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.
Guo Qi-Heng,Jin Zhen-Kui,Zhu Lei et al. Mechanism for silicification of ooid:Example from the Cambrian Zhangxia Formation at Xiaweidian section in Western Hills of Beijing[J]. JOPC, 2019, 21(4): 627-635.
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