Palaeoenvironmental and chronological constraints on the Tuglu Formation (Cankiri Basin, Central Anatolia, Turkey)

The Cankiri Basin, located in the northern part of the Central Anatolian Plateau, is a large Tertiary basin where thick Miocene to Quaternary continental sediments overlay the Cretaceous-Tertiary units. This investigation focuses on the Tuglu Formation, an Upper Miocene succession mainly composed of dark grey silty and organic rich clays. The type section of Tuglu has been sampled for an array of multidisciplinary analyses. The palaeontological proxies included ostracod, foraminifer, nannoplankton, pollen, molluscs, charophytes, small mammal assemblages, fish, and crab remains. The abiotic parameters studied were: palaeomagnetism and environmental magnetism, stable carbon and oxygen isotope ratios (on ostracods and bulk sediment samples), strontium isotope ratios (on ostracods and foraminifera), and major elemental composition of the sediments. All analysed proxies point to a continental setting characterised by permanent water bodies affected by strong salinity oscillations. A shallow saline lake developed in a permanent freshwater lake. Barren layers, potentially linked to a short subaerial exposure, mark the end of the saline lake and the transition to a fluvial environment. Geochemical analysis confirms aridity-humidity oscillations as recorded by the micropalaeontological proxies. Analysis of small mammal assemblages refined the chronology of the Tuglu Formation, with the onset of the deposition at the base of the mammal zone MN9 (around 11 Ma) and continuous deposition until the MN11 zone (around 8 Ma). The stable oxygen isotope records from the Tuglu section point to Miocene delta O-18 water values consistent with subdued topography where no prominent mountain belts were yet developed at the northern plateau margin. If correct, this suggests that at least until the end of the deposition of the Tuglu Formation, the Cankiri Basin did not yet experience rain shadow conditions, and the regional surface uplift of the area most likely occurred after 8 Ma.