塔里木盆地志留系古海洋沉积环境的元素地球化学特征

The Element Geochemical Features of Ancient Oceanic Sedimentary Environments in the Silurian Period in the Tarim Basin

通过对各元素的系统分析,塔里木盆地志留系水体基本属于正常海水。纵向上柯坪塔格组中段与上段的分界处古盐度最低;塔塔埃尔塔格组下段沉积时期古盐度最高,可能为局限海沉积。横向上塔中北部地区盐度较高,并且盐度变化大;通过古水深分析,志留系沉积时期为浅海沉积,盆地西北部为海水入口处,并通过稀土元素分析确定了沉积物的来源方向,盆地中央的沉积物具有同源性,来源于周围的沉积地层。根据化学岩石学分析,塔里木盆地志留系砂岩类型比较复杂,从石英砂岩到岩屑砂岩、长石砂岩都有分布。砂岩的母岩中斜长石含量比钾长石要高,可能在花岗闪长岩和花岗岩2个端员之间变化。

Systematic analysis of each element shows that the water body was of normal seawater in the Silurian period in the Tarim Basin. The paleosalinity was lowest in the dividing location of the middle member and the upper member of the Kepingtage Formation; and it was highest in the lower member of the Kepingtage Formation in portrait, implying that it may be of localized sea sediment. The paleosalinity was highest in the northern area of the central Tarim Basin, and it changed greatly; Paleo-depth analysis shows that the sediment in the Silurian period was of shallow sea sediment, when seawater entered from the northwest of the Tarim Basin, confirm the source orientation by analyzing REE, showing that the sediments in the basin are of the same provenance, all from the surrounding sedimentary stratum. According to the analysis of chemical lithology, the sandstone style in the Silurian period in the Tarim Basin was complex relatively, ranging from quartz sandstone to lithic sandstone and felspar sandstone with a high average plagioclase to alkali feldspar ratio in the provenance, which may change between the two end members： granodiorite and granite.