The present study aims to illustrate the paradigms of saturated and aromatic biomarker distributions in the lithotypes of Lower Gondwana bituminous coals (R̄_r = 0.50–0.68%), perhaps for the first time. The coal samples were collected from the Early Permian Barakar Formation of the Rajmahal Basin, India. These coals mostly comprise three lithotypes, i.e., vitrain, durain, and fusain. The durain shows a considerable abundance than the other two bands and represents the bulk coal characteristics. The total organic carbon (TOC), S1, and S2 parameters from the Rock-Eval pyrolysis depict insignificant variations among the lithotypes, unlike the hydrogen index (HI), which peaks in the durain samples. The micropetrography furnishes a significant amount of liptinite macerals (30.6–51.3 vol% on the mineral matter free basis) present in the samples, dominated by the sporinite and cutinite. These hydrogen-rich macerals, being one of the crucial micropetrographic constituents, would have enhanced the HI values of the durain lithotype. The waxy nature of durain is also substantiated by the long chain-length n-alkane (LCLAs) distributions, while the plausible scarcity of wax in the lignocellulosic plant materials would have led to lower abundances of the LCLAs in vitrain (detected only from the 2D-Gas chromatography coupled with time-of-flight mass spectrometry (GC × GC-TOFMS)). Further, although the saturated diterpenoids are abundant in the durain and vitrain, their extremely low abundances (identified only through the GC × GC-TOFMS) along with the degraded LCLA signature in fusain may hint toward its source from the biomass combustion. Besides, the distributions and interrelations of the 4-, 5-, and 6-ringed polycyclic aromatic hydrocarbons (PAHs; m/z 202, 206, 228, 252, 276, and 278), like fluoranthene, pyrene, chrysene, benzo[g,h,i]perylene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[e]pyrene, and the isomers of the dimethylphenanthrene, dibenzanthracene, and benzochrysene further support the pyrogenic origin of the fusain lithotype. Meanwhile, these PAHS would have derived from diagenetic/catagenetic origin to mixed sources (diagenetic/catagenetic maturation of organic matter and combustion origin) in vitrain. The durain shows a mixed to pyrogenic origin of these PAHs and represents the PAH distributions of the bulk coal samples. Besides, the thermal maturity assessment of these lithotypes may suggest that the molecular parameters respond more sensitively to the thermal maturation compared to the bulk organic geochemical proxies.

本研究旨在说明下冈瓦纳烟煤岩型中饱和和芳香生物标志物分布的范式（R̄ _r = 0.50–0.68%），也许是第一次。煤样采集自印度 Rajmahal 盆地的早二叠纪 Barakar 组。这些煤主要由三种岩型组成，即 vitrain、durain 和 fusain。坚韧带比其他两个带显示出相当多的丰度，代表了散装煤的特征。Rock-Eval 热解的总有机碳 (TOC)、S1 和 S2 参数描绘了岩型之间的微不足道的变化，这与在 durain 样品中达到峰值的氢指数 (HI) 不同。显微岩相学提供了样品中存在的大量亮晶石微晶质（30.6-51.3 vol%，以无矿物质为基础），以孢子石和角质岩为主。这些富含氢的矿物，是重要的微岩相成分之一，会提高 durain 石型的 HI 值。长链也证实了杜兰的蜡质性质正构烷烃 (LCLAs) 分布，而木质纤维素植物材料中蜡的可能稀缺会导致玻璃体中 LCLAs 的丰度降低（仅从二维气相色谱结合飞行时间质谱法 (GC) 检测到） × GC-TOFMS))。此外，虽然饱和二萜类化合物在 durain 和 vitrain 中含量丰富，但它们的极低丰度（仅通过 GC × GC-TOFMS 确定）以及 fusain 中降解的 LCLA 特征可能暗示其来源来自生物质燃烧。此外，4-、5-和6-环多环芳烃（PAHs；m/z 202、206、228、252、276和278）的分布和相互关系，如荧蒽、芘、芘、苯并[ g,h,i ]苝，苯并[ b]荧蒽、苯并[ k ]荧蒽、苯并[ a ]芘、苯并[ e ]芘以及二甲基菲、二苯并蒽和苯并苯的异构体进一步支持了fusain石型的热源。同时，这些 PAHS 将在玻璃体中从成岩/变质起源到混合来源（有机物的成岩/变质成熟和燃烧起源）。durain 显示了这些 PAH 的混合至热成源，并代表了散装煤样品的 PAH 分布。此外，这些岩型的热成熟度评估可能表明，与大块有机地球化学代理相比，分子参数对热成熟度的响应更敏感。