The Pliocene initiation and Early Pleistocene volcanic disruption of the palaeo-Gediz fluvial system,Western Turkey |
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| Institution: | 1. ITC Faculty, Twente University, P.O. Box 6, 7500 AA Enschede, the Netherlands;2. Department of Geography, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK;3. Soil Geography Group, Wageningen University, P.O. Box 47, 6700 AA Wageningen, the Netherlands;4. Department of Geography, University of Newcastle, Newcastle upon Tyne, NE1 7RU, UK;5. Department of Geography, Harran University, 63300 Sanliurfa, Turkey;1. National and Kapodistrian University of Athens (NKUA), Division of Physics, Department of Environmental Physics and Meteorology, Build. Phys. V, University Campus, Zografou, 157 84 Athens, Greece;2. Bergische Universität Wuppertal (BUW), Faculty of Natural Sciences and Mathematics, Department of Chemistry, Laboratory for Physical Chemistry, 42097 Wuppertal, Germany;3. Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany;1. Westfählische-Wilhelms-Universität Münster, Institut für Mineralogie, Correnstr. 24, 48149 Münster, Germany;2. Johannes Gutenberg-Universität Mainz, Institut für Geowissenschaften, Becherweg 21, 55099 Mainz, Germany;3. University of Belgrade, Faculty of Mining and Geology, Djušina 7, 11000 Belgrade, Serbia;4. Dokuz Eylül Üniversitesi, Mühendislik Fakültesi, Jeoloji Mühendisliği Bölümü, TR-35160 Buca, Izmir, Turkey |
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| Abstract: | In this paper, we report our latest observations concerning a Pliocene and Early Pleistocene record from Western Turkey. The sedimentary sequence described comprises the fluvial deposits of an Early Pleistocene palaeo-Gediz river system and its tributaries prior to the onset of volcanism around Kula and the subsequent lacustrine, volcaniclastic and fluvial deposits associated with the first phase of volcanism (∼1.2 Ma) in this area.Early development of an east–west drainage system in this area resulted from tectonic adjustments to north–south extension and the formation of east–west-oriented grabens. Headward erosion of drainage entering the main Alaşehir graben led to the progressive capture of pre-existing drainage systems as eastward (headward) erosion upstream tapped drainage networks previously formed in internally draining NNE–SSW-oriented basins. Within one of these, the Selendi Basin, part of this evolutionary sequence is preserved as a buried river terrace sequence. Eleven terraces are preserved beneath alluvial fan sediments that are, in turn, capped by basaltic lava flows. Using the available geochronology these terraces are considered to represent sedimentation–incision cycles which span the period ∼1.67–1.2 Ma. Although progressive valley incision is a fluvial system response to regional uplift, the frequency of terrace formation within this time period suggests that the terrace formation resulted from sediment/water supply changes, a consequence of obliquity-driven climate changes. The production of sub-parallel terraces suggests that during this period the river was able to attain a quasi-equilibrium longitudinal profile adjusted to the regional uplift rate. Thus, the incision rate of 0.16 mm a−1 during this period is believed to closely mirror the regional uplift rate.After the onset of volcanism at ∼1.2 Ma, there is a destruction of the dynamic link between fluvial system behaviour and climate change. The repeated damming of the trunk river and its tributaries led to the construction of complex stratigraphic relationships. During the first phase of volcanism the palaeo-Gediz river was dammed on numerous occasions leading to the formation of a series of lakes upstream of the dams in the palaeo-Gediz valley. Variations in lake level forced localised base-level changes that resulted in complex fluvial system response and considerable periods of disequilibrium in profile adjustment. Furthermore, response to these base-level changes most likely disrupted the timing of the incisional adjustment to the on-going regional uplift, thus making the use of this part of the archive for inferring regional uplift rates untenable. |
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