Proterozoic–Paleozoic Sedimentary Rocks and Mesozoic–Cenozoic Landscapes of the Cape Mountains Across the Kango Complex Reveal ‘More Gaps Than Record’ from Rodinia and Gondwana to Africa

The Kango (Cango) region flanks the northern margins of the Klein Karoo and the Cape Mountains across the Western Cape Province of South Africa. It preserves a condensed Proterozoic–Paleozoic stratigraphy exposed via a Mesozoic–Cenozoic morphology with a present Alpine-like topography. Its rocks and landscapes have been repeatedly mapped and documented for the past 150 years. Over the last 25 years, we remapped and dated a central-eastern section of this region. The subvertically bedded and cleaved rocks reveal an 8–10 km thick stratigraphy covering more than 700 million years between ca. 1200 and 500 Ma with several unconformities and disconformities. At ca. 252 Ma, during the Cape orogeny, this Kango Complex was deformed along thrusts and sub-isoclinal folds producing steeply dipping phyllites and slates. It was uplifted by 3–5 km during the Kalahari epeirogeny between 140 and 60 Ma while eroding at ca. 100–200 m/m.y. (120–80 Ma). During the Cenozoic, the rate of uplift decreased by an order of magnitude and today is ca. 0.4–0.7 m/m.y. across steep slopes and canyons in contrast to the Himalayas where erosion rates are about hundred times faster. A recent publication about this central-eastern section of the Kango region disputes the existence of regional isoclinal folds and suggests that deposition of the oldest sedimentary successions, including carbonate rocks of the Cango Caves (limestone-marble with enigmatic microfossils) was simple, continuous and restricted to between ca. 700 and 500 Ma, decreasing earlier estimates of the stratigraphic age range by 60–80%. Similarly, recent interpretations of the complex landscapes link the northern contact between the Kango and Table Mountain rock sequences to Quaternary faults. We present a new geological database, mapped between 1:500 and 1:10,000 scales, and twelve stratigraphic sections with younging directions linked to structural and isotopic data that support repetitions along regional isoclinal folds and thrust zones of the Kango sequences during the Permo–Triassic Cape orogeny, and geomorphic data that link the origin of its landscapes to weathering and erosion during the Cretaceous–Cenozoic Kalahari epeirogeny. During its evolution, the Kango Basin directly flanked both Grenvillian and Pan-African Mountain systems. But, at an average sedimentation rate of ca. 1 mm/70 years (0.014 mm/year) and with present low erosion rates (0.005 mm/year), there is likely more time missing than preserved of the tectono-erosion across these different regions of Rodinia and Gondwana before Africa emerged. To further evaluate the geodynamic significance of these time gaps requires more field mapping linked to new transdisciplinary geosciences. RÉSUMÉLa région du Kango (Cango) flanque les marges nord du petit Karoo et des montagnes du Cap dans la province du Western Cape en Afrique du Sud. Elle préserve une stratigraphie condensée protérozoïque–paléozoïque exposée via une morphologie mésozoïque–cénozoïque avec une topographie actuelle de type alpin. Ses roches et ses paysages ont été cartographiés et documentés durant les 150 dernières années. Au cours des 25 dernières années, nous avons re-cartographié et daté une section du centre-est de cette région. Les roches litées de manière subverticale et clivées révèlent une stratigraphie de 8 à 10 km d'épaisseur couvrant plus de 700 millions d'années entre environ 1200 et 500 Ma avec plusieurs non-conformités et disconformités. À 252 Ma, au cours de l'orogenèse du Cap, ce Complexe du Kango s'est déformé le long de chevauchements et de plis isoclinaux produisant des schistes à fort pendage. Il a été soulevé de 3 à 5 km au cours de l'épirogenèse du Kalahari entre 140 et 60 Ma, tout en s'érodant à 100–200 m/m.a. (120–80 Ma). Pendant le Cénozoïque, le taux de soulèvement a diminué d'un ordre de grandeur et il est aujourd'hui d'environ 0,4 à 0,7 m/m.a. à travers des pentes abruptes et des canyons, contrairement à l'Himalaya où les taux d'érosion sont environ cent fois plus rapides. Une publication récente sur cette section du centre-est de la région du Kango conteste l'existence de plis isoclinaux régionaux et suggère que le dépôt des plus anciennes successions sédimentaires, y compris les roches carbonatées des Grottes du Cango (marbre calcaire avec des microfossiles énigmatiques) était simple, continu et limité entre environ 700 et 500 Ma, diminuant les estimations antérieures de la tranche d'âge stratigraphique de 60-80%. De même, des interprétations récentes des paysages complexes relient le contact nord entre les séquences rocheuses du Kango et de Table Mountain à des failles quaternaires. Nous présentons une nouvelle base de données géologiques, cartographiée à des échelles entre 1:500 et 1:10,000, et douze coupes stratigraphiques avec des directions de superposition liées à des données structurales et isotopiques qui concordent avec les répétitions le long des plis isoclinaux régionaux et des zones de chevauchement des séquences du Kango pendant l’orogenèse permo–triassique du Cap, et des données géomorphiques qui relient l'origine de ses paysages à l’altération et à l'érosion au cours de l'épirogenèse du Kalahari au Crétacé–Cénozoïque. Au cours de son évolution, le bassin du Kango flanquait les systèmes montagneux grenvillien et panafricain. Mais, à un taux de sédimentation moyen d’environ 1 mm/70 ans (0,014 mm/an) et avec les faibles taux d'érosion actuels (0,005 mm/an), il manque probablement plus d’enregistrements de la tectonique et érosion de ces différentes régions de Rodinia et Gondwana avant l'émergence de l'Afrique que ce qui est actuellement préservé. Pour évaluer la signification géodynamique de ces intervalles de temps manquant, il faut d’avantage de cartographie de terrain associée à de nouvelles géosciences transdisciplinaires

