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The Stormberg Group is the name given to the sedimentary geological formations of the Late Triassic Period and the Jurassic Period, found in Karoo Basin region of Southern Africa They are of the Karoo Supergroup, immediately above the Beaufort Group, and consist mainly of sandstones and mudstones. They preserve a record of gradual desertification. ==Formations== The Stormberg Group is subdivided into three formations: *Sandstone of the oldest, the Molteno Formation, was formed from river sands in the Upper Triassic. This is now exposed as cliffs in the Drakensberg and can be easily recognised by its sparkling appearance. This is due to minute quartz crystals that coat and bind together the sand grains. :The Molteno Formation consists of two major coarsening-upward sequences, the basal sequence is made up by the ''Bamboesberg and Indwe Sandstone'' and the upper sequence by the Transitional Member. Tabular sheets of horizontally and cross stratified medium- to coarse grained sandstone dominate the formation. The sandstones were deposited by braided streams on a vast braidplain.〔Catuneanu, O., Hancox, P. J. and Rubidge, B.S. (1998). Reciprocal flexural behaviour and contrasting stratigraphies: a new basin development model for the Karoo retroarc foreland system, South Africa. Basin Research, 10, 417-439〕 *The Molteno Formation is in turn overlain by red mudstone of the Elliot Formation which contains dinosaur fossils such as the 12 metre long Melanorosaurus. :The Elliot Formation is dominated by red floodplain mudstones with subordinate channel and crevasse splay deposits. These were interpreted as a mixed load dominated meandering system in an increasingly arid setting.〔Visser, J.N. J. and Botha, B.J.V. (1980). Meander belt, point bar, crevasse splay and aeolian deposits from the Elliot Formation in Barkly Pass, northeastern Cape. Transactions of the Geological Society of South Africa, 83, 55–62.〕〔Bordy, E.M., Hancox, J.P. and Rubidge, B.S. (2004). Provenance study of the Late Triassic – Early Jurassic Elliot Formation, main Karoo Basin, South Africa. South African Journal of Geology, 107, 587-602.〕 Towards the top of the formation aeolian sediments occur as metre-scale intercalations in the fluvial deposits of the Elliot Formation. *The white cliffs of the middle Drakensberg are composed of Clarens Formation sandstone. These sandstones were deposited as large dunes in a desert environment. Worm burrows and dinosaur footprints can also be found in these rocks. :The Clarens Formation consists of yellow fine-grained sandstones, sandy siltstones and mudstones. This indicates strong aridification of the climate.〔Beukes, N.J. (1970). Stratigraphy and sedimentology of the Cave Sandstone Stage, Karroo System. In: S.H. Haughton (Editor). Proceedings 2nd IUGS Symposium on Gondwana Stratigraphy and Palaeontology, CSIR, Pretoria, South Africa, 321–341.〕 Wind blown dunes suggest deposition in a desert environment with shallow playa lake and river deposits in the wetter parts of the basin,〔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.〕〔Catuneanu, O., Hancox, P. J. and Rubidge, B.S. (1998). Reciprocal flexural behaviour and contrasting stratigraphies: a new basin development model for the Karoo retroarc foreland system, South Africa. Basin Research, 10, 417-439〕 producing a complex interaction of aeolian and aqueous sedimentation. 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「Stormberg Group」の詳細全文を読む スポンサード リンク
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