脂类单体碳同位素在湖沼古环境和古生态重建中的研究进展

地质载体中保存的脂类来源于生物细胞膜、叶片蜡质层等,能够指示特定的生物分类学类群或微生物功能群,也能够记录生物生长或早期成岩过程中的生态环境信息,已经成为第四纪古环境和古生态研究的重要手段。除了化合物含量和分子组成,脂类的碳同位素组成也蕴含着重要的生态或环境信息。对于光能自养生物,这些信息来自光合作用和脂类的生物合成过程;对于异养生物,信息则来自摄食的底物和脂类的生物合成过程。总结了近些年来湖沼沉积中脂类单体碳同位素的研究进展,从长链正构烷烃、脂肪酸、陆源五环三萜等高等植物脂类和磷脂脂肪酸、藿类、四醚膜脂等微生物脂类等2个领域进行了系统阐述。在今后的发展中,需要重视实验技术,开发适合小样品量的分析方法,建立直接测试藿类和四醚类等分子量相对大的脂类碳同位素组成的新技术,加强单体放射性碳同位素的应用;可以考虑多种脂类碳同位素的联合、同一脂类单体碳同位素和单体氢同位素的联合;建议加强脂类单体碳同位素在生物地球化学过程,特别是微生物地球化学过程对过去全球变化的响应研究。     

泥炭沼泽有机地球化学研究进展

近几十年来，国内外泥炭沼泽地球化学研究取得了一系列重要进展，特别是在脂类化合物和稳定同位素等方面。泥炭沼泽是一个良好的地质档案，泥炭纤维素碳、氢和氧同位素组成和比值是环境变化的综合参数，沉积脂类化合物含有反映有机质母源先质的骨架结构，这些标志物高分辨率地记录了全新世以来古气候、古植被和古环境的演变信息，在当今全球变化研究中占有相当重要的地位。本文综述了泥炭沼泽地球化学研究进展，侧重于泥炭沼泽脂类化合物和稳定同位素等标志物的地球化学研究现状和发展趋势；侧重论述了研究技术的发展、定性说明到定量分析的过渡、研究精度的提高及存在的问题，分析了这些分子标志物与植被演替、气候变迁和环境变化间的对应关系，指出了我国在该方面的薄弱之处以及需加强的领域。     

生物标志化合物稳定碳同位素地球化学

回顾和展望了生物标志化合物稳定碳同位素地球化学的发展，讨论了它在石油勘探和其它学科中的应用问题。     

生物降解稠油沥青质热解产物中生物标志化合物与单体烃碳同位素组成研究

本文运用热解技术对采自准噶尔盆地风城地区6个重度生物降解稠油进行沥青质热解实验。通过分析沥青质热解产物中生物标志化合物组成和单体正构烷烃碳同位素组成,探索其在降解稠油油源研究中的应用。研究结果显示,沥青质热解产物中生物标志化合物组成特征易受热解温度的影响,指示母质沉积水体环境的参数 Pr/Ph比值随热解温度升高逐渐增大,在较高的温度下,高碳数、高环数的生物标志化合物易裂解生成低碳数、低环数的化合物,导致C20三环萜烷/C30 藿烷和孕甾烷/αααC29R甾烷两个参数的比值随热解温度升高逐渐增大,表明利用沥青质热解产物生物标志化合物组成进行降解稠油油源判识易出现偏差。而沥青质热解产物单体正构烷烃碳同位素组成随热解温度升高并没有明显的变化, 6个降解稠油沥青质热解产物单体正构烷烃碳同位素分布曲线呈水平分布,与来自风城组烃源岩的典型原油基本相似,说明沥青质热解产物中单体烃碳同位素组成特征可用于重度降解稠油油源分析。另外,通过对比稠油与其沥青质热解产物中单体正构烷烃单体碳同位素组成差异,可用于研究多油源以及后期混入的问题。     

生物标志物单体放射性碳同位素分析技术的发展

自Eglinton等(1996)首次将单体放射性碳同位素分析技术(CSRA)应用于海洋沉积物中生物标志物14C研究以来,该技术发展迅速,广泛应用于海洋科学、生物地球化学和古气候学等领域。但是,自然环境样品中生物标志物大多含量低、干扰基质复杂而且难以分离。因此,如何从基质组成复杂的样品中分离富集高纯度的目标化合物已经成为限制CSRA技术发展和应用的瓶颈。近些年来,不断改进的色谱分离富集技术不仅提高了目标化合物分离的纯度和回收效率,同时也扩展了生物标志物的碳同位素示踪应用。综合介绍了自然环境研究中单体化合物放射性碳同位素分析技术中常见生物标志物单体分离纯化的技术方法以及发展现状。     

