Molecular indicators for palaeoenvironmental change in a Messinian evaporitic sequence (Vena del Gesso, Italy). I: Variations in extractable organic matter of ten cyclically deposited marl beds

A ‘screening’ by direct desulphurization of extracts was employed for 21 immature, organic sulphur-rich marl samples from 10 of the 14 evaporite cycles in an Italian Messinian evaporitic basin (Vena del Gesso, Gessoso-solfifera Fm.). The combined information retrieved from free and sulphur-bound carbon skeletons enabled a detailed palaeoenvironmental reconstruction. The biomarker compositions of the marls point to large variations in the composition of species in the water column (e.g. dinoflagellates, diatoms and other algae, cyanobacteria, methanogens, green sulphur bacteria and bacterivorous ciliates) and in contributions from the continent (i.e. land plants) within each marl bed and between marl beds. The marl beds were deposited within a stratified lagoon where anoxic conditions extended into the photic zone for much of the time.