Western Yunnan Changning - Meng Associated Stratigraphic Sequence Of The Paleo-tethys Basin And Basin Evolution

Changning-Menglian zone is located in south section of famous Three-River orogenic belt in south-west of Yunnan Province. It is always hot area to oversea and Chinese geologists, because very important geographical place. Many productions included papers and monographs, which come down to all fields of geoscience, have been published so far. But different researchers, even same researchers in different times, have different opinions to stratigraphical division and sequence in the basin, sedimentary environment that magmatic action reflected, and basin's development and evolution because of there are many reasons. Some new ideals, about stratigraphical sequence and Paleozoic Tethyan forming and evolution in this area, are introduced in this paper, based on the some new discoveries in recent study, for instance a plenty of fossils is found in Gengma area, some basalt and ophiolite is determined.Changning-Menglian basin is N-S-tending now. Paleozoic stratum can be separated east and west stratigraphical areas, according to lithological character and palaeontological information, contacted relationships and diversification of stratigraphical units in horizontal and vertical etc. The stratums in west area can be divided Devonian-Carboniferous Nanduan formation and Permian Laba formation, which is passive continental margin-bathyal depositional sequences comprised argillaceous and detrital rocks, small siliceous and carbonatite in upper. The stratums in east area can be divided lower-middle Devonian Wenquan formation and middle-upper Devonian Manxin formation, upper Devonian-lower Carboniferous Pingzhang formation, Carboniferous-Permian Yutangzhai formation, middle Permian Damingshan formation, upper Permian Shifodong formation respectively, moreover, middle-upper Permian Huoju formation is exposed in Menglian area. It's depositional sequence, which shows a sedimentary cycle from shallower to deeper to shallower again, is detrital rocks + siliceousâ†'siliceous + volcanicsâ†' carbonatite.After'this study, we can get some new advances and cognitions as follow: (1)Nanpihe formation ought to be abolished; Shifodong formation belongs to Wujiaping-Changxing stage; stratigraphy in Changning -Menglian zone can be separated east and west stratigraphical areas and composes a whole basin system. (2)Chahe formation and Zhongzhai formation ought to be remained with Devonian Wenquan formation and Manxin formation respectively; and it is more reasonable that Muyinhe formation is remained with Laba formation. (3)Volcanism in this zone can be divided tow stages, namely late Devonian-early Carboniferous Pingzhang formation and Permian Huoju formation; picrite-porphyrite distributed in Manxin area is epizone intrusive, which emplaced in late Variscian, and not eruptive body. (4)There were not large scale ocean in Changning-Menglian zone, where continuously evolved in whole Paleozoic, in late Paleozoic. A small oceanic basin, largest width 800km and similarly late stage of Red Sea and early stage ofAtlantic, is inferred in Changning-Menglian zone from late Devonian to early Carboniferous. (5)Author thinks it is only assistant method to distinguish environments and genesis by means ofpetrochemical characters. ?Author thinks that suture zone don't exist in Changning-Menglianzone.