On the Transformation of Stalagmite Texture and Structure
Abstract: The study of many profile sections of stalagmites indicates that there are three types of stalagmite mineralogical composition: calcite type, aragonite type, and calcite—aragonite type of aragonite-calcite type. The texture, structure, deposit lamina characteristics of them are similar to each other and exist in the who1e growth process, but the microgranular texture, the radiating, lamina(or micro-lamina structures of aragonite stalagmite are more remarkable.The transformation of the texture and structure represents two aspects chiefly: the crystal transformation of aragonite to calcite; the secondary enlargement of the crystal which lead to the sustained crystallization.The aragonite transform into calcite reserving its acicular and prismatic crystals, presenting the pseudomorphy of aragonite. The calcite recrystallization often reserves the granular, rhombohedron, scalenohedron, multiple twin, prismatic, and tabular crystals. The conversion of the stalagmite texture and structure and the strength of the calcitization depend not only on the climate environment, dripping water(or condensation water from seepage water in the cave but also on the moisture content of the stalagmite. The crystallization, calcitization, and conversion of the carbonates is completely under the normal(or low)temperature and (or low)pressure conditions in which there is no foreign substances, as well as no effect to the isotopic fractionation and the information of paleo-climatic environment from the stalagmite records. The whole process plays a part of perfect self-regulation. So, the study on the conversion of stalagmite texture and structure is of great theory and practice significance in palaeoclimatic and Paleoenvironmental reconstruction, ecological rehabilitation, mineralogy and crystallography, isotopic dating, and correct on and so on.
Key words: stalagmite; texture and structure; calcitization; transformation; relict texture and structure
[摘 要] 大量大型石笋纵剖面研究表明，石笋矿物组成有方解石、文石、文石(方解石)一方解石(文石)三种类型，三类的结构、纹(微)层和放射状构造、结构构造转变等特征类同。并存在于碳酸盐沉积石笋生长的全过程，但文石笋的细微粒针(柱)状(微粒)结构、放射状、纹(微)层构造更显著。石笋结构构造转变的主要表现是：文石转变成方解石；文石、方解石次生增大，呈现不断晶化的成晶过程。文石转变为方解石，常保留文石的针状、针柱状结构和柱状聚晶体，呈文石假象。文石次生加大仍保存其结构构造和聚晶；方解石次生增大，常保存其粒状、菱面体、偏三角面体、聚片双晶和柱状、板状聚晶。石笋结构构造转变及其晶化强度，受控于洞穴温度、湿度、滴水和凝结水对石笋的渗透、淋漓，主要受石笋含水度大的制约。组成石笋的碳酸盐沉积、组合、结晶、晶化次生增大等，结构构造的形成及其弱、中、强转变，都在常(低)温常(低)压的洞穴气候环境中进行，是自调整作用的沉积、成晶、成岩晶化过程，没有外来物质加入，因而不影响同位素分馏和古气候环境记录。石笋结构构造转变研究，对古气候环境重建与生态修复、成晶成矿理论和实践、同位素测年校正和运用都有重要意义。