四川黄龙地区鲕状钙华包壳粒的发现及其特征

在雪宝顶北麓的黄龙地区新发现的鲕状钙华包壳粒，是高寒区钙华形成环境中产出的一类典型陆相包覆颗粒构造。通过系统采样鲕状包壳粒沉积剖面，并借助常规显微镜、扫描电镜与能谱分析等，揭示出鲕状钙华包壳粒的矿物组分、微观结构等特征。结果表明:研究区的鲕状钙华包壳粒分为同心圆状、同心圆—放射状、薄壁同心圆状3种基本类型，包壳粒核部是由异地的钙华碎屑构成，外壳层是由泥晶与微亮晶方解石纹层围绕核部逐层形成的圈层构造；微观特征显示泥晶层无明显微生物成因发育特征。鲕状钙华包壳粒的微观形态与组构特征反映出壳体中的泥晶圈层可能形成于相对深的静水环境，亮晶圈层可能形成于浅水高能环境，鲕状钙华包壳粒的成因偏于鲕类而非核形石类。 

Discovery and feature of oolitic coated grains of travertine in the Huanglong area, Sichuan

In the Huanglong area of the Xuebaoding watershed，oolitic coated grains of alpine travertine were newly discovered. It is a continental cladding grain type with coating sedimentary structure， which formed in a cold environment with high elevation. Through systematic sampling and classification of the sedimentary profiles of travertine coated grains，with the help of conventional microscopes，scanning electron microscopes，energy spectrum testing and other technical means，this work reveals the mineral composition of these oolitic travertine coated grains. These particles can be divided into three basic types，concentric circle layer，concentric circle-radial circle layer，and thin-walled concentric circle layer. The core of the encapsulation particle is composed of ex-situ travertine clastics. The outer shell of the coated grains developed a ring structure composed of different mineral combinations such as mud crystals and micro-shiny crystals. Composition，micro-microbial structure and calcification characteristics are not obvious. According to the morphology and microstructure characteristics of the coated grains，it is speculated that the micrite ring layer in the shell might be formed in a relatively deep static water environment，and the sprite ring layer was formed in a shallow water high-energy environment. Research suggests that the genesis of the oolitic travertine coated grains in the study area tends to be oolitic rather than oncolite.