Quaternary geomorphology of Kahta Stream terraces (Adıyaman)

In this study, geomorphological features of terraces formed by Kahta Stream, one of the important branches of Fırat River are analysed. The Kahta Stream Basin, Southeastern Fault located over the belt of Southeastern Taurus Mountains and Edgefolds displays a problematic topography intersected by the Southeastern Anatolia Overlap and the Adıyaman Fault. The deformation occurring with tectonic movements and climate changes in the Quaternary have accelerated erosion. The material that has undergone a process of severe erosion in the upper basin and carried by the branches of Kahta Stream has accumulated in the lower basin. Terraces are formed by the same stream running through these fills accumulated on the large valley bottom. 6 terrace systems have been determined in Kahta Stream Valley. The number of terraces has been brought down to 5 by incorporating 1-2 m terraces into 3-5 m ones. These terraces range at altitudes of T1 90-120 m; T2 50-70 m; T3 30-40 m; T4 10-20 m and T5 3-5 m from the North of Yarlıca Mount to the Reservoir Lake Atatürk Dam. With the aforementioned terraces considerably affected by young tectonic movements in the east of Kahta, the terraces of T3, T4 and T5 have submerged under the waters of the Atatürk Dam. As a result of the effect of tectonics, the highest terrace in the east of the Cendere George is 150-160 m higher than the valley bottom. Young tectonic movements which are effective in the area have affected and deformed the terrace fills. Pebbles, XRD and SEM-EDX have been analysed over 11 samples from the terraces of Kahta Stream and 7 samples from the terraces of the Stream of Göksu in order to identify the sedimentological features of the terraces of the Stream of Kahta. The samples taken with the purpose of aging terraces have been aged by the method of OSL (Optically Stimulated Luminescence). According to the OSL results, all the terraces 10 m higher than the valley bottom have developed in the last 10.000 years and those in higher areas more than 10.000 years ago. In other words, terraces up to T5 developed in the Pleistocene and the lower ones in the Holocene. The Lower Kahta Stream Basin is an area where, except for terraces, typical braided drainage is seen in Turkey. Furthermore, this basin is quite an interesting area which includes such historical places as Nemrut Mount, Cendere Bridge and Karakuş Hill.