From source to sink in central Gondwana: Exhumation of the Precambrian basement rocks of Tanzania and sediment accumulation in the adjacent Congo basin

Apatite fission track (AFT) and (U-Th)/He (AHe) thermochronometry data are reported and used to unravel the exhumation history of crystalline basement rocks from the elevated (>1000 m above sea level) but low-relief Tanzanian Craton. Coeval episodes of sedimentation documented within adjacent Paleozoic to Mesozoic basins of southern Tanzania and the Congo basin of the Democratic Republic of Congo indicate that most of the cooling in the basement rocks in Tanzania was linked to erosion. Basement samples were from an exploration borehole located within the craton and up to 2200 m below surface. Surface samples were also analyzed. AFT dates range between 317 ± 33 Ma and 188 ± 44 Ma. Alpha (Ft)-corrected AHe dates are between 433 ± 24 Ma and 154 ± 20 Ma. Modeling of the data reveals two important periods of cooling within the craton: one during the Carboniferous-Triassic (340–220 Ma) and a later, less well constrained episode, during the late Cretaceous. The later exhumation is well detected proximal to the East African Rift (70 Ma). Thermal histories combined with the estimated geothermal gradient of 9°C/km constrained by the AFT and AHe data from the craton and a mean surface temperature of 20°C indicate removal of up to 9 ± 2 km of overburden since the end of Paleozoic. The correlation of erosion of the craton and sedimentation and subsidence within the Congo basin in the Paleozoic may indicate regional flexural geodynamics of the lithosphere due to lithosphere buckling induced by far-field compressional tectonic processes and thereafter through deep mantle upwelling and epeirogeny tectonic processes

Old, strong continental lithosphere with weak Archaean margin at - 1.8 Ga, Kaapvaal Craton, South Africa

Low elastic strength of ancient lithosphere based on flexural analyses has been interpreted to reflect elevated regional geothermal gradients in response to higher global heat production in the past. Here we present a flexural analysis of Archean/Palaeoproterozoic sediment cover along the western margin of the Archaean Kaapvaal craton based on seismic stratigraphy. Our results show that between ~1.93 and ~1.75 Ga, the Archaean margin of the craton had an effective elastic thickness of 7.5 to 10km compared to its present day value of 60 to 70km. Because the Kaapvaal craton had already stabilized by ~2.7 Ga and was underlain by 150 to 300km thick strong mantle lithosphere, it is unlikely that the relatively thin elastic thickness along this old margin reflects a change in secular cooling of the Earth. Instead, we interpret the low elastic strength to be a transient marginal tectonic effect similar to that recorded along modern continental margins

Possible lack of full cross-resistance of 5HT3 antagonists; a pilot study

We investigated the potential of cross-over to the serotonin receptor (5HT3) antagonist ondansetron after protection failure with tropisetron. Several cases of complete protection were observed. These limited data suggest that there is an indication for retreatment with a different 5HT3 antagonist after an initial failure to another and also stress the need and relevance for comparative studies between 5HT3 antagonists

A subduction origin for komatites and cratonic lithospheric mantle

We present a model in which the generation of komatiites in Archaean subduction zones produced depleted mantle residues that eventually formed the highly depleted portions of the Kaapvaal lithospheric mantle. The envisioned melting process is similar to that which has formed boninites in Phanerozoic subduction zones such as the Izu-Bonin-Mariana arc. The primary differences between the Archaean and Phanerozoic melting regimes are higher mean melting temperatures (1450 versus 1350 °C) and higher mean melting pressures (2.5 versus 1.5 GPa) for the komatiites. The komatiites from the Komati Formation in the Barberton greenstone belt are mafic enough to have produced the depletion seen in most Kaapvaal granular peridotite xenoliths. However, the most highly depleted Kaapvaal xenoliths require an even more Mg-rich magma than the Komati komatiites (Kk). Samples of boninite mantle residues from the fore-arc of the Marianas subduction zone are nearly as depleted as the Kaapvaal cratonic mantle, indicating that buoyant, craton-like mantle is being produced today. We speculate that production rates of cratonic mantle were greater in the Archaean due to the greater depth of melting for komatiites (relative to boninites) and greater worldwide arc length. The high production rates and high buoyancy of the komatiite mantle residues gave rise to the rapid growth and stabilization of the Kaapvaal craton in the Archaean

