Kalahari Basin Research Articles

Depth estimation of pre-Kalahari basement in Southern Angola using seismic noise measurements and drill-hole data

The remote Southern region of Angola is covered by siliciclastic Kalahari Cenozoic formations that host underground aquifers of great importance to local populations affected by water scarcity problems. These aquifers are well developed where Kalahari sands reach appropriate thicknesses. On the other hand, at the eastern end of this area, regional aeromagnetic data recently acquired suggested the possibility of the continuity of the geological structures of the Lufilian Arc, sited in the nearby Zambia and Congo, southwestwards into Angola under the Kalahari formations. Once the Lufilian Arc is associated with the presence of the so-called Central African Copperbelt, this possibility increased the interest in determining the depth to Pan-African rocks under the Kalahari basin. To estimate the thickness of Kalahari formations in this area of difficult access and poor logistics, an expedited and non-invasive geophysical method was needed. Seismic noise and the single-station Nakamura technique were chosen, but due to the large distance of the study area from the ocean, one of the major sources of seismic noise, a test survey was acquired in the Cuvelai region to assess the signal quality, where the data was calibrated using available drill-holes. >170 points of seismic ambient noise were later acquired and the horizontal/vertical (HVSR) amplitude versus frequency curves were 1D inverted for the best velocity/density model for each station. The results were compared with 1D inverted legacy vertical electrical soundings reprocessed and validated in this work, showing similar depth-to-basement, while interpreted velocities/densities of geological formations were sampled and confirmed with measurements. A depth-to-basement map was produced using seismic information, mechanical soundings, and geological information. Despite the relatively reduced geographical area covered, the map presents valuable information for hydrogeology and mineral exploration purposes and agrees with a previously available coarser map of Kalahari thickness and with observations from geological surveys simultaneously conducted at the time of the seismic surveys.

Chronology of Sedimentation and Landscape Evolution in the Okavango Rift Zone, a Developing Young Rift in Southern Africa

AbstractThe Kalahari Basin in southern Africa, shaped by subsidence and epeirogeny, features the Okavango Rift Zone (ORZ) as a significant structural element characterized by diffused extensional deformation forming a prominent depocenter. This study elucidates the Pleistocene landscape evolution of the ORZ by examining the chronology of sediment formation and filling this incipient rift and its surroundings. Modeling of cosmogenic nuclide concentrations in surficial eolian sand from distinct structural blocks around the ORZ provides insights into sand's residence time on the surface. Sand formation occurred from ∼2.2 to 1.1 Ma, coinciding with regional tectonic events. Notably, provenance analyses of sand within ORZ's lowermost block where large alluvial fans are found indicate different source rocks and depositional environments than those of the eolian sands found at a higher elevation. This suggests that the major phase of rift subsidence and the following incision of alluvial systems into the rift occurred after eolian dune formation. Luminescence dating reveals that deposition in alluvial fan settings in the incised landscape began not later than ∼250 ka, and that a lacustrine environment existed since at least ∼140 ka. The established chronological framework constrains the geomorphological effects of the different tectono‐climatic forces that shaped this nascent rifting area. It highlights two pronounced stages of landscape development, with the most recent major deformation event in the evolving rift probably occurring during the middle Pleistocene transition (1.2–0.75 Ma). This event is reflected as a striking change in the depositional environments due to the configurational changes accompanying rift progression.

The Kalahari sediments and hominins in southern Africa

The temporal coupling of the structural evolution of the Kalahari Basin and the accumulation of the Kalahari Group sediments has been an accepted paradigm leading to the assumption that the Kalahari group sediments have been accumulating gradually since the mid-Cretaceous. Here we review the first actual ages for the Kalahari Group based on cosmogenic ages from six geological localities. These results demonstrate that Kalahari Basin infill was a more dynamic process than previously thought and that the Kalahari Group sediments are mostly Plio-Pleistocene in age (∼4 Ma to 1–2 Ma). The hiatus between the initial structural subsidence of the basin, during the Cretaceous, and the general young age of the investigated sediments, implies a dynamic landscape in which significant phases of erosion occurred during the Mesozoic and Cenozoic. The magnitude of erosion is manifested by the fact that in many locations Kalahari Neogene to Quaternary sediments overlie Precambrian basement.The age of the present infill of the Kalahari thus falls within the temporal range of the genus Homo. In light of this new understanding, we provide a review of the archaeological evidence from the Kalahari Basin and along its southern fringe. Initial hominin presence is found at Wonderwerk Cave during the Olduvai Event and there is subsequent high-density occupation along the southern fringe of the Kalahari Basin during the Acheulean and the Fauresmith. Middle Stone Age occupation is limited to localities of limited size and small artifact counts and it appears that the focus of human occupation, particularly in the later stages of the Middle Stone Age, shifts southward, including along the coastal regions.

