Geochemical characteristic of the Lutetian black shale (Bayburt, NE-Turkey): amount, nature, origin of organic matter and palaeo-environment conditions

Abstract

To define the amount, thermal maturity and type of organic matter (OM), a comprehensive analysis of major and trace elements, organic carbon isotope and organic geochemistry was conducted on Lutetian black shales found in the Everek (Bayburt) region of northeastern Turkey. Total organic carbon (TOC) levels in the shale samples range from 0.62% to 6.75%, and type II–III to type III kerogen is generated, displaying a combination of high terrigenous and low marine OM. The δ13C values (ranging from –28.22 to –28.23), aromatic hydrocarbon compounds (methyl phenanthrene, dibenzothiophene, tri-aromatic and monoaromatic steroids), saturated hydrocarbon compounds (sterane and terpane), acyclic isoprenoids, n-alkane distribution (n-C13–n-C36) and inorganic geochemical characterization support that the black shales were deposited in a terrestrial-marine transition environment and had a high proportion of terrestrial OM with small amounts of marine OM preserved in relatively arid to hot climate and oxic to suboxic conditions. The analysis of biomarker thermal maturity markers, Tmax (ranging from 449–458oC) and estimated vitrinite reflectance (varying from 0.92 to 1.08%) values suggest that the black shales have reached the oil window. As a result, black shales are thought to contain low to high amounts of TOC, have a mixed kerogen type, reach a high thermal maturity level and produce little hydrocarbons. © The Author(s), 2024.