Fluvial response to rising levels of the Black Sea and to climate changes during the Holocene: Luminescence geochronology of the Sakarya terraces

Abstract

The Sakarya River is among the largest fluvial systems of the southern Black Sea basin, draining most of NW Anatolia. The river crosses the high relief of the Pontide mountain range through successive narrow gorges and strike-slip basins formed by the North Anatolian Fault (NAF) System. We have investigated this fluvial record along the course of the main river channel at its lower reaches. The study site is located south of the Adapazarı Basin, ~50 km inland from the Black Sea, where remnant floodplains are preserved as a three-step terrace staircase resulting from continuous uplift to the south of the NAF. The combination of high resolution mapping with a detailed luminescence (OSL and p-IR-IRSL) and radiocarbon geochronology has shed light on changes in the level of the Black Sea and in the hydrological system during the late Pleistocene to recent. The last glacial period is represented by the highest terrace (T3) indicating deposition during marine isotope stage (MIS) 3 in between two low stands of the Black Sea. Following a long-term erosional period initiated prior to last glacial maximum (LGM), the initiation of the deposition (T2) was synchronous with the proposed catastrophic sea level rise of the Black Sea (cal. C¹⁴ 9.3 ka BP) which continued throughout the Holocene until the Roman warm period (1.8 ka BP). The late-Holocene to recent morphological evolution of the region is marked with two sequential erosional and depositional (T1 and T0) periods, which can be correlated with the well-documented historical climate shifts affecting the hydrological system. These results reveal that the erosional and depositional periods on the Sakarya River floodplain are controlled by major sea level changes and climatically induced fluctuations in discharge and sediment supply.