Karoo Rocks Research Articles

New high precision U-Pb ages and Hf isotope data from the Karoo large igneous province; implications for pulsed magmatism and early Toarcian environmental perturbations

To better constrain the age and duration of the magmatism associated with the Karoo large igneous province (LIP), we present new U-Pb ID-TIMS dates and εHf values from baddeleyite and zircon grains from Karoo basin mafic sills and from felsic samples from the Lebombo and Mwenezi monoclines, together with an 40Ar/39Ar age database of Karoo rocks that has been filtered for true plateau ages with >70% of 39Ar released and in which all 40Ar/39Ar ages were recalculated using the current best estimates for the decay constants. Zircon and baddeleyite ages from three Karoo basin sills range from 183.36 ± 0.17/0.27 to 183.06 ± 0.07/0.21 Ma, where the two uncertainties reflect the analytical error and the additional error associated with decay constant uncertainty. Zircon from the Mutandawhe pluton are dated to 176.84 ± 0.06/0.20 Ma, which represents the first high-precision U-Pb age of the late stage Karoo-LIP magmatism in the northern Lebombo-Mwenezi region. Initial hafnium isotopes are close to chondritic for the Karoo basin and central Lebombo samples (εHf from −2 to +3), but more negative for zircon grains from the Mutandawhe pluton (−11.3 ± 1.1, 2SD). In combination with previous studies and in agreement with the updated 40Ar/39Ar ages, we show that the sill complex that intruded the Karoo basin was short-lived at ~320 ± 180 ka and that it pre-dated the magmatism of the Ferrar-LIP by around 460 ka, whereas the entire Karoo-LIP was emplaced over a period of ca. 6.5 Ma. Based on high-precision U-Pb geochronology, Karoo-LIP magmatism occurred after 183.36 ± 0.17 Ma and therefore postdated the extinction pulses of the late Pliensbachian and likely the Pliensbachian-Toarcian boundary. However, we support previous conclusions that the start of the Karoo-LIP activity agrees with the onset of the Toarcian oceanic anoxic event and the early Toarcian warming, indicating that these environmental changes were likely a response to the magmatic activity of the Karoo-LIP.

Natural Attenuation of Acid Mine Drainage by Various Rocks in the Witbank, Ermelo and Highveld Coalfields, South Africa

In the Karoo coalfields, mining operations that release acid mine drainage (AMD) are threatening groundwater resources. An important parameter controlling the extent and severity of AMD impact is the natural attenuation of rocks in response to AMD. Very little is known about such response of Karoo rocks in saturated and unsaturated conditions, a research gap filled by this paper. Laboratory column leach experiments were used to study the responses of different rock types from the Witbank, Ermelo and Highveld coalfields of South Africa. The results of the experiments show that rock samples with high quartz mineral content offered little attenuation of AMD and those consisting of plagioclase and clays offered some attenuation, while those with high carbonate mineral content, neutralized and reduced the concentration of heavy metals from AMD. The presence of oxygen increased the rate of heavy metal removal from AMD. For all rock samples under saturated and unsaturated conditions, the sulfate and chloride concentrations of AMD remained unchanged after the leaching process, showing that these parameters are conservative and can be used as potential natural tracers of AMD movement in the subsurface. The research shows that laboratory leach tests may be used to rank the various rock types in the Karoo coalfields in terms of their capacity to buffer the impacts of AMD. Such a ranking could inform policy and decision makers in regard to handling and storage of AMD-generating wastes, as well as to location and design of AMD waste storage facilities.

The influence of angled survey lines on 2D ERT surveys using the Wenner (α) array with implications for groundwater exploration in Karoo rocks

Two-dimensional (2D) electrical resistivity tomography (ERT) surveying systems typically use standard protocols that assume straight survey lines and collinear electrodes. However, due to the presence of infrastructures and other surface constraints, it is not always possible to conduct 2D ERT surveys along straight lines. When survey lines are angled, the apparent resistivity data are affected for measurements where electrodes occur on either side of the position of the angle, since the assumed distances between some of the electrodes are larger than the true distances. This study investigates the impact of angled survey lines on 2D ERT data and inverse resistivity models for the Wenner (α) array. Theoretical considerations show that measurements along angled survey line are sensitive to resistivity changes at position laterally displaced from the survey line, while both the calculated apparent resistivities and the depths of investigation are affected when electrodes straddle the angle. The resulting errors are, however, small. Even for a large angle of 45°, the errors are smaller than 6.5% for the affected apparent resistivity measurements, and smaller than 3.8% for the median depths. Since the apparent resistivity data and the pseudo-depths are affected by angles in the survey lines, the inverse resistivity models are also affected. Numerical modelling shows that even small input errors may be propagated (both in magnitude and spatially) during inversion, thereby distorting the resulting resistivity models. The distorted inverse resistivity models could lead to the incorrect interpretation of the locations, geometries and orientations of subsurface structures, which could lead to poorly sited production boreholes. The results of field surveys show that apparent resistivity data sets recorded along angled lines may be partially corrected by calculating the true geometric factors and by adjusting the apparent resistivity data accordingly. Significantly improved inverse resistivity models are found for corrected data sets.

