渤海海域曹妃甸A构造带混积岩储层白云岩化成因机理分析

渤海海域曹妃甸A构造带混积岩储层主要是以生物成因碳酸盐组分为主的混积岩，多发生白云岩化。目前对该区白云岩化的成因机理研究不够，限制了对白云岩储层沉积和成岩过程的理解。通过对岩心与薄片的精细观察及描述，结合多项地球化学测试手段，对该区古近系沙河街组一、二段混积岩储层中白云岩化特征及成因机理进行研究，共识别出4种主要白云岩类型:泥晶白云岩、含生屑泥晶白云岩、生物碎屑白云岩和含砂屑生物碎屑白云岩。进一步分析发现，白云岩中碳、氧同位素均发生负偏，呈正相关关系，且氧同位素分布分散，变化大；微观照片显示只有生物碎屑及其环边胶结物发生了白云岩化，后期发育的连晶胶结和碎屑内部充填物没有被白云岩化。Mn/Fe、Sr/Ba等元素指标指示，研究区湖平面发生多次变动，导致构造带暴露遭受淡水淋滤。综合分析认为，混合水白云岩化为该区白云岩的主要成因。 

Dolomitization genetic mechanism of carbonate-siliciclastic mixed rock reservoir in CFD-A Tectonic Belt,Bohai Sea

The mixed rock is a rock that consists of a mixed deposition of siliciclastic and carbonate. It was dominated by biogenic carbonate in the CFD-A tectonic belt in the Bohai Sea where dolomitization was found. Research on the CFD-A tectonic belt was rarely reported, especially aiming at the genetic mechanism of dolomite reservoir. Based on the observation and identification of cores and rock slices, combined with a number of geochemical tests, the characteristics and genetic mechanism of dolomitization in mixed rocks in the first and second members of Shahejie Formation at the CFD-A tectonic belt were studied. Four dolomite types were identified:dolomicrite, bioclastic-containing dolomicrite, bioclastic dolomite and sand-containing bioclastic dolomite. Further analyses showed that negative bias and positive correlation were both found in carbon and oxygen stable isotopes. Dispersed distribution and large variation were also revealed in oxygen stable isotopes. Dolomitization was found only in bioclastic and its ring cement through microscopic photos, which did not occur in interlocking cementation and bioclast filling. Lake surface fluctuation can be revealed by Mn/Fe, Sr/Ba index, indicating that the tectonic belt has suffered from fresh water leaching because of exposure. Mixed water dolomitization is the dominated genetic mechanism of dolomites in the study area.