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.
Shi Xin,Cheng Xubin,Wang Juan et al. Geochemical characteristics of the Carboniferours KT-Ⅰ interval dolostone in eastern margin of coastal Caspian Sea Basin[J]. JOPC, 2012, 14(6): 777-786.
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