The Karoo Basin of South Africa: type basin for the coal-bearing deposits of southern Africa

On the fundamental difference between coal rank and coal type

“…Along with the west-east trend in rank across South Africa, there is a general increase in vitrinite content and sulfur, and a decrease in mineral matter (Cadle et al, 1993). The higher vitrinite content (average of 35% by vol.…”

“…Coals in the main Karoo Basin (South Africa) formed in similar tectonic environments to Carboniferous coals in the USA (Appalachian, Illinois, and Michigan Basins) and the Wolfang and Blair Athol Basins of Australia (Cadle et al, 1993), in that they formed on the distal or passive margin of a retroarc foreland basin. The coal-forming period spanned the early to mid-Permian, during which the palaeoenvironment changed from glacial, to marine, fluviodeltaic, fluviolacustrine, to dry-wet desert conditions (Cadle et al, 1993;Falcon, 1989). The post-glacial climatic setting resulted in a distinct floral assemblage, different from the Northern Hemisphere Laurasian coals.…”

“…There is a general west-east increase in coal rank across the main Karoo Basin (De Jager, 1983), with vitrinite reflectance values around 0.55% in the western, Free State coalfield (Snyman and Barclay, 1989), to meta-anthracite (N 4.0%) (Cadle et al, 1993) in the eastern Vryheid Kwazulu-Natal coalfields and Swaziland. Localized contact metamorphism was a result of dolerite intrusions (sills and dykes), which intruded the entire Karoo Basin during the Jurassic (Drakensberg Formation), following the close of the coalforming period.…”

“…in the No. 4 seam (Cadle et al, 1993)) is related to the more distal setting of the peat mires, and accelerated rates of subsidence; the higher rank is related to the palaeotopography and the thickness of the Earth's crust in the Kwazulu-Natal Basin. The very high inertinite content (N 75% by vol.…”

“…Coals in the Permian Karoo Sequence of southern Africa (Tanzania southwards, including Mozambique, Zambia, Namibia, Botswana, Zimbabwe, Malawi, Swaziland, and South Africa) typically have high inertinite content, with variable semifusinite and vitrinite contents, and are low in sulfur compared to Laurasian coals (Cadle et al, 1993;Hower et al, 2012). Coals in the main Karoo Basin (South Africa) formed in similar tectonic environments to Carboniferous coals in the USA (Appalachian, Illinois, and Michigan Basins) and the Wolfang and Blair Athol Basins of Australia (Cadle et al, 1993), in that they formed on the distal or passive margin of a retroarc foreland basin. The coal-forming period spanned the early to mid-Permian, during which the palaeoenvironment changed from glacial, to marine, fluviodeltaic, fluviolacustrine, to dry-wet desert conditions (Cadle et al, 1993;Falcon, 1989).…”