The organic geochemical characteristics of Soma-Eynez coals located in the southwest section of the Soma Neogene Basin in Turkey were examined, and the depositional environment and maturity levels were evaluated. The analyzed samples were drilling samples taken from the Lower Coal Seam (KM2) to represent the basin. The coal’s total organic carbon (TOC) content is 28.45–73.38%, potential yield (PY) value is 22.43–168.29, and extractable organic matter (EOM) yield is 1204–29774 ppm, which are all indicators that the source rock has excellent hydrocarbon-production potential. T max values are between 389 and 430 °C, indicating an immature stage for hydrocarbon production. This is further supported by biomarker maturity parameters (a high odd-to-even predominance index (OEP), low 20S/(20S + 20R) sterane ratio, low ββ/(ββ + αα) sterane ratio, low 22S/(22S + 22R)­(C32) homohopane ratio, and low C29Ts/C29Ts + C29H ratio). Unresolved complex mixtures (UCMs) observed in gas chromatograms point to immature–low mature nonbiodegraded organic matter. The saturated biomarker fractions of KM2 coals are characterized by a high Tm/Ts (C27 17α-trisnorhopane/C27 18α-trisnorhopane) ratio, high Pr/Ph ratio, dominant C29 regular sterane presence, and high C30*/C29Ts ratio. All biomarker parameters showed that terrestrial higher plant materials and algal/bacterial source organisms collectively deposited in the paleo-swamp and under suboxic–oxic conditions.

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Tunçbilek-Tavşanlı (Kütahya) Basin is among the most important Neogene coal deposits of Turkey. This study aims to determine the mineralogical and geochemical properties of the rocks (coal, roof, floor and parting) in the Tunçbilek-Tavşanlı coal field. The main abundant minerals in Tunçbilek-Tavşanlı coals are quartz, kaolinite, illite-smectite and siderite. Dolomite, illite, smectite, mica, feldspar, pyrite, chlorite and jarosite are less abundant minerals. The mineralogy of non-coal rocks is similar to that of coals, but pyrite is absent. The most abundant major oxides in the studied samples are SiO2, Al2O3 and Fe2O3, respectively. The SiO2, Al2O3 and MgO are the most abundant major oxides, respectively, in the claystone samples representing partings. Trace element concentrations of Tunçbilek-Tavşanlı coal samples mostly showed higher concentrations (excluding Ba, Sr, Pr, Tb, Dy, Ho, Tm, As, Cd and Bi) compared to the world low-rank coal average. According to the relative enrichment of the elements, the concentration coefficients (CC) of the coal samples are generally in the range of slightly enriched-normal; The CC of the non-coal samples mainly indicate the normal. The average REY concentration in the studied samples is higher than the world low-rank coal concentration and mostly showed L-type enrichment. Moreover, the REY concentration of the supercritical groups constitutes a significant part of the REYtotal concentration in the samples taken from the coal horizon. However, the studied samples are in the unpromising area according to the low cut-off grade value and the relationship between cut-off grade-Coutl. The high correlation coefficient between ash content and REY concentrations also indicates a mineral substance relationship. Al2O3/TiO2 (between 12.5-31.7) ratios of Tunçbilek-Tavşanlı samples show intermediate and felsic source rocks.