古海洋研究中的地球化学新指标

有机地球化学与微量元素地球化学古环境指标及其相关的同位素指标已成为追溯古全球变化与古海洋生物地球化学演化的有力工具。从古环境替代指标的示踪原理和应用的角度，综述了有孔虫碳同位素、有机地球化学整体指标、生物标志化合物、单体有机分子同位素、微量元素等在古海洋古环境研究中的应用及相关的研究动态与进展。指出古海洋研究正从以恢复古海洋的物理参数（温度、盐度、古洋流等）为主，向着揭示古水团演化、古生产力、古营养状况、碳贮库及碳循环等古生物地球化学演化过程方向纵深发展。     

天然气中微量烃类化合物碳同位素分析方法研究

<正>1研究背景单体化合物稳定同位素组成分析技术已逐渐发展成为重要的示踪工具,其在地球科学、环境科学、生态学等诸多学科领域中日益起到重要的作用。例如:在油气地球化学研究领域,可利用天然气中甲烷、乙烷、丙烷等烃类化合物的碳同位素组成特征来判识天然气的沉积环境、成因类型、演化程度、运移方式等,从而为油气勘探开发起到指导作用。但由于上述烃类分子结构简单、种类单一,其同位素组成易受到多种地质作用的影响,使结果具有多解性。因此开展更高碳数烃类化合物的同位素组成分析对进一步探索新的     

广西香田弗拉斯-法门阶界线事件标志——碳、氧稳定同位素异常特征

本文对广西香田晚泥盆世弗拉斯-法门阶界线剖面进行了系统的碳、氧稳定同位素研究。发现随着弗拉斯-法门期之交的生物大量死亡和绝灭,在弗拉斯-法门阶界线层中,碳、氧稳定同位素组成出现了明显的异常。这和白垩—第三系界线灾变事件中出现的异常颇为相似。碳同位素异常达-6.6‰左右,氧同位素出现正异常达2‰。此外,在界线层中出现铱异常为230×10^-12g/g。这些表明,上述同位素地球化学异常是地球历史中生物绝灭灾变事件的重要标志。     

八面河低成熟油生物标志化合物碳同位素分析和研究

利用化学预处理与气相色谱－同位素质谱相结合的分析手段，在 内首次完成了原油中甾萜生物标志化合物的碳同位素鉴定。选择我国济阳坳隐八面河油田典型低成熟油作为样品，对其甾萜生物标志化合物的碳同位素的特征进行了初步探讨。     

河北宣龙地区微生物铁岩有机地球化学特征及成因意义

通过对宣龙铁矿生物结构类型铁质叠层石、核形石和微生物鲕石所作的有机碳、正烷烃、生物标志物及干酪根红外扫描、元素组成和碳同位素分析,结合地质背景资料、微生物化石等地质标志探讨有机质在铁矿形成中的作用。研究表明,从有机地球化学的角度也可提供生物参与铁质沉淀的证据。     

Isotopic order, biogeochemical processes, and earth history: Goldschmidt lecture, Davos, Switzerland, August 2002

The impetus to interpret carbon isotopic signals comes from an understanding of isotopic fractionations imposed by living organisms. That understanding rests in turn on studies of enzymatic isotope effects, on fruitful concepts of isotopic order, and on studies of the distribution of ¹³C both between and within biosynthetic products. In sum, these studies have shown that the isotopic compositions of biological products are governed by reaction kinetics and by pathways of carbon flow.Isotopic compositions of individual compounds can indicate specific processes or environments. Examples include biomarkers which record the isotopic compositions of primary products in aquatic communities, which indicate that certain bacteria have used methane as a carbon source, and which show that some portions of marine photic zones have been anaerobic. In such studies, the combination of structural and isotopic lines of evidence reveals relationships between compounds and leads to process-related thinking. These are large steps. Reconstruction of the sources and histories of molecular fossils redeems much of the early promise of organic geochemistry by resolving and clarifying paleoenviron-mental signals. In turn, contemplation of this new information is driving geochemists to study microbial ecology and evolution, oceanography, and sedimentology.     

