A comparative petrological study of some sedimentary rocks from South Africa and the surrounding continents and the significance of their heavy mineral contents
Wardhaugh, Theo Grote
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The heavy residues, the light constituents and grain size of 150 samples of Devonian to Jurassic sandstones, conglomerates, tillites and siltstones were studied. Most of the samples were collected in South Africa but a number were obtained from Australia, Tasmania, Brazil, Antarctica and the Falkland Islands. The South African Cape System (Devonian to Carboniferous) residues were found to be quite different from those of the Karroo System, but the residues of the two groups are remarkably uniform in composition. The Cape System is characterised by an essentially simple assemblage of heavy minerals, the Table Mountain and Witteberg Series usually containing small percentages of red zircon. The Karroo System, on the other hand, is characterised by the presence of garnet, a rare mineral in other South African sedimentary rocks. The concentrates of these two systems resemble the concentrates of the equivalent Brazilian, Antarctica and Falkland Island rocks. Especially close is the resemblance between the South African and the Falkland Island samples, indicating similar source rocks, tectonism and conditions of sedimentation. Whether the two regions once formed part of the same sedimentation basin cannot be deduced from the evidence available at present. The technique used is fully described and discussed.