Formation of the Upper Pleistocene terraces of Lake Van (Turkey)

Sediment logical and geomorphological studies of terraces around Lake Van (1647 m) provided a preliminary framework for lake-level variations. The elevations of terraces and past lake level were measured with a differential global positioning system. A chronology is developed using U-234/Th-230 dating of travertines, Ar-39/Ar-40 dating of pyroclastites and C-14 dating of organic matter. Facies and stratigraphic correlations identify four transgressions (C1', C1 '', C2' and C2 ''), each followed by a regression which ended with low lake levels that caused river incision and terrace formation. Evidence of the oldest transgression (C1') is found in the uppermost reaches of valleys up to 1755 m, an altitude higher than the present lake threshold (1736 m). This C1' transgression may be related to pyroclastic flows which dammed an outlet located in the western part of the lake basin and which is dated to before 105 ka. After 100 ka, a second transgression (C1 '') reached 1730/1735 m, possibly related to a younger ignimbrite flow, in association with high water inflow (warm and/or wetter conditions). The two younger transgressions reached 1700-1705 m. The first one (C2') is dated to 26-24.5 cal. ka BP and the second one (C2 '') to 21-20 cal. ka BP. Available data suggest that the long-term lake-level changes responded mainly to climate oscillations. Additional events such as river captures caused by volcanic falls filling valleys, tectonism, erosion and karstic diversion may have impacted these long-term lake-level changes. Copyright (C) 2010 John Wiley & Sons, Ltd.