根据野外与室内观察及测试分析，研究了陕甘宁地区奥陶系３种主要白云岩，即准同生白云岩、混合水白云岩和回流渗透白云岩的岩石学特征和形成机理，在此基础上，归纳出这３种不同成因的白云岩的稀土分布型式、δＣｅ和δＥｕ的富集特征。认为云坪型准同生白云岩中，δＣｅ＜１，负铈异常，δＥｕ＞１，正铕异常，指示蒸发作用和氧化环境；回流渗透白云岩中，δＣｅ＞１，正铈异常，δＥｕ＞１，正铕异常，指示封闭盆地与缺氧环境；混合水白云岩中，δＣｅ≈１，铈无明显异常，δＥｕ＜１，负铕异常，指示淡水的注入与弱氧化－弱还原环境 According to field and indoor observation and test analysis, the petrological characteristics and formation mechanism of three major Ordovician dolomites in the Shaanxi-Gansu-Ningxia region, that is, quasi-syngenetic dolomite, mixed-water dolomite and recirculation infiltration dolomite are studied. On the basis of this, the REE distribution patterns, δCe and δEu enrichment characteristics of dolomite in these three different genera are summarized. ΔCe <1, negative cerium anomaly, δEu> 1, positive europium anomaly indicating evaporation and oxidative environment. In the infiltration dolomite, δCe> 1, normal cerium anomaly and δEu> 1, positive Eu anomalies, indicating that the closed basin and anoxic environment; mixed water dolomite, δCe ≈ 1, cerium no obvious anomaly, δEu <1, negative europium anomaly, indicating freshwater infiltration and weak oxidation - weak reduction environment