Türkiye Jeoloji Bülteni

Investigating the Fluvial Response to Late Pleistocene Climate Changes and Vertical Deformation: Yeşilırmak Terrace Staircases (central north Anatolia)

Abstract: River terraces are remnants of former river floodplains that are fossilized above present-day river channels,often in staircase systems. The formation of terrace staircases is attributed to both tectonic, climate and sea/base levelchanges. Variations in tectonic and climatic conditions cause perturbations in the fluvial system, which, over time,lead to widening of valley floors, aggradation and incision, thereby producing terraces representing the complexresponse of the fluvial system to the chances in variables listed above.This study reports on the formation of terrace staircases at Yeşilırmak River system of central northwest Anatolia,near Geldingen Plain (Amasya). The depositional steps reaching +70 m (above today’s recent floodplain), havebeen mapped and dated by using luminescence method which reveals that terrace formation started at early latePleistocene and continued within Last Glacial Period. The terrace steps, namely T3 (+70 m), T2 (+35 m) and T1(+15) were deposited during MIS5a, MIS3 and end of LGM. The correlation with the adjacent climate archivesreveals that the terraces are formed primarily in response to climatically induced fluctuations in river discharge andsediment supply. Relative positions of the terrace risers and abandonment ages, enables us to calculate a long-termvertical uplift rate of 0.94±0.26 mm/year at the study area, located to the south of the North Anatolian Fault Zone.