Organic geochemistry and depositional environments of Eocene coals in northern Anatolia, Turkey

This study is the first attempt which provides information regarding the organic geochemical, biomarker and petrographical characteristics of the Eocene coal deposits found in the Yeniceltek, Eskiceltek, Armutlu (Amasya), Aspiras (Kastamonu) and Salipazari (Bolu) fields in the northern part of Turkey. Proximate analyses including total ash and total sulphur contents and upper heat values of the coal samples from each fields exhibit significant differences. The Armutlu coal samples have the highest ash value (average 42.25%) and represented by relatively low upper calorific value (3868 kcal/kg). In contrary, the Salipazari coal samples have the lowest ash content (average 3.37%) and the highest upper calorific value (7250 kcal/kg). The average total % sulphur contents of all samples are generally high and quite different for each field. Total sulphur contents of Eskiceltek, Yeniceltek and Armutlu samples are similar and vary from 1.01% to 1.86. Samples from Aspiras and Salipazari fields have high total sulphur contents as 6.29% and 13.82%, respectively. Based on the vitrinite reflectance values, all coals are in the diagenetic stage and their coalification degrees are subbituminous A or high volatile bituminous C for the Yeniceltek (0.55% R-o), Eskiceltek (0.50% R-o) and Armutlu (0.50% R-o) coals, and subbituminous C for the Salipazari (0.39% R-o) coals, and lignite for the Aspiras (0.36% R-o) coals. All samples have high Total Organic Carbon (TOC) values, but low bitumen/TOC ratios. The average TOC values of Yeniceltek, Eskiceltek, Armutlu, Aspiras and Salipazari fields are 49.67%, 68.51%, 35.35%, 46.27% and 66.47%, respectively. Extraction analysis applied to one sample from each field yielded very low bitumen/TOC values ranging from 0.01%, to 0.07. The Hydrogen Index values of the Yeniceltek, Eskiceltek and Salipazari samples between 272 mgHC/gTOC and 329 mgHC/gTOC indicate that their organic matter type is Type II kerogen, whereas the other coal samples have Type III and Types II-III kerogen. Gas chromatograms indicate dominant odd-carbon-number n-alkanes, indicating terrestrial organic matter. The parameters obtained from mass spectrometer data on m/z 191 and m/z 217 indicate that the Yeniceltek and Eskiceltek coals were deposited in suboxic lakes or lacustrine swamps; the Armutlu and Aspiras coals were deposited in suboxic brackwater swamps (paralic environment); and the Salipazari coals were deposited in suboxic lakes or lacustrine swamps. An Unresolved Complex Mixture (UCM) observed in the gas chromatograms display immature organic matter and biodegradation. The T-max, mean reflectance and biomarker maturity data show that coal samples are thermally immature. (C) 2013 Elsevier Ltd. All rights reserved.