Paper No. 6
Presentation Time: 2:15 PM
NEW DETRITAL ZIRCON AGE CONSTRAINTS ON THE PALEOPROTEROZOIC WOLHAARKOP-DRAKENSTEIN LATERITIC PALEOSOL, GAMAGARA KARST LATERITES AND THE LUCKNOW HEAVY CARBONATE CARBON ISOTOPE EXCURSION, GRIQUALAND WEST, SOUTH AFRICA
The age of the Paleoproterozoic Wolhaarkop-Drakenstein lateritic paleosol with associated ancient supergene Sishen-Postmasburg iron and manganese deposits is important because it holds important clues as to oxygen concentrations in the ambient atmosphere of the time. In addition the immediately overlying Gamagara/Mapedi to Lucknow sequence, known as the Elim Group, represents one of the oldest known red bed successions with associated pisolitic karst laterites near the base and stromatolitic carbonates, with heavy carbonate carbon isotope values, in the upper Lucknow Formation. The carbonates have been linked to the suggested global Lomangundi carbonate excursion formed as aftermath to the Great Oxidation Event. Based on lithostratigraphic similarities the Elim Group has been correlated with the pre-Bushveld, 2,22 -2,054 Ga Dwaalheuwel-Magaliesberg succession of the Pretoria Group hosting the Silverton heavy carbonate carbon isotope excursion. However, recent detrital zircon SHRIMP and LA-ICP-MS age analyses revealed a well-defined population of zircons in redbeds of the Elim Group with ages between that of the 2,054 Ga Bushveld Complex and disconformably overlying 1,92 Ga Hartley bimodal lava succession. This data invalidates the correlation with the Pretoria Group, makes the lateritic weathering profiles and associated supergene iron and manganese ores younger than previously thought and implies that the there are at least three Lomangundi-type heavy carbonate carbon excursions present in the Transvaal-Elim succession each punctuated by carbonates with normal marine isotopic composition in the interval ~2,4 – 1,92Ga. Results also impact on the Paleoproterozoic polar wander path of the Kaapvaal Craton and invalidate suggested synchronism of the Hekpoort and Drakenstein-Wolhaarkop paleosols.