The Oligocene Maikop series of Lahich (eastern Azerbaijan): Paleoenvironment and oil-source rock correlation

Maceral composition, as well as biomarker and stable isotope (C, N) data indicate a major contribution of aquatic organisms and variable inputs from macrophytes and land plants to organic matter deposition during the Oligocene. Microbial communities most probably included heterotrophic bacteria and cyanobacteria, as well as green sulfur bacteria. Higher inputs of terrigenous organic matter occurred during deposition of the lower part of the succession. Increased remineralisation of organic matter in the water column is suggested to result in low TOC and hydrocarbon contents, as well as 15N enriched total nitrogen of the Eocene to earliest Oligocene sediments. Organic carbon accumulation during the Oligocene occurred in a stratified, episodically euxinic environment. This is indicated by low TOC/S ratios and higher contents of aryl isoprenoids in several samples from the upper units. A moderate to good oil-source rock correlation with oils from the Kura Depression is indicated by sterane and triterpane fingerprints as well as carbon isotopic composition of hydrocarbon fractions.