Open-cup nesters in the Kalahari: Incubation and egg-shading behaviour in passerines cannot be detected with temperature dataloggers during hot periods

Birds that build open-cup nests in semi-arid or arid habitats have difficulty in maintaining clutch temperatures during incubation in a suitable incubation range due to high air temperatures and solar radiation, resulting in either embryo death or behavioural responses to preserve clutch viability. We investigated how Southern Fiscals (Lanius collaris), open-cup nesting passerines with female-only incubation in the Kalahari basin, allocated time for self-care (off-bouts) and incubation (on-bouts) and whether egg shading, a previously described behaviour in this species, is a widespread response during hot periods. We used a dual approach combining temperature dataloggers in the nest and behavioural observations during the hottest hours of the day. We found that in the early morning and late evening, Southern Fiscals behaved similarly to species incubating in temperate habitats by alternating off- and on-bouts, but during the hottest hours of the day, shading became the main activity. Behavioural observations were key to describing this behaviour indicating that it is necessary to combine different data collection strategies to successfully assess the behaviour of open-cup nesters in hot environments.

Near-surface pedosediments of Takatokwane saline pan, southern Botswana: Properties, pedogenic processes, and inferences of environmental change

Natural pans are an important feature of dry landscapes worldwide. The purpose of this study was to characterize, for the first time, the near-surface pedosediments of the prominent Takatokwane pan in southern Botswana using their physical, geochemical, and mineralogical properties, to explore past and active pedogenic processes, and to interpret the properties of the pedosediments in light of environmental change. Pedogenic parameters including particle size distribution, reaction, electrical conductivity, and organic matter content were determined using routine laboratory procedures. The total elemental composition was analyzed using inductively coupled plasma optical emission spectroscopy and inductively coupled plasma mass spectrometry. The clay mineralogical compositions of the pedosediments were determined using a Bruker D8 Advance X-ray diffractometer. A suite of geochemical coefficients was used to quantify the weathering and pedogenic processes. Granulometric analysis showed that the pedosediments were dominated by fine sand (380 – 890 g/kg). The two pedons were greenish-gray in color at a depth of 140 cm. The elemental abundances followed the order of SiO2 > Al2O3 > Fe2O3 > TiO2. The TiO2/Al2O3 coupled with mineralogy indicated a uniform origin of the parent materials and feldspathic sandstone components, which were redeposited in the pan environment. The geochemical weathering coefficient indicates incipient weathering. Smectite-enriched clay deposits in the basin paved the way for the formation of the vertical layers. At the meso-morphological scale, reworked pedofeatures indicative of clay illuviation and gleisation processes were observed. The dominant pedogenic processes in soils include hydrolysis, lessivage, illuviation, and gleisation. This set of processes indicates the cycles of humid pedogenesis. This study confirmed three cycles of deposition, chemical precipitation, and post-depositional alteration under changing environmental conditions. Evidence from this study points to the seasonality of the environment, which could be explored for an improved understanding of the evolution of the Takatokwane pan and the Kalahari Basin.

Towards a phonological typology of the Kalahari Basin Area languages

Abstract This article reports some results of the first large-scale, comprehensive survey of the phonological systems of the Khoisan languages of the Kalahari Basin Area. These languages are famous for their large sets of click phonemes, a typologically rare characteristic otherwise found only in a limited number of languages worldwide. They are also unique because the click phonemes carry a high functional load in terms of phonemic and lexical distinctions in the respective systems. Finally, these languages have strikingly similar and highly skewed root phonotactics. The article provides empirical support for a range of claims and speculations that have been made about these typologically rare systems of the Kalahari Basin Area.

