Discussions on the Jurassic strata in the Coqen region, Xizang

The strata in the Coqen region, Xizang have long been defined as the Middle and Upper Jurassic strata of the Daxiong and Jienu Groups. The authors argued, on the basis of abundant fossils including bivalves, gastropods, echinoids, ammonoids and plant remains found in these strata during the regional geological survey of the 1:250 000 Coqen Sheet, that the preceding fossils are characteristic of the features of the Early Cretaceous biotas. According to the fossil assemblages and stratigraphic correlation, the strata of the Daxiong and Jienu Groups should be redefined to the upper part of the Lower Cretaceous Zenong Group.