Morphological characteristics and geological significance of karst landforms developed in red-bed strata of the western Sichuan foreland basin

YU Lei; FAN Shijie; LIANG Hong; YU Tianqi; WANG Bo; MAI Gaofei

doi:10.11932/karst2025y006

Abstract：As a uniquely developed karst type in terrestrial clastic rocks,red-bed karst is widely distributed across the mountainous terrain of the western Sichuan foreland basin.Its development rules and evolution model differ significantly from those of traditional carbonate karst systems.Although academic research on traditional carbonate karst has reached a relatively advanced stage,systematic investigations into the spatial distribution characteristics,genetic mechanisms,and evolution models of red-bed karst still require in-depth exploration.In recent years,transportation tunnels and water resource allocation projects in western Sichuan have frequently encountered geological hazards such as water inrush and collapses caused by red-bed karst.These engineering-induced changes in water environment have become increasingly severe.Therefore,systematically revealing the spatial distribution patterns of red-bed karst and exploring its formation mechanisms are not only critical for deepening the scientific understanding of red-bed karst development,but also of great significance for ensuring the safety and sustainability of major engineering projects in mountainous areas of western Sichuan. This study is supported by the National and Sichuan Provincial Water Network Key Project-the Dadu-Minjiang Water Diversion Project.Based on red-bed karst morphology data collected during the engineering investigation phase in the Lianhua Mountain area(southern segment of the Longmenshan Fault Zone and western margin of the western Sichuan foreland basin),this study applied comprehensive mathematical statistics and digital terrain analysis methods.By quantifying the parameter characteristics of red-bed karst landforms,it clarified their spatial distribution patterns(including planar distribution and vertical zoning)and examined the driving factors behind the spatial differentiation of red-bed karst landforms,as well as the impact of neotectonic movements on the evolutionary stages of red-bed karst geomorphology. The results show:(1)Vertical distribution of red-bed karst landforms exhibits a significant elevation aggregation effect.Karst springs are primarily concentrated in the elevation ranges of 797 m to 852 m,962 m to 1,017 m,and 1,037 m to 1,292 m,while karst depressions are predominantly distributed at 775 m to 875 m,1,075 m to 1,175 m,and 1,575 m to 1,675 m.Results from K-function and kernel density analyses indicate that the spatial distribution of red-bed karst landforms is significantly scale-dependent,with rock mass solubility and fracture density serving as the main controlling factors.Further analysis shows that red-bed karst depressions tend to aggregate in areas with high concentrations of soluble components in clastic rocks and well-developed groundwater runoff paths.Karst springs in red-bed strata are generally characterized by rapid recharge,short flow paths,low discharge,and a scattered distribution from multiple points.However,in regions with intense tectonic activities,large karst springs with concentrated discharge can still be developed,though their scale is significantly smaller than that of springs in carbonate karst areas under similar tectonic conditions. (2)As a typical karst feature in red beds,depressions show smaller morphological parameters(e.g.,major axis,minor axis,perimeter,and area)compared to those developed in carbonate rocks,with a significantly negatively skewed distribution,indicating smaller scales in red-bed strata.The eccentricity(E)predominantly ranges from 0.75 to 1,and the compactness coefficient is mainly concentrated in the interval of 1 to 1.6,suggesting simpler edge morphology of red-bed karst depressions. (3)The spatial distribution pattern of Hypsometric Integral(HI)values further reveals that red-bed karst development is strictly controlled by tectonics and lithology,indicating that the overall geomorphic evolution of the study area has reached the mature stage.In the area where calcareous conglomerate is distributed,the drainage basin landforms exhibit significantly higher HI values than the regional average due to the highest solubility of the rock mass.This results in geomorphic evolution predominantly in the youthful stage,corresponding to active karst development.However,the low degree of actual evolution of karst landforms in these basins highlights a tectonically induced geomorphic rejuvenation process.The core of the Gaojiachang Anticline and the limbs of the Nanbaoshan Syncline,characterized by intensive structural fracture development,actively respond to tectonic uplift and are currently undergoing geomorphic rejuvenation. These results reveal significant differences in spatial distribution patterns and formation-evolution models between red-bed karst and carbonate karst.This study examines the spatial differentiation characteristics of red-bed karst and its primary developmental drivers,thereby enriching the theoretical framework of red-bed karst research.The findings provide a theoretical basis for analyzing potential red-bed karst hazards in transportation and water diversion projects in this region.