滇西思茅盆地景谷地区曼岗组石英颗粒表面特征及其指示意义

石英具有硬度大和化学稳定性高的特点,其颗粒表面特征能很好的反映沉积环境,通过扫描电镜观察石英表面微细特征是判别沉积环境行之有效的方法。思茅盆地白垩系曾一度被认为是陆相水成沉积,笔者通过野外识别及室内基础研究发现,景谷地区下白垩统曼岗组具有风成沉积特征,需对该套地层开展石英颗粒表面特征的系统研究来进一步确定其沉积相,研究结果表明:研究区曼岗组石英颗粒表面具有明显的风成特征,磨圆度高,普遍发育典型的蝶形撞击坑、新月形撞击坑、毛玻璃化表面,存在沙漠漆,极易与水成特征相区别;而其较强的溶蚀作用与沉淀作用则显示了当时干旱炎热的气候条件。在风成沉积确定的基础上,笔者再结合典型沉积构造,粒度分析、岩性特征等沉积特征进行综合分析,认为研究区曼岗组应属沙漠沉积。

Surface Features of Quartz Grains of the Mangang Formation in Jinggu Area, Simao Basin, Western Yunnan and Their Sedimentary Significance

The surface features of quartz grains can be used as an indicator for their depositional environments due to its large hardness and high chemical stability. And Scanning Electron Microscopy is a useful tool to identify the features of quartz grains. The Cretaceous in the Simao Basin was generally considered to be hydrothermal deposit, however, after field identification and indoor basic research, the authors consider that the Mangang Formation in the Jinggu area shows typical features of eolian sediments, so much research on surface features of quartz grains is needed to figure out the sedimentary facies. The result shows that quartz grains of the sample of the Mangang Formation in the Jinggu area are well rounded, and massively developed dish shaped impact scars, crescent shaped impact scars, and frosted surface, thus suggesting typical features of eolian environment. The surface features are different from those in aqueous environment. The high intensity dissolution and precipitation indicate the dry and hot climate. Based on the fact that they are in origin eolian deposits analysis of the Mangang Formation in the Jinggu area, sedimentary features such as typical sedimentary structure, grain size analysis, lithologic features, etc, authors finally considered that it belongs to desert deposit.