens toward the south, away from the centre of the basin and reaches thickness of greater than 3680 m. The correlation of the depositional surfaces with the isochore thickness maps revealed that the sediments in structural high areas were subsided, eroded and deposited in structural low areas. Consequently, the structural low areas are characterised by thick sediments cover and vice versa.

Stratigraphic Architecture of the Karoo River Channels at the End-Capitanian

The main Karoo Basin of southern Africa contains the continental record of the end-Triassic, end-Permian, and end-Capitanian mass extinction events. Of these, the environmental drivers of the end-Capitanian are least known. Integrating quantitative stratigraphic architecture analysis from abundant outcrop profiles, paleocurrent measurements, and petrography, this study investigates the stratigraphic interval that records the end-Capitanian extinction event in the southwestern and southern main Karoo Basin and demonstrates that this biotic change coincided with a subtle variation in the stratigraphic architectural style ∼260 Ma ago. Our multi-proxy sedimentological work not only defines the depositional setting of the succession as a megafan system that drained the foothills of the Cape Fold Belt, but also attempts to differentiate the tectonic and climatic controls on the fluvial architecture of this paleontologically important Permian succession. Our results reveal limited changes in sediment sources, paleocurrents, sandstone body geometries, and possibly a constant hot, semi-arid paleoclimate during the deposition of the studied interval; however, the stratigraphic trends show upward increase in 1) laterally accreted, sandy architectural elements and 2) architectural elements that build a portion of the floodplain deposits. We consider this to reflect a long-term retrogradational stacking pattern of facies composition that can be linked to changes on the medial parts of southward draining megafans, where channel sinuosity increased, and depositional energy decreased at the end-Capitanian. The shift in the fluvial architecture was likely triggered by basin-wide allogenic controls rather than local autogenic processes because this trend is observed in the coeval stratigraphic intervals from geographically disparate areas in the southwestern and southern main Karoo Basin. Consequently, we propose that this regional backstepping most likely resulted from tectonic events in the adjacent Cape Fold Belt.

The birth and demise of the vast epicontinental Permian Irati-Whitehill sea: Evidence from organic geochemistry, geochronology, and paleogeography

Organic-rich shale deposits of the Irati (Brazil) and Whitehill (South Africa) formations represent the most important sedimentary remnants of a huge Permian sea that occupied an estimated 5 million km2 before drying out and disappearing. To unravel the evolution and final demise of the Irati-Whitehill sea, we present a paleogeographic and organic geochemical characterization as well as a precise tephrochronology of the sea. Constrained by new high-resolution chemostratigraphic data (biomarker data combined with carbon and nitrogen isotopes) of two boreholes from central and southern areas of the Paraná Basin (Brazil), the evolution of the sea is divided into five stages. These stages reflect the transition from a marine realm (stage I) to an environmentally restricted sea characterized by major ecosystem changes (stages II and IV) where water renewal controlled the post-salinity environmental dynamics (stages III and V). A zircon UPb TIMS age of 277.26 ± 0.62 Ma of stage V correlates with the age of the San-Rafaelic orogeny along the paleo-Pacific South American margin and the rising of the Cape Fold Belt. We conclude that the convergent tectonic dynamics may have acted as the main agent in the entrapment and disappearance of the sea, ending a history of no more than four-million-year of the Irati-Whitehill sea.

Lithostratigraphy and sedimentology of the Middle Devonian Tra-Tra Formation, including the Grootrivier Member (Bokkeveld Group, Cape Supergroup), South Africa

Abstract The Tra-Tra Formation is a predominantly argillaceous, shallow marine to paralic sedimentary succession of Eifelian (Middle Devonian) age within the Bokkeveld Group (Cape Supergroup) that crops out extensively within the Cape Fold Belt of South Africa. It comprises three discrete lithofacies associations (termed E-G) which are interpreted as deposits of channelised tidal flat-lagoons, transgressive beach-barriers and wave-influenced prodeltas to distal delta-fronts. They accumulated within a series of incised coastal-plain valley-fill system along the palaeoshoreline of the Cape Basin following a protracted forced regressive phase during sedimentation of the underlying Hex River Formation. A discrete, geographically-extensive, 25 to 30 m thick, single or double, positive-weathering tabular sandstone within the Tra-Tra Formation is recognised herein as the Grootrivier Member. Palaeontologically, the Tra-Tra Formation comprises a restricted fauna of Malvinokaffric Realm invertebrates, fish and plant fossils that are of biostratigraphic importance in inferring its Eifelian age.

Exploration into the potential for a low-enthalpy geothermal power plant in Cape fold belt

