Quaternary deposits of the Büyük Menderes Graben in western Anatolia, Turkey: Implications for river capture and the longest Holocene estuary in the Aegean Sea

The Büyük Menderes Graben is a seismically active depositional basin in the N–S extensional tectonic region of western Anatolia, Turkey. It extends in an E–W direction and is bounded by the Aegean Sea to the west. The infill of this tectonic basin comprises ca 850 m and 245 m thick clastic sequences of Neogene and Quaternary, respectively and the Quaternary part of the basin-fill is presented here by the help of seismic sections and boreholes. Results show that the studied succession was made of unconsolidated, mostly fine-grained clastic sediments of marine and continental sequences interfingered with each other. The marine counterpart forms three relatively short (approx. 30 km) and one long (approx. 100 km from modern coastline) sediment wedges representing sea transgressions onto the graben. The last one was a rapid incursion that occurred in the Middle Holocene, forming the longest estuary of the Aegean Sea in western Anatolia. The filling of this estuary caused the decline of some historical harbours and settlements in the region. While marine-based events occurred in the west of the graben, alluvial and fluvial processes produced marginal and axial deposits in the east of graben, respectively. In general, the continental succession of Quaternary is thinner than its marine equivalent, probably due to sea-level fluctuations. In addition, the sedimentation rate increased suddenly during deposition of the last marine sequence (estuarine deposits) in the Holocene. It is likely that this was the result of enlargement of the drainage area of the River Büyük Menderes due to a river capture that occurred in the latest stages of Pleistocene.