A juvenile specimen of Anteosaurus magnificus Watson, 1921 (Therapsida: Dinocephalia) from the South African Karoo, and its implications for understanding dinocephalian ontogeny

Anteosaurid dinocephalians were the apex terrestrial predators of the latter part of the Guadalupian (middle Permian) and became extinct at the end of that epoch. The group was relatively diverse in Russia, but represented by only two genera, Australosyodon and Anteosaurus, in the Karoo rocks of South Africa. A newly discovered skull of Anteosaurus magnificus from the Abrahamskraal Formation is unique among specimens of this taxon in having most of the individual cranial bones disarticulated, permitting accurate delimitation of cranial sutures for the first time. The relatively large orbits and unfused nature of the cranial sutures suggest juvenile status for the specimen. A computer-aided 3D reconstruction of the skull, and comparison with 11 additional individuals, enabled an allometric study of cranial growth in the species. Positive allometry for four of the measurements suggests rapid growth in the temporal region, and a significant difference in the development of the postorbital bar and suborbital bar between juveniles and adults. Pachyostosis was an important process in the cranial ontogeny of Anteosaurus, significantly modifying the skull roof of adults. This condition is more obvious in large individuals of the species, but it is recognized that variation may also be independent of growth and could be related to sexual dimorphism. Growth of the skull in Anteosaurus shows similar morphological trends to that of the Russian Titanophoneus and the Chinese Sinophoneus. The overall morphology of the juvenile Anteosaurus is clearly reminiscent of the adult skull of the Russian medium-sized Syodon, a condition that is more likely a result of similar skull sizes and the lack of strong pachyostosis in adult Syodon.

Waterford Formation in the south-eastern Karoo: Implications for basin development

Extensive research on the rocks of the Karoo Supergroup has shown that this sequence, which contains an unsurpassed record of Permian–Jurassic tetrapods, records a largely unbroken stratigraphic succession from 300 Ma to 180 Ma. This Gondwanan succession was deposited in a changing environmental setting reflecting glacial marine through deltaic to fluvial and aeolian desert conditions. The contact between the Ecca and Beaufort Groups (at the top of the Waterford Formation of the Ecca Group) in the southern and western Karoo represents a change in depositional environment from a subaqueous to a subaerial delta plain. By contrast, the Waterford Formation has not yet been recognised in the south-eastern Karoo Basin, which might imply that a major unconformity is present between the Fort Brown Formation of the Ecca Group, deposited in a prodelta environment, and the overlying fluvially deposited Koonap Formation of the Beaufort Group. From careful documentation of lithofacies and sedimentological data, it can be demonstrated that the Waterford Formation is indeed present in the south-eastern part of the basin and that no major unconformity is present – a fact that has implications for the mapping of Karoo rocks in the Eastern Cape Province of South Africa, for understanding the depositional environment of ’reptilian‘ fossils from the lowermost Beaufort in this part of the Karoo basin, and for basin development models.

Aspects of the lateral and vertical resolution of surface electroseismic data with implications for groundwater exploration in fractured Karoo rocks

