Influence of climate on the late Pleistocene depositional history of the Gulf of Gemlik (Sea of Marmara)

Abstract

The late Pleistocene climate-induced water level fluctuations in the Gulf of Gemlik have been first documented in detail by analyses of high-resolution seismic reflection profiles that are tied to radiocarbon-dated sediment cores. In this study, synthetic seismogram for seismic-to-core comparison has enabled a precise correlation between seismic units and core sediments, on which basis it was possible to establish an accurate chronology of the sedimentary successions deposited in the gulf. In the seismic profiles, pre-Holocene depositional units reflect distinctive hydrological and sedimentological processes due to the fluctuating water levels in response to high climate variability. Progressive drop in water level, due to a dry climate phase in the Last Glacial Maximum, is marked by a progradation of a lacustrine delta on the northern shelf of the gulf. Post-glacial warming prior to ca. 18 cal ka BP gave rise to meltwater-driven, high-energy currents on the shelf slopes, producing erosional gullies. The later transgressive freshwater stage of the Gemlik “Lake” began as a result of the meltwater discharge to the gulf basin, which is associated with deposition of the retrograded clinoforms on the shelf margin and infilling the gullies along the slopes. The final post-glacial water level rise in the gulf was mediated by a regressive phase, inferred by seaward-dipping clinoforms and deltaic deposition on the shelf margin. Such a climatic shift to a drier period may coincide with the Heinrich event 1. In the Gulf of Gemlik, transition from the Bolling/Allerod to Younger Dryas periods is recognized by deposition of small clinoform packages on the shelf margin, marking a decrease in water level due to low precipitations on the catchment area. The lake level decrease in the gulf during the YD was modulated by a stillstand, producing a – 65-m erosional terrace and a beach-berm elsewhere along the gulf shelves.