Pliocene and Quaternary surface uplift of western Turkey revealed by long-term river terrace sequences

• Published in: Current science (Bangalore) 2003-04, Vol.84 (8), p.1090-1101
• Main Authors: Westaway, Rob, Pringle, Malcolm, Yurtmen, Sema, Demir, Tuncer, Bridgland, David, Rowbotham, George, Maddy, Darrel
• Format: Article
• Language: English
• Subjects: Alluvium; Altitude; Basalt; Canyons; Fluvial deposition; Gravel; Mammals; Marl; Sediments; SPECIAL SECTION: LATE CENOZOIC FLUVIAL DEPOSITS; Terraces
• ISSN: 0011-3891

Western Turkey forms the eastern part of the Aegean extensional province. In the 1980s it was accepted that vertical crustal motions in this region are caused solely by this active normal faulting, with footwall localities uplifting and hanging-walls subsiding. The presence of marine sediments, interpreted as Pliocene, at altitudes in excess of 400 m in some hanging-wall localities provided – in the late 1980s – the first clear evidence of Pliocene–Quaternary regional surface uplift. However, it has since been argued that the incision of river gorges in this region has been caused instead by localized uplift in normal-fault footwalls. We review the available geomorphological and sedimentary evidence from the Denizli area, within the drainage catchment of the Büyük Menderes river, in support of ~ 400 m of PlioQuaternary regional surface uplift. We also examine the gorge reach of the Gediz river near Uşak, where a staircase of four high terraces, formed of cemented fluvial gravel at ~ 360, ~ 330, ~ 255, and ~ 225 m above river level, is identified. Farther downstream, a similar terrace, ~ 200 m above this river and so tentatively correlated with the ~ 225 m terrace upstream, was also identified within the Quaternary volcanic Held around Kula. Nearby, a slightly lower (~ 190 m) terrace gravel is capped by basalt, K–Ar dated to ~ 1.2 Ma; below this, other similar terraces form a lower-level staircase. We interpret this evidence as indicating uplift rates of ~ 0.1 mm a-1 or more in the latest Pliocene, when the staircase of cemented high terraces appears to have formed, relative stability for much of the Early Pleistocene, but renewed uplift at rates approaching ~ 0.2 mm a-1 in the Middle and Late Pleistocene. The resulting uplift history resembles what is observed in other regions, and has been modelled as the isostatic response to changing rates of surface processes linked to global environmental change, with no direct relationship to the crustal extension occurring in western Turkey. Our results thus suggest that the present, often deeply-incised, landscape of western Turkey has largely developed from the Middle Pleistocene onwards, for reasons not directly related to the active normal faulting, the local isostatic consequences of which are superimposed onto this 'background' of regional surface uplift.