Sedimentary Characteristic And Rock Magnetism Research Of The Nantuo Formation In Northeast Guizhou

Two glacial events(Sturtian and Marinoan)took palce in the Neoproterozoic are regarded as the extreme climate change events, which inspired “Snowball Earth” hypothesis. The Marinoan glaciation is the severer,which is called Nantuo glaciation in South China. There are complete records of Nantuo Formation in South China. We analyses detailed lithologic characteristics of three drill-core(Daotuo ZK 1909、ZK2103、Xixibao ZK1012)of Nantuo Formation in Tongren region of the northeast Guizhou province, South China. In order to study the sedimentary and magnetic characteristics, we carry on the detailed field geological logging, lithologic unit division and stratigraphic profile correlation and rock magnetic experiments, to reveal the sedimentary environment, ancient climate change characteristics of Nantuo Formation, and to provide evidence for the glacial deposition mode, to gain the basic data for more in-depth understanding the climate model during the Neoproterozoic.Rock magnetism research was carried on the Nantuo Formation and upper Datangpo Formation of the Daotuo ZK1909, the strata can be divided into four sections based on the variation characteristics of the magnetic susceptibility with depth. Section A、B、C and D respectly are correspond to the coarse clastic rock of the upper Nantuo Formation, normal fine clastic rock of the middle Nantuo Formation、coarse clastic rock of the lower Nantuo Formation and normal fine clastic rock of the upper Datangpo Formation. The variation of the magnetic susceptibility indicates that the values of magnetic susceptibility from section A and C are similar, the values of magnetic susceptibility from section B and D are also similar, but the values from section B and D are significantly higher than these from the section A and C. The K-T curves indicate that magnetite is the principal magnetic mineral in the four sections. So we think that the increase of the content of magnetite is the main reason that caused the enhancement of magnetic susceptibility from section B and D. At the same time, reflects that section A and C deposited during the sedimentary environment was relative reduction, section B and D deposited during the sedimentary environment was relative oxidation, which were respectively corresponded to the relatively cold and warm climate conditions.We make a detailed description and analyses of sedimentary characteristics of the Nantuo Formation of the drill-core, comparing with previous researches, sedimentary characteristics of the Nantuo Formation in the northeast Guizhou province, are different from Yichang regions(continental glacier facies). And Nantuo Formation of the drill-core are comformably with the upper Doushantuo Formation, and comformably with the lower Datangpo Formation, we regard the Nantuo Formation of the drill-core represents the sedimentary of sea glaciar facies. In addition, we find that there is a noramal interbeded siltstone/mudstone segment in the Nantuo Fm, but it isn?t occure in every core, so it maybe not represent a worldwide geological event or interglacial deposits during the "snowball earth" epoch. As a conclusion, our analyses and results provide a kind of evidence and constraint for the Neoproterozoic “Snowball Earth” hypothesis.