渤海湾盆地黄河口凹陷沙河街组白云岩成因机理

Dolomite Origin of Shahejie Formation in Huanghekou Sag, Bohai Bay Basin

为了研究渤海湾盆地黄河口凹陷沙河街组白云岩成因机理,通过岩心观察、薄片鉴定、阴极发光、X衍射、扫描电镜、背散射、碳氧同位素等方法,分析白云石岩石学、形貌学和同位素地球化学特征.结果表明,白云岩呈黄棕色,发育大量溶蚀孔和高岭石、燧石等矿物,δ13C值为-0.50‰~4.58‰,δ18O值为-14.58‰^-2.19‰,总体具有δ13C低正值,δ18O负值的特点.泥晶白云石,由微米级球状白云石和白云石化蓝细菌组成,亚微米级孔隙发育,见薄片状细菌丝和草莓状黄铁矿;纤维状白云石环边胶结物充填在溶蚀孔洞或围绕颗粒表面生长;菱形白云石,漂浮状分散在孔隙中.准同生期,硫酸盐还原菌的催化作用形成球形白云石;随后,受大气淡水淋滤,在湖底成岩环境微生物影响下形成纤维状白云石环边胶结物;浅埋藏期,由于埋藏白云岩化形成菱形白云石.这为古老湖相白云岩微生物成因提供具体实例,且对该地区勘探提供参考.

To study the dolomite origin of Shahejie Formation in Huanghekou sag,Bohai Bay basin,the petrology,morphology and isotopic geochemical characteristics of the dolomite were analyzed through core observation,thin section identification,cathodoluminescence,X-ray diffractometry(XRD),scanning electron microscopy(SEM),back-scattered electrons(BSE)and carbon and oxygen isotopes.The results show that the dolomite is yellow brown and has a lot of dissolution pores,chert and kaolinite develops.δ13 C values range from-0.50‰to 4.58‰,andδ18 O values range from-14.58‰to-2.19‰.Micritic dolomite consists of microsphere dolomite and dolomized cyanbacteria accompanied with a lot of submicron pores,sheet-like bacterial filaments and strawberry pyrite.Fibrous isopachous dolomite cements fill in the dissolution pores or grow around particle surfaces.Rhombic dolomite is dispersed in pores.During penecontemporaneous stage,sulfate reducing bacteria induced spherical dolomite precipitation.Subsequently,fibrous isopachous dolomite cements were influenced by microbes under lake floor diagenetic environment,being affected by meteoric fresh water.During shallow burial stage,rhombic dolomite precipitates by buried dolomitization.This study can provide a specific sample for microbial induced lacustrine dolomite precipitation in ancient strata and reference for exploration in the study area.