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Recent advances in South African Neoproterozoic-Early Palaeozoic biostratigraphy: correlation of the Cango Caves and Gamtoos Groups and acritarchs of the Sardinia Bay Formation, Saldania Belt

Departamento de Geología, Facultad de Ciencias. Igua 4225, 11400 Montevideo, Uruguay. e-mail: gaucher{at}chasque.net

Gerard J.B. Germs

Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park, 2006 Johannesburg, South Africa e-mail: gagerms{at}global.co.za

Organic-walled microfossils (acritarchs) of the Cango Caves and Gamtoos Groups and Sardinia Bay Formation of the Saldania Belt were studied with the aim to unravel the Neoproterozoic to early Palaeozoic geology of South Africa. Such a micropalaeontological study will also contribute to establish a world-wide biostratigraphy of the Neoproterozoic to early Paleozoic. Distinct assemblages of organic-walled microfossils occur in the Cango Caves (CCG) and Gamtoos Groups (GG). Eleven species of organic-walled microfossils are described from the CCG, six from the GG, and three from the Sardinia Bay Formation. In the CCG, the mixed clastic-carbonatic Nooitgedagt Member and the overlying, predominantly carbonatic Kombuis Member of the Matjies River Formation are dominated by Bavlinella and Soldadophycus respectively. The overlying, mainly siliciclastic Groenefontein and Huis Rivier Formations are leiosphaerid dominated. In the GG, carbonates of the Lime Bank and lower Kaan Formations are Bavlinella-dominated, the asssemblage of the uppermost Kaan and the lower Van Stadens Formations being dominated by Soldadophycus. The microflora of the Kleinrivier Formation is dominated by leiosphaerids. The acritarch assemblages and lithostratigraphy indicate that correlations between units of the GG and CCG become possible and that possible tectonic duplication of lithostratigraphic units occurs in the GG. The acritarch assemblages of the Lime Bank and most of the Kaan Formations of the GG are similar, and can be correlated with the Nooitgedagt Member of the CCG. The uppermost Kaan Formation can be correlated with the Kombuis Member (CCG). The Kleinrivier and the upper Van Stadens Formations are correlative to the Groenefontein Formation and the overlying Huis Rivier Formation. The generally accepted lithostratigraphic subdivision of the GG does not represent a true stratigraphic section, but reflects most probably stacking of thrusted sheets. The acritarch assemblages of the CCG and GG indicate a late Ediacaran age for these units. Correlative successions in southwestern Gondwana include the Nama Group (Namibia), the Arroyo del Soldado Group (Uruguay) and the Corumbá Group (Brazil). The occurrence of Leiosphaeridia associated with heavily mineralized, undetermined acritarchs in the Sardinia Bay Formation is also reported.