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The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup of geological strata in Southern Africa. It follows conformably after the Ecca Group and consists essentially of sandstones and shales, deposited in the Karoo Basin from the Middle Permian to the early part of the Middle Triassic periods. In the Eastern Cape Province the Karoo Basin fill commenced with the deposition of the Dwyka Group, followed by the Ecca Group, the Beaufort Group, the Molteno, Elliot, and Clarens formations of the Stormberg Group and the igneous Drakensberg Group. The basin followed the typical evolution of foreland basins, with the Ecca Group representing the ‘flysch’ component and the Beaufort Group, the overlying Molteno and Elliot Formations representing the ‘molasse’-fluvial type sediments.〔Johnson, M.R. (1991). Sandstone petrography, provenance and plate tectonic setting in Gondwana context of the south-eastern Cape Karoo basin. South African Journal of Geology 94, 137-154.〕〔Catuneanu, O. (2004). Retroarc foreland systems – evolution through time. Journal of African Earth Sciences, 38, 225-242.〕 Deposits in this group include (in order of deposition): *Lower ''Adelaide Subgroup'' comprising: * *''Koonap Formation:'' Transitional brackish lacustrine to fluvial. Greenish-grey sandstones grading upwards into fine-grained siltstones and mudstones. * *''Middleton Formation:'' Semi-arid climate supported a lush flora and fauna that thrived along meander belts and semi-permanent lakes.〔Smith, R.M.H., Eriksson P.G. and Botha W.J. (1993) A review of the stratigraphy and sedimentary environments of the Karoo-aged basins of Southern Africa. Journal of African Sciences, 16, 143-169〕 Cyclic deposits of lenticular sandstone bodies grading into greenish-grey mudstone. The thickest formation in this succession, constituting 37% of the Beaufort Group and 47% of the Adelaide Subgroup.〔Johnson, M.R. (1976). Stratigraphy and sedimentology of the Cape and Karoo Sequences in the Eastern Cape Province. Ph.D. thesis (unpubl.), Rhodes Univ., Grahamstown, 336pp.〕 The formation has lenses of red mudstone which are likely to have been deposited in a sub-aerial fluvial environment. * *''Balfour Formation:'' The upper part of the Adelaide Subgroup and part of what was called lower to middle Beaufort. *Upper ''Tarkastad Subgroup'' comprising: * *''Katberg'' Formation: Arenaceous deposits of red and olive-yellow mudstones. Deposited in a braided fluvial system. * *''Burgersdorp'' Formation: Deposited in a low-sinuosity fluvial system.〔Neveling, J. (2003). Stratigraphy and sedimentological investigation of the contact between the Lystrosaurus and the Cynognathus Assemblage Zones (Beaufort Group: Karoo Supergroup). Council for Geoscience, Bulletin 137, 165pp.〕 ==Paleontology== Fossils of tetrapods, especially therapsids, are common, and the vertebrate biostratigraphy has been mapped out in detail, beginning with the work of Robert Broom at the start of the 20th century and developed and revised a number of times since. Currently eight faunal zones are recognised, tracing the development of terrestrial life through the Permo-Triassic, and named after a characteristic genus that serves as an index fossil. In order the assemblage zones are: * ''Cynognathus'' Assemblage Zone (Youngest) * ''Lystrosaurus'' Assemblage Zone * ''Dicynodon'' Assemblage Zone * ''Cistecephalus'' Assemblage Zone * ''Tropidostoma'' Assemblage Zone * ''Pristerognathus'' Assemblage Zone * ''Tapinocephalus'' Assemblage Zone * ''Eodicynodon'' Assemblage Zone (Oldest) The Beaufort Group deposits also yield numerous plant and insect fossils. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Beaufort Group」の詳細全文を読む スポンサード リンク
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