Folding of the Gediz Graben Fill, SW Turkey: Extensional and/or Contractional Origin?

Abstract

Folds constitute a significant part within the dominantly extension-related deformation pattern of the Gediz Graben and their origin either extensional or contractional has been the subject of debate. Field and subsurface data presented in this paper suggest that folds of contractional and extensional origin coexist in the graben-fill sediments. Contractional folds are predominantly observed within the Alasehir formation. A north vergent, plunging, asymmetrical to overturned geometry characterizes these folds and they are commonly observed in association with south dipping both thrust and reverse faults; the presence of thrust/reverse faults in the Gediz Graben is documented for the first time here. Fault data suggest an approximately N–S direction of compression that has governed the contractional deformation. Yet the limited distribution of these structures prevents to relate them with confidence to a regional deformation phase. Extensional folds occur in association with normal faults either as structures longitudinal or transverse with respect to the general graben trend. Transverse folds are a very common within the buried graben block, owing to the lateral displacement gradients (lateral difference in offset) on the individual fault segments along the southern margin of the graben. Synclines and anticlines have formed at displacement maxima and minima, respectively. Thickness of strata increases at synclines and decreases at anticlines, thus indicating the syn-depositional origin of the folding.