Hydrogen-isotopic variability in fatty acids from Yellowstone National Park hot spring microbial communities

We report the abundances and hydrogen-isotopic compositions (D/H ratios) of fatty acids extracted from hot-spring microbial mats in Yellowstone National Park. The terrestrial hydrothermal environment provides a useful system for studying D/H fractionations because the numerous microbial communities in and around the springs are visually distinct, separable, and less complex than those in many other aquatic environments. D/H fractionations between lipids and water ranged from −374‰ to +41‰ and showed systematic variations between different types of microbial communities. Lipids produced by chemoautotrophic hyperthermophilic bacteria, such as icosenoic acid (20:1), generally exhibited the largest and most variable fractionations from water (−374‰ to −165‰). This was in contrast to lipids characteristic of heterotrophs, such as branched, odd chain-length fatty acids, which had the smallest fractionations (−163‰ to +41‰). Mats dominated by photoautotrophs exhibited intermediate fractionations similar in magnitude to those expressed by higher plants. These data support the hypothesis that variations in lipid D/H are strongly influenced by central metabolic pathways. Shifts in the isotopic compositions of individual fatty acids across known ecological boundaries show that the isotopic signature of specific metabolisms can be recognized in modern environmental samples, and potentially recorded in ancient ones. Considering all sampled springs, the total range in D/H ratios is similar to that observed in marine sediments, suggesting that the trends observed here are not exclusive to the hydrothermal environment.     

含油气盆地油气同位素地球化学研究概述

以气体地球化学国家重点实验室工作为主，简要概述了对我国含油气的同位素地球化学研究。1．烃气的同位素地球化学：讨论了天然气成因新模式与气藏烃气同位素组成的关系，低演化阶段天然气同位素分馏的二阶段模式，云南中小盆地天然气低演化系列同位素特征及用储层解析气作油气源对比。2．稀有气体同位素地球化学：阐述了^3He/^4He值与中国构造分区，幔源氮的复合成藏和幔源甲烷问题以及气源对比等。3．液态烃同位素地球化学：简述了轻烃碳氢同位素特征及氢同位素作为判别古沉积介质盐度的指标，概述了未熟一低熟油同位素特征及在自然剖面上油和源油抽提物碳同位素分馏特征及其机理。     

Carbon isotopic fractionation in lipids from methanotrophic bacteria II: the effects of physiology and environmental parameters on the biosynthesis and isotopic signatures of biomarkers

Controls on the carbon isotopic signatures of methanotroph biomarkers have been further explored using cultured organisms. Growth under conditions which select for the membrane-bound particulate form of the methane monooxygenase enzyme (pMMO) leads to a significantly higher isotopic fractionation than does growth based on the soluble isozyme in both RuMP and serine pathway methanotrophs; in an RuMP type the delta delta 13Cbiomass equaled -23.9% for pMMO and -12.6% for sMMO. The distribution of biomarker lipids does not appear to be significantly affected by the dominance of one or the other MMO type and their isotopic compositions generally track those of the parent biomass. The 13C fractionation behaviour of serine pathway methanotrophs is very complex, reflecting the assimilation of both methane and carbon dioxide and concomitant dissimilation of methane-derived carbon. A limitation in CH4 availability leads to the production of biomass which is 13C-enriched with respect to both carbon substrates and this occurs irrespective of MMO type. This startling result indicates that there must be an additional fractionation step downstream from the MMO reaction which leads to incorporation of 13C-enriched carbon at the expense of dissimilation of 13C-depleted CO2. In these organisms, polyisoprenoid lipids are 13C-enriched compared to polymethylenic lipid which is the reverse of that found in the RuMP types. Serine cycle hopanoids, for example, can vary anywhere from 12% depleted to 10% enriched with respect to the CH4 substrate depending on its concentration. Decrease in growth temperature caused an overall increase in isotopic fractionation. In the total biomass, this effect tended to be masked by physiological factors associated with the type of organism and variation in the bulk composition. The effect was, however, clearly evident when monitoring the 13C signature of total lipid and individual biomarkers. Our results demonstrate that extreme carbon isotopic depletion in field samples and fossil biomarker lipids can be indicative of methanotrophy but the converse is not always true. For example, the hopanoids of a serine cycle methanotroph may be isotopically enriched by more than 10% compared to the substrate methane when the latter is limiting. In other words, hopanoids from some methanotrophs such as M. trichosporium would be indistinguishable from those of cyanobacteria or heterotrophic bacteria on the basis of either chemical structure or carbon isotopic signature.     

