地质科技通报 (Sep 2022)
History of karstification and groundwater flow field within Triassic water-bearing strata in Julongshan syncline
Abstract
The Triassic water-bearing strata in the Julongshan syncline experienced the comprehensive effect of multiple periods of karstification, and the evolution law of karst development is of great significance for understanding hydrogeological conditions and analyzing the groundwater flow field in this region. In this paper, the history of the characteristics of tectonic evolution and karst development in the Julongshan syncline were studied by means of history comparison and combined with data on water chemistry, isotopes and drilling of Triassic water-bearing strata, and the evolution process of the groundwater flow field was preliminarily restored. Our results showed that the tectonic movement in the study region was characterized by vertical rise or fall during the Sinian and the Middle Triassic, which provided materials for karst development in marine sedimentary strata. However, there was no condition for karst development. The main ancient karstification ocourred in the period of time at the top of the Permian Maokou Formation and Triassic Jialingjiang Formation. From the Late Triassic to the Early Jurassic, the crustal movement in the Julongshan syncline was dominated by slow uplift, and terrigenous clastic strata were successively deposited in the lake basin of the Jingdang Basin due to the clastic rocks of the Triassic Badong Formation, which were widely overlying carbonate rocks and had just undergone denudation. This period mainly manifested as burial karst under the water. From the Middle Jurassic to the Early Cretaceous, the EW-NW folds and faults or fissures were formed by Yanshanian movement, controlling the plane distribution pattern of carbonate rocks. During this period, part of the carbonate rock was exposed, karstification began to develop, and the surface water and the underground water converged into the Jingdang Depression. From the Late Cretaceous to Paleogene, with the formation of the Jianghan fault depression basin, the clastic denudation line of the caprock of the Badong Formation gradually retreated to the south, and the development of karst was further strengthened. The old karst drainage system and part of the groundwater drained to the lowest datum level of the Jiangling fault depression. Since the Neogene, the intermittent and rapid uplift of tectonic movement has caused the development of karst to depth, the formation of the Grade Five karst planation surface and multistage groundwater flow system, and the drainage of surface water and groundwater to the Yangtze River. The groundwater flow field has a multilevel evolution mechanism from the limestone region to the depression-faulted basin and the Yangtze River.
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