Horizontal bedding-plane fractures are of prime importance for the drilling of successful water-supply boreholes in Karoo rocks, but usually have very localized occurrences and small aperture widths. Geophysical methods conventionally used for groundwater exploration in Karoo rocks are unable to detect these fractures. Electroseismic (ES) methods make use of the fact that electromagnetic waves are radiated when seismic waves cause fluid flow across interfaces between porous media of different electrokinetic properties. Since the electrokinetic contrast between a fluid-filled fracture and its host is likely to be high, ES signal generation may occur at both the top and bottom interfaces of the fracture. The ability of surface ES methods to detect and resolve the fractures depends on the lateral and vertical resolution of ES data. The ES Fresnel zones are larger than their seismic equivalents and the lateral resolution of ES data is correspondingly poorer. Seismic velocity increases with depth have an additional negative impact on the lateral resolution of ES data. Assuming that a fracture has a measurable surface ES response, a simplified model shows that the response from a localized fracture may be observed at surface positions laterally displaced from the fracture. The presence of large localised unfractured areas occurring within fractured areas may not be detected at all. Rayleigh’s vertical resolution criterion applied to electroseismic data requires that an embedded thin layer have a minimum thickness of half the dominant wavelength of the seismic wave. Since the Biot slow wave has a much smaller wavelength than the Biot fast wave, it would seem that the limits of vertical resolution are determined by the dominant wavelength of the slow wave. The dissipative nature of the slow wave, however, may cause the practical limit of vertical resolution to be more dependent on the wavelength of the fast wave. The detection of a thin embedded layer depends on the conditions of constructive and destructive interference of signal generated at its top and bottom interfaces. For both the fast and slow wave a thin bed with a thickness less than a quarter of the dominant wavelength results in a total ES response that is weaker than the response from the top interface alone. For both fast and slow pressure waves this thickness is much larger than the aperture width of the bedding-plane fractures in Karoo rocks, and detection of these fractures with surface ES methods seems unlikely.

Tectonic and climatic events controlling deposition in Tanzanian Karoo basins

The depositional megasequence of the Tanzanian Karoo resulted from an intracratonic phase of sedimentation prevailing during the maximum extension of Pangea in Late Palaeozoic and Triassic times. Karoo rocks are contained in a number of basins, extending from northeastern-most Tanzania to Lake Nyasa and beyond into neighbouring countries. The type section of the Tanzanian Karoo is the Songea Group of the Ruhuhu Basin, situated at the NE-shoulder of the Nyasa Rift. The succession, which reaches a thickness of more than 3000 m, is of Late Carboniferous to Mid-Triassic age. It exhibits five distinctive sequences, each commencing with rudaceous sediments and fining up towards the top. A sixth sequence of Middle to Late Triassic age is recognized in the Selous Basin, NE of the Ruhuhu Basin. The climate ranged from cold, semi-arid conditions in the Stephanian and Asselian to generally warm to hot climates, with fluctuating precipitation in the remaining Permian and Triassic. A marked peak in precipitation is evidenced in the Early Triassic. Each of the sedimentary sequences reflects tectonic movements related to the formation of non-volcanic rift systems during the Permian, and to detachment faults and crustal foundering during the Triassic. The intracratonic Karoo rifts were part of the Malagassy Trough, a large chasm emanating from the Tethyan margin of Gondwana in early Permian times. The Karoo rifts were terminated by their transformation to a pericratonic, passive margin in the Early Jurassic.

Interpretation of refelction seismic data from the Usangu Basin, East African Rift System

Reflection seismic data collected by AMOCO Tanzania Oil Company in the 80s, are herin used to correlate the main Usangu Basin parameters to those estimated from outcrop, gravity and aeromagnetic data. The seismic data are further used to constrain the geometry of crustal extension in this south-western sector of the East African Rift System (EARS) in Tanzania. Three distinct sedimentary packages on top of the basement reflector are interpreted and correlated to the Permo-Carboniferous Karoo rocks, the Jurassic/Cretaceous and Miocene Red Sandstone Group and Miocene to recent Lake Beds in the adjacent Rukwa basin, where the ages of the sedimentary sequences have been established on the basis of drill hole data. The Karoo beds, deposited on an undulating weathered basement surface are relatively thin (~ 200m). The Red Sandstone Group reach a maximum thickness of up to 420 m while the Lake Beds are up to 289 m thick. Beneath the Karoo, seismic reflections show interval velocities of 3.22 km/s, which are less than typical crystalline basement velocities of 4.2 km/s in the adjacent Rukwa Rift. These “sub-basement” velocities are attributed to the slightly metamorphosed sediments of Upper Proterozoic, Buanji Group that crop out extensively on top of the Chimala scarp. Previous estimate of the thicknesses of Buanji sediments from outcrop data has been up to 1.086 km. The present study, however, suggests a thickness of more than 2 km for the Buanji sediments beneath the Mesozoic to recent sediments in the Usangu Basin. Age wise the Usangu Basin, which has always been considered to be much younger than its south-western continuation, the Luangwa valley, is here suggested to be an old structure in which sedimentation has been going on since Karoo time. Recent faulting mechanism inferred from recent earthquake data and the present interpretation of seismic sections suggest that deformation in the Usangu Basin has been predominantly strike slip. Thus, the Usangu Basin is best interpreted as a transfer fault, accommodating the relative movement between the southern-most sub-basin of the Rukwa Rift and the northernmost sub-basin of the Malawi Rift. Tanzanian Journal of Science Vol. 28(1) 2002: 83-97

