MOLECULAR INDICATORS FOR PALEOENVIRONMENTAL CHANGE IN A MESSINIAN EVAPORITIC SEQUENCE (VENA-DEL-GESSO, ITALY) .1. VARIATIONS IN EXTRACTABLEORGANIC-MATTER OF 10 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 evapo rite cycles in an Italian Messinian evaporitic basin (Vena del Gesso, Gessoso-solfifera Fm.). The combined information retrieved from free a nd sulphur-bound carbon skeletons enabled a detailed palaeoenvironment al reconstruction. The biomarker compositions of the marls point to la rge 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 contribution s from the continent (i.e. land plants) within each marl bed and betwe en marl beds. The marl beds were deposited within a stratified lagoon where anoxic conditions extended into the photic zone for much of the time.