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
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摘要: 硅质岩的稀土特征如ΣREE、Ce/Ce*、LaN/YbN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100.4×10-6,轻稀土明显富集,LaN/YbN最高为2.51,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28.5×10-6,重稀土相对富集,LaN/YbN 2.51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-深水盆地沉积环境。Abstract: The depositional environment can be inferred according to theΣREE characteristics,such asΣREE,Ce/Ce*,LaN/YbN.In the lower part of the section,theΣREE is very high with 100.4×10-6,the LREE is relative enrichment with LaN/YbN 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 isΣREE on an average value 28.5×10-6 and the HREE is significant enrichment with most LaN/YbN 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.
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Key words:
- Funing /
- Yunnan /
- Lower Carboniferous /
- REE elements
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