Links between host rock, water, and speleothems of Xueyu Cave in Southwestern China: lithology, hydrochemistry, and carbonate geochemistry

A systemic study was conducted to understand the links between the host rock, water, and speleothems of Xueyu Cave in Southwestern China. An outcrop section of the host rock of Xueyu Cave was surveyed, the stratum that the host rock belongs to was subdivided into 11 lithofacies, and the Xueyu Cave is developed in the grainstone facies segment. Lithological characteristics and chemical components of the host rock indicate that its predominant mineral component is low magnesium calcite (LMC). To understand the hydrochemical characteristics of percolating water in Xueyu Cave, three drip water monitoring sites were taken to collect water samples for a whole monsoon year. The temperature (T), pH, electronic conductivity (EC), drip rate, Ca2+, Mg2+, Na+, K+, Ba2+, Sr2+, HCO3−, SO42−, NO3−, Cl−, partial pressure of CO2 (pCO2), saturation indexes, and precipitation rate of carbonate minerals were investigated monthly. The data reveals that the pH, EC, drip rate, Ca2+, Mg2+, HCO3−, pCO2, saturation indexes, and precipitation rate of carbonate minerals exhibit seasonal variation; these are due to the seasonal change of precipitation and soil CO2 concentration that are driven by monsoon climate. The petrological and geochemical characteristics of speleothems were also investigated, and results indicate that the main chemical and mineral components of speleothems are quite similar to the host rock; this is because the main material source of drip water and speleothems are governed by the host rock. This study reveals the main mineralogical and geochemical characteristics of host rock and speleothems, further discussing the seasonal variation of hydrochemical indexes of drip water. All these works will be helpful to more thoroughly understand the operation regularity of karst dynamic system (KDS) of the Xueyu Cave.

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