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Fluvial Archive of Sakarya River 

Sakarya River, the second longest river in Turkey, drains a large portion of NW Anatolia. 

We investigate the fluvial record along the middle and lower reaches of the main river and its tributaries to reveal the driving mechanisms of the fluvial episodes (erosion and deposition) under control of climate cycles, sea level changes and active tectonics.

Detail mapping and measuring of the terrace staircases and systematic luminescence dating of each step was the primary goal. Our research now extends towards different approaches such as

  1. monitoring and assessment of environmental impact of sand mining

  2. deciphering the changes in the hydrological regime and detecting hydrological extremes (HEX) by detailing flood plain deposits using multi-proxy approach

Supported by TUBITAK 112Y132, 115Y132, 117Y426 and 121Y110 Grants​

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Scope

River terraces are remnants of former river floodplains that are fossilized above present-day river channels, often in staircase systems.
The formation of terrace staircases is attributed to both uplift, climate and sea/base level changes. Variations in the crustal movements and climatic conditions cause perturbations in the fluvial system, which, over time, lead to widening of valley floors, aggradation, and incision, thereby producing terraces.
We use conventional mapping tools to map the terrace staircases and measure absolute positions of their base and threads by using rtk-GPS and drone photogrammetry. 
 Building up a precise chronology of each step was possible with luminescence dating protocols (OSL and IRSL) focusing on pristine quartz and feldspar crystals enable us to date the burial time of inorganic sediments for ~200 thousand years.

River terraces express fluvial response to the major changes in the earth's system. 

The geomorphological and tectonic setting of the Sakarya River enables the sedimentary record to cover a lot more data. 

The flood plain sediments of the river at the Adapazarı tectonic basin, controlled by the northern strand of the North Anatolian Fault. 

Adapazarı Basin

The Late Pleistocene-Holocene evolution of the Adapazarı Basin was investigated using the stratigraphy, geometry, and absolute luminescence dating of the 4-step fluvial terrace staircases of the Sakarya River. The results revealed that the fluvial cycle was primarily related to relative sea level changes of the Black Sea. The initiation of deposition and the abandonment ages of the terraces indicated relative high stands during marine isotope stage (MIS) 5a (~84–72 ka), 3 (40–30 ka), and 1 (9 ka-recent). The erosional periods in between the terrace steps reflected the response of the Sakarya River to the significantly low stands of the sea. The spatiotemporal position of the high terraces (T4 and T3) yielded an average of 0.78 ± 0.03 mm/year, and uniform and aseismic rock uplift rate for the NW part of the Anatolian Plate bounded by the North Anatolian Fault, which ruptured during the 1999 İzmit earthquake. The lower terrace (T1) was used to determine the horizontal slip rate of the Sapanca-Akyazı segment of the earthquake rupture and reported as 16.7 + 3.6/–2.5 mm/year. Further displacement measurements from the surfaces of T2 and T1 yielded a vertical slip rate of 1.49 ± 0.2 mm/year, calculated for the Late Holocene. 

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Hydrological Extremes (HEX)

The Holocene interglacial (last 11700 years) which precedes the last Glacial Period witnessed major climate fluctuations which are evidenced by geological records (lake sediments, stalagmites, tree rings etc.) and Rapid Climate Changes (RCC’s) are documented. Recently fluvial record has been evaluated to understand climate, base level change and tectonic activity.

Hydrological extremes and critical events (HEX) are defined as abrupt changes in river’s discharge above (flood) or below (drought) average threshold. HEX studies now extend beyond the instrumental (long term monitoring) data towards compiling historical record and detailing fluvial record for past hydrological and climatological changes in the river’s basin. 

The study area is the flood plain of the Sakarya River at Adapazarı Basin, east of Marmara Sea in NW Turkey. We focus and detail the fluvial record of the recent floodplain of the river which deposited 4.5 meters of fine grained sediment since 1300 CE. This time period corresponds to the Little Ice Age (LIA) and the ruling period of the Ottoman Empire. Our multi-disciplinary and multi-proxy approach aims to determine the HEX events with absolute dating methods. 

This study is funded bu TÜBİTAK 121Y110 project.

Mehmet Korhan Erturaç, Hilal Okur, Meltem Çelen, Eren Şahiner, Alper Gürbüz, Özlem Makaroğlu, Sena Akçer-Ön, Nurgül Karlıoğlu-Kılıç, Burçin Aşkım Gümüş, Hüseyin Tuncay Güner,  Zeki Bora Ön, Emrah Bulut, Fatma Küçük, Burak Berkay Babadağ, Nesibe Köse, Mehmet Salim Öncel 

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