中文摘要：

渤海湾盆地塘沽地区古近系沙河街组三段沉积早期为半封闭的湖湾沉积环境，底部发育一套白云岩储集层，其产出受区域内北东向古潜山基底断裂控制，沿古潜山两侧发育，分布面积较大，累计厚度可达100多米。系统的岩石学、矿物学和地球化学特征研究表明，该套自云岩常与泥岩互层产出，白云石主要为铁白云石和含铁自云石，普通显微镜下呈微晶状，扫描电镜下可见菱面体状晶型；X射线衍射分析表明其形成于准同生期，是快速结晶的产物；碳氧同位素分析及稀土元素分析显示，这类微晶白云岩形成于较为封闭的高盐度蒸发环境中，具统一的流体来源和相同成因机理。基于上述研究成果，认为塘沽地区沙河街组三段微晶自云岩的形成主要经历了准同生期回流渗透作用和成岩期埋藏环境下类质同象交代作用两个阶段。

英文摘要：

The Member 3 of Paleogene Shahejie sion, Bohai Bay Basin, was formed in semi-enclosed ervoir developed at its bottom. The dolostone, with a Formation, in the Tanggu area of Huanghua Depres- lake bay environment, with one set of dolostone res- cumulative thickness up to 100 meters, was mainlydistributed along the sides of a buried hill as controlled by a NE trending basement fault. Generally, it was interbedded with mudstone in this area. Petrological, mineralogical and geochemical characteristics were studied, which shows： （1） The dolomite minerals are mainly ankerite and ferruginous dolomite, which are micrites under an optical microscope while rhombohedral crystals under a scanning electron mi- croscope （SEM）. （2） X-ray diffraction analysis indicates that this kind of micritic dolostone was formed during the penecontemporaneous period, and is the product of rapid crystallization. （3） The analytical result of the carbon and oxygen isotopes and the rare earth elements shows that it was formed in a relatively closed and high salinity evaporitic environment, and owns an unified fluid source and the same genetic mechanism. Based on the above analyses, the author holds the view that the micritic dolostone experi- enced two stages, namely the seepage-reflux dolomitization during penecontemporaneous period and the i- somorphous replacement during burial diagenesis period.