A multi-method approach for the investigation of termite mound structures (Kalahari Basin, Botswana)

Fungus-growing termites (FGT) are important agents in subtropical and semiarid ecosystems for the biological and geological modifications they bring through the construction of their mounds. In order to survive and thrive, the mounds are designed to host the Termitomyces fungus in pre-set conditions of humidity and temperature. The interior structure of FGT mounds has only been scarcely studied in the scientific literature, making knowledge about mound morphology and development incomplete. In this study, a relic FGT mound in northern Botswana was analyzed using a combination of electrical resistivity tomography (ERT), particle size distribution (PSD), X-ray computed microtomography (X-ray micro-CT), and soil micromorphology methods. Specifically, we set out to investigate (i) whether changes in the measured soil resistivities reflect expected changes between the various functional compartments of the mound; (ii) what changes in soil texture and structure are associated with the resistivity variations; and (iii) whether this information can be used to better understand the mound compartments and their development. Our results suggest that ERT may eventually provide an attractive and efficient method to investigate the interior structure of FGT mounds that is non-destructive. The use of ERT does not require to remove the epigeal of the mound. The modifications brought by FGT to the texture and structure of the soil, respective to the function of each mound compartment, can increase resistivity of up to three orders of magnitude. Further, the work presented in this paper helps to (i) identify processes involved in the sediment transfer between the mound and its surroundings, (ii) increases the understanding of mound morphology, and (iii) show that fungus-growing termitaria affect durably savanna landscape. Finally, this study demonstrates that ERT is a pertinent non-destructive method to investigate mound structure.

Kathu Pan 6: Observations on the First Known Buried High-Density Open-Air Holocene Occupation on the Southern Margin of the Kalahari Basin

Abstract This paper presents preliminary results from a newly excavated open-air Later Stone Age site attributed to the Wilton Industry at Kathu Pan 6 in the Northern Cape Province of South Africa. Basic data on the lithics, fauna (including a large ivory fragment), and ostrich eggshell (including beads) recovered during two seasons of excavation (2016–2017) are presented and this material is contextualized through comparison with neighboring sites. Spatial analysis of the artifact distribution from the small exposure from the 2017 season suggests a spatially structured occupation. The Wilton open-air occupation of Kathu Pan 6 offers a new perspective on the poorly understood Later Stone Age of the southern fringes of the Kalahari.

A Carboniferous apex for the late Paleozoic icehouse

Abstract Icehouse climate systems occur across an abbreviated portion of Earth history, constituting c. 25% of the Phanerozoic record. The Late Paleozoic Ice Age (LPIA) was the most extreme and longest lasting glaciation of the Phanerozoic and is characterized by periods of acute continental-scale glaciation, separated by periods of ice minima or ice-free conditions on the order of <10 6 years. The late Paleozoic glaciogenic record of the Paraná and Kalahari basins of southern Gondwana form one of the largest, best-preserved and well-calibrated records of this glaciation. In the Carboniferous, the eastern and southern margins of the Paraná Basin and the Kalahari Basin were characterized by subglacial conditions, with evidence for continental and upland glaciers. In the latest Carboniferous, these basins transitioned from subglacial reservoirs to ice-free or ‘ice distal‘ conditions evidenced by the widespread deposition of marine deposits juxtaposed on subglacial bedforms. High-precision U–Pb zircon chemical abrasion thermal ionization mass spectrometry geochronological constraints from volcanic ash deposits in the deglacial marine black shales of the Kalahari Basin and from fluvial and coal successions, which overlie marine deposits in the Paraná Basin, indicate subglacial evidence in these regions is constrained to the Carboniferous. The loss of ice in these regions is congruent with a late Carboniferous peak in p CO 2 and widespread marine anoxia in the late Carboniferous. The permeant retreat of glaciers in basinal settings, despite an early Permian p CO 2 nadir, highlights the influence of short-term perturbations on the longer-term CO 2 record and suggests an ice threshold had been crossed in the latest Carboniferous. A definitive driver for greenhouse gases in the LPIA, such as abundant and sustained volcanic activity or an increased biological pump driven by ocean fertilization, is unresolved for this period. Lastly, the proposed Carboniferous apex for the high-latitude LPIA record is incongruent with observations from the low-latitude tropics where an early Permian peak is proposed.

