Investigation of organic and elemental geochemical properties of the Hançili bituminous shales (Dodurga/Çorum)

To determine the various paleoenvironmental conditions under which the Early-Middle Miocene Hançili shale was deposited, the petroleum potential of the shale, and the mineralogical composition of the bituminous shale samples, a total of 70 samples were studied using a variety of methods. XRD data verified that the samples include rich clay minerals, K-feldspar, and carbonate, as indicated by Pearson's correlation coefficients of chosen elements. Overall, the abundances of major, trace, and rare earth elements indicate that the investigated oil shale in the Çankırı-Çorum Basin is primarily composed of intermediate rocks, with minor amounts of basic rocks, and that their source rocks were primarily deposited in the continental collision setting. In general, the paleoclimate index (C-value) and Rb/Sr and Sr/Cu ratios indicate semi-arid to humid climates. Pyrolysis results as well as microscopic and isotopic investigations suggest that rocks are rich in organic carbon and that the organic matter in the samples is primarily oil-prone and of algal origin. In addition, the isotopic and biomarker data confirm that the materials under study were deposited in a lacustrine environment. Ni, V, Cu, and Mo are marginally enriched compared to the typical shale, whereas Zn, Pb, and U are depleted. These redox-sensitive trace elements imply an environment where an oxic-dysoxic water column was prevailing. The absence of a link between TOC content and redox indicators shows that the formation of organic-rich shales was controlled by a rapid sedimentation rate and periodic eutrophication.