Depositional Environment and Organic Facies of Coal-Bituminous Marl Association in Seyitomer (Kutahya) Region

In Neogene basins in the Aegean region of Turkey, the association of coal seams with bituminous shales and/or bituminous marls is common. The association of humic coals consisting of terrestrial organic matter with bituminous shaleshnarls rich in sapropelic organic material is rather unusual. In order to investigate the causes of this unusual association, a lithological section in Seyitomer-Kutahya region was studied for its different properties. Lithological, petrographic, mineralogical and geochemical composition of sediments, chemistry and redox potential ofwater-column, amount, type and maturity of organic material in sediments, depositional environment and organic facies were investigated. The evaluation and interpretation of the analytical data resulted in differentiation of two intervals along the coal-bituminous marl transition. The four-meter-thick interval at the base of the section represents a period when fine clastics rich in terrestrial organic matter and even humic coals were deposited in a low energy fresh water environment with high redox potential. The following section is represented by carbonate-rich fine clastics, which were deposited as a result of enhanced chemical sedimentation in brackish to saline water. These units are rich in sapropelic organic material, indicating that reducing conditions still continued. Sedimentological and organofacies properties of the coal-bituminous marl transition indicate a lacustrine environment with fluctuating water level in general. At the beginning the depositional environment was a balanced-fill fresh water lake, where coal and fine clastics were deposited under temperate and humid conditions suitable for flourishing flora. The lake was then converted from time to time into a lake with brackish water due to climate changing towards drier conditions. Thus, material transport into the lake was reduced and chemical deposition was dominant. This paleoclimatic change at the end of the mid-Miocene was the main cause of the transition from humic coals to bituminous marls in the Seyitomer region.