Geomorphological evolution of Harmankaya canyon (Bilecik)

Abstract

The Değirmendere basin is located in the Sakarya River basin in the eastern part of Bilecik and corresponds to the 494 km2 area drained by Değirmendere, also known as Harmanköy Stream. Değirmendere roughly flows in the northeast southwest direction and reaches the Sakarya River by splitting of the Akköy Plateau, which is a threshold for 1100–1200 m of elevations such as Gök Tepe, Harmankaya Tepe and Sivri Tepe. Harmankaya (Kayaboğazı) Canyon is the subject of many geological-geomorphological studies owing to its formation and development because of the said splitting. Different views have emerged on the geomorphological evolution and formation mechanism of the canyon, and several issues remain regarding its mechanism owing to many geomorphological issues that are yet to be comprehensively examined. Therefore, understanding the regional fluvial processes and providing satisfactory geomorphological information for canyon visitors are imperative. The canyon was protected under the “Harmankaya Canyon Natural Park” initiative in 2012, and the number of visitors to the canyon has been increasing daily. As the main element of the drainage network developed in the basin, Değirmendere is currently located in the upper ground in a manner that suits construction lines and layer dives. However, monoclinal shift remains missing due to the slopes of the canyon. Furthermore, a clear vertical cleavage independent of the layer dips indicates the effect of epigenesis. Moreover, the effects of active tectonism in the field were concluded by analysis of the valley base–valley height ratio to the valleys in the canyon. Because of such findings, the occurrence of Upper Eocene–Lower Miocene lake sediments at a height of 850 m around Selim village in the northeast of the canyon indicates the occurrence of ponding after epigenesis and before antesedance.