Miocene sedimentary evolution of the NE–SW-trending Selendi and Gördes Basins, W Turkey: implications for extensional processes

Abstract

Western Turkey is one of the classic regions for the study of extensional processes. In a recent interpretation, the regional metamorphic basement, the Menderes Massif, was exhumed related to large-scale extensional processes, possibly during latest Oligocene time. Regional-scale NE–SW-trending basins, including the Gördes and Selendi basins, were created, associated with this exhumation. The NE–SW-trending basins are seen as regional-scale “corrugations” (10–15 km across) in the surface of an extensional detachment orientated parallel to the direction of extension. The detached upper plate is represented by erosional remnants of unmetamorphosed Tethyan ophiolitic melange. We describe and interpret the Gördes and Selendi basins separately and then show that their sedimentary facies and evolution are very similar. Basal coarse alluvial fan deposits accumulated after extensional removal of the upper plate. These basal sediments, rarely exposed, were rotated by up to 50°, probably as a result of local extension or transtension. Later during the early Miocene, the Gördes and Selendi basins were infilled by a generally fining-upward succession derived from the south, based on palaeocurrent evidence. Coarse alluvial fan deposition was followed by the deposition of finer-grained alluvial deposits from braided streams flowing northwards over a topographically subdued flood plain. Later, deposition was within shallow ephemeral lakes after a possible change to a moister climate. Calc–alkaline magmatism was initiated with the fall-out of fine-grained silicic ash, followed by coarser-grained tuff derived from local magmatic centres. During early Pliocene time, the basins were dissected by E–W extensional faults, associated with the establishment of the modern pattern of westward drainage to the Aegean Sea. We use the assembled sedimentary evidence to test alternative tectonic models for Miocene basin formation in western Turkey. Our preferred tectonic model emphasises the importance of deposition in regional basins created by exhumation of metamorphic basement that was previously assembled during early Tertiary closure of the Tethys ocean.