摘要： 鲕粒作为碳酸盐岩中非常重要的指相颗粒,其研究主要集中在成因上面,而成岩作用研究较少。北京西山地区下苇甸剖面寒武系张夏组发育大套鲕粒灰岩,通过对该剖面野外实测、薄片观察、XRD测试等手段,结合有机碳、热解等地化参数,对鲕粒的硅化机制及其硅质来源做了系统的研究。结果表明,鲕粒溶蚀再沉淀或者新生变形作用造成鲕粒边缘有机质富集,有机质演化释放的有机酸是硅质沉淀的主要因素,硅质来源主要为陆源输入和黏土矿物的转化。由于有机质主要富集在鲕粒边缘,形成有机质膜,从而造成硅质的沉淀主要沿鲕粒边缘发生,形成鲕粒边缘特有的硅化套,这种结果也从侧面反映了微生物在原始鲕粒形成中发挥了重要作用。

关键词: 鲕粒, 硅化作用, 张夏组, 寒武系, 下苇甸剖面, 北京西山

Abstract: As one type of important facies-incaditing grains in carbonate rocks,previous studies on ooids mainly focused on their origin,and there are few studies on diagenetic alternations of ooids. The Cambrian Zhangxia Formation at the Xiaweidian section in Western Hills of Beijing is characterized by a thick succession of oolitic limestone. In this paper,based on outcrop and thin-section observation and combined with geochemical data such as XRD,organic carbon and pyrolysis,we described the features of silicfied oolites,discussed the sources of silica and provided a silicification mechanism. The results show that the dissolution and refilling or neomorphism of ooids resulted in enrichment of organic matter at the edges of the ooids,and the organic acids,released from evolution of organic matter,are the main controlling factors for siliceous precipitation. Silica mainly derives from input of the terrestrial siliciclastics and transformation of clay minerals. Due to the concentration of organic matters and formation of the organic membranes at the edges of the ooids,silica precipitation mainly occurred along the edges of the ooids,forming a specific silicified sheath along ooid edges. The result also suggests that microbes played an important role in the formation of ooids.

Key words: ooid, silicification, Zhangxia Formation, Cambrian, Xiaweidian section, Western Hills of Beijing

中图分类号: 

• P588.24+5