Diagenesis of organic matter—A study using stable isotopes of individual carbohydrates

This paper presents data on the isotopic compositions of individual carbohydrates which have been isolated from both living organisms and from a depositional environment. Through recent developments in chromatography, isolation of monosaccharides quantity for isotopic analysis is possible. Carbohydrates isolated from marine and terrestrial plants and animals have carbon isotopic compositions which clearly indicate biosynthetic processes which are recognized to be associated with isotopic fractionations during the incorporation and metabolism of carbon. Stable nitrogen isotopic compositions of N-acetyl-d-glucosamine, isolated from a variety of chitins, indicate a common fractionation of nitrogen which may be associated with transamination. This fractionation is estimated to be about –9%₀ relative to the whole organism. Through the isotopic label, the source or history of an organic material may be traced through diagenesis. Further, production of non-indigenous carbohydrates, which may be associated with fungal or bacterial action, can be identified through depleted isotopic compositions. Xylose, for example, isolated from a peat, was approximately 8% more depleted in carbon than the whole peat or mannose isolated from the same peat. The isotopic distributions of carbohydrates isolated from living organisms are essential for the interpretation of those characterized in natural mixtures from an environment.     

Carbon isotopic fractionation in lipids from methanotrophic bacteria: relevance for interpretation of the geochemical record of biomarkers

Experiments with cultured aerobic methane oxidising bacteria confirm that their biomarker lipids will be significantly depleted in 13C compared to the substrate. The methanotrophic bacteria Methylococcus capsulatus and Methylomonas methanica, grown on methane and using the RuMP cycle for carbon assimilation, show maximum 13C fractionation of approximately 30% in the resultant biomass. In M. capsulatus, the maximum fractionation is observed in the earliest part of the exponential growth stage and decreases to approximately 16% as cells approach stationary phase. This change may be associated with a shift from the particulate form to the soluble form of the methane monooxygenase enzyme. Less than maximum fractionation is observed when cells are grown with reduced methane availability. Biomass of M. capsulatus grown on methanol was depleted by 9% compared to the substrate. Additional strong 13C fractionation takes place during polyisoprenoid biosynthesis in methanotrophs. The delta 13C values of individual hopanoid and steroid biomarkers produced by these organisms were as much as l0% more negative than total biomass. In individual cultures, squalene was 13C-enriched by as much as 14% compared to the triterpane skeleton of bacteriohopaneaminopentol. Much of the isotopic dispersion in lipid metabolites could be attributed to shifts in their relative abundances, combined with an overall reduction in fractionation during the growth cycle. In cells grown on methanol, where there was no apparent effect of growth stage on overall fractionation there were still significant isotopic differences between closely related lipids including a 5.3% difference between the hopane and 3 beta-methylhopane skeletons. Hopane and sterane polyisoprenoids were also 13C-depleted compared to fatty acids. These observations have significant implications for the interpretation of specific compound isotopic signatures now being measured for hydrocarbons and other lipids present in sediments and petroleum. In particular, biomarker lipids produced by a single organism do not necessarily have the same carbon isotopic composition.     

Compound-specific isotopic analyses: a novel tool for reconstruction of ancient biogeochemical processes

Patterns of isotopic fractionation in biogeochemical processes are reviewed and it is suggested that isotopic fractionations will be small when substrates are large. If so, isotopic compositions of biomarkers will reflect those of their biosynthetic precursors. This prediction is tested by consideration of results of analyses of geoporphyrins and geolipids from the Greenhorn Formation (Cretaceous, Western Interior Seaway of North America) and the Messel Shale (Eocene, lacustrine, southern Germany). It is shown (i) that isotopic compositions of porphyrins that are related to a common source, but which have been altered structurally, cluster tightly and (ii) that isotopic differences between geolipids and porphyrins related to a common source are equal to those observed in modern biosynthetic products. Both of these observations are consistent with preservation of biologically controlled isotopic compositions during diagenesis. Isotopic compositions of individual compounds can thus be interpreted in terms of biogeochemical processes in ancient depositional environments. In the Cretaceous samples, isotopic compositions of n-alkanes are covariant with those of total organic carbon, while delta values for pristane and phytane are covariant with those of porphyrins. In this unit representing an open marine environment, the preserved acyclic polyisoprenoids apparently derive mainly from primary material, while the extractable, n-alkanes derive mainly from lower levels of the food chain. In the Messel Shale, isotopic compositions of individual biomarkers range from -20.9 to -73.4% vs PDB. Isotopic compositions of specific compounds can be interpreted in terms of origin from methylotrophic, chemautotrophic, and chemolithotrophic microorganisms as well as from primary producers that lived in the water column and sediments of this ancient lake.     

