川东北盘龙洞长兴组-飞仙关组白云岩化特征及成因

Characteristics and genesis of dolomitization in Changxing and Feixianguan Formations in Panlongdong,northeastern Sichuan Basin

陈琪 胡文瑄 李庆 朱井泉

Chen Qi Hu Wenxuan Li Qing Zhu Jingquan

通过系统的野外调查和薄片鉴定,结合电子探针分析,认为四川盆地东北部盘龙洞长兴组-飞仙关组地层普遍发生白云岩化作用。不同类型的白云岩较发育,在纵向分布上具明显的分带性,由下至上依次为:生屑(含砂砾屑)白云岩、礁白云岩、结晶白云岩、鲕粒白云岩和泥-微晶白云岩。进一步研究表明,上述白云岩的成因模式主要有三种,即混合水白云岩化、渗透回流白云岩化和准同生白云岩化。混合水白云岩化为生屑(含砂砾屑)白云岩和礁白云岩的主要形成模式,这两类白云岩保持了岩石原始的沉积结构,白云岩化受原始结构的影响,具有离散的δC值和较负的δO值,反映其形成于有大气淡水参与的相对开放的成岩环境。渗透回流白云岩化为结晶白云岩和鲕粒白云岩的主要形成机制,这两类白云岩具有一致的δC值和相对较高的δO值,较高的Fe、Mn含量。准同生白云岩化是泥-微晶白云岩的成岩模式,岩石以岩性致密,碳氧同位素值集中偏高为特征。

Systematic field investigation and thin section observation as well as electron microprobe determination reveal that dolomitization is common in the Changing and Feixianguan formations in Panlongdong,northeastern Sichuan Basin.Various types of dolomites are developed and distributed vertically in obvious zonation.From bottom to top,they are biological clasitic dolomite,reef dolomite,crystalline dolomite,oolitic dolomite and micrite dolomite respectively.Our study showed that three genetic models could account for the formation process of the dolomites,including mixed-water dolomitization,infiltration and circumfluence dolomitization as well as penecontemporaneous dolomitization.The biological clasitic and reef dolomites were mainly formed through the mixed-water dolomitization,which occurred in relatively open diagenesis environment with meteoric water input.These dolomites had different δC values and more negative δO values and remained original sedimentary structure of rocks which restricted dolomitization.The infiltration and circumfluence dolomitization resulted in the formation of the crystalline and oolitic dolomites which have same δC values,less negative δO valuse,Fe and Mn contents.The penecontemporaneous dolomitization created the micrite dolomite with tight lithology and less negative δC and δO values.

10.11743/ogg20120111