渤海沙西北构造带下古生界碳酸盐岩潜山白云岩形成机制研究  

Formation Mechanism of Lower Palaeozoic Dolomites in the Carbonate Buried Hill of the Shaxibei Structural Belt, Bohai Sea

作　　者：华晓莉 李慧勇 孙希家 于海波 史盼盼 HUA Xiaoli;LI Huiyong;SUN Xijia;YU Haibo;SHI Panpan(Tianjin Branch of CNOOC Ltd,Tianjin 300452,China)

机构地区：[1]中海石油(中国)有限公司天津分公司,天津300452

出　　处：《高校地质学报》2018年第6期833-840,共8页Geological Journal of China Universities

基　　金：国家科技重大专项(2011ZX05023-002);国家科技重大专项(2011ZX05023-006-002)联合资助

摘　　要：通过岩心薄片、扫描电镜、碳氧锶稳定同位素、X衍射有序度及微量元素特征分析,系统研究了渤海湾盆地沙西北构造带碳酸盐岩潜山白云岩的地球化学特征及成因机制。结果表明,沙西北构造带下古生界白云岩可划分为泥晶白云岩、颗粒白云岩、泥质/灰质白云岩和鞍状白云岩四类,各类白云石特征差异明显。泥晶和颗粒白云岩δ^(18)O大于-7‰,^(87)Sr/^(86)Sr值与海水值接近,为0.7090～0.7120,Na_2O含量较高,大于0.06%,有序度偏低,薄片中可见石膏,为准同生成因。泥质/灰质白云岩为细晶结构,δ^(18)O偏负,为-8‰～-10‰,^(87)Sr/^(86)Sr为0.7120～0.7140,Na_2O含量降低,有序度变大,镜下见次生加大亮边,为埋藏成因。鞍状白云岩为中粗晶结构,贫δ^(18)O,^(87)Sr/^(86)Sr较高,薄片中见辉绿岩,为热液成因。本区白云岩以准同生和埋藏成因为主,局部沿断裂可能存在热液成因。奥陶系沉积时期主要发生埋藏白云石化和溶蚀作用,是增加白云岩有效孔隙的重要阶段,为优质储层形成起到了建设性作用。Based on core and thin-section observations,and analyses including scanning electron microscope,carbon,oxygen and strontium stable isotopes,X-ray diffraction and trace elements,the geochemical characteristics and genetic mechanism of dolomites in the carbonate buried hills of the Shaxibei structural belt(Bohai Bay Basin)were studied systematically.Results show that the dolomites can be divided into four types,including micritic dolomite,granular dolomite,muddy/limy dolomite and saddle dolomite.They vary in distinguished characteristics.The micritic dolomite and granular dolomite are formed under penecontemporaneous environments,as implied byδ^18O greater than-7‰,^87Sr/^86Sr ratio in the range of 0.7090-0.7120 that is close to the seawater value,relatively high Na2O content with value greater than 0.06%,low degree of order,and gypsums observed under thin section.In contrast,the muddy/limy dolomite is formed under burial environments,as implied by fine crystalline structure,relatively negativeδ^18O values of-8‰--10‰,^87Sr/^86Sr of 0.7120-0.7140,lower Na2O content,higher degree of order,and bright secondary-enlarged edge observed under microscope.The saddle dolomite is of hydrothermal origin,as implied by medium and coarse crystalline structure,negativeδ^18O values,high^87Sr/^86Sr values,and diabase observed under microscope.Therefore,the dolomites in the study area were mainly of penecontemporaneous and burial origins,and some may be formed under hydrothermal environments along faults.The burial dolomitization and associated dissolution during the Ordovician increase the effective porosity of dolomite,which plays a postive role in the formation of high quality reservoirs.

关 键 词：渤海湾盆地 沙西北构造带 下古生界 碳酸盐岩潜山 白云岩形成机制 

分 类 号：P318.130.21[天文地球—固体地球物理学]