Organic-rich claystones and mudstones can be very good source rocks for hydrocarbons. Middle Jurassic organic-rich siliciclastic horizons are known from the Polish Basin area, however, there are no hydrocarbon accumulations associated with these horizons. The main scientific goal of this paper is to propose why these horizons did not produce significant hydrocarbons quantities. To deal with it, we characterised organic matter origin, maturity level, and hydrocarbon potential of Middle Jurassic strata. Palaeoenvironmental conditions of the Middle Jurassic Polish Basin were also described. The samples were examined by geochemical (Rock-Eval and GC–MS) and petrological (macerals content, vitrinite, and fusinite reflectance values) analyses. The analyses revealed that the Middle Jurassic strata at the study area, in general, contain mixed terrigenous/aquatic organic matter with a significant content of pyrogenic origin polycyclic aromatic hydrocarbons (PAHs). Inertinite and liptinite group macerals dominate in maceral composition. This suggests that analysed samples contain a mixture of type IV and II kerogens. Most of the analysed samples contain immature or early-mature organic matter. In general, the maturity level is higher in the southern part of the study area, where higher subsidence of Polish Through allowed to reach greater burial depths. Sediments were deposited in anoxic basement conditions of the epicontinental sea with the serious influence of deltaic/estuarine systems. The water and air transport are responsible for significant input of terrigenous organic matter, mostly reworked in frequent palaeo-wildfire events. The high content of charred organic matter is the main reason why despite high total organic carbon (TOC) values, the hydrocarbon potential of analysed horizons is poor/fair. Fire maceral index (FMI) was proposed and juxtaposed with pyrolytic input ratio (PIR) to propose that PIR is sensitive mostly to higher-temperature palaeo-wildfires products.

富含有机物的粘土岩和泥岩是很好的烃源岩。波兰盆地地区已知中侏罗统富含有机质的硅质碎屑层位，然而，这些层位没有油气聚集。本文的主要科学目标是提出为什么这些层位没有产生大量碳氢化合物。为了解决这个问题，我们描述了中侏罗统地层的有机质成因、成熟度和油气潜力。还描述了中侏罗纪波兰盆地的古环境条件。通过地球化学（Rock-Eval 和 GC-MS）和岩石学（微晶质含量、镜质体和软质体反射率值）分析检查样品。分析表明，研究区中侏罗统地层总体上，含有混合的陆源/水生有机物，其中含有大量热源多环芳烃 (PAHs)。Inertinite 和 liptinite group macerals 在 maceral 组成中占主导地位。这表明分析的样品含有 IV 型和 II 型干酪根的混合物。大多数分析的样品含有未成熟或早熟的有机物。总体而言，研究区南部的成熟度较高，波兰通的沉降程度较高，可以达到更大的埋藏深度。在三角洲/河口系统的严重影响下，沉积物沉积在陆表海的缺氧基底条件下。水和空气运输是陆源有机物质的重要输入，主要是在频繁的古野火事件中重新加工。高含量的烧焦有机物是尽管总有机碳 (TOC) 值较高，但分析层位的碳氢化合物潜力较差/一般的主要原因。提出了火物质指数（FMI）并将其与热解输入比（PIR）并列，以表明PIR主要对较高温度的古野火产物敏感。