Sediments of the Konya basin, central Anatolia, Turkey

Abstract

The present environmental conditions are not responsible for the major geomorphologic features of the Konya basin, located on the semi-arid Central Anatolian Plateau in Turkey. Such characteristics features as abandoned shore lines, wave-cut cliffs, sand spits and massive deltas provide evidence for lake conditions during the recent geologic past. Depositional processes of present-day environmental forces are chiefly constricted to the sides of the basin, where several alluvial fans are formed, burying sedimentary deposits of previous lake environments. In the basin, different types of sediment are present, clastics, as well as nonclastics. The latter consists of fresh-water limestone, chiefly Neogene in age. Among the clastics, fine-grained lake-deposited sediments (marl and calcareous clay) have the greatest distribution. Sand-size sediments and gravels are restricted to the mouths of indraining streams and of mountain canyons. In general, from the mouths of the rivers towards the center of the basin the sediments show a progressive change to finer sediments. Study of the heavy minerals shows that the sediments in the basin are derived largely from the nearby Taurus mountains, where such volcanic rocks as andesite and tuff cover large stretches. The prevalent clay minerals in the basin sediments are muscovite and illite, with minor admixtures of kaolinite. Study of the molluscan fauna encountered in the lake sediments, as well as in the sand spits shows that the water of the lake was fresh, notwithstanding the lake had no surface outlet. Since “cold” species are lacking and most of the elements are still living in the present-day lakes of Turkey, there are no indications for a cold climate during the lake stage. Archaeologic evidence shows that the basin was largely dry and inhabited already some 8,500 years ago. Unless some other factor was involved, we may infer that at the end of the Würm glacial minor climatic changes disturbed the delicate balance between incoming and outgoing water, resulting in a complete drying up of the lake.