The Quaternary fluvial-lacustrine system in the Akarçay Basin (SW Anatolia): depositional environments and paleoclimatic interpretation

The Akarçay Closed Basin, located in southwest Anatolia, contains deformed formations and the drying Akşehir and Eber lakes. This study aimed to interpret the paleoenvironmental and paleoclimatic conditions of the Akşehir and Eber lakes, which are reported to have been connected during the Pleistocene. Based on sedimentological and mineralogical data, three different depositional subenvironments were defined, corresponding to the formation and development stages of the lake. Sedimentary facies analysis of the Pleistocene deposits in the basin revealed the following facies associations, listed from bottom to top: 1) an alluvial fan and fluvial facies association, representing the formation stage of the lake, which developed due to tectonic activity and a humid/wet climate; 2) a lakeshore facies association, corresponding to the expansion stage when the lake spread shallowly, and 3) a lake center facies association, corresponding to the closing stage when the lake began to dry, characterized by limited levels of clastic deposition under very shallow lake conditions. In the lakeshore and lake center facies association, Valvata piscinalis, Dreissena iconica and D. polymorpha species living in shallow waters and streams, as well as Laevicaspia caspia species living in mesohaline environments were identified. X-ray diffraction analysis was performed on the levels that best represented the facies associations in the basin, revealing that the dominant clay minerals in the sequence were illite and kaolinite. Combined evaluation of the sedimentological, mineralogical, and paleontological data suggests that the abundance of Valvata piscinalis and Dreissena iconica—both stream-dwelling species—at levels with increased kaolinite content indicates rainy and humid climatic periods when stream-fed conditions prevailed in the basin. Conversely, the dominance of Laevicaspia caspia and the intervals marked by illite deposition indicate cold and arid climatic periods.