北京周口店地区杨家屯组粒度特征及沉积环境分析

Grain Size Analysis on Yangjiatun Formation's Sedimentation Conditions in Zhoukoudian Area in Beijing

北京周口店地区下二叠统杨家屯组是研究区内特征比较显著的岩组,以碎屑杂砂岩类为主,前人对该组沉积环境的研究比较薄弱。选择薄片粒度分析法进行粒度分析,应用Strain Desk软件辅助测量,对获得的粒度参数和粒度概率累积曲线、频率直方图以及C-M图、S_(KI)-σ图进行了分析。结果表明该区发育的碎屑杂砂岩类岩石的粒度特征是:粒度范围较大、分选在总体上差但在单层内则中等、总体粒度偏粗缺少悬浮组分、距物源区较近和属于河流砂。结合野外观测资料和前人研究成果,推测区内杨家屯组系山区河流和上游辫状河河床沉积,在沉积过程中沉积环境略有变化。

The Zhoukoudian-area＇s Yangjiatun formation is a formation which has comparatively remarkable feature. They mainly consist of litharenite. Grain size analyses of the samples have been done by means of statistical data based on sandstone slices. Based on the analyses data of grain size,the characteristics of the granularty＇s parameters ,probability cumulative grain size curve, the histogram, C-M chart and SKI-σ chart have been introduced.The researches show that the grain size distribution has many characteristics. The grain size range is comparatively biger. As a whole its sorting is comparatively bad,but as a monolayer is much well. Most of the grain size data is bigger than 2. 5Ф＂, and there is very little levitation. The sediment source comes from river and the source area is quite near. Based on such analyses, together with field observational data which think Yangiatun formation＇s sediment conditions is rough country stream and above braid river channel. During the sedimentary process the sedimentary context has a little variance.