The obliquity-controlled early Pleistocene terrace sequence of the Gediz River, western Turkey: a revised correlation and chronology

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.

The Gediz River fluvial archive: A benchmark for Quaternary research in Western Anatolia

“…The new higher gradients (~0.004 -0.005) were consistent with the modern river gradient and as a result, a revised correlation model for the outcrops was proposed ( Figure 6, after Maddy et al, 2012a). The recognition that the deposits of the palaeo-Gediz river could, on the basis of their lithological composition and sedimentary properties, be readily mapped Page 11 of 61 and distinguished from all other stratigraphical units led Maddy et al (2012a) to propose that these distinctive sediments should be formally recognised as the Gediz Valley Formation.…”

“…This conclusion is further supported by the stratigraphy of key GT6 exposures beneath both the Burgaz and Sarnıç plateaux. Beneath the Sarnıç plateau, the sedimentology of GT6 deposits near Çakırca (Figure 3; see also figure 9A in Maddy et al, 2012a) strongly suggests deposition in standing water, a conclusion supported by the presence of thick lacustrine sediments that include substantive amounts of tephra in adjacent exposures. Similarly, beneath the Burgaz plateau, GT6 sediments are overlain by lacustrine sediments that onlap the older terraces (up to GT9), suggesting the formation of a large standing water body.…”

“…Table 1 shows the Cenozoic Page 5 of 61 stratigraphy based upon Ersoy et al (2010), with the addition of the Gediz Valley Formation (see Maddy et al, 2012a).…”

“…The recognition that the deposits of the palaeo-Gediz river could, on the basis of their lithological composition and sedimentary properties, be readily mapped Page 11 of 61 and distinguished from all other stratigraphical units led Maddy et al (2012a) to propose that these distinctive sediments should be formally recognised as the Gediz Valley Formation. The numbering of individual terraces remains only an interim measure, each of these stratigraphical units will be replaced with appropriate Member names once work on the complete Gediz Valley Formation i.e.…”

“…The onset of local volcanism is signalled by a change in lithological content with the influx of substantive quantities of basalt into the river bedload post GT6 (Maddy et al, 2012a). This conclusion is further supported by the stratigraphy of key GT6 exposures beneath both the Burgaz and Sarnıç plateaux.…”