云南富宁地区早石炭世硅质岩稀土元素特征及沉积环境分析

The REE characteristics and depositional environment analysis of silicolites in Funing,Yunnan

硅质岩的稀土特征如 Σ REE、Ce/ Ce* 、La N/ Yb N 可以反映成岩时的沉积环境。笔者所研究的富宁剖面属于早石炭世大塘组 ,其下部沉积了一套灰白色硅质岩 ,稀土总量较高 ,最高达 10 0 .4× 10 -6,轻稀土明显富集 ,La N/ Yb N 最高为 2 .5 1,Ce的负异常不明显 ,Ce/ Ce* 平均为 0 .81;中上部为一套深水相的硅质岩组合 ,岩石中富含放射虫、硅质骨针 ,发育有水平纹层 ,部分层位含分散状黄铁矿颗粒 ,稀土总量较低 ,平均值为2 8.5× 10 -6,重稀土相对富集 ,L a N/ Yb N 平均为 0 .75 ,多数样品在 0 .6以下。由这些特征可以推断 ,云南富宁地区早石炭世早期可能处于盆地裂陷阶段的初期 ,在早石炭世的中晚期 ,盆地进一步拉张 ,处于中

The depositional environment can be inferred according to the REE characteristics, such as ΣREE,Ce/Ce *,La N/Yb N.In the lower part of the section, the ΣREE is very high with 100.4×10 -6, the LREE is relative enrichment with La N/Yb N 2.51, there is a slight negative Ce abnormally with Ce/Ce * 0.81, reflecting the characteristics of basin-margin depositional environment. In the middle and upper part of the section, there is ΣREE on an average value 28.5×10 -6 and the HREE is significant enrichment with most La N/Yb N less than 0.6. There is a negative Ce abnormally with Ce/Ce * 0.75, the significant one C-23 is 0.5. These indicate that the basin had already been in the rift period in Early Carboniferous, and in the middle and later period of Carboniferous, the basin had formed and Funing is in a deep-water basin depositional environment.