Origin Of The Ordovician Cherts At Southeastern Sichuan And Northeastern Chongqing,South China,And Their Geoche Mical Characteristics

Black shale, cherts and bentonites occur in the Wufeng Formation deposited at The Late Ordovician which across late Katian through Hirnantian and widely exposed along the northern and eastern part of Yangze block. Predecessors have already analysis the black shales in Wufeng Formation systematic, but the mechanism for the formation of siliceous rocks and sedimentary environments of of Wufeng Formation is still controversial.This paper based on the study of petrological characteristics of siliceous rocks, geochemical characteristics and paleontological features regional tectonic background of Wufeng formation. This paper will mainly d iscuss the Siliceous sources, Formation mechanism of the cherts and its ancient sedimentary environment.The evidence of Radiolarie at chert in the Wufeng Formation at northeast Sichuan-Southeast C hongqing, C hina. And geochemical characteristics including major elements, trace elements, rare earth elements, silicon isotope analysis of cherts in the Wufeng Formation shows that the origins of Cherts is mainly sedimentary and biogenic not hydrothermal sources.The causes of chert is mainly sedimentary rather than hot water or metasomatic genesis.The Sedimentary characteristics of the study area in northeast Sichuan- Southeast Chongqing shows that the sedimentary environment of the Wufeng Formation is deep water shelf environment of the hypoxic reduction condition. The water is more quiet, easy to preservation of organic matter. Lithological composition of the Wufeng formation is black carbonaceous shale, chert, siliceous shale. Geochemistry of C herts reflects the Wufeng Formation at water exhibit hypoxia shallow continental margin environment, presumably in the continental shelf, continental slope transition region. Based on of cherts of Sedimentary features and geochemical characteristics at the Wufeng Formation support the shallow sedimentary opinion.