Stratigraphical Sequence and Geochronology of the Volcanic Rock Series in Caifang Basin,South Jiangxi

The late Mesozoic volcanic rocks in Jiangxi constitute two volcanic belts:the northern is Xiajiang-Guangfeng volcanic belt,the volcanic rocks series belong to one volcano cycle and named Wuyi group which is subdivided into three formations(Shuangfengling formation,Ehuling formation and Shixi formation); the southern is Sannan-Xunwu volcanic belt,the volcanic rocks series in Caifang basin which locates on Sannan-Xunwu volcanic belt also belong to only one volcano cycle.It can be subdivided into two lithology and lithofacies units(upper and lower):the lower unit consists of sedimentary rocks and associated with a subordinate amount of volcanic rocks,it belongs to erupt-deposit facies which is the product of early volcanic stage; the upper unit is mostly composed of volcanic rocks,it belongs to erupt facies that is the volcanic eruption product. SHRIMP zircon U-Pb age of rhyolite?which locates at the top of the upper unit is (130.79±0.73) Ma. According to the new International Stratigraphic Chart,the boundary of Jurassic and Cretaceous is (145.4±4.0) Ma,so the age shows that the geologic period of Caifang volcanic rocks series is early Early Cretaceous epoch. On the basis of lithological correlation,lithofacies and stratigraphic horizon analysis,the volcanic rock series in Caifang basin fall under Wuyi group,and the lower unit could be incorporated into Shuangfengling formation,the upper unit could be incorporated into Ehuling formation.The subdivision of sequence and the determination of geochronology of the volcanic rock series in Caifang basin provide some references for the study of the late Mesozoic volcanic rocks series of the Sannan-Xunwu volcanic belt.