Stratigraphic division of the Jiufotang Formation in Kazuo Basin of western Liaoning and related issues

Abstract：According to the present various division schemes and related issues for Jiufotang Formation in western Liaoning, the authors remeasured the type section of Jiufotang Formation in Xiaogushan-Jiushaoguo. In consideration of the lithofacies and sedimentary characteristics of other sections in Jiufotang Formation of Kazuo basin, the authors chose the tuffaceous rock association as the marker bed or the bed set and, on such a basis, divided the type section of Jiufotang Formation into four members called 1, 2, 3, 4 respectively. The authors found that the Jiufotang Formation is mainly composed of siltstone and pelite, intercalated with numerous extremely tiny layered limestone or marl, characterized by the upward sedimentary evolution from shore shallow lake facies through deep lake facies intercalated with shallow lake facies to shallow lake facies. The differences between Xiaogushan-Jiushaoguo section and other sections in Jiufotang Formation indicate that the clastic rock granularity of Xiaogushan-Jiushaogou section was finer in general, without the development of delta facies and fan delta facies. In addition, three beds of moderate and thin silicified tuff are developed at the bottom of member 2, and the type section of Jiufotang Formation fails to appear at the top of member 4 and member 5. To comprehensively understand Jiufotang Formation, the authors propose that the auxiliary sections should be introduced on the basis of the type section, and Huimingou-Pingfangdonggou section, Fuzhangzi-Shaoguojie section and Zhangmazigou-Taohuachi section can serve as the auxiliary sections of member 1, member 4 and member 5 of Jiufotang Formation respectively.