新生碳酸钙沉积矿物形态的影响因素分析

石笋是古气候重建的重要地质载体，文石与方解石是石笋碳酸钙晶体的常见矿物形态。根据现代洞穴监测数据分析洞穴新生碳酸钙沉积物 (Active Speleothem: AS)的矿物形态的研究较少。本文在重庆武隆芙蓉洞三个滴水点 (MP2、MP5、MP9)下放置玻璃片，收集新生碳酸钙沉积物和滴水样品，监测新生碳酸钙沉积物矿物形态、滴水的Mg/Ca比值、pH、滴率和洞穴环境等指标，分析玻璃片正面和反面新生碳酸钙沉积物的δ18O、δ13C和Mg/Ca比值。研究发现:(1) MP2滴水点下的玻璃片正反面新生碳酸钙沉积物的矿物形态均为方解石；MP5和MP9滴水点的正面沉积方解石和文石-方解石混合两种情况，反面沉积文石-方解石，且反面文石多于正面。 (2) MP2滴水Mg/Ca比值小于MP5和MP9，说明滴水Mg/Ca比值是影响新生碳酸钙沉积物矿物形态的重要因素；而滴水pH值对AS矿物形态的影响在不同滴水点有差异。(3) 不论是玻璃片正面还是反面，文石-方解石混合的新生碳酸钙沉积物δ18O和δ13C比以方解石为主的沉积物偏正，说明AS矿物形态的变化会导致δ18O和δ13C发生变化。通过在芙蓉洞的系统监测和分析，发现新生碳酸钙沉积物的矿物形态与地表环境、洞穴上部岩溶水文地质条件密切相关，并验证了洞穴新生碳酸钙沉积物的矿物形态对石笋δ18O和δ13C具有重要影响。 

Analysis of influencing factors on mineral morphology of active speleothemA case study of Furong cave in Chongqing

Stalagmites, secondary mineral deposits forming in karst caves, record much paleo-climate and paleo-environment information. In stalagmites, the mineral forms of calcium carbonate are aragonite and calcite. It is considered that the properties of bedrock, discharge of drip water, pH, and the Mg/Ca ratios of drip water are the important factors affecting the crystal morphology. In addition, the changes of mineral morphology in stalagmites are thought to indicate the changes of paleo-climate and paleo-environment. At present, most studies focus on inferring the change of paleoclimate through the crystal morphology in stalagmites, while there are few studies on analyzing the mineral crystal morphology of active speleothem (AS) according to modern cave monitoring data. In this study, in order to collect active speleothem and drip water samples during 2017-2018, glass plates were placed under 3 drip water sites (MP2, MP5, MP9) in Furong Cave located in Wulong District, Chongqing. The mineral crystal morphology of AS was identified by polarizing microscope. Systematic monitoring was performed on Mg/Ca ratios, pH, the discharge of drip water, the cave environment, as well as δ18O, δ13C and Mg/Ca ratios of the active speleothem deposited on the front and back sides of glass plates. The results suggest that, (1) The mineral crystal morphology of active speleothem that deposit on both sides of glass plates at MP2 is calcite. There are calcite and aragonite-calcite mixture on the front side of glass plates at MP5 and MP9. However, aragonite-calcite crystals deposit on the back side of the glass plates, and there are more aragonites than those on the front sides. (2) The Mg/Ca ratios of drip water collected from MP2 is less than the ratios from MP5 and MP9, which indicates that the Mg/Ca ratio of drip water is an important factor affecting the mineral morphology of active speleothem. And the effect of pH values of drip water on AS mineral crystal morphology is different at different drip sites. (3) Regardless of the front or back side of glass plates, the δ18O and δ13C of AS mixed with aragonite-calcite are more positive than the calcite-dominated AS, which suggests that changes in the AS mineral morphology will lead to changes in δ18O and δ13C. The systematic monitoring and analysis in Furong Cave show that the mineral form of AS is closely related to the surface environment and the karst hydrogeological conditions in the upper part of the cave, and it has been verified that the mineral form of AS in caves has important influence on the δ18O and δ13C of stalagmites.