The Lithostratigraphy And Geochronology Of Neoproterozoic Glaciogenic Sediments In South China

The continuous deposition layers developed from the Jiangkou glaciation to the Nantuo glaciation in South China,which completely record the Neoproterozoic "Snowball Earth" event and provide a good geological condition for the surface environment information of the event.Based on the detailed description of the drilling fresh samples in Tongren Guizhou Province and Xiangtan Hunan Province,we established the rock stratigraphic column of Nantuo Formation.Using the technology of isotope chronology,we defined the end age of Jiangkou glaciation.All of these provide basic geological data for deeply understanding the internal environment of Neoproterozoic "Snowball Earth".Main achievements of the study are summarized as following:1.The lithology of Nantuo formation,which is in the drilling of Daotuo mining area Guizhou provincial,can be divided into five sections from the bottom up: pebbly sandstone;siltstone,mudstone,carbonate;pebbly greywacke,siltstone;siltstone;pebbly sandstone.And there are two free siltstone and mudstone been sandwiched in its moraine conglomerate,which is different from the large set of moraine conglomerate of this profile.These formations are also developed in the Xixibao mining area.2.The entirely Nantuo formation of South China is widely developed siltstone,mudstone,carbonatite and other lithologic sections,same as the corresponding layers in other international regions,which illustrates that there is small interglacial during the Marinoan,or there is relatively warm period during the cold Nantuo glacial period.3.The U-Pb ages of zircon,which is in the tuff interlayers at the top of Tiesiao formation in Guizhou Songtao area Jiangjun hill profile,are 658.4 ± 2.2 Ma and 657.3 ± 3.2 Ma.These are consistent with the Re-Os age of black shale and U-Pb ages of zircon of the other parts in the world.So,we defined the end of the Neoproterozoic Jiangkou glaciation(Sturtian glaciation)not later than 657 Ma.