Paleoclimate and paleodepositional condition of Ekizköy (Muğla-Milas) Middle Miocene coals: Implications from biomarker data

Abstract

In this study, saturated, aromatic biomarker distributions and organic geochemical characteristics and depositional environments of Middle Miocene aged coals in Ekizköy (Muğla-Milas) region were investigated. The average TOC, HI and OI values are 46.24 %, 153 mg HC/gTOC and 77 mg CO/gTOC, respectively. Pr/Ph ratio is 0.9 and Pr/C and Ph/C are 0.2 and 0.3. Considering the paleoclimate data (TOC, CPI, ACL, P, P, Q, Q and Q), it is likely that the climate was moderately humid and hot for the period represented by sample M-4 and relatively more humid and temperate for the period represented by sample M-8. High C(C + C) MA steroid ratio indicates that Ekizköy coals are composed of terrestrial OM (Organic Matter). 20S/(20R + 20S) (for C), 22S/(22R + 22S) homohopane (for C), ββ/(αα + ββ) sterane, moretane/hopane ratios that show the maturity of OM are indicative of immature OM. CTA/(CMA + CTA) steroid and MA(I)/MA(I + II), TA(I)/TA(I + II), MDR, MPI, MPR ratios obtained from aromatic biomarkers are low and show an immature character. Since coals contain Type III kerogen and immature organic matter, they can only generate gas under appropriate temperature and pressure. Saturated and aromatic biomarker data in Ekizköy coals show that they precipitate in a lacustrine environment dominated by suboxic conditions.