滨里海盆地东缘石炭系KT-Ⅰ油层组白云岩地球化学特征

哈萨克斯坦滨里海盆地东缘上石炭统KT-Ⅰ油层组主要发育局限海台地-开阔海台地碳酸盐沉积，间夹蒸发岩层。由于区域性白云石化作用，KT-Ⅰ油层组中白云岩广泛分布，为主要油气储集层。研究表明，白云岩中白云石为泥晶、粉晶或细晶，半自形-他形；略富钙，有序度较低(0.336～0.504)；δ¹⁸O_PDB值在-1.06‰～+2.45‰之间，比石炭纪海水(δ¹⁸O_PDB值介于-1‰～-2‰之间)偏正；δ¹³C_PDB值在+3.36‰～+5.94‰之间，与石炭纪海水(δ¹³C_PDB值介于+3.1‰～+4.7‰之间)接近；锶同位素值接近石炭纪海水(⁸⁷Sr/⁸⁶Sr值在0.7082～0.7088之间)；微量元素Mn含量平均为92.57 μg/g，Fe含量平均为447.52 μg/g，接近被交代的灰岩含量；Na和K含量的平均值分别为198.80 μg/g 和5.89 μg/g，显示交代流体为蒸发海水。上述岩石学和地球化学资料表明，研究区石炭系KT-Ⅰ油层组白云岩具有渗透-回流机理白云岩的特征。

Geochemical characteristics of the Carboniferours KT-Ⅰ interval dolostone in eastern margin of coastal Caspian Sea Basin

The KT-Ⅰ interval carbonate unit of the Upper Carboniferours is composed of a shallow marine carbonate rock with some evaporate strata，which is dolomitized in the Coastal Caspian Sea Basin，Aktyubinsk，Kazakstan.The fine-crystalline dolostone(mud-dominated)with vug porosity is the most important oil reservoir in the KT-Ⅰ interval carbonate unit. Study shows that the KT-Ⅰ interval dolomite is characterized by micrite, silt or fine crystals with subhedral or anhedral form, ordering index of 0.336～0.504, and slight enrichment of calcium. The dolomite contains stable isotopic oxygen composition of -1.06‰～+2.45‰ PDB(average，+0.4‰)，which is positive to sea water(Carboniferous), and carbon composition of +3.36‰～+5.94‰ PDB which is approximate to sea water.Its stable isotopic strontium composition is 0.708 265～0.708 750， which is approximate to that of sea water or evaporative sea water.The trace element content of 92.57 μg/g(average) for Mn，and 447.52 μg/g (average)for Fe of the KT-Ⅰ interval dolostone，are lower than Mn and Fe content in the burial dolostone,while the trace element content of Na,K and Sr are more than those in the replaceable limestone.The above data about the KT-Ⅰ interval dolostone show that the dolomitization was formed in the near surface evaporative condition，which is characterized by seepage-reflux.