Jia-Peng Liang

The characteristics and stages of collapse–filling in paleo-underground rivers vary in recharge–runoff–discharge zones, constraining the associated fracture-caved reservoirs in carbonate strata. This paper comprehensively uses core, fluid inclusion, and carbon–oxygen isotope to probe the evolution process and migration of collapse–filling in paleo-underground rivers in the Northern Uplift of the Tarim Basin. The results show that 1) more than three stages of collapse–filling were identified in recharge–runoff–discharge zones, and a four-stage differential collapse–filling process was proposed to summarize the evolution of paleo-underground rivers. 2) The collapse–filling process varies spatiotemporally in the recharge, runoff, and discharge zones. Hydrodynamic strength and filling capacity migrate gradually from the recharge zone to the discharge zone. 3) Collapse–filling mechanisms, including gravity, suffusion, and suction–erosion mechanisms, also vary along with the collapse–filling evolution process of paleo-underground rivers. The research provided a new insight to recognize and interpret the differential planar distribution and vertical filling of the paleo-underground river system, which can be further applied to investigate the fracture-caved karst reservoirs.

Hypogene karst is a special manifestation of karst development in spatial scale. Intensive study of its development mechanism has significant meaning for engineering construction, shale gas and geothermal exploitation. To reveal the developing pattern of hypogene karst in Huanjiang syncline, karst groundwater at different depths in wells HD1-2 and HD1-4 and karst springs was selected as the research object. Through the analysis of geochemistry and stable isotopes of karst groundwater, it was revealed that the circulation pattern of deep karst water came from the common recharge of meteoric water and fossil water hosted in karst caves, runoff of deep faulting belts and discharge of large karst springs, over Huanjiang syncline, which provides good hydrodynamic conditions for hypogene karst development. Meanwhile, the widely developed faulting belts and structural fissures provide primitive dissolution space. Through the above analysis, the paper constructs a hypogene karst development pattern controlled by the deep cycle of groundwater in Huanjiang syncline.