Study on the characteristics of karst development in Beijing

The distribution area of carbonate rocks in Beijing is about 5071.44 km 2 , accounting for 30.19% of the land area in Beijing. The distribution areas of bare, covered and buried carbonate rocks are 2862.21 km 2 , 401.86 km 2 , 1803.37 km 2 , respectively. The carbonate rocks mainly includes dolomite in Changcheng Group of Jixian System (Jxg), dolomite in Wumishan Group of Jixian System (Jxw), dolomite in Tieling Group of Jixian System (Jxt), Cambrian limestone (Є), Ordovician limestone (O) and carbonate rocks with different ages. The characteristics of karst development in Beijing differ from region to region. In the mountainous areas of dolomite in Changcheng System and Jixian System of Proterozoic, the karst landforms such as hoodoos, series of peaks and gorges are formed by the influence of rock differential solution and shear joints. In the Cambrian and Ordovician limestone distribution areas, middle-low mountains and uvalas are formed; the covered karst is affected by rock composition, regional structure control and environment, and the degree of karst development varies in different regions. According to the ground karst, karst caves distribution and karst spring distribution in Beijing area, the karst development in Beijing is summarized into three types: karst system-based (mainly developed karst cave system), fissure-based (basically undeveloped caves and karst springs, mainly for the development of underground joint fissures in the concealed area) and composite type (the karst spring with relatively large distribution, and a small number of ground karst caves, and the development of underground joint fissures). According to the distribution characteristics of 271 karst water boreholes, 563 geothermal boreholes, 258 ground surface karst caves and 499 karst springs in Beijing, the karst development in Beijing also has typical characteristics of heterogeneity, stratification and staging.