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 Alaşehir 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.

The Gediz Supradetachment System (SW Turkey): Magmatism, Tectonics, and Sedimentation During Crustal Extension

“…The obliquity of the strike of the detachment with respect to the rift is only localized close to the Dereköy valley; to the east of this valley the detachment likely recovers its orientation parallel to the rift, similarly to what proposed by Brun and van den Driessche (1994) for gneiss domes (see their Figure 3). This is also consistent with images of the subsurface reconstructed by seismic reflection profiles which show the NE dipping Gediz Detachment at depth in the Alasehir area (see Çiftçi & Bozkurt, 2008;Demircioğlu et al, 2010;Yılmaz & Gelişli, 2003;Çiftçi & Bozkurt, 2010).…”

“…High-angle normal faults in the hanging wall, cutting the Neogene-to-Quaternary basin fill, root into the detachment surface. This observation is consistent with seismic reflection profiles showing high-angle normal faults rooting on the Gediz Detachment at depth in the Alaşehir area (Çiftçi & Bozkurt, 2008(Çiftçi & Bozkurt, , 2010Demircioğlu et al, 2010;Yılmaz & Gelişli, 2003). Major synclines and anticlines in the hanging wall, with axes near parallel to the strike of the detachment, may reflect the ramp-flat geometry of the detachment surface at depth (e.g., Gibbs, 1984; Figure 8 A-A', B-B′, and C-C′ cross sections).…”

“…The contractional structures (folds and reverse faults) observed in the Alaşehir Fm (see section 4.3.3 and Figure 4e) are interpreted as related to a N-S oriented compressional phase (e.g., Çiftçi & Bozkurt, 2008), or as being extension related (Şengör & Bozkurt, 2013). In our opinion, these apparently compressive structures may have formed in an extensional setting, possibly due to large-scale slumps in unconsolidated deposits.…”

Reconstructing the stratigraphy and structure of the Alaşehir Graben (Western Anatolia): Evidence for a high-angle origin of the Alaşehir detachment fault and layer-parallel shortening during the Miocene time

“…The evolution of the Alaşehir Graben has been the focus of much work over the past thirty years (Emre, 1990(Emre, , 1996Cohen et al, 1995;Koçyiğit et al, 1999;Yılmaz et al, 2000;Seyitoğlu et al, 2002;Bozkurt and Sözbilir, 2004;Çemen et al, 2005;Purvis and Robertson, 2005;Çiftçi and Bozkurt, 2008;Öner and Dilek, 2011;Seyitoğlu and Işık, 2015). However, the development of the Alaşehir Graben has remained controversial, mainly on the basis of tectonic/ structural and stratigraphic inferences.…”

“…Different researchers stated that extension in the Alaşehir Graben was initiated in the latest Oligoceneearly Miocene time and formed in two different deformation types; (1) the latest Oligocene-Miocene core-complex formation in the footwall of the present low-angle normal faults, and (2) the post-Miocene actual graben formation as a result of Plio-Quaternary high-angle normal faults (Bozkurt and Sözbilir, 2004;Seyitoğlu and Işık, 2015 and references therein). A major debate has remained unresolved as to whether the two distinct styles developed continuously without a temporal break (Seyitoğlu et al, 2000(Seyitoğlu et al, , 2002(Seyitoğlu et al, , 2004, or episodically, with more than one phase of expansion separated by periods of contraction (Koçyiğit et al, 1999;Yılmaz et al, 2000;Bozkurt and Sözbilir, 2004;Çiftçi and Bozkurt, 2008; and tectonic quiescence (Emre, 1990(Emre, , 1996 during the Pliocene.…”