The 1998 edition of the National Geological Map of Botswana

A new National Geological Map of Botswana incorporates data acquired from a variety of sources; the map is produced as a 1:1 million hardcopy as well as in digital format. The new map shows the pre-Kalahari Group geology. The oldest rocks are exposed in eastern Botswana where three Archaean terranes are recognised: the western parts of the Kaapvaal and Zimbabwe Cratons and the western part of the Limpopo Mobile Belt. All three terranes are lithologically similar but differ in their structural styles and in the timing of major thermal events. The oldest (pre-3.0 Gal high-grade metamorphic rocks are found in the Kaapvaal Craton, and the youngest in the Limpopo Mobile Belt, which appears to record Palæoproterozoic ductile shearing. Proterozoic orogenic belts, mostly concealed beneath Karoo rocks, define the western limits of the Archaean terranes and pprogressively young westwards away from the Archaean rocks. The Palwoproterozoic Magondi and Kheis Belts are well-defined by regional magnetic maps, but both are very poorly exposed in Botswana. The Kheis Belt trends due north from South Africa into central Botswana to define the western edge of the Kaapvaal Craton. The western part of the Magondi Belt, as well as all of a Mesoproterozoic (Kibaran) belt and rift are overprinted by the Neoproterozoic Damara Belt; all have pronounced northeasterly trends. During the Palæoproterozoic, there was also significant intraplate magmatism, sedimentation and deformation within the Archæan terranes. Some of the magmatism (in southeastern Botswana) was contemporaneous with, and lithologically similar to, the Bushveld Igneous Complex of South Africa. The main feature of the Mesoproterozoic geology of Botswana is a northeast trending rift that extends right across the northwest of the country and which is partly infilled with ca 1 106 Ma volcanic rocks. Neoproterozoic sedimentary rocks overlie the volcanics within the rift. The various rocks are exposed along the Ghanzi Ridge and to the northeast in the Chobe District. New detailed airborne magnetic surveys in northwest Botswana (Ngamiland) show the detailed geology of the northeast trending inland branch of the Damara Belt and exactly define its northwestern and southeastern boundaries. The southeastern part of the Damara Belt comprises the Mesoproterozoic volcanics of the Kgwebe Formation and the Neoproterozoic Ghanzi Group sedimentary strata. The full extent of the volcanics, and of the three formations recognised in the Ghanzi Group, is shown on the new map. Deformation of these rocks increases to the northwest where they are bounded by the tectono-stratigraphical Roibok Group. To the northwest of the Roibok Group are poorly dated granitoid rocks separated into several units that are locally overlain by carbonate-dominated sequences. A cover sequence of metasedimentary rocks with northnorthwest trending folds lies northwest of the Damara Belt. These sediments may overlie the southernmost part of the Congo Craton in the extreme northwest of Botswana. Neoproterozoic/ Lower Palæozoic sediments of the Nama Group partly infill a foreland basin to the south of the Damara belt in western Botswana. Karoo strata deposited within the Kalahari Basin underlie central Botswana. The distribution of the four major sedimentary groups, as well as of the capping basalts, is shown. The total thickness of the sediments is < 2000 m and the basalts are up to 1000 m in thickness. The sediments comprise a lower sequence (Dwyka and Ecca Groups) related to regional sagging and an upper sequence (Beaufort and Lebung Groups) that succeeded regional uplift that created intra-Karoo unconformities. Karoo sedimentation commenced towards the end of the Carboniferous Period and the basalts were extruded at about 180 Ma before Present. Wherever there have been detailed studies undertaken on the Karoo rocks, they show intense faulting that may or may not mimic structures in the pre-Karoo bedrock. The faulting appears to be post-sedimentation. No evidence was found for growth faults producing abnormal thicknesses of Karoo sediments. It is always possible to correlate the internal stratigraphy, at least at the formational level across the faults. Abnormal thicknesses of the basalts are preserved on the downthrow sides of the major faults. A major dyke swarm coeval with the extrusive basalts trends east-southeast right across north-central Botswana to cut across older structural trends. Over 200 kimberlites are shown on the new map. The kimberlites are distributed throughout Botswana in a number of separate clusters. Most of the kimberlites are of Cretaceous age. Isopachs are shown of the Kalahari Group, which is generally < 180 m in total thickness.

