塔里木盆地古城低凸起中下奥陶统白云岩稀土元素地球化学特征及其成因

REE Geochemical Characteristics and Genesis of the Middle-Lower Ordovician Dolomite in the Gucheng Low Uplift of the Tarim Basin

中下奥陶统白云岩是塔里木盆地古城低凸起主要的天然气储集层,按结构特征将其分为粉-微晶白云石、粉-细晶级他形脏白云石、粉-中晶级自形白云石、中-粗晶脏白云石、中-粗晶干净白云石和鞍形白云石等6种类型,对不同类型白云岩的稀土元素分析结果表明,研究区样品的ΣREE总体含量偏低,与La_N/Yb_N、LREE/HREE大致呈正相关,与δEu、δCe的相关性较差。不同类型白云石稀土元素配分曲线差别不大,均为总体平缓、略向右倾,显示轻稀土略微富集。不同类型白云石成因类型略有不同,主要为同生期蒸发泵成因、同生期渗透回流成因、浅埋藏成因和热液成因等4种成因类型。

The Middle-Lower Ordovician dolomite in the Gucheng Low Uplift of the Tarim Basin is the main reservoir of natural gas in the area. Based on characteristics of texture and structures, six kinds of dolomite have been classified in this paper. They include fine to micritic dolomite, fine to crystalline anhedral dirty dolomite, fine to medium sized euhedral dolomite, medium to coarse grained dirty dolomite, medium to coarse grained clean dolomite, and saddle dolomite. Their REE contents have been measured. Results show that the total contents of REE are relatively low, with positive correlations between the ~REE and LaN/YbN or LREE/HREE ratios, but poor correlations between the ~REE and ~Eu or ~Ce values. The REE distribution patterns of various types of dolomite are generally fiat, slightly right declined, and LREE slightly en- riched, with very limited differences among them. The genetic types of various kinds of dolomite are slightly different. They include penecontemporaneous evaporative pumping dolomitization, penecontemporaneous seepage reflux dolomitization, shallow burial dolomitization , and hydrothermal dolomitization