中文摘要：

岩石学与地球化学研究表明，塔里木盆地和田1井中寒武统膏岩层中白云石为原生白云石。岩石学特征上，白云石晶体微小，属隐晶—微晶（〈5μm），呈他形—次圆形，并且不含灰质前驱物。白云石与自生石膏有密切联系，根据其与石膏的关系及岩石学特征，可以将其分为两类：A类原生白云石，包裹在石膏内，晶体较大，一般大于3μm；B类原生白云石，石膏分散在其中，具有极好的长柱状晶形，白云石晶体较小，一般小于3μm。地球化学特征上，两类白云石差别也较明显。A类白云石具有高的n（Mg）/n（Ca）比，平均为0.96，接近化学计量白云石。Na2O，SrO，FeO，MnO平均含量分别为160 μg/g, 270 μg/g, 2250 μg/g, 120 μg/g。δ^13C（PDB）与δ^18O（SMOW）平均值分别为0.3‰，24.6‰；与A类原生白云石相比，B类原生白云石n（Mg）/n（Ca）比较低，平均值为0.90。具有较高的Na2O， FeO，MnO含量与稍低的SrO含量，平均值分别为290 μg/g，2540 μg/g，200 μg/g，200 μg/g。δ^13C（PDB）与δ^18O（SMOW）变化不大，δ^13C稍低，平均值为-0.3‰，δ^18O值较高，平均值为25.2‰。研究表明，文中白云石为原生沉淀，而非交代前驱物灰岩形成，Mg的来源为强烈蒸发形成的高盐度咸水。微生物可能参与了白云石沉淀过程。

英文摘要：

Objectives： Dolomite, as an important type of sedimentary rock, has attracted significant research attention due to its significance in either science or industry. Despite research over than 200 years, the origin of dolomite still remains one of the most debated subject in sedimentary geology, as commonly termed as Dolomite Problem. Recent culture experiments have demonstrated that microbial mediation helps to overcome the kinetic barriers limiting the formation of dolomite; dolomite can precipitate from aqueous solutions under Earth surface conditions. However, the occurrences of primary dolomite in ancient rocks, especially in paleozoic rock records, have rarely been reported. In this study, we reported the observations of primary dolomite in the Middle Cambrian evaporate sequences （Awatage Formation） from Well Hetian-1 in Tarim Basin, NW China. The results will improve our knowledge on the origin of dolomite in geological past. Methods： We observed the well cores to investigate the lithology and distribution of dolomite. The properties of dolomite crystals were investigated by back scattered electron imaging and field emission scanning electron microscopy （LEO1530VP）. The elemental compositions of dolomite were analyzed by a JEOL JXA8100 electron microprobe analyzer. The stable carbon and oxygen isotopic compositions of dolomite were analyzed by a MAT 252 mass spectrometer. Results： Petrographically, the dolomite is crypto-microcrystalline （ 〈 5 μm in diameter） and lacks any direct or indirect evidence of a precursor mineral. Based on the association between dolomite and gypsum and the petrography of dolomite, the dolomite occurs in two modes ： （A） dolomite enwraped in gypsum with relative larger crystal of 〉 3 μm in size; and （B） gypsum bearing dolomite, the dolomite minerals are relative small, generally less than 3 μm. In addition, some sheet-like dolomites were observed, which can be interpreted as the mineralization of extracelluar polymeric substance （EPS）. Geochemi