Abstract Upper Jurassic Naokelekan Formation, being part of the intercepted strata of the well-known Miran oilfield in Kurdistan region of Northern Iraq, has been previously extensively evaluated as a potential/effective source rock, mainly by means of organic geochemistry. In the present study, a total of 60 samples were collected from four Naokelekan Fm. outcrops, those of Banik, Galy-Derash, Barsarin and Dwawa, in order to conduct organic petrographical study and organic geochemical assessment, including both biomarker and Rock-Eval analyses. The average recorded TOC content for Banik, Galy-Derash, Barsarin and Dwawa section is considerable to very high, corresponding to values of 27.5, 9.0, 3.5 and 5.2 wt%, respectively, with the highest values representing the notably organic-rich bottom part of the Formation, known as “coal layer”. According to the petrographical analysis, solid migrabitumens comprise the predominant component for all the analysed samples, whereas the maceral groups of vitrinite, liptinite and/or inertinite showcase a minor to trace occurrence. In terms of organic geochemistry, each of the four sections of interest shows a different biomarker profile. Nevertheless, a number of calculated parameters related to kerogen type and depositional conditions, including the isoprenoids/n-alkanes ratios, suggest a mixed terrestrial-marine organic matter. Furthermore, as indicated by the Ro (%) measurements along with Rock-Eval parameters and the vitrinite reflectance equivalent based on aromatic compounds, the maturity level is marginally mature in the cases of Banik and Galy-Derash, whereas in the cases of Dwawa and Barsarin sections it is mature to post-mature. A synthesis of the organic petrography and geochemical appraisal applied in the present study, suggests that the reported solid hydrocarbons in Naokelekan Fm., particularly at its basal layers are non-indigenous/migrated and the precursor organic matter was deposited in a marine environment, under oscillating conditions ranging from euxinic to well‑oxygenated. Accordingly, the organic features of the notably bitumen-rich “coal-bed” fit the profile of a reservoir and/or migration path.

中文翻译：

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伊拉克库尔德斯坦上侏罗统 Naokelekan 组有机岩石学和地球化学评价

摘要 上侏罗统Naokelekan组是伊拉克北部库尔德斯坦地区著名的Miran油田截获地层的一部分，以前主要通过有机地球化学方法被广泛评价为潜在/有效烃源岩。在本研究中，总共从四个 Naokelekan Fm 收集了 60 个样品。Banik、Galy-Derash、Barsarin 和 Dwawa 的露头，以进行有机岩相研究和有机地球化学评估，包括生物标志物和 Rock-Eval 分析。Banik、Galy-Derash、Barsarin 和 Dwawa 部分的平均 TOC 含量记录相当高，分别对应于 27.5、9.0、3.5 和 5.2 wt% 的值，最高值代表富含有机物的底部地层，称为“煤层”。根据岩相分析，固体迁移是所有分析样品的主要成分，而镜质体、脂质体和/或惰性的微晶组显示出少量到痕量的存在。在有机地球化学方面，四个感兴趣的部分中的每一个都显示了不同的生物标志物概况。尽管如此，许多与干酪根类型和沉积条件相关的计算参数，包括类异戊二烯/正烷烃的比率，表明存在混合的陆海有机质。此外，如 Ro (%) 测量值以及基于芳族化合物的 Rock-Eval 参数和镜质体反射当量所示，Banik 和 Galy-Derash 的成熟度水平略为成熟，而在 Dwawa 和Barsarin 部分是成熟到后成熟。本研究中应用的有机岩石学和地球化学评价的综合表明，Naokelekan Fm. 中报告的固体烃，特别是在其基底层是非本土/迁移的，前体有机物质沉积在海洋环境中，在振荡条件范围从 euxinic 到充氧良好。因此，显着富含沥青的“煤层”的有机特征符合储层和/或迁移路径的剖面。