西沙石岛西科1井深层致密白云岩岩相学特征再研究

石岛致密白云岩-铁白云岩发现6年，再研究聚焦于岩相学特征。针对西科1井致密白云岩层段完成最新采样，开展系统常规岩石薄片磨制和偏光显微镜和扫描电镜鉴定，提供了系列照片和鉴定分析的认识。确定偏光显微镜下深层白云岩岩相学显微特征，揭示了微晶—细晶—凝块泥晶白云石构成致密藻礁白云岩的特征，它们发育粉晶-细晶、凝块、生物结构。细晶白云石自形—半自形，雾心亮边，0.05～0.25 mm，多世代特征；生物碎屑是珊瑚藻和仙掌藻白云岩，2～3 mm，部分3～5 mm，少部分5～10 mm，生物体内部白云石多粉晶，生长或充填于生屑孔隙，藻体中白云石不规则状，0.3～0.5 mm，星散状、镶嵌状白云石包体，涉不透明矿物；发现块状、不规则状凝块泥晶白云石，部分凝块聚集在一起，凝块内部主要充填泥晶白云石和少量有机质，发育隐晶结构。多个深度白云石含量90%～95%或95%～100%，镜下无色，有时呈浑浊的灰色，闪突起显著，完全解理，高级白干涉色；部分含5%～10%细晶方解石，半自形，0.05～0.25 mm，星散状分布在白云石之间；粉晶方解石自形—半自形粒状，0.01～0.05 mm，镶嵌状分布于生屑边部或充填在生屑内部孔隙中；扫描电镜系统分析主要是针对致密白云岩样品进行，选取典型照片分析了白云石颗粒特征和充填特征，发现2类不同的充填样式，一种是细晶白云石间孔缝中的泥晶类充填露头，另一类是细晶白云石上泥晶类面积覆盖。

RESTUDY ON PETROGRAPHIC CHARACTERISTICS OF DEEP TIGHT DOLOMITE IN WELL XIKE 1 OF SHIDAO,XISHA ISLANDS

Six years after the discovery of tight dolomite and ferroan dolomite in Shidao island, further studies have focused on the petrographic characteristics. The latest sampling of the tight dolomite strata in well Xike 1 was completed, and the systematic routine rock slice grinding and polarizing microscope and scanning electron microscope identification were carried out, which provided a series of photos and understanding of identification analysis. The petrographic microscopic characteristics of deep dolomite under polarized light microscope were determined, and the characteristics of tight algal reef dolomite composed of microcrystallite-fine-crystallite-clotted micritic dolomite were revealed. They developed fine crystallite-fine-grained, clotted and biological structure. Fine grained dolomite idiomorphic to hypoidiomorphic, bright edge of fog center, 0.05～0.25 mm, multi-generation characteristics; The bioclasts are coralophyta and cellophyta dolomite, 2～3 mm, some 3～5 mm, a few 5～10 mm. The internal dolomite of the organism is mostly silt-crystal, growing or filling in the bioclastic pores. The dolomite in the algae is irregular, 0.3～0.5 mm, scattered and inlaid, involving opaque minerals. Massive and irregular clumps of micritic dolomite were found, and some clumps gathered together. The inside of the clumps was mainly filled with micritic dolomite and a small amount of organic matter, and cryptocrystalline structure was developed.Multiple depth dolomite content of 90%～95% or 95%～100%, under the mirror colorless, sometimes cloudy gray, flash prominent, complete cleavage, senior white interference color; Some of them contain 5%～10% fine crystalline calcite, semi-idiomorphic, 0.05～0.25 mm, scattered among dolomites. The silt-crystal calcite is idiomorphic to hemiidiomorphic granular, 0.01～0.05 mm, Mosaic distributed in the edge of the bioclasts or filled in the internal pores of the bioclasts; The scanning electron microscope (SEM) system analysis is mainly carried out on the tight dolomite samples, and the typical photos are selected to analyze the dolomite grain and filling characteristics. It is found that there are two kinds of filling styles, one is micrite filling outcrops in the pores and cracks between the fine-grained dolomite, the other is micrite area coverage on the fine-grained dolomite.