A fault controlled, newly discovered Eskişehir Alpu coal basin in Turkey, its petrographical properties and depositional environment

In the studied area, there are two coal horizons in the Middle Miocene aged m2 unit. The average mineable coal seam thickness is approximately 13-14 m. In order to determine the coalification degree, petrographic composition and depositional environment of the coals, petrographic and XRD analyses were conducted on coal samples taken from three boreholes which were drilled by MTA in the Eskişehir-Alpu Basin. According to the ASTM classification, the rank of the coals is sub-bituminous. Alpu coals contain two prominent types of maceral assemblages: either containing high amounts of funginites, macrinites, ulminite and gelinites, or high amounts of liptinites associated with detrital huminites (attrinite and densinites). The first type exhibits rather more homogeneous features, but the second has a more complex, mixed appearance with detrital macerals, intensive lineation, laminations and considerably higher pyrite contents. The Alpu coals contain montmorillonite, heulandite, α-quartz, pyrite, gypsum, kaolinite, illite, illite-montmorillonite, orthoclase and clay minerals which indicate variation in the pH conditions. The tissue preservation index (TPI) and gelification index (GI) indicate a limnic environment. The sample points are located between open marsh and clastic marsh areas on the TPI-GI diagram. This case indicates that the water table was variable during the coal formation.