South Africa has long been dependent on coal and other fossil fuels for cheap electricity generation. While there has been an increase in utilising renewable energy over the last two decades, the main focus has been on solar and wind, which are intermittent, with geothermal energy not even considered. With advances in technology that harness geothermal energy, geothermal resources as low as 85 °C have been reported attainable when using low-enthalpy technologies as such binary systems. This makes geothermal energy a reality for regions in South Africa where moderately high geothermal gradients exist.The initial high level assessment of the geothermal potential of the Cape Fold Belt region was done through accessing eight hot springs found to have the highest temperature from previous studies. Temperature measurements were taken as close to the source as possible as well as collection of water samples for ICP-AES analysis for major cations. The cation concentrations from the ICP-AES analysis (completed with the Thermo ICap 6200 ICP-AES) allowed for geothermometry calculations to be conducted which gave the minimum temperature estimates of the reservoirs of each hot spring. Both the surface temperature measurements and the estimates of the reservoir temperature resulted in two locations that were in the top three for both measurements. These two locations were Calitzdorp and Caledon, having water temperatures of 47 °C and 45 °C at surface and estimates of the reservoir temperatures of 117 °C ± 13 °C and 108 °C ± 21 °C respectively.The hydro-geological analysis of the Oudtshoorn region, where the Calitzdorp hot spring is located, was conducted using published geophysical data in the form of magneto-telluric (MT) survey that was carried out in 2005 by the Agulhas-Karoo Geoscience Transect project. The MT data was presented in a paper by Weckmann et al. (2012) as a cross sectional profile from Mossel Bay to Prince Albert to a depth of 30 km, where a large region of low resistivity was found below the Oudtshoorn basin. The Calitzdorp hot spring is positioned at the surface above this region. The geological cross sections and regional interpretation presented in this study infers that a major syncline of the Cape Supergroup exists below the basin, potentially as deep as 10 km, and covers the low resistivity area shown in the MT profile. This led to the inference that the large region of low resistivity is most probably due to a large water reservoir. This potential reservoir is about 40 km in length with a depth of 2.5 km–7 km at its thickest, tapering out towards the edges.The depth to the top of the potential reservoir and the estimated reservoir temperature from the geothermometry results in a geothermal gradient of 39 °C/km ±4.3 °C/km. Thus Calitzdorp was identified as a promising location for further exploration, ideally deep boreholes or more geophysical surveys, to validate the existence of a reservoir and take down-hole temperature measurements. The depth and size of this potential reservoir would make it a favourable candidate for a pilot low-enthalpy geothermal power plant within the Cape Fold Belt and South Africa.

Introduction to the tetrapod biozonation of the Karoo Supergroup

Research Article| June 01, 2020 Introduction to the tetrapod biozonation of the Karoo Supergroup R.M.H. Smith; R.M.H. Smith Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, 2050 South Africa Karoo Palaeontology, Iziko South African Museum, P.O. Box 61, Cape Town, 8000, South Africa e-mail: Roger.Smith4@wits.ac.za Search for other works by this author on: GSW Google Scholar B.S. Rubidge; B.S. Rubidge Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg 2050, South Africa e-mail: bruce.rubidge@wits.ac.za Search for other works by this author on: GSW Google Scholar M.O. Day; M.O. Day Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg 2050, South Africa e-mail: michael.day@nhm.ac.uk Search for other works by this author on: GSW Google Scholar J. Botha J. Botha National Museum, P.O. Box 266, Bloemfontein, 9300, South Africa Department of Zoology and Entomology, University of the Free State, 9300, South Africa e-mail: jbotha@nasmus.co.za Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2020) 123 (2): 131–140. https://doi.org/10.25131/sajg.123.0009 Article history first online: 18 Jul 2020 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation R.M.H. Smith, B.S. Rubidge, M.O. Day, J. Botha; Introduction to the tetrapod biozonation of the Karoo Supergroup. South African Journal of Geology 2020;; 123 (2): 131–140. doi: https://doi.org/10.25131/sajg.123.0009 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietySouth African Journal of Geology Search Advanced Search The main Karoo Basin of South Africa contains the most abundant, diverse, and time expansive record of terrestrial vertebrates around the Palaeozoic-Mesozoic transition. This 10 km thick sedimentary succession accumulated in a large intracratonic, retro-arc, foreland basin (Johnson 1991; Catuneanu et al. 2005) in front of the rising Cape Fold Belt portion of the Gondwanide Mountain range that fringed the southern margin of Gondwana. Today, rocks of the Karoo Supergroup have a spatial distribution of some 300 000 km2 (Smith 1990), which is more than one-half the land surface of South Africa. They were... You do not currently have access to this article.

Biomes, geology and past climate drive speciation of laminate-toothed rats on South African mountains (Murinae: Otomys)

Abstract Mitochondrial DNA sequences (1137 bp) of the cytochrome b gene and craniodental and craniometric data were used to investigate the evolutionary relationships of six putative rodent taxa of Otomys (family Muridae: subfamily Murinae: tribe Otomyini) co-occurring in the Western Cape and Eastern Cape provinces of South Africa. Phylogenetic analysis of 20 new sequences together with craniodental and craniometric characters of 94 adult skulls reveal the existence of a unique lineage of Otomys cf. karoensis (named herein Otomys willani sp. nov.) from the Sneeuberg Centre of Floristic Endemism in the southern Drakensberg Mountain Range. Craniometric analysis distinguished O. karoensis from O. willani and identified a further four localities in the range of the latter species. We document southern range extensions of both Sloggett’s ice rat, Otomys sloggetti, and the vlei rat Otomys auratus to the Sneeuberg Mountain Range, in addition to appreciable genetic divergence between Sneeuberg and southern and central Drakensberg populations of O. sloggetti. Our results demonstrate parallel patterns of cryptic speciation in two co-occurring species complexes (Otomys irroratus s.l. and O. karoensis s.l.) associated closely with the boundaries of biomes (fynbos vs. grassland biomes) and geological formations (Cape Fold Belt vs. Great Escarpment).