黄骅坳陷奥陶系古岩溶储层锶同位素地球化学特征

Strontium Isotope Geochemistry of Ordovician Paleokarst Reservoirs in Huanghua Depression

为研究古岩溶储层锶同位素地球化学特征,以同位素地球化学实验为手段,结合全球锶同位素背景,探讨黄骅坳陷奥陶系岩溶储层锶同位素地球化学特征成因,分析其南、北区差异性。研究结果表明,黄骅坳陷奥陶系各组地层87Sr/86Sr值变化范围高于全球所在沉积时期的变化范围值,87Sr/86Sr值变化趋势与全球奥陶系所在沉积时期的变化趋势具有相似性;奥陶系原始碳酸盐岩地层经历了后期古岩溶作用和流体的改造,古陆富87Sr流体对各类岩溶岩和填充物岩反应后大幅度提高87Sr/86Sr值;白云岩87Sr/86Sr值均明显高于同层位的灰岩,证实白云岩对87Sr捕获能力普遍强于灰岩;黄骅坳陷北区经历的表生岩溶作用时间远大于南区,岩溶作用强度高于南区,北区富87Sr流体置换作用亦强于南区,构成了锶同位素87Sr/86Sr值南低、北高的差异性。

To study the strontium(Sr)isotopic characteristics of paleokarst reservoirs,the origin of Sr isotope in Ordovician karst reservoirs in Huanghua depression was discussed via isotopic experiments and comparison with the global Sr isotope background.Isotopic differences between the southern and northern parts of the Huanghua Depression were analyzed.The results show that the 87Sr/86Sr variation range of the Ordovician strata in the Huanghua depression is wider than that of the global Ordovician sedimentation,but their 87Sr/86Sr variation trends are similar.The Ordovician primitive carbonate strata have undergone late paleokarstification and fluid transformation,and the paleo-continental 87Sr-rich fluids were used for various types of karst and filling.The dolomite 87Sr/86Sr values are distinctly higher than those of the limestone in the same horizon,suggesting that the dolomite captures 87Sr more readily than the limestone.Duration of supergene karstification in the northern Huanghua depression is much longer than that in the southern part.The karstification intensity of the former is also higher,and its 87Sr-rich fluid displacement stronger,which probably generates the higher 87Sr/86Sr values in the northern part of Huanghua depression.