3D electrical structure definition of aquifer systems in the Kalahari basin in Southern Angola based on legacy data reprocessing

The Kalahari-Ohangwena transboundary aquifer system, recently identified in Northern Namibia, comprises 3 major aquifers with very different characteristics. The shallowest is discontinuous and with limited reserves, but it has local importance in water supply for the population, since it is easy to reach, and often presents good hydrochemical quality. An intermediate deeper aquifer is characterized by high salinity while the deepest aquifer, also mostly saline, can present zones with fresh water. However, the latter is located at considerable depths and is shaped by the bottom of the basin basement. There hasn't been a systematic hydrogeological data acquisition for decades in this area of Angola, but legacy electrical resistivity data reprocessing from geophysical surveys conducted >50 years ago in the Cunene Province allowed the construction of a quasi-3D geoelectrical model for the Angolan side of KOH aquifer system in the Cuvelai-Etosha basin. This model is based on 482 vertical electrical soundings carried out in 1966–67, using the Schlumberger array, that contribute to confirming the presence of the Kalahari-Ohangwena aquifer system in Angola. The obtained quasi-3D model highlights the geoelectrical features of hard bedrock and is validated with other hydrogeological and geophysical information. The quasi-3D electrical resistivity data is interpreted using selected boreholes and two time-domain electromagnetics transects carried out in Namibia, in the 2000s. Although both geophysical data acquisitions were >40 years apart, the results show a very good correlation between the deeper aquifer and the aquitard separating the intermediate aquifer from the deeper aquifer either with the results from Namibia or the borehole data. This is a direct result of the lack of alteration in the hydraulic conditions over these decades, without significant anthropogenic activity and negligible extraction from deep wells. Based on this analysis, the original dataset was considered a reliable source and this quasi-3D model was validated. Furthermore, the model can be considered in the future as an important tool for groundwater resources management, as well as a good starting point for further hydrogeological research in the province of Cunene.

Juncture-Verb Constructions in Northeastern Kalahari Khoe: A comparative perspective

Multiverbal predicates constitute a defining feature of the Kalahari Basin linguistic area of southern Africa encompassing the Kx’a, Tuu, and Khoe-Kwadi language families. Here, we focus on a complex predicate type restricted to the Khoe-Kwadi family’s Khoe branch which involves a linker morpheme and is thus referred to as Juncture-Verb Construction (JVC). While JVCs have synchronically been interpreted as Serial Verb Constructions (SVC), their origin and relationship with SVCs in the narrower sense as found in the Kx’a and Tuu families remain debated. The Kalahari Khoe languages Ts’ixa, Shua and Northern Tshwa spoken along the northeastern Kalahari Basin fringe present a convenient case study to expand the descriptive corpus on Khoe JVCs while addressing the limits of areal spread and contact influence. We show that all languages under consideration present JVCs with formal and functional properties corresponding to those found in other Kalahari Khoe languages, while also sharing features with SVCs as attested in the Kx’a and Tuu families. Both JVCs and SVCs contrast with conjoined predicates and are defined by single-eventhood. JVCs cover the same semantic domains found among SVCs of the Kx’a and Tuu families, can be subdivided into symmetrical and asymmetrical constructions, and show the same potential for lexicalization and grammaticalization, respectively.

When verbs ‘stay (and) go’ together: Pseudo-coordination in Juǀ’hoan and ǃXun

Multi-verb constructions are an areal feature of Kalahari Basin Area languages (“Khoisan”), a Sprachbund comprising the Kx’a, Tuu, and Khoe-Kwadi families. Presently, these languages are characterised by two distinct multi-verb constructions with specific distributions: strictly contiguous serial verb constructions in Kx’a and Tuu correspond to multi-verb constructions involving a morphophonological linker, or “juncture”, in Khoe-Kwadi. This paper describes an additional multi-verb construction, namely pseudo-coordination. Drawing on a corpus of spontaneous discourse data, this paper demonstrates the rise of pseudo-coordination from a biclausal construction in Juǀ’hoan and ǃXun (Ju, Kx’a). The comparative analysis highlights the verbs that typically arise the context of pseudo-coordination and the resulting functions. This paper describes the polygrammaticalisation resulting from pseudo-coordination, including other multi-verb constructions.

