Geologic conditions and distribution features of Tiankeng groups in Hanzhong, Shaanxi Province

An extensive investigation determines the Tiankeng groups in Hanzhong, Shaanxi Province which are concentrated at four places, Chanjiayan of Ningqiang, Chanjiayan Group, Nanzheng Xiaonanhai of Nanzheng, Luojiaba of Xixiang and Sanyuan of Zhenba. Their geological conditions and genesis are analyzed from stratum lithology, geomorphology and structure. It is considered that the very thick carbonate strata of Permian-Triassic was the material basis for development of these big karst caves. Faults and folds controlled their generation, especially the secondary structure determined their locations. New tectonic uplift and hot and humid climate provide karst dynamic power for the formation of Tiankeng.These Tiankeng groups are clustered in a belt-like pattern in plane with large differences in vertical direction. Most of the caves are located at altitudes of 1,000-2,000 m. These results allow us to understand that the formation of Tiankeng groups has undergone four stage evolution.