Cosmogenic data about offset uplifted river terraces and erosion rates: implication regarding the central North Anatolian Fault and the Central Pontides

Abstract

River terraces are geomorphological markers recording deformation. Here, we use four strath and fill river terraces along the Kızılırmak River in Turkey to unravel the deformation along the convex arc formed by the central North Anatolian Fault (NAF), a continental transform fault. 10Be, 26Al, 36Cl cosmogenic exposure ages of T3 and T2 strath terraces constrain their formation at 83 ± 15 ka and 67 ± 7 ka, respectively. We evidence frost-cracking during humid cold periods that bought younger carbonate cobbles on both terraces. T1, a younger fill terrace was probably emplaced during the MIS3 (30–40 ka) aggradational period or during the last glacial–interglacial transition. T0, the most recent fill terrace, was incised shortly before the 1668 earthquake based on 14C dating. It records a cumulated 14 ± 2 m offset linked to the 1943 and 1668 earthquakes. T3 shows a maximum offset of ~ 845 m and constrains a 10 mm/year geological slip rate that is lower than Holocene slip rates. It suggests temporal change in slip rates along the NAF. T2 and T3 also evidenced an uplift of 1 mm/year induced by transpressive deformation accommodated close to the NAF. Compared to the 0.28 mm/year obtained to the north, a larger portion of the shortening in the Central Pontides is accommodated close to the driving plate boundary. We also evidenced high cosmogenic-based erosion rates in Pontides during the Holocene, and even higher rates during T3 planation. Erosion rates were combined with present-day relief to infer a first-order minimal shortening of 12–16 km using simple mass balance principles in the Central Pontides. This long-term shortening is larger than the one induced by the Anatolian rotation suggesting a far field effect of the collision.