Phylogeny of sand termites

The sand termite Psammotermes allocerus is widely distributed in in southern Africa. To investigate the genetic diversity of this species 113 samples were collected in the arid regions of South Africa, Namibia and Angola in fairy circles and also in landscapes without fairy circles. The mitochondrial markers COI and COII were selected to perform Bayesian Inference analysis. The phylogenetic tree is composed of eight well-supported genetic groups within the species complex. In a synopsis with also studied morphological features the eight groups Northern Namib, Western Kalahari Basin, Nama, Southwestern Kalahari, East Gariep, Southern Namib, Tsau IIKhaeb and Succulent Karoo should be considered as distinct species. The species name P. allocerus should be used for termite collections of the Succulent Karoo due to their basal position in the phylogeny.

Spatial variations in sediment production and surface transformations in subtropical fluvial basins (Caculuvar River, south‐west Angola): Implications for the composition of sedimentary deposits

AbstractSeveral compositional features of sedimentary deposits can be used to reconstruct environmental conditions of source areas. In this research, bulk X‐ray diffraction mineralogy, heavy and clay mineral assemblages and geochemistry obtained for modern deposits of the Cunene River and its tributaries Caculuvar–Mucope are integrated with geological/geomorphological characteristics of respective catchment areas to evaluate to what extent sediment production is spatially variable and source materials are differently affected by exogenous transformations. Detrital sources can be classified into four main types based on sediment composition: felsic, mafic, recycled and mixed. Source contributions obtained with unmixing models using distinct input data reveal some disagreements, with heavy mineral assemblages pointing to higher mafic contribution and bulk XRD‐mineralogy favouring the recycled sedimentary component. However, the three datasets coincide showing a lower supply from the Kalahari Basin than the large outcropping areas of its sedimentary units would suggest, which is attributed to the relatively low rainfall and relief in this region. Where multiple depositional cycles are involved in sediment production the composition of the river deposits, even their clay fractions, will not reflect coeval weathering transformations and an under‐estimation of the mafic component probably occurs. This research reveals how exogenous processes may deviate the composition of the produced sediment from a simple weighted by outcropping area average of the source units and compromise (palaeo)environmental interpretations based on sediment composition.

Eolian chronology reveals causal links between tectonics, climate, and erg generation

Evaluating the impact and implications of eolian repositories that mark large-scale climatic transitions requires knowledge about the timing of their emplacement and the mechanisms responsible for their production, which remain highly uncertain. Here we apply numerical modeling of cosmogenic nuclide data, measured in the largest continuous terrestrial body of sand on Earth, to determine settings under which the sand was generated, by constraining the timing of sand introduction into the interior of southern Africa. Our findings reveal that major events of sand formation and accumulation in the Kalahari Basin occurred between ~2.2 and 1 Myr ago. The establishment of the Kalahari sand field corresponds to regional, continental, and global scale morphotectonic and climatic changes that contributed to the mass production and widespread dispersion of sand. These changes substantially altered existing habitats, thus constituting a crucial milestone for flora, fauna, and hominins in southern Africa during the Pleistocene.

Cryptic subterranean diversity: regional phylogeography of the sand termite Psammotermes allocerus Silvestri, 1908 in the wider Namib region

