Liantuo sandstones: sedimentary records under cold climate before the Nanhua big glaciations
莲沱砂岩——南华大冰期前气候转冷的沉积记录

Chemical Index of Alteration(CIA)values of argillites,from the middle and upper parts of the Liantuo Formation exposed in Yichang region,Hubei province,range from 60 to 70,suggesting that they were deposited under frigid climate.Comparing with major elements and CIA values of the Liantuo Formation,provenance areas of the middle and upper parts of the Banxi Group would undergo more severe weathering under warm and wet climate,while provenance areas of the Liantuo Formation would be less weathered.Therefore,there were two different kinds of climates in which the Liantuo Formation and Banxi Group were deposited. Based on CIA values,the Liantuo Formation can be correlated to the middle and up parts of the Banxi Group.The research from CIA values of the Liantuo sandstones implicates a transition from greenhouse to icehouse,moreover,the upward lowering of CIA values indicates the coming of the global glaciation,and after that the so called "Snowball Earth" began.