Showing papers by "Jan Kramers published in 2016"

Detrital zircon U–Pb ages of the Palaeozoic Natal Group and Msikaba Formation, Kwazulu-Natal, South Africa: provenance areas in context of Gondwana

Abstract: The Natal Group and Msikaba Formation remain relatively poorly understood with regards to their provenance and relative age of deposition; a much-needed geochronological study of the detrital zircons from these two units was therefore undertaken. Five samples of the Durban and Mariannhill Formations (Natal Group) and the Msikaba Formation (Cape Supergroup) were obtained. A total of 882 concordant U–Pb ages of detrital zircon populations from these units were determined by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Major Neoproterozoic and secondary Mesoproterozoic detrital zircon age populations are present in the detrital zircon content of all the samples. Smaller contributions from Archean-, Palaeoproterozoic-, Cambrian- and Ordovician-aged grains are also present. Due to the presence of a prominent major population of 800–1000 Ma zircons in all the samples, late Stenian – Tonian ancient volcanic arc complexes overprinted by Pan-African metamorphism of Mozambique, Malawi and Zambia, along with areas of similar age within Antarctica, India and Sri Lanka, are suggested as major sources of detritus. The Namaqua–Natal Metamorphic Complex is suggested as a possible source of minor late Mesoproterozoic-aged detritus. Minor populations of Archean and Palaeoproterozoic zircons were likely sourced from the Kaapvaal and Grunehogna Cratons. Post-orogenic Cambrian – Lower Ordovician granitoids of the Mozambique Belt (Mozambique) and the Maud Belt (Antarctica) made lesser contributions. In view of the apparent broad similarity of source areas for the Natal Group and Msikaba Formation, their sedimentation occurred in parts of the same large and evolving basin rather than localized in small continental basins, and the current exposures merely represent small erosional relicts.

Response to Thackeray (2016) - the possibility of lichen growth on bones of Homo naledi: Were they exposed to light?

Abstract: [Extract] Thackeray questions the hypothesis of deliberate body disposal in the Rising Star Cave by Homo naledi, as proposed by Dirks and colleagues. Thackeray proposes that lichens produced mineral staining on the skeletal remains of H. naledi. As lichens require some exposure to light, in Thackeray's opinion, the presence of mineral staining necessitates either a direct entrance deep into the Rising Star Cave that once admitted light into the Dinaledi Chamber, or relocation of mineral-stained bones from a location exposed to light. Here we consider multiple lines of evidence that reject Thackeray's hypothesis that lichens deposited mineral staining upon the surface of these skeletal remains. We welcome the opportunity to address the inferences presented by Thackeray, and further hope that this response may dispel misinterpretations of our research, and of other areas of the scientific literature that bear upon site formation processes at work within the Rising Star Cave system.

The geology of the Matala Dome: an important piece of the Pan-African puzzle in Central Zambia

Abstract: The Matala Dome (MD), an ENE-trending structure located at the junction between the Pan-African Lufilian and Zambezi belts, is cored by a Gneiss-Schist Unit with uncertain age overlain by a metasedimentary section (Quartzite-Schist Unit, Marble Unit and Carbonate-Siliciclastic Unit) of the Neoproterozoic to Cambrian Katanga Supergroup. The top of the Katangan stratigraphy is represented by synorogenic sedimentary rocks—Upper Siliciclastic Unit. An early event D1 resulted in the development of shallow-dipping metamorphic foliation S1 and pre- to syntectonic growth of garnet and kyanite in the schists of the Quartzite-Schist Unit. Pseudosections and garnet isopleth modelling on schist from this unit defined the peak metamorphism at P = 7.5–9.3 kbar and T = 620–700 °C. U–Pb detrital zircon dating revealed ca. 2.7 Ga source and a high-grade metamorphism during Pan-African times. The S1 foliation was affected by upright folding F2 with ENE-trending axes and associated subvertical crenulation fabric S2 development. The syn-D2 retrogression in the schists is marked by post-S1 staurolite crystallisation and further by chloritisation followed by sericitisation. The D2 event is interpreted to have exhumed the orogenic middle crust and to be responsible for the domal structure of the MD. 40Ar/39Ar dating of muscovite at 529.3 ± 5.6 to 526.3 ± 6.2 is interpreted to date the exhumation event. D2 is correlated with regional N–S shortening event at ca. 530–520 Ma. Based on the lithology, structural record, and time and facies of the metamorphism, a correlation between the MD and the northern part of the Zambezi Belt is suggested.