分子有机地球化学与古气候、古环境研究

MOLECULAR ORGANIC GEOCHEMISTRY AND ITS APPLICATION TO THE STUDY OF PALEOCLIMATE AND PALEOENVIRONMENTS

分子有机地球化学可以从分子级水平研究地质体中有机分子化合物的演化规律。本文报道了应用生物标志化合物指标探讨古气候和古环境,例如探讨古生物(含古植物)的输入,淡水、半咸水和高盐度水古环境的判识以及大气飘尘的来源和成因等。

Molecular organic geochemistry, a major branch of organic geochemistry, is a subject which deals with distribution patterns and evolution history of organic compounds, especially biological marker compounds, in geological record. 1. Biological marker Compounds, including terpenoid and steroid compounds, can be applied as useful indicators of biological inputs to Sediments. Acyclic isoprenoid compounds, especially high molecular weight isoprenoids are indicators of paleobacteria. Most of common sesquiterprenoids are known to have come from higher plants, such as cedrane and cuparene have been reported to be the characteristic constituents of the essential oils of the Cupressaceae and Coniferales. Most cyclic diterpenoid compounds have also been identified in higher plant resins, including dehydroabietane, sandaracopimarane, retene etc. Steroid compounds may have different sources, some from aguatic biota and less from higher plants. Most important triterpenoids are hopanoid compoumds. It is c(?)mmonly accepted that many of hopanes are derived from a C_(35)-bacteriohopanetetrol precurson. Some triterpenoids are typical indicators of higher plants, including oleanane, ursane, lupane etc. 2. The biomarker research results reveal significant differences in the chemical features of the various lacustrine environment samples, ranging from fresh water, brackish/fresh water to hypersaline, which enables them to be characterized and identified in terms of environment and/or related parameters. The diagnostic parameters that allow this assessment are: the relative abundances of n-alkanes, acyclic isoprenoid alkanes and 4-methyl sterane, hopane/ sterane ratio, gammacerane and homohopane indexes, etc. The principal characteristics of the biomarker of hypersaline sediment extracts are a dominance of phytane, high content of gammacerence and abnormal distribution of homohopanes. Small differences are found between fresh and brackish/fresh lacustrine mudstones, with fresh water sediments providing strong evidence of terrestrial highor plant input. 3. The preliminary investigation of lipids of aerosol samples, which were collected from three Chinese major cities, shows that all samples contain aliphatic hydrocarbons including nalkanes, steranes and triterpanes, derived from both biogenic source (vascular plant waxen input) and fossil fuel contamination (coal, crude oil, etc.). Polynuclear aromatic hydrocarbons, which are considered to be combustion products from fossil fuels, such as petroleum and coal, are also widely distributed in all samples. Oxygenated compounds are present as major fractions and are derived from mainly natural source.