Discovery of Ordovician-Devonian strata in the south of the Qiangtang area, Tibet

Low-grade metamorphic rocks are exposed extensively in the Qiangtang area, Tibet. There is a great dispute about the age of the strata because of no reliable fossil evidence and other chronological evidence. Cephalopods, crinoids, graptolites and tentaculites fossils are discovered at Tashi Hill north of Gangtang Co. Primary identification indicates that the cephalopod is Sinoceras,Michelinoceras, Wennanoceras, Archigeisonoceras etc. and the crinoid is Monograptus. The Sinoceras-Michelinoceras assemblage is the key fossil assemblage of Mid Ordovician Baotaan age, which reflects the Mid Ordovician aspects. There are several tens of meters of fossil-free clastic rocks below the Mid Ordovician cephalopod-bearing horizon, which are probably Ordovician sediments. The discovery of Ordovician-Devonian biotas and strata provide new important evidence for the stratigraphic division and correlation and the study of the tectonic evolution of the Qiangtang area.