Evolution of Neogene Sedimentary Rocks on the Southern Margin of the Alaşehir Graben: Evidence for Termination of Tectonic Activity on the Alaşehir Detachment Fault During the Late Miocene

The southern margin of the Alaşehir Graben is bounded by the Alaşehir Detachment Fault (ADF), comprising ductile-brittle cataclastic rocks within the same extensional regime. This fault surface is exposed over ~150 km from Turgutlu to Alaşehir and dips to the north at a low-angle (10°-30°). There are two main interpretations about the termination of tectonic activity on the ADF. The first is that recent movement of the fault ended in the late Miocene, based on the fact that it is cut by Plio-Quaternary high-angle normal faults. The second view suggests that tectonic activity continued until the Plio-Quaternary, based on the exhumation ages obtained from cataclastic rocks. We present measured stratigraphic logs of the Neogene sequence in the hanging wall of the ADF in the Salihli and Alaşehir areas to contribute to this discussion. The depositional evolution of the Alaşehir Graben can be described in three assemblages, including Miocene (Gerentaş, Kaypaktepe and Acıdere Formations), Late Miocene-Late Pliocene (Göbekli, Yenipazar and Erendalı Formations) and Plio-Quaternary sedimentary rocks (Asartepe Formation). The Miocene and Plio-Quaternary assemblages are represented by similar depocenters, including lacustrine, fluvial and alluvial-fan environments in the Alaşehir Graben. They are separated by the Late Miocene to Late Pliocene, which represents the depocenter of the floodplain. The floodplain deposits are a monotonous sequence that repeats itself and is not tectonically mobile after the first 140 meters from the stratigraphic bottom based on sub-rounded to rounded clasts from the cataclastic rocks belonging to the ADF. They represent a time of tectonic quiescence during the Late Miocene-Late Pliocene, indicating that tectonic activity on the ADF terminated in the Late Miocene. However, tectonic activity may have rejuvenated in the Plio-Quaternary as indicated by E-W oriented normal faults cutting through the Alaşehir Graben.