Organic geochemistry and origin of Late Glacial-Holocene sapropelic layers and associated sediments in Marmara Sea

Organic geochemistry of two sapropel/sapropelic sediment units dated 10.6-6.4 and 3.8-3.2 kyr BP and associated sediments in two gravity cores from the Marmara Sea were studied to characterize the organic matter and discuss its paleoceanographic implications. Vertical trends of C/N ratio, delta(13)C and hydrogen indices show that the flooding of the Marmara Sea by the Mediterranean waters at 12 kyr BP and onset of deposition of the lower sapropelic layer at 10.6 yr BP are characterized with a high input of terrestrial organic matter. This terrestrial input decreased and marine organic matter contribution increased in time towards the top of the upper sapropelic layer at 3.2 kyr BP. The lower sapropelic layer is broadly the same age and has a similar distribution of organic-matter type as the S, sapropel of the Aegean Sea, suggesting their depositions may have been controlled by the same events. Both the lower Marmara sapropelic layer and the Aegean S, sapropel were probably deposited during a time of high influx of organic-rich river waters from the Black Sea. This influx of Black Sea water could have induced water stratification in the Marmara Sea and Aegean Sea and lead to the deposition of the sapropels. (C) 2002 Elsevier Science B.V. All rights reserved.