Organic petrography, biomarkers, and stable isotope (δ13C, δD, δ15N, δ18O) compositions of liptinite-rich coals

IF 5.6 2区 工程技术 Q2 ENERGY & FUELS
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引用次数: 0

Abstract

Liptinite-rich coals were evaluated using organic petrography, biomarkers, and stable isotopes to investigate their origin and paleoenvironmental significance, particularly, to explore fractionation characteristics of stable isotopes (δ13C, δD, δ15N, and δ18O) between bulk coal, extractable organic matter (EOM), and extracted coal residue (ER). The samples were collected from Cenozoic coal seams from the Yunnan and Liaoning Provinces in China. The samples are characterized by the enrichment of different types of liptinite. The late Pliocene sample YNP (liptinite = 73.5%) is dominated by sporinite and bituminite, whereas the late Pliocene sample YND (liptinite = 65.5%) is characterized by isolated resinite particles and amorphous resinite. The liptinite in the Eocene sample SB (46.0%) is represented by blocky resinite with homogeneous morphology. The differences in distribution and morphology of liptinite are due to the different coal-forming plants and depositional environments, as indicated by the biomarker compositions. Biomarker results indicated that the sample YNP was formed mainly by Pinaceae and angiosperms under oxidizing conditions with bacterial/fungal degradation, whereas the sample YND was derived from the woody parts of gymnosperms with lower contributions of angiosperms under reducing conditions with low microbial activity. The sample SB predominantly originated from Cupressaceae/Pinaceae under reducing conditions with a lack of bacterial/fungal degradation.

The fractionations of δ13C, δD, δ15N, and δ18O between bulk coal, EOM, and ER in the liptinite-rich coals are different. The δ13C values of bulk coal, EOM, and ER are mostly controlled by precursor paleovegetation and isotopic composition of CO2. The lower δ13C values of samples YNP and YND from the late Pliocene compared to that of the Eocene sample SB resulted from the change of palaeoconditions (e.g., δ13C of atmospheric CO2, cooling, and decrease of CO2 concentration). The δ13C values of EOM in the samples YNP and YND are about 3‰ lower than δ13C values of bulk coal/ER, whereas δ13C fractionation between EOM and bulk coal/ER is small (< 0.8‰) in the sample SB, probably due to the very limited microbial/fungal degradation. The δD values of EOM are 50 to 90‰ lower than that of bulk coal/ER within the same sample, reflecting different isotopic compositions of monomeric compounds compared to the macromolecular matrix of kerogen most probably due to differences in H-isotope fractionation during biosynthesis. The δ15N of bulk coal and ER show limited fractionation (< 0.5‰) and are mainly controlled by precursor paleovegetation and microbial induced degradation processes. The studied liptinite-rich coals yield higher δ18O values than those detected in humic coals. The differences of δ18O values (bulk coal, EOM, ER) between the samples YNP/YND and the corresponding δ18O values of the sample SB indicate that this isotope parameter is mostly controlled by the δ18O value of source water. The weaker fractionation of oxygen isotope between EOM and bulk coal/ER compared to δ13C and δD may be attributed to the fact that oxygen-containing compounds within EOM did not experience a cleavage or any change of the O-containing bonds. The calculated δ18O and δD values of source rain waters fall in the range of modern rain waters at different sites.

富锂辉石煤的有机岩石学、生物标志物和稳定同位素(δ13C、δD、δ15N、δ18O)成分
利用有机岩石学、生物标志物和稳定同位素对富含锂辉石的煤炭进行了评估,以研究其起源和古环境意义,特别是探讨了稳定同位素(δ13C、δD、δ15N和δ18O)在原煤、可提取有机质(EOM)和提取煤渣(ER)之间的分馏特征。样品采集自中国云南省和辽宁省的新生代煤层。这些样品的特点是富含不同类型的锂辉石。晚更新世样本 YNP(锂辉石 = 73.5%)主要为辣晶和沥青质,而晚更新世样本 YND(锂辉石 = 65.5%)则以孤立的锂辉石颗粒和无定形锂辉石为特征。始新世样品 SB(46.0%)中的锂辉石是形态均匀的块状锂辉石。从生物标志物成分来看,不同的成煤植物和沉积环境导致了硫铁矿在分布和形态上的差异。生物标志物结果表明,YNP 样品主要由松科和被子植物在氧化条件下形成,并伴有细菌/真菌降解;而 YND 样品则来自裸子植物的木质部分,被子植物在还原条件下形成,微生物活性较低。富含锂辉石的煤炭中,散煤、EOM 和 ER 之间的 δ13C 值、δD 值、δ15N 值和δ18O 值的分馏不同。原煤、EOM 和 ER 的 δ13C 值主要受前生古植被和 CO2 同位素组成的控制。与始新世样品 SB 相比,上新世晚期样品 YNP 和 YND 的 δ13C 值较低,这是由于古环境的变化(如大气中 CO2 的 δ13C 值、降温和 CO2 浓度的降低)造成的。样品YNP和YND中EOM的δ13C值比块煤/ER的δ13C值低约3‰,而样品SB中EOM与块煤/ER的δ13C分馏很小(< 0.8‰),可能是由于微生物/真菌降解非常有限。在同一样品中,EOM的δD值比散煤/ER的δD值低50-90‰,这反映了单质化合物的同位素组成与角质的大分子基质不同,很可能是由于生物合成过程中H同位素分馏的不同造成的。块煤和 ER 的 δ15N 显示出有限的分馏(< 0.5‰),主要由前体古植被和微生物诱导的降解过程控制。与腐殖质煤相比,所研究的富含磷灰石的煤产生了更高的δ18O值。YNP/YND 样品的 δ18O 值(块煤、EOM、ER)与 SB 样品的相应 δ18O 值之间的差异表明,该同位素参数主要受源水 δ18O 值的控制。与δ13C和δD相比,EOM和块煤/ER之间氧同位素的分馏较弱,这可能是因为EOM中的含氧化合物没有发生裂解或含氧键的任何变化。计算得出的源雨水δ18O和δD值属于不同地点现代雨水的范围。
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来源期刊
International Journal of Coal Geology
International Journal of Coal Geology 工程技术-地球科学综合
CiteScore
11.00
自引率
14.30%
发文量
145
审稿时长
38 days
期刊介绍: The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.
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