Browsing by Author "Guillou, Herve"

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Formation of the Upper Pleistocene Terraces of Lake Van (Turkey)
(Wiley, 2010) Kuzucuoglu, Catherine; Christol, Aurelien; Mouralis, Damase; Dogu, Ali-Fuat; Akkoprou, Ebru; Fort, Monique; Guillou, Herve
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.
The Pyroclastites Around Southwestern Part of Van Lake (Eatern Anatolia, Turquey): Implications on The Regional Palaeohydrography
(Soc Geologique France, 2010) Mouralis, Damase; Kuzucuoglu, Catherine; Akkopru, Ebbru; Dogu, Ali Fuat; Scaillet, Stephane; Christol, Aurelien; Guillou, Herve
THE PYROCLASTITES AROUND SOUTHWESTERN PART OF VAN LAKE (EATERN ANATOLIA, TURQUEY): IMPLICATIONS ON THE REGIONAL PALAEOHYDROGRAPHY Located in eastern Anatolia (Turkey), Lake Van is the fourth largest lake in the world. Along the banks of the lake, several lake terraces record Pleistocene variations of the lake levels. In the terraces, the lake deposits are often interbedded with pyroclastites emitted by the volcanoes located on the northern side of the lake. Our research focuses on the south-western part of the lake, where several pyroclastites interbedded with lake deposits allow establishing a regional tephrostratigraphy, which is being Ar/Ar dated. In this area, the study of the pyroclastites allows to understand the impact of volcanism on the palaeohydrography: all the valleys where filled-in with pyroclastites which induced heavy disruptions of the drainage network. Moreover, our research enlightens evidences that volcanic activity was responsible for the enclosure of the lake and that the major transgression of the lake, dated ca. 100 ka, is not only linked to changes in the water balance, but at first linked to volcanic activity.