Geochemical characteristics and paleodepositional setting of coal-bearing strata in Konya-Karapınar Basin, Central Anatolia, Turkey

Abstract

The Neogene coals of the Hotamış Formation in the Konya-Karapınar basin were examined, and the organic matter type, thermal maturity, paleodepositional environment, and Rock-Eval pyrolysis characteristic of coal samples obtained from boreholes. The total organic carbon (TOC) values of coal vary between 15.2 wt% and 47.0 wt% and the yield of extractable organic matter (EOM) values varies between 0.5% and 1.0% indicating a limited hydrocarbon production potential. Bitumen index (BI) and Quality index (QI) values were calculated for coal samples and vary from 1 to 13 mg HC/g TOC and from 75 to 260 mg HC/g TOC, respectively. Due to BI and QI values, coal samples have limited gas generation potential. The type of organic matter was determined as Type III kerogen according to Rock-Eval data. The coal samples have Tmax values between 414 and 443 °C, and huminite reflectance values with 0.20%–0.41% Ro indicating that they are in the immature-early mature stage. This is supported by biomarker maturity parameters 20S/(20S + 20R) (C29) sterane (0–0.59), ββ/(αα + ββ) (C29) sterane (0–0.58), MPI-1 (0.18, 0.31) and MPI-1* (0.21, 0.37). The relative abundance of C27–C28–C29 normal steranes and aromatic steroids and the abundance of partially low carbon number tricyclic terpanes of the Konya-Karapınar coals showed that the organic matter consisted of terrestrial higher plants with a small contribution of algae and microorganisms. Homohopane distributions, V/(V + Ni), V/Sc ratios show that organic matter accumulated in an environment that varies between oxic-anoxic conditions and that medium-high gammacerane index, C27–C28–C29 sterane distributions, and low DBT/P ratios are compatible with the weak brackish water-fresh water depositional environment of organic matter.