Lutetian–Bartonian (Middle Eocene) micropalaeontology, biostratigraphy and palaeoecology of the Mengen Coal Basin, Northwest Türkiye (Turkey)

This study focuses on the upper Lutetian–lower Bartonian Tokmaklar Formation in the Mengen Basin of Northwest Türkiye (Turkey), examining various aspects such as biostratigraphy, palaeoecology, and isotope data (δ¹⁸O and δ¹³C), providing insights into the geological history and environmental conditions during this interval. Moreover, the study incorporates coal petrography on four samples to explore a potential correlation between the coalification process and the preservation of palynomorphs. The formation is informally divided into two distinct categories: a coal-bearing sequence positioned at the base of the formation and a coal-free sequence above it. However due to dense vegetation and soil cover in the area, the availability of suitable outcrops for measured sections and obtaining samples is severely limited. Therefore, we relied on drilling data from Turkish Coal Enterprises (TCE) for the purpose of coal exploration, as well as two partial sections (Ender and Çorak) from underground mining. Microapalaeontological evidences involving benthic foraminiferans, ostracods, and palynomorphs, along with isotope data (δ¹⁸O and δ¹³C), suggest that the Tokmaklar Formation was deposited as a result of a local transgressive process during the late Lutetian–early Bartonian. Furthermore, palynological data, particularly the existence of mangroves such as Nypa, lepidocaryoid palm and Acrostichum aureum, coupled with quantitative palaeoclimate analysis, the negative δ¹⁸O values, and the lower δ¹³C values indicate a warm, probably tropical climate under high rainfall.