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.