The history of this geosyncline is divided into three stages: (1) Devonian and older ; (2) late Devonian to middle Triassic; and (3) la ter Mesozoic period. The socalled Pre-Cambrian metamorphic rocks require a further confirmation of their ages Upper Cambrian is the oldest dated sediment of the geosyncline. Three facies named Shihtien, Naungkangyi, and Thungson, can be distinguished in the Ordovician formation. In the later Palaeozoic sequence carbonate-rich and carbonate-poor facies alternate twice or more with intercalations of graptolites and tentaculites facies and other clastic facies . Broadly speaking, the early stage was the age of epirogenic undulations, whil e the second stage was the age of embryonic foldings by which the geosyncline was partly modified, and at length it was wholly deformed and consolidated by Mesozoic orogenies.

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