ÇAĞRILI KONUŞMALAR / KEYNOTES Invited Speeches ... - TPJD

Study and Interpretation of Sedimentation Rates within Turkish Lakes
Nizamettin Kazancı, Koray Koç, Sonay Boyraz
Ankara University, Faculty of Engineering, Department of Geological Engineering, Ankara
Lakes are sensitive to environmental circumstances, thus it is accepted that these geographic
elements are archives of climatic records for the relevant region. Some parameters, i.e dimensions
of of both lake itself and drainage basin, local climate, lake system (open or closed), lithological
variety of source rocks, active tectonism, altitudes play important roles on the lacustrine
deposition and sediment thickness. In order to detect which parameters were prominent within
Turkish lakes, sedimentation rates of twenty-two lakes were examined using original data
together with results from literature. Authors were aware that deposition in lake margins should
not be used for a proper sedimentation rates. Some of the studied lacustrine records (cores)
were 0-2 m long formed within last 250 years (i.e lakes Ladik, Borabay, Aşağıtepecik, Yeniçağa,
Sünnet, Sakarya Akgöl, Gravgaz), while others were 4-10 m long core covering a time span of
1000 to 7000 years (i.e lakes Manyas, Ulubat, Bafa, Burdur, Işıklı, Akgöl). Some lakes provided
long cores and long deposition time i.e lakes Gölhisar, Elmalı Karagöl, Van, Konya, Tuzgölü,
Pınarbaşı. Based on sediment thicknesses only, deposition rates of Turkish lakes were between
1.56 and 7.48 mm/year, mostly above 2.95 mm/year with an average of 3,5 mm/year during the
last 250 years. It is worthy to note that recent lake sediments contain significant amount of pore
water and it was not below 25 % even in the longest core. The sedimentation rates of Turkish
lakes during the last 1250 years became 0.64 to 3.56 mm/year and their average was 1.98 mm/
year. In the last 5000 years it was between 0.30 and 0.91 mm/year with an average of 0.56 mm/
year. It is surprising that the value of the last 10 000 years (Holocene) is almost same (= 0.56
mm/year) with the previous one. Deposition rates of dead lakes (i.e dry lakes Konya, Sultaniye,
Pınarbaşı) are between 0.05 and 0.39 mm/year. They are very close to watery but old lakes which
are successors of old lakes, i.e lakes Tuz, Hotamış, Van). Overall, sedimentation rates of Turkish
lakes are high significantly and average value of even old and dry lakes is around 0.22 mm/year.
This is high four and ten times at least compared to values of modern and geological records in
the world respectively. It may indicate that tectonism has been primary controlling factor on
deposition in Turkish lakes since the late Quaternary.
Keywords: Sedimentation rate, Turkish lakes, Holocene
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