Geomorphology of Central Sakarya Valley between Hamitabat - Gemiciköy (Bilecik)

This study aims to present geomorphologic units with its formation and development of area between Hamitabat-Gemiciköy settlements which are located in Bilecik province. In deciding study area which is drained by Sakarya River that is biggest in river Northwest Anatolia, it was effective forming a small model to explain geomorphological development of central Sakarya Valley. Sakarya River and its branches sinked into basement by partly meandering with ongoing tectonic movements in the study area from Pliocene which is regarded as establishment period of present river system in Anatolia, and created deep epeirogenic (superempose) gorges (Hamitabat, Şeytankaya and Kıralbağı) which link Geçitli and Gemiciköy closed basins in the area. On the other hand, during the Quaternary under control of global sea level changes and ongoing tectonics, depositions aggregated in these closed basins either are transported by wholly erosion or gain a feature of terrace which can be seen as a few levels. The terraces of Gemiciköy basin which is the best area to observe these levels, come over Upper Eocene-Lower Miocene aged Gemiciköy formation with an angular uncomformity. The metric measurings reveal that there are two traceable levels in both sides of valley in the basin. These are high terraces (T1) at +149 m (from valley floor +49 m) altitude and low terraces (T2) at +131 m (from valley floor +11 m) altitude above sea level. Key Words: Central Sakarya Valley, Sakarya Valley, Geomorphology, Epeirogenic Gorge, Terrace.