Paleomagnetism of Permian sedimentary rocks from Tanzania and the Permian paleogeography of Pangea

We report new paleomagnetic results from Karoo (Permian) rocks in Tanzania. K1 and K3 redbeds and K5 siltstones and limestones from the Songwe-Kiwira Basin, Ndeke redbeds from the Mikumi Basin, and group VIII redbeds from the Nyakatitu Basin were sampled and thermally demagnetized. Palynologic data and lithologic correlations suggest that the K1 redbeds are Lower Permian, and that the K3, Ndeke, and group VIII redbeds, as well as the K5 siltstones and limestones, are Upper Permian. Stable magnetic directions were obtained from the K3, Ndeke, and group VIII redbeds, yielding an Upper Permain pole at 26°N, 267°E. Characteristic remanence directions were also obtained from the K5 siltstones and limestones. However, because these directions define a pole (66°N, 269°E) that is very close to the Upper Cretaceous pole for Africa and significantly different from the Upper Permian redbed poles, these rocks may have been remagnetized. The K1 redbeds did not yield stable results. Using our new results together with published Permian poles for Africa and the other Gondwanan continents, we revise the mean Lower and Upper Permian poles for Africa, West Gondwana, and Gondwana, and investigate whether or not these revised poles can discriminate between the various Pangea reconstructions proposed for the Permian with any greater certainty than previous (unrevised) mean poles. When compared to the mean Lower and Upper Permian poles for Laurussia, we find that our revised West Gondwanan and Gondwanan poles do not necessarily provide stronger support for any particular Pangea reconstruction than the previous poles. Therefore, even though this study improves the paleomagnetic data base for Gondwana for the Permian, it is not clear that the combination of our results with other paleomagnetic data from the Gondwanan continents yields significant new insights about the Permian configuration of Pangea. As suggested previously, strong non-dipole fields during the Permian may provide an explanation for why it is not easy to discriminate with certainty between the various Permain Pangea reconstructions, even with new paleomagnetic results.

A review of the stratigraphy and sedimentary environments of the Karoo-aged basins of Southern Africa

The Karoo Basin of South Africa was one of several contemporaneous intracratonic basins in southwestern Gondwana that became active in the Permo-Carboniferous (280 Ma) and continued to accumulate sediments until the earliest Jurassic, 100 million years later. At their maximum areal extent, during the early Permian, these basins covered some 4.5 million km 2. The present outcrop area of Karoo rocks in southern Africa is about 300 000 km 2 with a maximum thickness of some 8000 m. The economic importance of these sediments lies in the vast reserves of coal within the Ecca Group rocks of northern and eastern Transvaal and Natal, South Africa. Large reserves of sandstone-hosted uranium and molybdenum have been proven within the Beaufort Group rocks of the southern Karoo trough, although they are not mineable in the present market conditions. Palaeoenvironmental analysis of the major stratigraphic units of the Karoo succession in South Africa demonstrates the changes in depositional style caused by regional and localized tectonism within the basin. These depocentres were influenced by a progressive aridification of climate which was primarily caused by the northward drift of southwestern Gondwana out of a polar climate and accentuated by the meteoric drying effect of the surrounding land masses. Changing palaeoenvironments clearly influenced the rate and direction of vertebrate evolution in southern Gondwana as evidenced by the numerous reptile fossils, including dinosaurs, which are found in the Karoo strata of South Africa, Lesotho, Namibia and Zimbabwe. During the Late Carboniferous the southern part of Gondwana migrated over the South Pole resulting in a major ice sheet over the early Karoo basin and surrounding highlands. Glacial sedimentation in upland valleys and on the lowland shelf resulted in the Dwyka Formation at the base of the Karoo Sequence. After glaciation, an extensive shallow sea covered the gently subsiding shelf, fed by large volumes of meltwater. Marine clays and muds accumulated under cool climatic conditions (Lower Ecca Group) including the distinctive Mesosaurus-bearing carbonaceous shales of the Whitehill Formation. Subduction of the palaeo-Pacific plate reslted in an extensive chain of mountains which deformed and later truncated the southern rim of the main Karoo Basin. Material derived from these “Gondwanide” mountains as well as from the granitic uplands to the north-east, accumulated in large deltas that prograded into the Ecca sea (Upper Ecca Group). The relatively cool and humid climate promoted thick accumulations of peat on the fluvial and delta plains which now constitute the major coal reserves of southern Africa. As the prograding deltas coalesced, fluvio-lacustrine sediments of the Beaufort Group were laid down on broad gently subsiding alluvial plains. The climate by this time (Late Permian) had warmed to become semi-arid with highly seasonal rainfall. Vegetation alongside the meander belts and semi-permanent lakes supported a diverse reptilian fauna dominated by therapsids or “mammal-like reptiles”. Pulses of uplift in the southern source areas combined with possible orographic effects resulted in the progadation of two coarse-grained alluvial fans into the central parts of the basin (Katberg Sandstone Member and Molteno Formation). In the upper Karoo Sequence, progressive aridification and tectonic deformation of the basin through the late Triassic and early Jurassic led to the accumulation, in four separate depositories, of “redbeds” which are interpreted as fluvial and flood-fan, playa and dune complexes (Elliot Formation). This eventually gave way to westerly wind-dominated sedimentation that choked the remaining depositories with fine-grained dune sand. The interdune areas were damp and occasionally flooded and provided a habitat for small dinosaurs and the earliest mammals. During this time (Early Jurassic), basinwide volcanic activity began as a precursor to the break-up of Gondwana in the late Jurassic and continued until the early Cretaceous. This extrusion of extensive flood basalts (Drakensberg Group) onto the Clarens landscape eventually brought Karoo sedimentation to a close.

