Discussion on the extensional folding in the Alașehir (Gediz) Graben, western Turkey

Abstract

Erdin Bozkurt writes: Seyitoglu et al. (2000) described their interpretation of the broad folds exposed in the Miocene sediments—exhumed on the southern margin of the Gediz graben (western Turkey)—as products of extensional tectonics. They also concluded that present-day north–south extensional tectonics and consequent east–west graben formation in western Turkey commenced by Early Miocene and continued since then. Previously, Kocyigit et al. (1999a) provided the first ever field evidence for the presence of east–west folds in the Gediz graben and interpreted these structures as suggesting a shortlived north–south compressional deformation during the late Serravalian–late Early Pliocene times. As much of the evidence presented by Seyitoglu et al. (2000) contradicts the available literature on the origin of extensional folding, in particular rollover anticlines; and as other detailed publications on the age and origin of extensional tectonics in western Turkey and that of the east–west folds in the Gediz graben present evidence for a contradictory model(s), I would like this opportunity to describe diffculties that arise over the published evidence and interpretation of Seyitoglu et al. (2000). Tectonic significance of Sart Formation. The map pattern of various lithologies and the relationships between the structures in Figures 2 and 3 of Seyitoglu et al. (2000) are useful to drive a relative chronology of faulting. The Pliocene Sart Formation lies unconformably above the Miocene Kursunlu Formation in the hanging wall of the fault II, indicating synchronous faulting and sedimentation, i.e. the movement along FII commenced by the Pliocene. As the Sart Formation is exhumed in the footwall of fault III and FII antithetic is cut by FIII, FIII faulting must postdate Pliocene. Since the folds in extensional terrains form at the same time or just prior to the faulting, the folds in the Miocene Kursunlu Formation cannot be attributed to …