Original paper

Late Pleistocene fault-induced uplift and consequent fluvial response in Eskisehir Fault Zone, NW Anatolia

Ocakoglu, Faruk; Açikalin, Sanem

Abstract

Geomorphological and sedimentological investigations coupled with cosmogenic datings from a Plio-Pleistocene fluvial succession and fluvial landscape atop along the southern Eskişehir Fault Zone allowed understanding the morphotectonic history and the rate of vertical displacement in Eskişehir region. Our observations showed that the north-flowing aggradational rivers at 920 m altitude became degradational ca. 150 ka ago due to tectonically induced base-level drop in the nearby fault zone. While the two parallel-running meandering valleys were still developing at 850 m altitudes, one of the branches of eastern river captured the western river. This event caused the western valley abandoned and the terrace formations in the eastern valley. Near to and within the fault zone, both the abandoned valley floor and the fluvial terrace that dated back to 35-39 ka by 14C and 35Cl cosmogenic methods has been vertically displaced about 40 m since their formation. The calculated uplift rate of ca. 1mm/a for the southern Eskişehir Fault Zone and its presumed onset age were compared with existing data from various sources. It is concluded that this intermediate uplift rate better conforms with the significant seismicity prevailing in the Zone. It is also suggested that the relatively younger age (ca. 150 ka) of the southern Eskişehir Fault Zone may be genetically related with the increased extension rates due to full development of North Anatolian Fault Zone in the Sea of Marmara at about 200 ka.