Chapter 18 The Karoetjes Kop and Bloupoort formations, Gifberg Group, South Africa

Abstract

AbstractThe Vredendal Outlier near the South African west coast lies in an intermediate position between the late Neoproterozoic Gariep Belt further north and the Cambrian Saldania Belt further south. It consists of a sedimentary succession of siliciclastic and carbonate rocks, unified as the Gifberg Group, which contains two diamictite-bearing units, the Karoetjes Kop Formation at the base and the Bloupoort Formation near the top of the group. The diamictite of the Karoetjes Kop Formation represents mainly debris flow deposits in a continental rift setting, with some contribution from retreating glaciers. In contrast, the younger diamticite in the Bloupoort Formation is glaciomarine, is associated with banded iron-formation, is underlain by stromatolitic reef carbonates and is overlain by carbonates. Most of the Gifberg Group is poorly exposed and poorly investigated. In the absence of radiometric age data, stratigraphic interpretation and correlation is based on lithological and chemostratigraphic evidence. The entire Gifberg Group is considered to be equivalent to the much better investigated Port Nolloth Group in the Gariep Belt (sensu stricto). Whereas the Karoetjes Kop Formation is correlated with thec.750 Ma Kaigas Formation of the Gariep Belt, the diamictite and associated banded iron-formation of the Bloupoort Formation are regarded as correlatives of the Numees Formation of the Gariep Belt. The entire Gifberg Group was subjected to transpressional deformation and accompanying low-grade metamorphism during continental collision between the Rio de la Plata and Kalahari plates at the end of the Neoproterozoic and again during the Cambrian accretionary orogeny along the southwestern margin of Gondwana, which led to the development of the Saldania Belt further south.