Late Quaternary Mediterranean sapropels II. Organic geochemistry and palynology of S 1 sapropels and associated sediments

Abstract

Six S 1 sapropel samples from the eastern Mediterranean were investigated organic geochemically to study the lateral variation within this organic-rich layer. Five of these samples were also analyzed palynologically. In addition, some sediment samples from below and overlying the sapropel intervals were investigated for their organic geochemical characteristics. Organic matter of S 1 sapropels is of a mixed marine, terrigenous and bacterial origin. A trend of relatively increasing amounts of continentally derived organic matter towards more seaward and deeper realms can be observed from both palynological and organic geochemical data. This trend is supported to some extent by δ 13C-values of the organic matter. The sapropelic intervals deposited on the Nile Cone are characterized by expanded thicknesses and a “diluted” organic carbon content due to a higher sedimentation rate. The environmental conditions (in terms of preservation) during sapropel formation over the eastern Mediterranean were probably not uniform. At site 29 the conditions were favourable for the deposition of sapropel with a higher organic carbon content than at the other locations. This might have been caused by better preservation conditions. An increasing discharge from the river Nile seems to be the driving force for formation of the S 1 sapropels. Based on this assumption a model for sapropel formation is proposed. Although not all the data could be explained properly by this model, most phenomena can be explained.