Dissolution characteristics of limestone conglomerate in the Paleogene Zhujiagou formation in the central and southern mountainous area of Shandong Province and hydrogeological implications

The research area is a low -hilly area located in the central and southern mountainous area of Shandong Province, where exist several fault-depression basins such as the Dawenkou, Laiwu, and Pingyi basin. Along the boundary faults and peripheries of these basins developed thick beds of Paleogene Zhujiagou formation limestone conglomerate. This work aimed to study the dissolution characteristics of this rock and their hydrogeological significance. On either side of the Dawenkou basin a series field work was conducted including drilling core cataloguing , well site surveys, CSAMT, and pumping tests. Taking the hydrogeological boreholes as examples, the water abundance law of limestone conglomerates was systematically summarized. The results show that， (1) Both karst holes formed by dissolution of limestone conglomerate and karst-like holes formed by cement softening and gravel component disintegration can be good storage spaces for groundwater. (2) The water outflow from single wells in the Zhujiagou aquifer ranges from 720 to 2,027 m3·d-1,which can be used as the target area of water exploration for centralized water supply in the basin.(3)Affected by sedimentary environment and tectonic development, the aquifers of Zhujiagou formation in the north and south of the basin have obvious differences in rock structure, physical properties, characteristics of dissolution development, sources of groundwater recharge and water abundance. (4)The hydrogeological characteristics, i.e. the law of water abundance, of limestone conglomerate of the paleogene Zhujiagou formation has universality and applicability in the central and southern mountainous area of Shandong Province, which can provide a reference for the study of the emergency water prospecting, the groundwater enrichment law and the hydrogeological mapping in karst mountainous areas.