Improved preservation of organic matter and pollen in eastern Mediterranean sapropels

Abstract

Here we investigate the processes leading to high organic content and high pollen concentration in pelagic marine sediments. Three marine cores near the base of the Nile River cone display the classical Quaternary sequence of sapropels and hemipelagic muds. Large variations in total pollen concentration, as well as in percentage composition of the pollen assemblage are clearly linked to the two lithological types. All pollen types have much higher concentration in sapropels than in muds, by 3 or 4 orders of magnitude. Within sapropels, the percentages of Gymnosperms (Pinus and Cedrus) pollen and Pteridophyte spores, are very low and the pollen spectrum is dominated by various Angiosperms. These variations in total pollen concentration as well as in percentages cannot be accounted for by variations in pollen production, or in efficiency of transport, because they similarly involve pollen of different areas and climates, transported to the sea by different means. The cause for these variations can only be a difference in preservation of pollen. Preservation is good in sapropels for all pollen types, but generally poor in muds. We believe that sapropels were deposited under reducing bottom waters which allowed a better preservation of the organic matter including pollen.