聚龙山向斜三叠系含水层岩溶发育史及地下水流场控制意义

History of karstification and groundwater flow field within Triassic water-bearing strata in Julongshan syncline

聚龙山向斜三叠系含水层经历了多期次岩溶综合作用,其岩溶发育演化规律对于深入认识该地区水文地质条件及分析地下水流场具有重要意义。运用历史比较法,结合研究区三叠系含水层水化学、同位素、钻孔等资料,对聚龙山向斜构造演化与岩溶发育史进行了探讨,进而恢复了地下水流场的演化过程。结果表明,震旦纪-中三叠世,研究区构造运动总体表现为垂向上的升降,沉积的海相地层为岩溶发育提供了物质基础,但不具备岩溶发育条件,主要在二叠系茅口组和三叠系嘉陵江组顶面形成古岩溶作用。晚三叠世-早侏罗世,聚龙山向斜以缓慢隆升为主,在荆当凹陷的湖盆中相继沉积陆源碎屑,由于广泛覆盖在碳酸盐岩之上的三叠系巴东组碎屑岩刚接受剥蚀,导致该时期主要表现为位于水下的埋藏型岩溶。中侏罗世-早白垩世,燕山运动产生的挤压应力促使研究区形成EW-NW向褶皱、断裂及裂隙,控制了碳酸盐岩的平面分布格局。部分碳酸盐岩裸露,岩溶开始发育,这时期地表水和地下水向荆当凹陷汇集。晚白垩世-古近纪,随着江汉断陷盆地形成,盖层巴东组碎屑岩剥蚀线逐渐向南退却,岩溶发育进一步加强,产生的老岩溶水系和部分地下水向最低基准面江陵断陷排泄。新近纪以来,构造运动的间歇性快速抬升使岩溶不断向深部发育,形成五级岩溶台面和多级地下水流系统,地表水和地下水最终排泄至长江。地下水流场具有山区到凹陷-断陷盆地-长江的多级次演化机制。

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.