The Gravel Statistics and Sedimentary Environment of Jiangbei Conglomerate in Chongqing

The analysis of gravel group of Jiangbei conglomerate and dating shows that Jiangbei conglomerate of Xishi Fuzhong section has experienced two sedimentary spinning back，fine to thick and thick to fine.Concretely speaking，it can be divided into seven sedimentary spinning backs and each spinning back represents a flood period.Based on it more small scale of crude，fine changes，it is speculate that these changes of gravel is caused by frequently fluctuations of climate.According to the research，in Chongqing and upstream area，the ancient flood had been broken out seven times between 24.3 kaB.P.and 10 kaB.P. Among them in 22.5 kaB.P.sedimentary which reach 31 cm，according to the calculated.At this time，the ancient flood capacity amounts to about 119 690.783 m3·s-1.It shows that the water power was very strong at that time.But the layer is thick，so we speculated that the rainfall took a short time.In particularly，the gravel degree has seven times from thick to fine，so the precipitation may has seven times from more to less in Chongqing and upstream area between 24.3 kaB.P.and 10 kaB.P.It shows that precipitation intensity changes greatly in this time.Relatively wet period abundant precipitation，the water power is stronger；the big gravel can be taken to the beach and sedimentary by the flood.Otherwise，relatively dry period less rainfall，the water power is weak，it can only bring small gravel and sedimentary，much fine sand was taken to sedimentary and in formed many sandstone layers.