Psammotermes allocerus Silvestri, 1908 is the only described species representing the genus Psammotermes Desneux, 1902 in Southern Africa. The large geographical range of this subterranean termite covers both summer and winter rainfall regimes. Deadwood is the preferred food when available, but in more arid habitats, both live and dead grasses form the major dietary component. Along the Namib Desert margins, the species’ localised herbivory creates circular bare patches known as fairy circles. For a regional phylogeographic study of this species, we sampled 65 sand termite populations within drier parts of Namibia, South Africa, and Angola. Based on combined molecular and ecological data, we found considerable genetic diversification within P. allocerus. Analyses of two mitochondrial markers (COI, COII), including a Bayesian inference tree, haplotype analysis and genetic distances suggest a delineation into seven highly differentiated genetic groups. The ‘Succulent Karoo’ group is additionally characterised by unique features of the royal chamber, nest and tunnel system. In conclusion, our data suggest that P. allocerus should be not regarded as one species but as a species complex. Termites of each analysed group ‘Northern Namib’, ‘Western Kalahari Basin’, ‘Nama’, ‘Southwestern Kalahari’, ‘East Gariep’, ‘Southern Namib’ and ‘Succulent Karoo’ should be considered as distinct species. The species name P. allocerus should be used for termites of the ‘Succulent Karoo’.

Geometry of sedimentary deposits and evolution of the landforms in the Chobe Enclave, Northern Botswana

The imprint of neotectonics is frequently obscured in low-relief environments by the sedimentary cover. This is the case in the Chobe Enclave, part of a pristine region of the Middle Kalahari Basin in northern Botswana, where numerous fossil landforms, such as sand dunes, pans, sand ridges, and carbonate islands, can be observed but whose detailed origins are unclear. In this study, a combination of near-surface geophysical surveys, sedimentological analysis, and optically-stimulated luminescence (OSL) dating were used to study the relationship between landscape development and neotectonic activity in one region of the Chobe Enclave. Specifically, electrical resistivity tomography (ERT) and ground penetrating radar (GPR) surveys were used to define the lateral and vertical distribution of sedimentary deposits associated with a prominent sand ridge and its margins. Sedimentological analysis and OSL dating of soil samples from pits taken along the survey lines were then used to calibrate the geophysical results and establish a chronostratigraphical framework. Our results lead to the following hypotheses regarding the evolution of this part of the Chobe landscape: (i) during the Late Pleistocene (>~25 ka), fluvial channels were buried due to epeirogenic movements, resulting in paleo-channels; (ii) between ~25 ka and ~6 ka, a paleo-lake shoreline formed, which resulted in the linear eastern margin observed on the considered sand ridge. Erosional bounding surfaces suggest the syndepositional uplift of the sand ridge morphologies during this time; (iii) a neotectonic influence on the evolution of the landscape is revealed by the incision of the sand ridge forming fluvial watergaps since ~6 ka ago; and (iv) due to continuous aeolian and fluvial reworking, the western-most ridge became gradually isolated from the floodplain resulting in an inherited relief. In conclusion, this investigation allowed the deformation caused by epeirogenic movements acting on a low relief landscape to be characterized in terms of landforms and sedimentary body properties.

Recording the largest gabbro-anorthositic complex worldwide: The Kunene Complex (KC), SW Angola

The Kunene Complex (KC) represents a large Mesoproterozoic igneous body, mainly composed of anorthosites and gabbroic rocks that extends from SW Angola to NW Namibia (18000 km2, N-S trend, and ca. 350 km long and 25–50 km wide). Although the KC has been studied from a cartographic and geochemical point of view, little is known about its structure at depth below the sedimentary deposits of the Kalahari basin. Hence, we use available satellite gravity data to estimate its extent and to unravel its morphology at depth. The Bouguer anomaly map depicts a gravity gradient from the coast (+200 mGal) towards eastern Angola (-150 mGal), which is explained by the transition from a young, dense and thin basaltic oceanic crust, formed during the Mesozoic Atlantic rifting, to an old, light and thick Archaean to Proterozoic continental crust (Congo Craton), to the east. The outcropping KC interrupts the gravity trend, showing at the western, southwestern and northeastern sides, several positive and isolated gravity anomalies linked to gabbroic intrusions associated to KC (ca. 50 km wavelength and −90 mGal). In contrast, the anomalies found at the central part of the massif (50 km wavelength and < -110 mGal) correspond to the dominant anorthositic members, according to the spatial correlation of the mapping. Five 2.5D gravity profiles have been modelled to investigate the unexposed eastern boundary, reconstructing the surface crustal structure (between 0 and 15 km depth) overlaid by the thin sedimentary cover of the Kalahari basin. The gravity modelling helps us to show that the KC was emplaced in the Upper Crust and extends in depth up to ca. 6 km, showing a lobular geometry and following a large NE-SW to NNE-SSW linear trend, presumably inherited from older Palaeoproterozoic structures. The lateral continuation of the KC to the east (between 50 and 125 km) beneath the Kalahari sediments suggests an overall size of at least twice the outcropping dimension (about 42500 km2). This statement clearly influences in the economic potential of this massif, related to the prospecting of raw materials and certain types of economic mineralization (Fe-Ti oxides, metallic sulphides or platinum group minerals).

