依据锶同位素比值判断麦盖提斜坡东缘晚奥陶世海平面变化

Sea-Level Variation of Late Ordovician in Eastern Margin of Maigaiti Slope by Strontium Isotope Ratio Analysis

对采自麦盖提斜坡M2井上奥陶统良里塔格组的23个碳酸盐岩样品进行了锶同位素分析,以此判断研究区晚奥陶世海平面变化。分析结果表明,^87Sr/^86Sr值为0.708 51~0.709 13,平均为0.708 78,这一比值明显高于全球正常海水的锶同位素比值,但与柯坪、巴楚和塔中地区同一层位的锶同位素比值较为一致。依据^87Sr/^86Sr值,获得了良里塔格组的锶同位素演化曲线,曲线与全球晚奥陶世锶同位素演化曲线具有良好的一致性;并且与巴楚地区、波罗的古陆和劳伦古陆地区的海平面变化具有良好的耦合性,较好地反映了该时期海平面的变化特征。这一认识对于研究整个盆地晚奥陶世的沉积物变迁和构造演化具有重要意义。

The strontium isotope characteristics of 23 carbonate samples of Lianglitage formation of Late Ordovician from Ma-2 well in Mai- gaiti area of Tarim basin were analysed for the purpose of making sure the sea-level changes at this period. The results show that the ratio of ^87Sr/^86Sr ranges from 0.708 51 to 0.709 01, with an average of 0.708 74, which is higher than the ratio of global seawater strontium isotope in the same period, but more consistent with those from the same horizons in such areas as Keping, Baehu and Tazhong regions. On the basis of the ratio of ^87Sr/^86Sr, the strontium isotope evolution curve of Lianglitage formation in Maigaiti area is obtained, which is consistent with the global seawater strontium isotope evolution curve of the Late Ordovician, better coupled with Bachu, Laurentia and Baltica old-lands, and well reflects the sea-level variation in this period. This understanding is of great importance for the study of the sediment changes and structural evolution of Late Ordovician in the whole Tarim basin.