Combined cardiological and neurological abnormalities due to filamin A gene mutation

Background: Cardiac defects can be the presenting symptom in patients with mutations in the X-linked gene FLNA. Dysfunction of this gene is associated with cardiac abnormalities, especially in the left ventricular outflow tract, but can also cause a congenital malformation of the cerebral cortex. We noticed that some patients diagnosed at the neurogenetics clinic had first presented to a cardiologist, suggesting that earlier recognition may be possible if the diagnosis is suspected. Methods and results: From the Erasmus MC cerebral malformations database 24 patients were identified with cerebral bilateral periventricular nodular heterotopia (PNH) without other cerebral cortical malformations. In six of these patients, a pathogenic mutation in FLNA was present. In five a cardiac defect was also found in the outflow tract. Four had presented to a cardiologist before the cerebral abnormalities were diagnosed. Conclusions: The cardiological phenotype typically consists of aortic or mitral regurgitation, coarctation of the aorta or other left-sided cardiac malformations. Most patients in this category will not have a FLNA mutation, but the presence of neurological complaints, hyperlaxity of the skin or joints and/or a family history with similar cardiac or neurological problems in a possibly X-linked pattern may alert the clinician to the possibility of a FLNA mutation

SAJS Volume 113 Issue 11/12 - Dhansay Supplementary Material

South Africa intends to mitigate its carbon emissions by developing renewable energy from solar, wind and hydro, and investigating alternative energy sources such as natural gas and nuclear. Low-enthalpy geothermal energy is becoming increasingly popular around the world, largely as a result of technological advances that have enabled energy to be harnessed from relatively low temperature sources. However, geothermal energy does not form part of South Africa’s future renewable energy scenario. This omission may be related to insufficient regional analysis of potentially viable geothermal zones across the country. We considered existing subsurface temperature and heat flow measurements and performed solute-based hydrochemical geothermometry to determine potentially anomalous geothermal gradients that could signify underlying low-enthalpy geothermal energy resources. We correlated these findings against hydro/geological and tectonic controls to find prospective target regions for investigating geothermal energy development. Our results show a significant link between tectonic features, including those on-craton, and the development of geothermal potential regions. In addition, potential regions in South Africa share similarities with other locations that have successfully harnessed low-enthalpy geothermal energy. South Africa may therefore have a realistic chance of developing geothermal energy, but will still need additional research and development, including new temperature measurements, and structural, hydrogeological and economic investigations. Significance:  • The regional low-enthalpy geothermal energy potential of South Africa should be further researched for consideration of low-enthalpy geothermal energy as a renewable energy option

The controversy of using PGA to define remission in RA

Abstract not provided for this lette

Assessing the effect of interventions for axial spondyloarthritis according to the endorsed ASAS/OMERACT core outcome set: a meta-research study of trials included in Cochrane reviews.

The Assessment of SpondyloArthritis international Society (ASAS) has defined core sets for (i) symptom-modifying anti-rheumatic drugs (SM-ARD), (ii) clinical record keeping, and (iii) disease-controlling anti-rheumatic therapy (DC-ART). These include the following domains for all three core sets: physical function, pain, spinal mobility, spinal stiffness, and patient\u27s global assessment (PGA). The core set for clinical record keeping further includes the domains peripheral joints/entheses and acute phase reactants, and the core set for DC-ART further includes the domains fatigue and spine radiographs/hip radiographs. The Outcome Measures in Rheumatology (OMERACT) endorsed the core sets in 1998.Using empirical evidence from axSpA trials, we investigated the efficacy (i.e., net benefit) according to the ASAS/OMERACT core outcome set for axSpA across all interventions tested in trials included in subsequent Cochrane reviews. For all continuous scales, we combined data using the standardized mean difference (SMD) to meta-analyze outcomes involving the same domains. Also, through meta-regression analysis, we examined the effect of the separate SMD measures (independent variables) on the primary endpoint (log [OR], dependent variable) across all trials.Based on 11 eligible Cochrane reviews, from these, 85 articles were screened; we included 43 trials with 63 randomized comparisons. Mean (SD) number of ASAS/OMERACT core outcome domains measured for SM-ARD/physical therapy trials was 4.2 (1.7). Six trials assessed all proposed domains. Mean (SD) for number of core outcome domains for DC-ART trials was 5.8 (1.7). No trials assessed all nine domains. Eight trials (16%) were judged to have inadequate (i.e., high risk of) selective outcome reporting bias. The most responsible core domains for achieving success in meeting the primary objective per trial were pain, OR (95% CI) 5.19 (2.28, 11.77), and PGA, OR (95% CI) 1.87 (1.14, 3.07). In conclusion, selective outcome reporting (and missing data ) should be reduced by encouraging the use of the endorsed ASAS/OMERACT outcome domains in clinical trials. Overall outcome reporting was good for SM-ARD/physical therapy trials and poor for DC-ART trials. Our findings suggest that both PGA and pain provide a valuable holistic construct for the assessment of improvement beyond more objective measures of spinal inflammation