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.

Temporal monitoring of vast sand mining in NW Turkey: Implications on environmental/social impacts

“…The terrace T3 started to form at 40 ka until 30 ka. It stands at +21.5 m afp and max observed thickness is 8-10 m. This terrace step forms a wide surface at the western part of the river, occupied by settlements (Kirazca and Karaçam, Figure 3) and mostly free of sand mining (Erturaç et al, 2019).…”

“…Adapazarı Basin Adapazarı Basin is an asymmetric trapezoid shaped Quaternary tectonic basin with 650 km 2 surface area, evolved under the control on the North Anatolian Fault Zone (Şengör et al, 2005) (Figure 2 B). The sedimentary sequence of the basin is formed of Early Quaternary Karapürçek formation deposited during the first phase of tectonic development (Qkpc; Emre et al, 1998) and Middle-Late Quaternary modern basin fill and river terraces (Adapazarı Plain, 330 km 2 , Erturaç, et al, 2019). The formation of the modern basin is controlled by rapid tectonic subsidence (1.5 mm/year) and regional uplift of the mountain range (0.78 mm/year).…”

“…The study area is extensively covered within the framework of studies concerning the timing and evolution of the Adapazarı Plain and terrace staircases (Erturaç et al, 2019;Erturaç, 2020). We have detailed the sedimentary facies of both terraces and the floodplain.…”

“…The base (pre-sand mining era) map was produced by digitizing the geomorphological map drawn by T. Bilgin (1984). The river/floodplain and terrace staircases was classified according to rtk-GPS profiling and field observations where the thickness of each sedimentary unit is determined (Erturaç et al, 2019). The initial land use of the study area was determined from 1975 keyhole imagery.…”

“…Observable sections of the Karapürçek formation are mostly abandoned and active sand quarries and consist of intercalation of coarse and fine grained clastic sediments. The terraces are formed by interactions between fluvial response to Black Sea level changes, climate pulses during Late Holocene and the steady regional uplift of the region (Erturaç et al, 2019). All the terraces sit unconformably on the Qkpc, hence will be called as substratum from this point forward.…”