Palynostratigraphy of the South African Karoo supergroup and correlations with coeval Gondwanan successions

Barbolini, Natasha
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The Main Karoo Basin of South Africa is renowned for its exceptional palaeontological record and while its vertebrate fossils have been extensively researched, Karoo floras have received considerably less attention. Poor yields of palynomorphs from the Beaufort and “Stormberg” groups have complicated the task of erecting a comprehensive palynozonation scheme for the Karoo Supergroup. For this study, 65 palynologically productive samples from the Dwyka, Ecca, Beaufort and “Stormberg” groups allowed for systematic descriptions of all palynomorphs, as well as the ranges of the different taxa through the entire Karoo stratigraphic succession. Taxa with restricted ranges are useful for biostratigraphic correlation and these palynomorphs were used to delineate microfloral zones for the Karoo basin. The Dwyka Group contains high numbers of acritarchs and is generally low in species diversity. Useful biostratigraphic taxa for the Ecca Group include Cannanoropollis, Hamiapollenites, Platysaccus and Striatopodocarpites. Aratrisporites is a marker for the Latest Permian / Early Triassic Beaufort Group, while Cyathidites, Dictyophyllidites, Equisetosporites and Uvaesporites are indicators of the Late Triassic / Early Jurassic “Stormberg” Group. Palynostratigraphic zones correlate largely with the Karoo vertebrate biozones and severe and sudden extinction events are recognised among Karoo palynomorphs in the upper Tapinocephalus and Dicynodon assemblage zones. The first comprehensive palynological biozonation scheme for the Main Karoo Basin is proposed and the study provides a broad overview of Gondwanan Carboniferous - Jurassic floras. This study demonstrates that palynology is useful in correlating age equivalent lithostratigraphic units in the proximal and distal sectors of the Karoo Basin. Microfloras from previous South African studies are integrated within the proposed palynostratigraphic scheme, and palynological signatures of the various Karoo formations are shown to be consistent. Despite the constraints of floral provincialism, South African microfloras can be correlated to selected Gondwanan biozonations from Australia, Africa, Antarctica, New Zealand and South America. Future studies should focus on sampling more intensively over smaller stratigraphic intervals, which will assist in the correlation of time equivalent lithostratigraphic units in the different sectors of the basin, thus aiding in refinement of basin development models. Key words: palynology, Karoo, vertebrate biozones, stratigraphy, Gondwana