Discovery of equivalent stratum to Dadianzi Formation of northern Hebei in the Jinpen area, Inner Mongolia, China.

During 1∶50000 scale regional geological survey carried out in Jinpen area, Early Cretaceous fossils were discovered in Inner Mongolia for the first time which distribut in Daqingshan Formation, Laohugou, west slope of Heishan, Sandaoying Town, Zuozi County, Ulanqab. Fossils include Cypridea ex gr. liaoningensis，Luanpingella sp.，Djungarica camarata，Clinocypris scolia，Rhinocypris echinta，Lycopterocypris infantilis，Darwinula contracta； Neimongolestheria? sp. Ferganoconcha quadrata and F. jorekensis etc. The lithology and fossil haracteristics of this lake facies stratum are different from that of the standard Daqingshan geological section; however it is comparable with Dadianzi Formation in northern Heibei. We believed that this new set of stratum should be separated from Daqingshan Formation, because it represents the Early Cretaceous lake facies stratum of Yinshan area. There is also Dadianzi Formation strata in Jinpen area which mainly developed in Luanping basin, northern Heibei.