Hydrocarbon generation potential and Miocene–Pliocene paleoenvironments of the Kangal Basin (Central Anatolia, Turkey)

Abstract

This study deals with the organic geochemical characteristics, hydrocarbon generative potential and Miocene–Pliocene paleoenvironments of the Kangal coal district, which developed in a limnic depositional environment and contains the Hamal, Etyemez and Kalburçayırı coal fields in the southern part of the Sivas Basin (Central Anatolia). Around Kalburçayırı, the average thickness of each of the two coal seams approximately 10 m are currently being exploited based on open-cast methods, the coal from which is used by the nearby lignite-fired Kangal power station. An attempt was made to elucidate depositional conditions through proximate and ultimate analyses, coal petrography and the geochemical characteristics of the Kangal coals. These coals have a huminite reflectance value of R max = 0.40%. Accordingly, from the standpoint of coal rank, this is a dull brown coal of the “subbituminous C” type. Huminite is the most widespread maceral type, while gelinites are the most often encountered macerals. Relative to liptinites, the proportion of inertinites is high. On the basis of maceral composition, the depositional environment of the Kangal coals was determined to be either a forest swamp or a lake bottom. The distributions of the C 27 and C 28–C 29 steranes for all these coal samples are very similar (C 29 > C 27 > C 28). Tricyclic terpanes have low concentrations in all samples of the Kangal coals, and are dominated by low molecular weight compounds (C 20–C 24) with a maximum at C 23. Total organic carbon (TOC, wt.%) values of the Kalburçayırı samples are 4.64–30.64 wt.%, in the Hamal samples 0.83–2.53 wt.%, and in the Etyemez samples 8.91–10.39 wt.%. On the basis of T max values, the samples are in the immature-early mature stage. According to Rock-Eval pyrolysis data, the coals have hydrocarbon source-rock potential, but the coaly shales and other organic-matter-rich levels have no hydrocarbon source-rock potential. The high inertinite levels and high vitrinite/inertinite ratios suggest that the Kangal coals have more potential for gas generation than oil.