We present a detailed structural and stratigraphic record of a Neogene–Quaternary supradetachment sedimentary succession in the Aegean extensional province of western Anatolia, and we compare its tectonic features and evolution to those of other well-documented supradetachment basins around the world. The sedimentary fill of the Alasehir basin records the uplift and exhumation of a core complex in the footwall of a detachment fault within the Central Menderes Massif. Accumulation of footwall-derived clastic sediments in this basin started ca. 20 Ma, shortly after the initiation of the approximately E-W–trending Alasehir detachment and its shear zone, and continued until ca. 2 Ma. Major sedimentary facies types include fluvial and alluvial-fan deposits, debris-flow and mass-flow deposits, and locally developed lacustrine rocks. These sedimentary units were accumulated largely in distal depocenters within the extending basin, as the low-angle (15°–28°) detachment faulting created little accommodation space near the basin margins while producing high back-shed topography in the uplifted Menderes core complex. The drainage system was dominated mainly by extension-parallel transverse streams during the main phases of basin evolution. Extension-parallel, scissor (hinge) faulting produced differential uplift and subsidence in the adjacent fault blocks, changed the direction of sediment transport and drainage patterns over short distances, and resulted in the local uplift of the older basin strata. These processes led to the development of subbasins with lateral variations in basement topography, strata thickness, and sedimentary facies distribution, and generated a segmented basin architecture. High-angle synthetic and antithetic faults that formed extensively after 3 Ma caused back-tilting of the sedimentary strata, formation of half grabens with their own axial drainage systems, and development of angular unconformities. With the onset of this crustal-scale block faulting, the detachment fault ceased to operate, and the Quaternary Gediz graben started to develop at the northern end of the Alasehir supradetachment basin. Our comparative evaluation of select basins shows a maximum sediment thickness of 3 km, average extension rates of 6 to 8–9 mm yr−1, and accumulation rates of 0.1–0.2 mm yr−1 (uncorrected for compaction) in supradetachment basins in general. The rates and amounts of extension, the geometry of detachment faulting, the rates of footwall uplift, and the kinematics and interplay of different fault systems are the most important factors controlling three-dimensional structural architecture and evolution of supradetachment basins.

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