IS THE NANTUO FORMATION GLACIAL DEPOSITS?

In the light of the theory of modern sedimentology, the author has made a systematic analysis and study of the material composition, regional distribution, features of sedimentary facies, paleostructure and paleoclimatic-paleogeographic environments of sandstone and conglomerate of the early Sinian Nantuo Formation in southwestern and south-central China. It is considered that the Nantuo Formation is the product of intermontane debris flow and marine gravity flow deposition. The formation may be divided into the following types: （1） intermontane-piedmont debris-flow deposits （e. g. in eastern Yunnan and at peripheries of the central Hubei oldland）; （2） volcanic debris-flow deposits （e. g. in Xichang, Sichuan）; （3） neritic gravity-flow deposits （e. g. in central Guizhou and the middle and lower Yangtze River valley）; and （4） deep-water slope gravity-flow deposits （e. g. in southeastern Guizhou, northern Guangxi and southern Hunan）. The main causes responsible for the generation of large-scale gravity-flows in the Nantuo’an Stage （early Sinian） are the following: （1） hard and very thick sandstone of the Nantuo Formation overlies pre-Sinian low-grade metamorphic slate and phyllite, forming a very easily sliding structural interface; （2） the tropical cyclore and volcanism in low-latitude areas triggered their occurrence.