Division and characteristics of the Cretaceous formation in southern Yarlung-Zangbo suture zone in Tibet

A large number of Radiolarian fossils were found in the southern Yarlung-Zangbo suture zone of Xiukang Group, Lake Rakshastal-Saga county, eastern Danga region through the 1∶250 000 regional geological survey. And lithostratigraphic units for seven formation from Jurassic to Eocene are disintegrated through the detailed investigation and the characteristic of Radiolarian fossils.The Cretaceous formations are defined as Zheba Formation and Sangdanlin Formation. The characteristic of Zheba Formation is mainly composed of siliceous rocks, mudstone, shale and basaltic sandstone, and Zheba Formation is a conformity between upper Jurassic Danga Formation and lower Cretaceous Sangdanlin Formation, and it is rich in Radiolarian fossils of lower Cretaceous. The characteristic of Sangdanlin Formation mainly consists of quartz sandstone, sandstone, mudstone, shale and siliceous rocks, intercalated with basalt. Sangdanlin Formation is a conformity between Zheba Formation of Early Cretaceous and Denggang Formation of Paleocene, and it is abundant in radiolarian and foraminifera fossils of Late Cretaceous. The establishment and research about the Zhaba and Sangdanlin Formations of Cretaceous can further enrich the basic information in southern Yarlung-Zangbo suture zone. It also improves our research level and provides new data for the sedimentary palaeogeographic and tectonic study in this area.