有机碳同位素示踪古环境变化研究  

COMMENT ON TRACING ENVIRONMENTAL CHANGE WITH ORGANIC CARBON ISOTOPES

作　　者：唐国军[1] 陈衍景[1] 

机构地区：[1]北京大学地球与空间科学学院,北京100871

出　　处：《矿物岩石》2004年第3期110-115,共6页Mineralogy and Petrology

基　　金：筠政基金项目(李政道夫妇设立)

摘　　要：　对有机碳同位素示踪环境变化的原理、研究对象、取得的进展和存在的问题等进行了详细研究,认识到C—H键比C—O键有利于富集12C,从而导致生物或有机碳δ13C为极低的负值,使有机碳与无机碳之间存在显著的碳同位素差异。光合作用类型的不同使植物分为C3,C4和CAM3种类群,并导致不同类群的植物具有不同的碳同位素组成,C3植物δ13C=-20‰～-32‰,平均-28‰,而C4植物δ13C=-9‰～-17‰,平均-14‰。气候环境的差异影响了光合作用的类型和强度,使不同环境的植物类群特征不同,不仅造成植物组合的碳同位素组成不同,而且导致不同食性的动物牙齿等化石的碳同位素组成的差异,甚至相应的无机碳同位素的变化,因此生物链及其衍生物的碳同位素研究也就成为反演某一地区或某一时期气候环境的有效手段。被作为研究对象的地质记录可分为有机和无机两类,有机类主要包括树轮等植物化石、牙齿等动物化石、煤等陆相沉积有机质、海相沉积有机质、土壤(前者的衍生物),这些研究对象分别适合于目的不同的环境研究,并获得了较好的效果。进而发现有机碳同位素在研究重大生物灭绝事件、C4植物起源、地球早期生命起源、地外生命存在与否、矿产资源形成时的有机质作用等问题上将有重要作为。As global change becomes a more important research topic, scientists tried different ways on various geologic records in their research. This paper introduces and reviews the organic carbon isotope method used to trace environmental change, including its mechanism, research objects, obtained results and problems.It is considered that ()^(12)C prefers to enrich in C—H bond rather than in C—O bond, causing much lower negative δ^(13)C for biotic matter or organic carbon than that for inorganic carbon. Difference in photosynthesis distinguishes plants into three groups with distinctive δ^(13)C, i.e. C_3, C_4 and CAM. The C_3 plants have δ^(13)C=-20‰～-32‰,average -28‰ and the C_4 plants have ()^(13)C=-9‰～-17‰,average -14‰. Climate affects the style and strength of photosynthesis, causing distinctive development of plant group in unique environment with distinctive total organic δ^(13)C value. The difference in δ^(13)C of total plants can further result in local characteristic δ^(13)C of animal fossils on the biological chain, such as fossil teeth, and even characteristic inorganic δ^(13)C. Therefore,carbon-isotopic study of biotic chains and their ramifications or products is an effective way to understand local or temporal environments. Accordingly, the geologic records are divided into two large classes, i.e. organic and inorganic records. Organic records include fossil plants,such as tree rings, fossil animals,such as teeth, continental sedimentary organic matter,such as coal, marine sedimentary organic matter and soils (ramification of biotic matter). These research records have been used successfully to trace environmental changes of various aims. The authors believe that organic carbon isotopic study will play a more important role in revealing significant mass extinction, finding oldest C4 plants, understanding origin of earliest life on earth, verifying the existence of extraterrestrial life and determining the relation between organic matter and mineral resources.More attention will

关 键 词：有机碳 同位素 示踪 古环境 分馏作用 

分 类 号：P597[天文地球—地球化学]