The analysis of termite hills to locate uranium mineralization in the Karoo Basin of South Africa

Uranium mineralization was located in a lacustrine paleodelta in the Main Karoo Basin of South Africa. It is situated in the lowermost unit of a sandstone package at a depth of up to 25 m below surface. The mineralized sandstone is mostly sandwiched between impervious mudstone units but is also intercalated with finer siltstones in places. As conventional prospecting techniques when applied to Karoo uranium deposits have largely provided unsatisfactory and inconclusive results in the past, total and leachable uranium analyses were conducted on termite hills on the assumption that the termites could penetrate down to the mineralization and bring it up to the surface. The close relationship between the anomalous zones with the known trend of uranium mineralization suggests that termite hills can be an effective tool for finding uranium deposits up to depths of at least 30 m in the Karoo rocks.

Geology, basin analysis, and hydrocarbon potential of Mozambique and the Mozambique Channel

The Phanerozoic structural and stratigraphic history of Mozambique can be separated into a “Karoo” and a post-Karoo phase. Outcrops of Karoo rocks, limited to the Zambezi valley and small outliers in the Mozambique belt to the north show an eastward facies change marked by an increased argillaceous content and the appearance of carbonates. The wide coastal plain and immediate offshore of southern Mozambique is marked by extensional horsts and grabens with a Mesozoic fill covered by Cenozoic sediments. Little is known of lower stratigraphic horizons. In this coastal province there is a facies transition from continental clastics in the northwest and west to more lacustrine and marine deposits to the southeast and east. Upwards the succession passes into the Cenozoic without a noticeable break. In the offshore in the north seismic lines help define two basins, the Zambezi Delta basin and the Mozambique Channel basin separated by the Beira High. In the south several offshore grabens have been defined, one of which, the South Mozambique graben, has been examined here by an integrated basin analysis technique. The technique, which uses available depositional, structural and thermal data, provides information on maturation and the timing of hydrocarbon maturation. The analysis showed variation in the extension rate with time, and two phases of rifting. The greatest rate of extension, accumulation and subsidence, between 96 and 76 Ma, depends upon interpretational assumptions. During this time interval fault blocks were systematically tilted “domino” fashion. This event broadly coincides with the rifting between Madagascar and Antarctica, a period of plate reorganization. The earlier rifting phase was probably related to the strike-slip separation of Madagascar from Africa. Modelling heat flow suggests that the later event is the more important from the maturation-hydrocarbon standpoint. The offshore, and potentially the deeper, onshore post-Karoo basins have traps, reservoirs and seals with the presumed source rock within Lower Cretaceous or Jurassic strata. There is, at the present time, no means to evaluate the potential of the Karoo rocks.

