地质科技通报 (Jan 2022)
Characteristics of karst groundwater flow systems of typical faulted basins in Yimeng Mountain area: A case study of Laiwu Basin
Abstract
China Geological Survey has organized and implemented 1:50 000 standard map hydrogeological survey with an area of more than 40000 square kilometers in Yimeng Mountain area. And it carried out a large amount of water prospecting and well drilling demonstration work in villages and towns with serious water shortage, obtained rich geological data and gained a new understanding of groundwater flow systems. Under the influence of Mesozoic and Cenozoic structures, the faults and folds, extensional detachment and magmatic intrusion occurred in Yimeng Mountain area, formed a series of graben-semi graben basins characterized by overlapping in the south and faulting in the north, and finally formed today's typical "basin-mountain" karst hydrogeological structure and the relatively independent karst groundwater system, which taking basin as unit. In order to study the development characteristics of groundwater flow system in Yimeng Mountain area, Laiwu Basin was selected as a typical study area. On the basis of the field geological survey, through comprehensively analyze the geomorphic units, the three-dimensional spatial distribution of water bearing rock groups, groundwater level, hydrochemistry, and water isotope results on the north and south sides of the basin, this paper comprehensively discusses the characteristics of multistage karst groundwater flow systems with typical "basin-mountain" structure in Yimeng Mountain area. The results show that, the karst groundwater in Laiwu Basin presents a "centripetal" runoff from the outer periphery to the center of the basin. Affected by human activities, controlled by geological structure and aquifer distribution, the characteristics of groundwater flow systems between the north and south sides of the basin are different. There are mainly intermediate and local groundwater flow systems in the south of the basin, while a single local groundwater flow system is developed in the north of the basin, however, it occupies nearly 1/2 of the groundwater sources that have been explored and demonstrated. In addition, it is found that at the lowest erosion base level of Dawen River, the voids separated by regional detachment structure and hydrothermal mixing, together with rock layer, interlayer fissures and bedding dissolution voids, form a three-dimensional karst groundwater network, which influence the circulation path and depth of karst water. Guided by this understanding, the completion rate of exploration production combined wells has reached 86%, which strengthens the combination of theory and practice of groundwater flow system theory in hydrogeological work in bedrock mountainous areas in North China.
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