摘要
碳酸盐岩碳稳定同位素组成数据能否有效地反应原始大洋的同位素组成是稳定同位素地层学研究成败的关键,因此,如何准确地判断碳同位素比值的有效性成为该稳定同位素地层学研究中的焦点问题之一。碳同位素值有效性受成岩作用、地层缺失、样品处理过程等多方面因素影响,但成岩作用是诸多因素中最普遍、最主要的,因而正确判别碳同位素值可靠性通常也就是对样品及其同位素组成经受成岩改造程度的评定。确保碳同位素测试结果可靠应主要把握前期严格选样和后期数据分析两个重要环节。前期选样包括野外和室内两步,是在宏观尺度上对数据可靠性的把握;后期数据分析则主要是在严格选样的基础上,利用碳(及附带的氧)同位素自身数据特征以及借助Mn、Fe、Sr等微量元素特征从元素级别的微观角度对同位素值有效性做出进一步判别。
Carbonate δ~13C data reflecting the primary marine isotope compositions, are crucial for the success of C-isotope chemo stratigraphy. Thus it is essential to evaluate the validity of δ~13C data in order to screen for factors that affect isotope Values particularly diageneitc alteration which is considered to be the most common and important factor. Based on many case studies, two important steps are proposed to evaluate credible isotope data in the study of C-isotope chemo stratigraphy. The first step is to carefully select samples for isotope analysis, using field-based investigation of the tectonic and sedimentary settings of the study area and thin-section petrographic ivestigation to exclude samples with visible evidence of secondary alteration.The second step is to evaluate the validity of δ~13C data using elemental geochemical data. Commonly used methods include δ~13C δ~18O crossplot （e.g. the presence of abnormal δ~13C values, the threshold value of O-isotope as δ~18O-10‰）, correlation with global secular variation, comparison with C-isotope profiles from other coeval sections,correlatio between δ~13C and Mn/Sr, and correlation between δ~13C and Fe/Sr. An integrative study is required to attain more reliable evaluation of carbonate δ~13C data in C-isotope chemo stratigraphic studies because each criterion has its limitations.
出处
《地层学杂志》
CSCD
北大核心
2010年第4期445-451,共7页
Journal of Stratigraphy
基金
国家重大科技专项课题"大型油气田煤层气开发"(No.2008ZX05004)
中国石油天然气股份公司重大科技专项"海相碳酸盐岩大油气田勘探开发关键技术"成果
