鄂尔多斯盆地奥陶系马家沟组白云岩是重要的油气储集层.斑状白云岩岩石学和地球化学特征研究表明,斑状白云岩中的斑块是由白云石颜色和晶粒大小的差异显示,斑块一般为粗粉晶至细晶白云石,发育白云石晶间孔.基质白云石晶粒小于斑块,较致密.白云石的δ13C平均值为0.72‰,δ18O平均值为-6.08‰.Fe2+平均值为2 689×10-6,Mn2+平均值为90.9×10-6,白云石CaCO3摩尔百分含量平均为51.6％,有序度介于0.674～0.940.粉-细晶白云岩中白云石及白云石亮边的均—温度为100℃～148℃,推算其形成时深度为2 100～4 100m.上述特征表明,斑状白云岩形成于中-深埋藏成岩过程,白云石化过程中受到大气淡水影响.研究区斑状白云岩孔隙结构组合为粗偏型,可形成裂缝-孔隙型储层.%The dolomite of the Ordovician Majiagou Formation is a significant reservoir in the Ordos Basin. The mottled dolomite was selected for detailed petrology and geochemistry study.The mottling can be seen because of the distinctive color and crystal size.The mottling part is composed of coarse powder crystal to fine crystal dolomite primarily.and there are dolomite intercrystal pores developed.However,the matrix is smaller and more densified.The average values of δ13C and δ18O of the dolomite are respectively 0.72‰ and -6.08‰.The average values of Fe2+ and Mn2+ are respectively 2689ppm and 90.9ppm.The molar percentage of CaCO3 is 51.6%,and the degree of order ranges from 0.674 to 0.940,both of which show that the dolomite was well-formed.The homogenization temperature of the dolomite is about 100 to 148 °C,and it can be demonstrated that the depth of the dolomitization is around 2100 to 4100 m.The mottled dolomite can be explained by that they are products of dolomitization during the deeply burial stage and may be affected by atmospheric fresh water. The mottled dolomite in research area has coarse partial pores and can form fracture porosity reservoir.
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