Matrix protected organic matter in a river dominated margin: A possible mechanism to sequester terrestrial organic matter?

The provenance of organic matter in surface sediments from the northern Gulf of Mexico was investigated by analyzing the compositions of lipid biomarkers (n-alkanes, fatty acids, sterols) liberated after a series of chemical treatments designed to remove different organo-mineral matrix associations (i.e. freely extractable, base-hydrolyzable, unhydrolyzable). Bulk analyses of the organic matter (carbon content, carbon:nitrogen ratios, stable and radiocarbon isotopic analyses) were also performed on the intact sediments and their non-hydrolyzable, demineralized residue. We found recognizable lipids from distinct sources, including terrestrial vascular plants, bacteria and marine algae and zooplankton, within each of the isolated fractions. Based on the lipid signatures and bulk compositions, the organic matter within the unhydrolyzable fractions appeared to be the most diagenetically altered, was the oldest in age, and had the highest abundance of terrigenous lipids. In contrast, the base-hydrolyzable fraction was the most diagentically unaltered, had the youngest ages and was most enriched in N and marine lipids. Our results indicate that fresh, autochthonous organic matter is the most important contributor to base-hydrolyzable lipids, whereas highly altered allochthonous sources appear to be predominant source of unhydrolyzable lipids in the surface sediments from the Atchafalaya River shelf. Overall, the lipid biomarker signatures of intact sediments were biased towards the autochthonous source because many of the organic compounds indicative of degraded, terrigenous sources were protected from extraction and saponification by organo-mineral matrices. It is only after these protective matrices were removed by treatment with HCl and HF that these compounds became evident.     

微生物降解有机物的碳氢同位素分馏研究进展

微生物降解使有机化合物的稳定碳、氢同位素发生不同程度分馏的研究在有机污染物来源和微生物环境修复等领域取得了长足进展,并对原油和天然气微生物降解研究有借鉴意义。微生物作用下的同位素分馏为动力同位素分馏,导致重同位素在残余物中富集。影响微生物降解有机物同位素分馏的主要因素有微生物的降解代谢途径、辅酶作用、降解类型与程度、同位素质量差异和有机物碳数等。不同的微生物代谢途径代表不同的生物化学反应,造成了同位素分馏的显著差异;辅酶对反应的催化作用使微生物作用造成的同位素分馏更加复杂。低碳数正构烷烃遭受微生物降解程度越高,碳、氢同位素的分馏也越大,同位素变重与降解程度之间有明显的相关性。但对于复杂化合物,由于降解的多级反应,同位素分馏与降解程度间的相关性并不明显。在同样降解程度下,氢同位素分馏大于碳同位素分馏,低碳数正构烷烃的同位素分馏大于高碳数正构烷烃的同位素分馏。     

An isotopic biogeochemical study of Neoproterozoic and Early Cambrian sediments from the Centralian Superbasin, Australia

Organic matter from Neoproterozoic and Early Cambrian sediments of the Amadeus and Officer basins of the Centralian Superbasin, Australia, has been studied for biomarker distributions and the carbon isotopic compositions of kerogen and individual hydrocarbons. These sediments represent both shallow and deep water marine facies in the older sections and marine and saline lacustrine carbonate deposits in the Cambrian. Hydrocarbon biomarker patterns were found to be quite consistent with the known sedimentary environments and provide valuable insights into the biogeochemical changes which accompanied the transition from a microbially-dominated ocean to the early stages of metazoan radiation. In particular, carbon isotopic data for n-alkyl and isoprenoid lipids presented here, and in earlier studies, showed a reversal in carbon isotopic ordering between the Proterozoic and Phanerozoic. By comparison with the delta 13C of kerogen, n-alkyl lipids from deep-water Proterozoic sediments were enriched in 13C and appear to be derived mainly from heterotrophs whilst open marine Phanerozoic counterparts are 13C depleted and evidently derived mainly from autotrophs. Data from the samples studied here are consistent with a model invoking a change in the redox structure of the ocean, possibly aided by the innovation of faecal pellets.