济阳坳陷沙河街组湖相页岩中风成粉砂的识别及其古气候意义

Identification of Aeolian Silty Sand in Lacustrine Shale of the Shahejie Formation in the Jiyang Depression and Its Indication to Paleoclimate

在济阳坳陷沙河街组远离古河口沉积的页岩纹层中发现了风成粉砂沉积。风成粉砂在页岩的纹层中往往星散分布，成层性差，多分布在富有机质纹层与（含粉砂）粘土纹层之间。在结构上，这些风成粉砂与黄土有很大的相似性，颗粒呈棱角状次圆状。粒度分布于4～60之间，一般正偏，代表冬春季节相对偏干旱时期不稳定的近源阵风沉积；而表层流或层间流沉积的粉砂在粒度上往往与同一纹层内共生的粘土逐渐过渡，粒度概率曲线上呈一段式，粒度变化范围大，粉砂的成层性好，多局限在含粉砂的粘土纹层中。在高频旋回中，当气候偏干旱时，页岩中的自生碳酸盐含量增加，同时风成粉砂在陆源碎屑中所占的比例也明显升高。页岩中风成粉砂沉积的发现，可以进一步为研究有关湖相页岩和第四纪纹泥的古气候变化、正确恢复古湖泊沉积环境提供良好的指标。

In lamina of shale which deposited in deep lake away from paleo-debouchment in the Shahejie Formation in the Jiyang Depression, some aeolian silty sand was discovered. The aeolian silty sand shows dispersed distribution and worse stratification, with subangular grain shape. The aeolian silty sand usually distributes between lamina rich in organic matter and clay lamina. The structure of the aeolian silty sand is very similar to that of loess in northwestern China. The grain shape can be angular or subroundish, the grain size is always between 4- 6 Ф, and show a positive skewed distribution on frequency curve. The aeolian silty sand in shale represents deposits during winter and spring because of unstable dried gust near by provenance. Silty sand depositing from superficial or laminar flow of paleolake shows obviously gradual change of grain size between silty sand and clay in lamina with better stratification of silty sand. The grain size probability cumulative curves are characterized by the model of single segment with greater change of grain size. In high-cycle, the content of aeolian silty sand of shale correlates with palaeoclimate closely. When palaeoclimate became arid, the content of authigenic carbonate increased, and the proportion of aeolian silty sand in terrigenous clast increased distinctly too. The aeolian silty sand in shale can provide good guide to study of paleoclimate about lacustrine shale and varve, and to reconstruct sedimentary environment of paleolake accurately.