SYN-RIFT SEDIMENTATION AND STRUCTURAL DEVELOPMENT OF THE GEDIZ AND BUYUK-MENDERES GRABEN, WESTERN TURKEY

The Buyuk Menderes and Gediz graben of western Turkey developed during Miocene to Recent extension in the Aegean region. New mapping of stru ctures and sedimentary lithofacies in exhumed basin-fill strata is use d to reconstruct the evolution of the graben. Field evidence shows tha t extension was primarily accommodated by tilted fault-blocks 0.2-0.8 km wide, bounded by planar faults, with some modification by antitheti c faulting. The basins are faulted on both margins, although they are highly asymmetric, with dominant 'footwall' margins characterized by s teeper topography and greater thicknesses of exhumed strata. Within ex humed graben-fill sequences, lacustrine, axial fluvial, and laterally- derived sedimentary facies can be identified. Palaeocurrent orientatio ns, divergent wedge geometries and intra-basin unconformities all indi cate that exposed sediments are syn-tectonic. The present day map patt erns demonstrate that the position of graben-bounding faults has migra ted basinward with time. As a result, large-scale erosion and recyclin g of the uplifted basin fill have created extensive footwall-derived a lluvial fans. These displace the axial drainage towards the hanging-wa ll margins, away from the locus of greatest subsidence.