Geochemical study of macromolecular organic matter from sulfur-rich sediments of evaporitic origin (Messinian of Sicily) by chemical degradations

Selective chemical degradations have been performed on sulfur-rich macromolecular organic matter from sediments of the Messinian of Sicily (Upper Miocene, Italy). The biomarkers released upon different desulfurization experiments are much more abundant than the free lipids and display completely different distributions, which reflect the selective trapping of (poly)functionalized molecules by inorganic sulfur species at an early stage of diagenesis. The bound biomarker distributions reveal a dominant phytoplanktonic input originating from an upper oxic water layer and a moderate bacterial reworking of the organic matter. A contribution from cyanobacteria to the organic matter cannot be excluded. The presence of carotenoids typical from photosynthetic sulfur bacteria attests to a stratified water body where an anoxic photic zone occurred. LiAlH4 hydrogenolysis of sulfur-rich macromolecules revealed that polysulfide bridges contribute to a large extent in the cross-linking. The results of deuterium labelling experiments are discussed in terms of sulfur incorporation on functionalized lipids.