Provenance analysis of selected clastic rocks in Neoproterozoic to lower Paleozoic successions of southern Africa from the Gariep Belt and the Kango Inlier

Beukes

et al. 2010

Section: Samplingmentioning

confidence: 99%

“…2). Recently, provenance studies in Neoproterozoic to Lower Palaeozoic successions of the Kalahari Craton were carried out, but did not provide a comprehensive view of the evolution of the craton (Naidoo 2008;Zimmermann et al 2008aZimmermann et al , b, 2010Van Staden et al 2006, 2010a.…”

Section: Introductionmentioning

confidence: 99%

Provenance and reconnaissance study of detrital zircons of the Palaeozoic Cape Supergroup in South Africa: revealing the interaction of the Kalahari and Río de la Plata cratons

Fourie

Beukes

et al. 2010

“…Trace element geochemistry of the clastic rocks Volcanic and clastic sedimentary rocks can be geochemically characterised using the ratios of Zr/Ti versus Nb/Y (after Winchester and Floyd 1977;Fralick 2003;Lacassie et al 2006;Van Staden et al 2006;Bertolino et al 2007), as these elements are strongly immobile. In Fig.…”

Section: Major Element Geochemistrymentioning

confidence: 99%

“…Diamictite or glaciogenic deposit which incorporates wide area of deglaciated craton surface rocks is expected to show a much broader spread of data (Young et al 2000;McLennan et al 2003). For comparison, data obtained from two other exposures of the Numees diamictite in this region (see Van Staden et al 2006) are also shown. These data are sampled in exposures defined by McMillan (1968) as the 'upper tillite', or as the 'major tillite' by Martin (1965), one close to the type section of the Numees Formation (Van Staden et al 2006).…”

Section: Major Element Geochemistrymentioning

confidence: 99%

The Witputs diamictite in southern Namibia and associated rocks: constraints for a global glaciation?

Tait²,

Crowley

et al. 2010

The Witputs section of the Gariep Belt (S Namibia) comprises a sequence of clastic and chemical sediments, which have been interpreted as representative of a Late Neoproterozoic global or near-global ice age event, and recent biostratigraphic work in the upper rocks of the Witputs suggest a Late Ediacaran age. To further characterise this sequence and provide additional age constraints, a detailed sedimentological and detrital zircon study has been carried out. The petrographic, sedimentological and geochemical characteristics of the Witputs diamictite determined in this study are homogenous and indicative of debris flow or palaeo-valley infill sediments, deposited in an oxic environment with no glaciogenic evidence. This homogeneity is also reflected in the detrital zircon age spectra with most ages falling between 1.0 and 1.3 Ga, representing the local geology, with the youngest grain at 1030.2 ± 10.9 (2r) (n = 92 \10% discordance), despite the fact that mid and Late Neoproterozoic volcanic activity is known in the local region. The overlying carbonate rocks, often considered to be 'cap carbonates', show high Mn (up to 60% MnO), with base metal precipitation (Zn, V, Co), and are recrystallised. Their d 13 C VPDB isotope ratios are homogeneous at around-3. Major and trace element ratios reach values which indicate that C-O isotopes may be disturbed and might not reflect primary global seawater composition, thus questioning their use for global correlation and comparison with composite chemostratigraphic curves. The contact to the overlying Late Ediacaran Sanddrif Member is not exposed, and the rocks dip in a different direction than the underlying carbonate rocks. The c. 40-m-thick section is characterised by rapid lithology changes including shales, calcareous sandstones and wackes, fine-grained conglomerates and rare clean quartz-rich sandstones, all of which have strikingly similar detrital zircon populations, and the youngest zircon is dated at 1082.8 ± 10 Ma (2r errors, from 72 grains with \10% discordance). Acritarchs earlier found in the Sanddrif Member, however, indicate a post-570 Ma depositional age. If the diamictites are glaciomarine deposits, then an interesting conclusion is that the clastic sediments can display a very immature geochemical signature, indicating a localised provenance, with derivation purely from the local basement rocks, which is also reflected in the detrital zircon populations. However, we would hesitate to assign a glacial origin to the deposits as no glacial indicators, other than a diamictitic texture, were observed. Clearly, far more work on the detailed mapping and sedimentology of the Neoproterozoic Gariep Belt deposits is required, particularly as many are currently used for global correlation. Age constraints derived from extensive detrital zircon work can only constrain the deposits as being post 1.03 Ma with the detritus being purely locally derived.Electronic supplementary material The online version of this article (

“…Values significantly above 1.0 can only be observed at the top of the Cerro Largo Formation and in the samples of the Las Á guilas Formation, and the samples of the Villa Mónica Formation show a definite trend from lower values to those close to 1 (Table 1). An estimation of the composition of the sources of the sedimentary rocks can be made using the Zr/Ti vs. Nb/Y ratio plot (Winchester and Floyd 1977;Fralick 2003;Lacassie et al 2006;Van Staden et al 2006;Bertolino et al 2007), as these elements are immobile (Fig. 5).…”

Section: Rare Earth Elements (Ree)mentioning

confidence: 99%

Neoproterozoic to Lower Palaeozoic successions of the Tandilia System in Argentina: implication for the palaeotectonic framework of southwest Gondwana

Poiré

Peral

2010