Organic Geochemistry of Black Sea cores

Six Black Sea bottom sediments samples were analyzed for their organic content (chloroform extract and humic compounds) by elemental analysis, liquid and gas chromatography, various chemical methods and especially infra-red spectroscopy. Four of these samples came from an euxinic facies (“unit 2”) and two from a normally oxygenated facies below (“unit 3”).Even though important differences exist between the two sets of samples, the origin of the organic matter was found to be the same for both facies; this origin is mixed, with the marine contribution slightly predominant over the terrestrial one.Consequently, the compositional differences originate in the different environmental conditions in the sedimentary basin. More precisely, the euxinic facies appears to “preserve” the organic matter, on both quantitative and qualitative grounds. This effect is due more to the anoxic and toxic nature of the environment than to the reducing conditions.The sulfur incorporation in relatively small molecules does not proceed by a rapid biochemical pathway, but by slow and abiotic reactions.