锶同位素地层学在海相地层定年中的潜在价值

锶同位素地层学在海相地层的对比和定年中具有十分重要的作用。随着锶同位素地层学的深入研究，人们清楚地认识到海水的锶同位素组成是全球变化的灵敏指示剂。显生宙以来全球海水的^87Sr／^86Sr比值是时间的函数，可以把锶同位素组成用于海相地层的定年和进行全球对比，估计沉积间断持续时间、生物带的时间范围和发展阶段，从而为重要地球化学周期的预测提供基础参数。当锶同位素地层学用于定年时，其地质年龄的精确度取决于几个因素，包括样品原始锶同位素组成的保存情况、分析精度、用于建立数据库样品年龄的可信度以及^87Sr／^86Sr比值—年龄曲线的最佳拟合方法等。

POTENTIAL VALUE OF THE STRONTIUM ISOTOPE STRATIGRAPHY IN DATING MARINE SEDIMENTS

The strontium isotope stratigraphy (SIS) is predominantly used for correlation and dating of marine sediments. The recent proliferation of strontium isotope stratigraphic studies has clearly documented that the world sea level change is the main and primary factor to control the strontium isotopic composition, i.e. the variation through geological time is the marine 87 Sr/ 86 Sr. The 87 Sr/ 86 Sr record can be used to date and correlate marine sediments, estimate the duration of stratigraphic gaps, estimate the duration of biozones and stages, and underpin speculation about major geochemical cycles. When SIS is used for dating, the quality of its numeric date depends upon the following several factors: the preservation quality of the original 87 Sr/ 86 Sr of a sample, whether artifacts are introduced during 87 Sr/ 86 Sr measurement , the slope of the curve of 87 Sr/ 86 Sr against numeric age, the accuracy of the age model used to assign a numerical calibration to the isotope curve, and finally, the way of the best fit curve and its associated uncertainty envelope are fitted to the Sr isotope date and used to derive a numeric age.