鄂尔多斯盆地奥陶系马家沟组马五段白云岩的同位素地球化学特征  

Isotope characteristics of dolomite from the fifth member of the Ordo vician Majiagou Formation, the Ordos Basin

作　　者：王保全[1] 强子同[1] 张帆[1] 王兴志[1] 王一[1] 曹伟[2] 

机构地区：[1]西南石油大学资源与环境学院,四川成都610500 [2]中国石油冀东油田分公司,河北唐山063004

出　　处：《地球化学》2009年第5期472-479,共8页Geochimica

基　　金：教育部新世纪优秀人才支持计划项目(NECT-04-0911)

摘　　要：鄂尔多斯盆地中央气田奥陶系马家沟组马五段白云岩是重要的油气储集层,多年来,马家沟组白云岩的成因问题一直是地质研究者讨论的热点话题。对马五段白云岩的C、O、Sr同位素地球化学资料的分析表明,孔洞充填的白云石(含鞍状白云石)和白云岩的δ13C、δ18O值极其近似,且白云岩的δ18OPDB值比奥陶纪海水值要偏负1.752‰～4.395‰(平均2.911‰);成岩流体(水)的δ18OSMOW平均值为+8‰,比当时海水值偏正;87Sr/86Sr比值比奥陶纪海水87Sr/86Sr比值要高。从C、O同位素数据上看,形成白云岩和沉淀于孔洞中的白云石(含鞍状白云石)的流体为同源流体;造成白云岩的δ18O值偏负的原因主要是埋藏条件的"温度效应";87Sr/86Sr比值偏高可能是交代流体来自或流经了富含放射成因Sr的铝硅酸盐基底或硅质碎屑岩。这些特征表明马五段白云岩很可能形成于埋藏环境。The dolomite from the fifth member of the Majiagou Formation in the Ordovician is a significant reservoir in the central gas field of the Ordos Basin. The origin of the Majiagou Formation in the Ordovician has been a hot topic for many years. The carbon, oxygen, strontium isotope compositions of dolomite developed in this deposit were determined in this study. The results show that the values of δ^13C and δ^18O of secondary void-filling dolomite （including saddle dolomite） are much similar to those of the dolomite. The δ^18O value of the dolomite is about 1.752‰-4. 395‰ （averaged 2.911‰） lower than that of the Ordovician seawater. The averaged value of diagenetic fluid （water） was ＋ 8‰with respect to SMOW, higher than that of the Ordovician seawater. The 87Sr/ 86Sr ratio was higher than that of the Ordovician seawater. According to analysis, the fluid that generated dolomite and void-filling dolomite （including saddle dolomite） may come from the same fluid sources. The negative value of 8180 of dolomite was likely due to ＂temperature effect＂ of buried process. The high value of 87Sr/86Sr may be explained by metasomatic fluids came from or flew though aluminosilicate basal rock or siliciclastic rock, which is rich in radioactive strontium. Those characteristics of dolomite from the fifth member of the Majiagou Formation were likely formed in the buried environment.

关 键 词：白云岩 稳定同位素 马家沟组 鄂尔多斯盆地 

分 类 号：P597[天文地球—地球化学]