Abstract

The Büyük Menderes and Gediz graben of western Turkey developed during Miocene to Recent extension in the Aegean region. New mapping of structures and sedimentary lithofacies in exhumed basin-fill strata is used to reconstruct the evolution of the graben. Field evidence shows that extension was primarily accommodated by tilted fault-blocks 0.2–0.8 km wide, bounded by planar faults, with some modification by antithetic faulting. The basins are faulted on both margins, although they are highly asymmetric, with dominant 'footwall' margins characterized by steeper topography and greater thicknesses of exhumed strata. Within exhumed graben-fill sequences, lacustrine, axial fluvial, and laterally-derived sedimentary facies can be identified. Palaeocurrent orientations, divergent wedge geometries and intra-basin unconformities all indicate that exposed sediments are syn-tectonic. The present day map patterns demonstrate that the position of graben-bounding faults has migrated basinward with time. As a result, large-scale erosion and recycling of the uplifted basin fill have created extensive footwall-derived alluvial fans. These displace the axial drainage towards the hanging-wall margins, away from the locus of greatest subsidence.

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