Organic Geochemistry and Depositional Environment of the Oltu Gemstone (Coal) in the Erzurum Area, NE Anatolia, Turkey

The Oltu Gemstone is located in the north of Oltu town (Erzurum-NE Turkey) city as a low rank coal. The Oltu Gemstone occurs as lenticular forms with thickness not exceeding centimeter size and lateral continuity of a few meters within the Liassic Lower Mahn Olurdere Formation consisting chiefly of claystone, sandstone, and volcanics. Coals that are operated as Oltu Gemstone are represented by very high TOC (67.39-78.56% wt), high hydrogen index (HI) values (314-379 mg HC/g TOC) and very low oxygen index (01) values (1-3 mg CO2/g TOC). Low Pr/Ph ratios indicate that coals were prevented from oxidation and deposited under anoxic conditions. In Oltu Gemstone samples, C-29 dominates over C-27 and C-28 steranes. In general, high (C-19 + C-20)/C-23 tricyclic terpane, low Ts/(Ts + Tm), diasterane/sterane, and C31R/C-30 hopane ratios were recorded. C-29 MA steroids dominate with respect to others, and the C-29/(C-28 + C-29) MA ratio is mostly high. DBT/P ratio of Oltu Gemstone samples has low values. T-max values of Oltu Gemstone samples (between 416 and 436 degrees C) reflect immature-early mature character. 22S/(22R+ 22S) homohopane, 20S/(20R + 20S), and beta beta/(alpha + beta beta) sterane ratios and low moretane/hopane ratios, relatively high C-28-TA/(C-29-MA + C-28-TA), MA(I)/MA(I + II), TA(I)/TA(I + II), MPI-3 (beta/alpha MP), and MDR ratios indicate early mature character for the Oltu Gemstone samples.