Lithostratigraphic subdivision of the Karoo rocks of the Luwegu Basin (Tanzania) and their biostratigraphic classification based on microfloras, macrofloras, fossil woods and vertebrates

For the first time a comprehensive stratigraphic classification of the Karoo deposits of the Luwegu Basin in southern Tanzania is presented. The Karoo strata attain a total thickness of almost 6000 metres and are composed of deltaic-lacustrine and fluvial deposits. The sedimentary sequence has been subdivided into nine major lithostratigraphic units. The results of biostratigraphic investigations (microfloras, macrofloras, fossil woods, vertebrates) indicate, that the Karoo Sequence ranges in age from Upper Permian to Lower Jurassic. The palynological sequence comprises microfloras of the Upper Permian, the Upper Triassic (Onslow and Ipswich type) and the Lower Jurassic. Their age is assessed from correlation with palynofloras of Malagasy, Australia and Zimbabwe. Resulting from this regional as well as intercontinental correlations with the Karoo strata of East and South Africa, the Karoo-type strata of North Africa and the Gondwana sequences of Australia and India can be proposed. Furthermore on the base of radiometric datings of hitherto unknown occurrences of volcanic rocks a Karoo volcanism and an Early Tertiary volcanism can be distinguished.

Rock mass characterization of weak bedded Karoo rocks for the design of a large span circular tunnel : Solesbury, F W; Speers, C R; Muniz, K K Proc of the Symposium on Rock Mass Characterization, Randburg, South Africa, 8 Nov 1985 P29–37 Publ South Africa: ISRM, 1985

Rock mass characterization of weak bedded Karoo rocks for the design of a large span circular tunnel : Solesbury, F W; Speers, C R; Muniz, K K Proc of the Symposium on Rock Mass Characterization, Randburg, South Africa, 8 Nov 1985 P29–37 Publ South Africa: ISRM, 1985

A new engineering-geological rock durability classification

The construction of the 5.3-m diameter, 82-km long Orange—Fish Tunnel in the Republic of South Africa, in sensibly horizontal beds of mudrocks, siltstones and sandstones of the Karoo Supergroup (Upper Carboniferous to Triassic age), revealed the paramount importance of rock durability. The presence of non-durable rock types was found to be one of the causes of the rock distress problems encountered in some tunnel sections during construction. Geomechanical tests conducted on representative samples of potentially difficult rock types from the Orange—Fish Tunnel, indicated important limitations of international rock material classifications, such as the Deere—Miller Modulus—Strength and the Deere—Gamble Durability—Plasticity systems. The inadequacy of these classifications in the case of the Karoo sedimentary rocks, underlined the need for a new rock durability classification which could be used for the timely indication of the presence of non-durable rock material sections at tunnel level. An account is given of the lithology, mineralogy and the postulated weathering mechanics of the Karoo rocks encountered, as well as the application of these parameters to the numerical methods used for the quantitative assessment of rock durability. It is considered that a reliable appraisal of this time-dependent parameter can be provided by the measurement of the strength and free swelling properties of the intact rock material. A new rock durability classification, styled the Geodurability Classification, is discussed. This empirical system appears to be practical and simple as it depends on the minimum number of index rock properties, which can be measured fairly rapidly in a field laboratory by means of simple test apparatus and semi-skilled labour. It is based on different ranges of ratios of the uniaxial compressive strength, σ c, and the “Duncan” free swelling coefficient, ε D, as index parameters. The intact rock material is classified according to a rating system which varies from “excellent” (Class A) to “very poor” (Class F). The extensive use of the Geodurability Classification indicated such a system to be particularly relevant to compacted and weakly cemented rocks, where the tendency of the rock material to deteriorate with time (and not the presence of rock discontinuities such as joints and bedding planes) dominates the time-dependent behaviour of tunnel rock masses.

III. Researches on the structure, organisation, and classification of the fossil reptilia. VII. Further observations on Pareiasaurus

The author distinguishes five zones of life in the Karoo rocks, which are termed, counting from the bottom, Mesosaurian, Pareiasaurian, Dicynodont, Theriodont, and Zanclodont. The Pareiasaurian zone extends between the Prince Albert Road station and the Hieuw veldt range of mountains. He obtained a nearly complete skeleton from Bad, east of Tamboer, a less complete skeleton from Tamboer Foutein, and a portion of jaw from near Klipfontein, on the summit of the Hieuwveldt range.