Tuncer Demir

Constraints on the timing and regional conditions at the start of the present phase of crustal extension in western Turkey, from observations in and around the Denizli region

The chronology of extension of the continental crust in western Turkey has been the subject of major controversies. We suggest that these difficulties have arisen in part because of past misuse of dating evidence; and in part because the assumption often made, that deposition of major terrestrial sedimentary sequences implies crustal extension to create the necessary accommodation space, is incorrect. We report evidence that the present phase of extension began in the Denizli region at ~ 7 Ma, around the start of the Messinian stage of the Late Miocene. This timing matches the estimated start of right-lateral slip on the North Anatolian Fault Zone, and corresponds to a substantial increase in the dimensions of the Aegean extensional province to roughly its present size: beforehand, between ~ 12 Ma and ~ 7 Ma, extension seems to have only occurred in the central part of this modern province. In some localities, terrestrial sedimentation that began before this start of extension continued into this extensional phase, both within and outside normal fault zones. However, in other localities within the hanging-walls of normal faults, the start of extension marked the end of sedimentation. Relationships between sedimentation and crustal extension in this region are thus not straightforward, and a simple correlation should therefore not be assumed in structural interpretations. During the time-scale of this phase of extension, the Denizli region has also experienced major vertical crustal motions that are unrelated to this extension. The northern part of this region, in the relatively arid interior of western Turkey, has uplifted by ~ 400 m since the Middle Pliocene, whereas its southern part, closer to the Mediterranean Sea and with a much wetter climate, has uplifted by ~ 1,200 m since the Early Miocene, by up to ~ 900 m since the Middle Pliocene, and by an estimated ~ 300 m since the Early Pleistocene. This regional uplift, superimposed on the local effects of active normal faulting, is interpreted as a consequence of lateral variations in rates of erosion. A reliable chronology for this phase of extension in western Turkey, in relation to changes in the geometry of motions of adjoining plates and Late Cenozoic environmental change, is now in place.

River terrace sequences in Turkey: sources of evidence for lateral variations in regional uplift

This paper reviews river terrace staircases in Turkey and examines their relation to regional uplift. Turkish fluvial records are shown to be similar to their counterparts in Europe, with aggradation concentrated in cold climatic stages, despite differences in present-day climate between these two regions. Furthermore, as in Europe, these Turkish river terrace sequences provide evidence for increases in regional uplift rates in the Late Pliocene and Middle Pleistocene. In both regions, this effect is unrelated to senses and rates of plate motion, being instead the result of crustal thickening caused by lower-crustal flow induced by surface processes. From the fluvial evidence, estimated amounts of regional uplift since the Miocene are typically c . 400 m in western Turkey and in the area of the border with Syria. However, they increase northward and eastward to c . 1 km or more in northeastern Turkey on this time-scale, reflecting the regional variations in mean altitude of the land surface. Estimated typical uplift rates during the Middle and Late Pleistocene have been c . 0.1 mm a −1 in the Arabian Platform and c . 0.2–0.3 mm a −1 in western and northern Turkey. These variations are interpreted as the isostatic response to lateral variations in erosion rates.

Kinematics of active left-lateral faulting in SE Turkey from offset Pleistocene river gorges: improved constraint on the rate and history of relative motion between the Turkish and Arabian plates

In the Arabian Platform of SE Turkey abundant evidence exists of fluvial incision by c. 110 ± 10 m since the late Early Pleistocene, starting in or around marine oxygen isotope stage 22 at 870 ka. This incision, which has accompanied regional surface uplift as the isostatic response to regional erosion, has progressively ‘locked’ rivers into their gorges in landscape that formerly had much lower relief. We use this effect to estimate 4.44 ± 0.06 km of left-lateral slip on this time scale on the Gölbaşı–Türkoğlu Fault, a segment of the East Anatolian Fault Zone, from offset river gorges, giving a slip rate of 5.10 ± 0.07 mm a−1. Piercing points indicate that this fault has slipped a total of 19 km, making its age 3.73 ± 0.05 Ma. A total of 33 km of relative motion between the Turkish and Arabian plates is documented on this time scale in the vicinity of Gölbaşı, at an overall time-averaged rate of 8.85 ± 0.12 mm a−1, the estimated Euler vector for relative motion between these plates being 0.89 ± 0.01° Ma−1 about 33.4°N, 42.3°E. This method can be readily applied to determine slip rates, time-averaged since the late Early Pleistocene, on other strike-slip fault zones worldwide.

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

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.