The Stratigrapy Divede And Area Contrast About Nanhua System And Zhendan System Of Zhenba, Southern Shanxi

In order to adapt to international trends in the development of stratigraphy,the Working Group meeting on cohort study was hold in December 1999.the The experts in working Group on Late Precambrian agreed that there is a need to redefine the Zhendan system The Sinian is redefined and Nanhua is devided from Sinian in the Third National Stratum Congress(May,2000),Formation in the Third National Conference(in May 2000,Beijing) was confirmed.The study area located in Nanhua system,Zhendan system in Zhenba region,southern Shaanxi has done so much.But we has been unable to complete formation of the Nanhua system.Discovering and establishing completely Nanhua system,Zhendan system in this region is the main contents of the study of the type of South China,and has important theoretical and practical significance.By outdoor and indoor comprehensive analysis about Nanhua system,Zhendan system in Zhenba region and based on a systematic summary of the results of previous studies we get the following main results:(1) Though the field observation and research,we also regard that Nanhua is composed of four rock stratigraphic units.From bottom to top:Liantuo Formation,Gucheng Formation, Datangpo Formation and Nantuo Formation.By contrasting to existed rock stratigraphic units deposited during the same period,there is great correspondence between them,which indicates our view of Nanhua is correct.(2) By the sampl collected from Nantuo formation and Liantuo formation in the Gaoqiao dam of Zhenba County.we get the sample analysis of test results.The age of Nantuo is no later than the lower limit 600Ma of the South no later than the lower limit 600Ma,about (634±15) The age of Liantuo formation is no later than the lower limit 670Ma,about (785±24) Ma.(3) Based on the further study,it is believed that the sedimentary environment of the Liantuo formation belongs to lacustrine-fluvial system,and Datangpo formation belongs to deep-water reducing environment,additionally,the set of coarse-grained rocks from Gucheng and Nantuo Formations were deposited in continental glacial environment,Doushantuo reflects the melting of glaciers after the deposition of deep water environment;Dengying depositional environment is a large area sea water in shallow sedimentary formation Baptist, or the Taiwan Strait-type deposition.(4) There are lots of observation and reserch work done on the two particular formation—Gucheng Formation and Nantuo Formation,and conjecture they are sedmentary attributable to both continental glaciation and glaciofluvial.They are homologous to two international important ice age(Sturtian Ice Age and Marinoan Ice age).(5) The deposition feature of Zhenba area is relating to the influence of the breakup of Rodinia supercontinent in Neoproterozoic in Yangtze Landmass.The clarification of Nanhua system is contributing to establishment of systemetic stratigraphic sequence of Zhenba area, South Shaanxi Province,and is contributing to reconstruction of the tectonic evolution history of northern margin of Yangtze Landmass.