论文部分内容阅读
塔里木盆地下奥陶统分布着规模巨大的白云岩地层,在这些白云岩地层中已经发现了工业油气藏,勘探潜力巨大。应用岩石学与地球化学方法,对塔中隆起—巴楚隆起内下奥陶统的云灰岩开展成因研究。根据岩石学特征,下奥陶统云灰岩分为低云化程度灰岩、高云化程度白云岩、与中云化程度云灰岩3个端元。地球化学分析结果显示,白云岩与云灰岩δ18 O值均比灰岩重约3.5‰,3个端元具有相似的稀土元素配分模式与相似的87Sr/86Sr同位素组成,表明云化流体主要来源于海水或蒸发海水。云灰岩与白云岩端元表现出富Fe、贫U和Mo、负Ce异常特征,指示其形成于水体偏浅的氧化环境中;相反,灰岩端元表现出形成水体偏深的还原环境中。利用白云岩—海水与灰岩—海水的氧同位素温度计估算岩石形成温度的结果显示,白云岩形成温度高于灰岩,表明温度可能是克服白云岩化动力学障碍的关键性因素。根据流体源、氧化还原条件、形成温度与水体深度的认识,建立了“层状水温控云灰互层模式”;并认为白云岩化主要发生在水体较浅(0~70m)、温度相对较高(夏季达30℃)的环境中,对应沉积相主要包括半局限台地潮坪亚相与潮下浅滩亚相;灰岩沉积水体相对较深,温度相对较低(~10℃),对应沉积相主要为半局限台地潮下滩或滩间海亚相。
The Lower Ordovician in the Tarim Basin is home to large-scale dolomite formations. Industrial gas reservoirs have been found in these dolomite formations and have great potential for exploration. Using petrology and geochemistry methods, the genesis of the Lower Ordovician limestone in the Tazhong uplift-Bachu uplift was studied. According to the petrologic characteristics, the Lower Ordovician limestone is divided into three stages: low-grade limestone, high-grade dolomite, and medium-cloud grade lithofacies. The results of geochemical analysis show that δ18O values of dolomite and limestone are both 3.5 ‰ heavier than that of limestone. The three end-members have similar REE patterns and similar 87Sr / 86Sr isotopic composition, indicating that the main source of cloud fluid In seawater or evaporation of seawater. The end-units of the limestone and dolomite show Fe-rich, depleted U, Mo, and negative Ce anomalies, indicating that they are formed in a shallow oxidizing environment. In contrast, the end units of limestone show a reduced environment that forms deep water bodies. The results of rock formation temperature estimation using dolomite-seawater and limestone-sea oxygen isotope thermometers show that the dolomite formation temperature is higher than that of limestone, indicating that temperature may be a key factor in overcoming dolomitization kinetic obstacles. Based on the understanding of fluid source, redox conditions, formation temperature and depth of water body, a “stratified water temperature-controlled cloud-interbedded interlayer model” was established. It is considered that dolomitization occurs mainly in shallow water (0 ~ 70m) In the relatively high temperature (up to 30 ℃ in summer), the corresponding sedimentary facies mainly include the sub-facies of the semi-confined platform Taiping subtidal and the subtidal shallow shoal; the sedimentary water of limestone is relatively deep and the temperature is relatively low (-10 ℃) , Corresponding to the sedimentary facies mainly semi-confined submarine beach or the beach between the sea phase.