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DOI

10.19111/bmre.18782

Abstract

Surface water and sediments derived from the southern Marmara region (= Susurluk
Drainage basin- SDH) transport to lakes Manyas and Ulubat first and then go to the Sea of
Marmara via the Kocasu River only. The present drainage system of the SDH provides a good
opportunity to study erosion rate and subsequently occurrence times of large-scale valleys in
the region. To achieve it, depositional characteristics and ion contents of the ancient
lacustrine sediment has been investigated and re-interpreted using cores taken from Lake
Ulubat. The boron content of these sediments increased upward suddenly at the 4 m level,
most probably due to starting of erosion at Emet borate beds in the drainage basin. Taking
into consideration equilibrium between natural erosion and sedimentation, the incision rate
in the Emet valley was found 1.4 cm.yr-1. From here one can calculate a time span of 75 ky
for the formation of the whole valley itself. However, it is known that working of the geological
processes was not monotonous in the past; hence, this date is not absolute. Newertheless,
formation of the large valleys of the southern Marmara region shouldn’t be older than 300
kyrs. An important reason on rapid erosion was likely lowered base-level as the Marmara Sea
was a closed lake during the last Glacial Period. High altitudinal difference between source
and depositional areas caused acceleration of the erosion.

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