Determination of total organic carbon content using Passey's method in coals of the central Kalahari Karoo Basin, Botswana

This paper focuses on determining total organic carbon (TOC) from boreholes in the Kalahari Basin, Botswana, using Passey's method. The Kalahari Karoo basin is one of several basins in southern Africa filled with Late Carboniferous to Jurassic sedimentary strata that host Permian age coal seams. Nine exploration boreholes (wells) drilled in the central Kalahari Karoo basin are used to determine the Total Organic Carbon potential. Vitrinite reflectance (Ro), proximate and ultimate analyses were conducted on cored coal intervals. Passey's ΔLogR method applied in this study employs resistivity and porosity logs to identify and quantify potential source rocks. Results of Passey's method compared with laboratory-measured carbon showed that Passey's method effectively identifies coal intervals. In terms of TOC calculations, the method works poorly in coal metamorphosed by dolerite intrusions. The heat affected coal samples had Ro from 0.77% to 5.53% and increased in maturity from primarily maceral controlled to high volatile bituminous and anthracite coal. Results from proximate analysis showed compositional changes in the coal were controlled by proximity to sill intrusion, with a decrease in Fixed Carbon and an increase in ash yield in the contact metamorphism zone (2–12 m from sill). For the unaltered coal that has undergone burial maturation displaying Ro of 0.44%–0.65%, the method works well. In unintruded boreholes, correlations between Carbon and calculated TOC indicate strong relationships. Passey's ΔLogR method proved to be a suitable method of estimating TOC on coal that has undergone burial maturation. This study has demonstrated that TOC calculated from the sonic log is more reliable in coal not affected by contact metamorphism than TOC calculated from the density log.

Detrital zircon in an active sedimentary recycling system: Challenging the ‘source‐to‐sink’ approach to zircon‐based provenance analysis

ABSTRACTThe age and properties of detrital zircon in a sediment reflect properties of the rocks in which the zircon crystallized, and not necessarily the immediate precursor of the host sediment. Where clastic sediments are recycled, these properties are preserved so that U‐Pb ages and Lu‐Hf data on zircon grains will no longer give information on the routing of detritus. Because the crustal evolution and sedimentary recycling history of Southern Africa is well‐established, Holocene sediments in the region provide a good test example for detrital zircon geochronology applied to sands or sandstones with a complex recycling history. Data from 16 samples of unconsolidated sand, including dunes from the southern part of the Kalahari Basin, beach sands at the Atlantic coast, and isolated inland dune occurrences, yield ranges of early Mesozoic to late Archaean ages. Uranium–lead and lutetium–hafnium isotope data provide no evidence of direct derivation of zircon from protosources in crystalline bedrock. The complex distribution patterns can be decomposed into seven ‘provenance components’ that have previously been encountered in Palaeoproterozoic to Jurassic sedimentary rocks in the region. These components occur in non‐random combinations, in proportions that suggest mixing of recycled material from different sedimentary precursors. Taking pre‐Cenozoic geology, Cretaceous to Pleistocene drainage history of southern Africa and Holocene wind and current patterns into account, it is possible to work out a consistent model for transport of detritus from sedimentary precursors into the basin, followed by aeolian remobilization within the basin itself. The detrital zircon distributions can thus be interpreted from prior knowledge of the basin filling history, regional geology, geomorphology, drainage evolution and wind pattern. This amounts to a line of reasoning from ‘sink back to (intermediate) ‘source’, which is the opposite of the ‘(proto)source‐to‐sink’ paradigm commonly invoked in detrital zircon studies.