Late Quaternary climate and sea-level changes recorded in sediment composition off the Büyük Menderes River delta (eastern Aegean Sea, Turkey)

Abstract

Influences of Holocene climatic and sea level changes on sedimentation on the continental shelf off the Büyük Menderes River delta, SW Turkey were investigated using grain size and X-ray clay mineralogical data on surficial and 14C-dated core sediments collected at 19–81m water depths. Modern, fine-grained, siliciclastic sediments cover most of the seafloor of inner to mid-shelf areas. A narrow, relict belt extends from northwest to south (at 66–81m water depths), where sediments are characterized by abundant sand and gravel (27–52%) and biogenic carbonate (16–44%) contents, and microscopic examination suggests an older origin. The radiocarbon ages of mid and lower sections in cores (3670–10,380yrBP) reflect sedimentation under depositional conditions from early to late Holocene in the study area. Additionally, downcore changes of grain size toward coarser-grained sediments most probably record global climatic effects with sea level changes, specifically the transition from lowstand in early Holocene to highstand at mid–late Holocene. The presence of this relict belt in offshore waters can be attributed largely to active uplift tectonics. The coarser-grained relict belt, compared with available seismic profiles, corresponds to an lowstand unconformity of bottomset beds of the prograding Büyük Menderes Delta.Reconstruction from nautical charts clearly showed the presence of an E–W-trending submarine canyon (“Paleo-Büyük Menderes River valley”) in the course of Büyük Menderes Graben. This is interpreted as product of combination of sea-level lowstands and subsidence tectonics throughout the late Quaternary.Smectite (35–62%), illite (28–51%) and kaolinite (12–19%) constitute the dominant clay minerals in the <2μm fraction of the surface sediments. The patterns of clay mineral distribution suggest sediment transport from the Büyük Menderes River and dispersal from the river to the outer continental shelf by the prevailing current regime. Downcore changes in the clay mineral assemblages (downward-decreasing smectite/illite ratios) reflect changes in weathering conditions of the terrigenous source, from a colder climate during early Holocene to relatively warmer periods toward the present. Widely occurring partly metamorphosed volcanic rocks characterize the major geological sources of clay minerals on the adjacent hinterland.