No abstract

The buried Early Pleistocene river terrace record of the Gediz River, around Kula, western Turkey has previously been considered to span the time interval equivalent to Marine Isotope Stages (MIS) 58–37 ( c . 1.6–1.2 Ma), with the frequency of terrace formation mirroring obliquity-driven climate change. Whereas progressive Pleistocene incision of the Gediz River is seen as a response to regional uplift, the timing of fluvial incision, leading to terrace formation and subsequent new floodplain development, is believed to be climate-controlled with incision–deposition cycles resulting from varying sediment–discharge conditions, a direct consequence of changing climate and related vegetation change. New outcrop observations downstream of the original field area, alongside recently published geochronological data and improved understanding of the volcanic sequence, all now suggest that the previously published interpretation is incorrect. Here we present a revised stratigraphy based upon terrace gradients of c . 0.004–0.005 (previously 0.001), in which 11 terraces are identified but only terraces GT11 (the oldest) to GT6 (pre-lava incursion) predate volcanism. The available geochronology suggests that terraces GT6 (post-first lava incursion) to GT1 relate to the time interval MIS38–28 ( c . 1.26–1 Ma). However, despite penecontemporaneous volcanism terrace formation continues to reflect sediment–discharge changes predominantly controlled by regional climate change.

No abstract

No abstract

Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACTThe Gediz River, one of the principal rivers of Western Anatolia, has an extensive Pleistocene fluvial archive that potentially offers a unique window into fluvial system behaviour on the western margins of Asia during the Quaternary. In this paper we review our work on the Quaternary Gediz River Project (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) and present new data which leads to a revised stratigraphical model for the Early Pleistocene development of this fluvial system.In previous work we confirmed the preservation of eleven buried Early Pleistocene fluvial terraces of the Gediz River (designated GT11, the oldest and highest, to GT1, the youngest and lowest) which lie beneath the basalt-covered plateaux of the Kula Volcanic Province. Deciphering the information locked in this fluvial archive requires the construction of a robust geochronology. Fortunately, the Gediz archive provides ample opportunity for ageconstraint based upon age estimates derived from basaltic lava flows that repeatedly entered the palaeo-Gediz valley floors. In this paper we present, for the first time, our complete dataset of 40 Ar/ 39 Ar age estimates and associated palaeomagnetic measurements. These data, which can be directly related to the underlying fluvial deposits, provide age constraints critical to our understanding of this sequence.The new chronology establishes the onset of Quaternary volcanism at ~1320ka (MIS42). This volcanism, which is associated with GT6, confirms a pre-MIS42 age for terraces GT11-GT7. Evidence from the colluvial sequences directly overlying these early terraces suggests that they formed in response to hydrological and sediment budget changes forced by climatedriven vegetation change. The cyclic formation of terraces and their timing suggests they represent the obliquity-driven climate changes of the Early Pleistocene. By way of contrast the GT5-GT1 terrace sequence, constrained by a lava flow with an age estimate of ~1247ka, span the time-interval MIS42 -MIS38 and therefore do not match the frequency of climate change as previously suggested. The onset of volcanism breaks the simple linkage of terracing to climate-driven change. These younger terraces more likely reflect a localized terracing process triggered by base level changes forced by volcanic eruption and associated reactivation of pre-existing faults, lava dam construction, landsliding and subsequent lavadammed lake drainage.Establishing a firm stratigraphy a...