山西省柳林奥陶系马家沟组第五段第一亚段的白云石化作用

山西省柳林奥陶系马家沟组第五段第一亚段主要由白云岩组成，顶部为灰岩、沉积于浅的、局限的、低能、基底起伏小、蒸发作用强的克拉通内陆表海环境下．白云石的δ１３Ｃ值为－８．１～０．１‰，平均－３．０‰；δ１８Ｏ值为－１０．９～７．１‰，平均－８．９‰；白云石的碳氧稳定同位素值与泥晶方解石差别不大．准同生白云石的δ１３Ｃ为－４．９～０．１‰，平均－２．１‰；δ１８Ｏ值为－１０．３～－７．１‰，平均－８．７‰．成岩白去石的δ１３Ｃ值为－８．１～－３．３‰，平均－５．４‰；δ１８Ｏ值为－１０．９～－７．７‰，平均－９．２‰．白云石的Ｆｅ２Ｏ３含量为０．５１％～２．９９％，平均１．３６％，白云石较泥晶方解石的铁含量高．白云石的Ｓｒ含量为１３～４７（１０－６），平均２３（１０－６），白云石和泥晶解石的Ｓｒ含量均低．白云石较方解石的晶胞体积减少１２．７％左右．白云石化所引起的体积缩小，产生了大量的晶间孔．有利于淡水的渗透、淋滤，晶间孔进一步改造，形成了晶间溶孔和溶蚀孔、洞、缝．白云石样品的ＭｇＣＯ３含量几乎都大于５０ｍｏｌ％，白云石化，是淡水与富镁海水混合的结果．

Dolomization of the lst Submember of the 5th Member of Majiagou FM in Liulin Ordovician System,Shanxi Province

The lst submember of the 5th member of Majiagou FM in Liulin,Shanxi Province mainly consists of dolomite.Its top is limestone. It was deposited in shallow,restricted and typical intracraton epicontinental environments with high salinity. The dolomite can be classified into penecontemporaneous dolomite and diagenetic dilomite. The δ13C and δ18O values of dolomite range from-8.1%, to 0.1%, and from-10. 9%, to-7. 1%, with the mean values of-3.0‰, and-8. 9‰, respectively,showing little difference from those of micrite.The δ13Cand δ18o values of penecontemporaneous dolomite range from-4. 9‰, to 0.1‰, and from- 10.3‰, to 7.1‰ withthe mean values of-2.1‰, and-8. 7‰ respectively. The δ13c and δ18o values of diagenetic dolomite range from -8. 1‰, to-3.3‰ and from-10.9‰ to-7.7‰ with the mean values of-5.4‰, and-9.2‰ respectively.The δ13c values of penecontemporaneous dolomite are higher than those of diagenetic dolomite.δ18o values of the two kinds of dolomite are similar. The contents of Fe2o3 for dolomite range from 0.51 % to 2.99% with the meanvalue of 1. 36%,and are higher than those of micrite. The contents of sr for dolomite range from 13ppm to 47 ppm with the mean value of 23ppm. The contents of sr for both dolomite and micrite are low. but the contents of sr for dolomite are little lower than those for micrete. The cell volume of dolomite has decreased about 12. 7 %in comparison with that of calcite. The dolomization caused volume decrease, forming intercrystalline pores which benefits the permeation and leaching of meteoric water' The permeation and leaching of meteroic water result of the mixing of meteoric water and seawarer with high concentration of magnesium.