中国−塞尔维亚中新世浅色褐煤生物标志化合物组成及其成因

Biomarker composition and origin of Miocene pale lignites in China and Serbia

  • 摘要: 浅色褐煤在全球新生代褐煤盆地广泛分布,但其成因仍存在争议,查明其有机质组成和形成机制对重建古气候变化以及褐煤资源清洁低碳利用具有重要意义。以塞尔维亚科卢巴拉盆地与中国云南弥勒盆地中新世浅色褐煤为对象,利用索氏抽提、柱色谱分离及气相色谱−质谱联用等有机地球化学方法,通过对脂肪烃和芳香烃等生物标志化合物进行定性和定量分析,探讨浅色和暗色褐煤成煤过程中植被组成、微生物降解作用及沉积环境的差异性。结果表明:弥勒盆地浅色褐煤中长链正构烷烃相对质量分数较高(达82.5%),显示出陆生高等植物(主要为被子植物)叶蜡的显著贡献,同时伴随较低的水生植物指数(Paq为0.16)和较高的植物叶蜡指数(Pwax为0.86),指示其成煤环境偏干燥且并伴有较强的微生物降解作用;而暗色褐煤中链和短链正构烷烃含量增加,表明在沉积过程中水生植物和低等生物的输入增强。科卢巴拉浅色和暗色褐煤均以裸子植物贡献为主,其脂肪烃中二萜相对质量分数极高(浅色为87.3%,暗色为82.5%),∑w(二萜)/∑w(二萜+三萜)值接近1,反映出古泥炭地中以针叶类植物为主的特点,同时,较高的w(C31(R)藿烷)/w(总藿烷)值和w(C30藿-17(21)-烯)/w(C30αβ藿烷)值表明科卢巴拉褐煤在相对氧化、酸性及低热演化条件下成煤。此外,苝及更高的CWDI值表明2个地方的浅色褐煤遭受更强烈的真菌作用,与藿烷的结果一致。通过对比新生代浅色与暗色褐煤的差异性,阐明了沉积环境是褐煤颜色变化的主控因素。

     

    Abstract: Pale lignites are widely distributed in Cenozoic lignite basins around the world, but their origin is still controversial. Identifying their organic matter composition and formation mechanism is of great significance for reconstructing paleoclimate changes and clean and low-carbon utilization of lignite resources. Taking the Miocene pale lignite from Kolubara Basin in Serbia and Mile Basin in Yunnan, China as the research objects, organic geochemical methods, such as Soxhlet extraction, column chromatography separation and gas chromatography-mass spectrometry, were used to qualitatively and quantitatively analyze biomarker compounds in aliphatic and aromatic hydrocarbons to explore the differences in vegetation composition, microbial degradation and sedimentary environment during the coalification process of light and dark lignites. The results show that the pale lignite in Mile Basin has a high content of long-chain n-alkanes (up to 82.5%), showing a significant contribution from leaf waxes of terrestrial higher plants (mainly angiosperms), accompanied by a lower aquatic plant indicator value (Paq of 0.16) and a higher plant leaf wax index (Pwax of 0.86), indicating that its coal-forming environment was relatively dry and accompanied by strong microbial degradation; while the dark lignite has an increased proportion of medium-chain and short-chain n-alkanes, indicating that the input of aquatic plants and lower organisms was enhanced during the sedimentation process in Mile Basin. Both the pale and dark lignite in Kolubara are mainly contributed by gymnosperms. Content of diterpenoids in their aliphatic hydrocarbons is extremely high (87.3% for pale and 82.5% for dark), and the relative mass fraction ratio of diterpenoids to diterpenoids + triterpenoids is close to 1, reflecting the predominance of conifers in the peatland. At the same time, the higher relative mass fraction ratio of C31(R)hopane to total hopane and C30 hop-17(21)-ene to C30αβhopane reveal that Kolubara lignites were formed under relatively oxidative, acidic and low thermal evolution conditions. In addition, perylene and higher CWDI values indicate that pale lignite in two basins was subjected to stronger degradation, which is consistent with the higher content of hopane. By comparing the differences between Cenozoic pale and dark lignite, it is clarified that the sedimentary environment is the main controlling color change of lignite.

     

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