Geochemical Characteristics of Dolomite from the Lower Ordovician in Northwest Ordos Basin

Based on origin,dolomite can be divided into two types including penecontemporaneous-contemporaneous dolomite and burial dolomite.The results show that the content of manganese,sodium and strontium is low. Meanwhile,the values of isotopes of δ 13 C and δ 18 O in micrite-micro crystalline powder dolomite and Coarse crystal powder-cryptomere dolomite are much similar to cryptomere and over-cryptomere dolomite.The δ 18 O values of the dolomite are lower than those of the Ordovician seawater.An analysis shows that micrite-micro crystalline powder dolomite and Coarse crystal powder-cryptomere dolomite might have come from the same fluid source. The 87 Sr/86 Sr ratio is higher than that of the Ordovician seawater,may be explained by the hypothesis that metasomatic fluids came from or flew though aluminosilicate basal rock or siliciclastic rock,which had rich radioactive strontium.