Abstract The paper reports the results of the organic petrological, palynological and geochemical characterization of lignite samples from the Kipra lignite seam (Late Miocene, Maritsa-West Basin, Bulgaria). The bulk of the organic matter (OM) is represented by highly gelified detrohuminite with locally abundant leaf-derived ulminite. Liptinite group is characterized by predominance of microsporinite and liptodetrinite, locally with cutinite and fluorinite. Terpene resinite and suberinite are rare. Low TPI and high GI indices indicate peat formation from vegetation with low preservation potential, deposited under water-logged environment of marsh- or fen-type. The palynological results reveal a vegetational community representing different habitats (i.e. mesophytic, marginal and aquatic). The relatively poor preservation of the palynomorphs, however, suggests vegetation that was more diverse during peat formation. Although gymnosperm palynomorphs predominate, the gymnosperm organic matter contribution was probably minor as indicated by the low contents of sesqui- and diterpenoid biomarkers. Because of the absence of triterpenoid biomarkers of neither oleanane, nor lupane or ursane-type, it is considered that angiosperms that do not synthesize their precursors predominated, or the depositional environment had unfavorable characteristics, which prevented the transformation of the triterpenoid precursors. The extractable organic matter yield from the Kipra lignite is low, and dominated by saturated compounds, while polar compounds and asphaltenes occur in low amounts. Aromatic compounds are completely absent. The saturated hydrocarbons are mainly composed of n-alkanes, accompanied by minor amounts of branched- (including isoprenoids) and cycloalkanes, sesqui- and diterpenoids, steroids and hopanoids. Straight chain alkanes are prevailed by long-chain homologues, but show rather mature distribution with CPI ~ 1. Biological (e.g. bacterial) activities and/or environmental control are considered as the main factor/s controlling the observed uncommon n-alkane distributions. A rather uncommon pentacyclic terpenoid, i.e. onocerane I, was tentatively identified in one sample, based on its characteristic fragmentation pattern. Based on its presence, a very specific plant community is considered, and/or specific palaeoenvironmental conditions occurred at least temporarily during the peat formation. However, the responsible plants could not be identified. The low amounts of hopanoid biomarkers, together with the low amounts of n-alkanones, are consistent with limited aerobic biodegradation of the plant remains. The mature 22S/(22S + 22R) C30 hopane ratio (~ 0.55), as well as the random huminite reflectance values (~0.3–0.4%), which are more than twice higher than previously reported, argue for a local increase of coalification degree, presumably due to increased thermal influx around major faults.

中文翻译：

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保加利亚东南部 Maritsa-West 盆地泥炭形成的意义：有机岩石学、孢粉学和生物标志物组合的见解

摘要 本文报告了来自 Kipra 褐煤煤层（晚中新世，Maritsa-West Basin，保加利亚）褐煤样品的有机岩石学、孢粉学和地球化学特征的结果。大部分有机物质 (OM) 由高度凝胶化的底腐殖质和局部丰富的叶衍生的腐殖质代表。Liptinite 组的特点是微孢子石和 liptodetrinite 占优势，局部有角质石和萤石。萜烯树脂石和软木石很少见。低 TPI 和高 GI 指数表明泥炭由低保存潜力的植被形成，沉积在沼泽或沼泽型的淹水环境下。孢粉学结果揭示了代表不同栖息地（即中生、边缘和水生）的植被群落。孢粉型保存相对较差，然而，表明在泥炭形成期间植被更加多样化。尽管裸子植物孢粉体占主导地位，但倍半和二萜生物标志物含量低表明裸子植物有机质的贡献可能很小。由于缺乏齐墩果烷、羽扇豆烷或熊果类三萜类生物标志物，认为不合成其前体的被子植物占主导地位，或沉积环境具有不利特征，阻止了三萜前体的转化。Kipra 褐煤的可提取有机物产率低，以饱和化合物为主，而极性化合物和沥青质含量较低。芳香族化合物完全不存在。饱和烃主要由正构烷烃组成，伴有少量支链（包括类异戊二烯）和环烷烃、倍半和二萜、类固醇和藿烷。直链烷烃以长链同系物为主，但显示出相当成熟的分布，CPI ~ 1。生物（例如细菌）活动和/或环境控制被认为是控制观察到的罕见正烷烃分布的主要因素。一种相当不常见的五环萜类化合物，即番石榴石 I，基于其特征性的碎裂模式，在一个样品中被初步鉴定。基于它的存在，考虑了一个非常特定的植物群落，和/或在泥炭形成期间至少暂时出现了特定的古环境条件。但是，无法确定负责的工厂。少量的hopanoid生物标志物，加上少量的正链烷酮，与植物残骸的有氧生物降解有限是一致的。成熟的 22S/(22S + 22R) C30 hopane 比率（~0.55）以及随机腐殖质反射率值（~0.3-0.4%），比之前报道的高两倍多，支持局部增加煤化度，大概是由于主要断层周围的热流入增加。