早三叠世海相碳酸盐碳同位素研究进展

早三叠世是地球发展史上的特殊时期,代表了古、中生代过渡时期的生态重建与复苏.随着各种“异常环境事件”信息在近年陆续被揭示,早三叠世地质学研究成为地学界新的热点领域.海相碳酸盐碳同位素组成记录了碳循环的变化,是理解重大突变期的生态环境事件和地球过程的重要切入点.最近10年的研究表明,过去集中在二叠纪/三叠纪界线附近发现的“负漂移”现象只能代表海洋化学持续了约5 Ma的动荡局面的开始,直到中三叠世才趋于平稳,高频率、大幅度的整体演变型式已很难用过去提出的机制进行解释.全球范围内缺乏可精确对比性以及高达+8‰的正向极值的成因等,都是值得深入思考的问题.

Review of the Carbon Isotope of Early Triassic Carbonates

The Early Triassic is a critical period in earth history, representing the ecosystem reconstruction and recovery after the end Permian biotic crisis. As a result of recent discoveries about a series of unusual environmental and evolutionary events, the research of the Early Triassic has become a focus topic in the geological fields. Variations in the carbon isotopic compositions of marine carbonate record the fluctuation of carbon cycle, and give information about ecosystem function and environmental change through the transitional period. The new carbon isotope data indicate that the P/T δ¹³C decline was just a start of a series of large fluctuations that continued throughout the Early Triassic before the early Middle Triassic. The high frequency and large amplitude of the δ¹³C excursions demonstrate that the catastrophic mechanisms proposed in the past become less attractive to explain the Early Triassic carbon isotopic record as a whole. The lack of comparability of δ¹³C curve globally and the genesis for the usually 8‰ positive shift are the problems worthy further consideration.