Studies On Stratigraphic Characteristics And Provenance Analysis Of The Neocene Sanying Formation In The Nanjian County,Yunnan Province

The Sanying formation of Neogene in 1959 is named by the Yunnan Geological Bureau of geological survey brigade area formation, which is characterized by gray, dark gray, brown gray, yellow, white, variegated mudstone(Nian Tu yan), siltstone, fine medium grained sandstone and conglomerate, glutenite and carbonaceous mudstone and coal seam and siderite ore convex body, with purple red strata. In mammals, plants, including gastropods, ostracods and sporopollen fossil. The plants fossil are Acer, Quercus, Celtis, Pinus and other. The bottom generally concrete-filled. Unconformity cover on the strata of different ages which include the Beiya formation, Sanhaogou formation or Shuanghe formation and so on; be unconformity covered by the Quaternary. Thick 49-1331 meters.Sanying Group basin on the both sides of Ailao Mountains in nanjian county of Yunnan Province,The two basin was for the Nanjian County of the Nanjian basin and the Deju Xiang to Duoyichang ancient architecture Deju-Duoyichang basin. After the basin measured stratigraphic section measurement system in detail, that Nanjian basin mainly developed alluvial fan fluvial sedimentary facies is combined, the composition of gravel is not only the external gravel, gravel layer of gravel is likely to be the basement strata in the external conditions of weathering denudation in situ gravel formation, Deju- by the basin mainly alluvial fan factory braided river sedimentary facies combination, the gravel weathered, grinding is not good, and there is obvious the granite gravel, gravel source is likely to come from Ailao Mountains structural belt.On the detailed study and analysis on five outcrop measuring points, with gravel property, gravel degree, gravel state and gravel direction of small-scale neogene Sanying Group basin on the both sides of Ailao Mountains in nanjian county of Yunnan Province. The paper compares the similarities and differences of combination feature of layers of conglomerate in the basins at the both sides of the fault zone of Ailao Mountain and holds that both the basins are formed under arid and semi-arid ancient climate. The south basin is an alluvial fan- coarse clastic sediments of fluvial facies, which has the feature of rapid accumulation. The combination feature of gravel ingredients of the south basin varies greatly in different positions of the basin, which reflects the complexity of provenance supply conditions.While Deju-Duoyichang Basin also takes on the feature of an alluvial fan- braided river- Pluvial phase coarse clastic sediments. According to combination feature of conglomerate, compared with the south basin, its hydrodynamic condition is relatively weak, because its gravel layers suffered from strong physical and chemical reactions before the deposition. On the basis of the statistics of basin bedrock and characteristics of the lithological association of the around formation lithology and also, by comparison of combination features of boulder bed on both two sides basin, Ailao Mountains fracture, combining the bed rock, characteristics around and statistics of gravel flat surface inclination, the paper well-founded to consider that the gravels of the Nanjian Basin mainly come from basin base and high mountains around, but the gravels of Deju-Duoyichang Basin mainly come from basin inner basement and east of the tectonic zone of Ailao Mountain.In order to explore the similarities and differences between the two basin in source. The author collected a debris zircon of each basin and use the LA-ICP-MS zircon U-Pb age data. The results shows that the age of the zircon of Nanjian basin ara between 222 to 1093 Ma, gathered near at 238 Ma, 436 Ma, 636 Ma and was discontinuited in 464-636 Ma. Compare the zircon age with the other zircon age in the research area. The Nanjian basin was probably existed for 3 or more likely source areas. The zircon age results of Deju-Duoyichang basin is very different with the zircon age of Nanjian basin and were measured in a highly centralized in a tiny interval(32.3-40Ma), This suggests that the resouce of Deju-Duoyichang basin was single, and formed in a very short time, sediment transport rate is rapid. The sediment of Deju-Duoyichang basin were serious weathered and has no Quaternary sedimentary phenomenon, wo can possibly imagin that the basin may has experienced a rapid accumulation and a rapid uplift process..