PROBLEM ABOUT THE STRATIGRAPHIC CLASSIFICATION OF THE LOWER CRETACEOUS IN NORTHERN HEBEI

In light of the wedge-like interlocking （interfingering） relationships between volcanic rock layers and sedimentary beds in continental volcanic sedimentary strata, the authors put forward a new idea about the lithostratigraphic classification and divide the Early Cretaceous strata in northern Hebei into the Xiguayuan Formation and Huajiying Formation as well as the overlying Qingshila Formation. The Huajiying Formation was formed by superimposition of intermediate to intermediate basic and small amount of acid subalkaline volcanic rocks in the basin during the deposition of the Xiguayuan Formation. So the two formations are contemporaneous but heteropic deposits and are listed in juxtaposition. The paper also discusses some major problems existing in the previous classification schemes.