THE MULHOUSE BASIN - EVIDENCE FROM PORPHYRIN DISTRIBUTIONS FOR WATER COLUMN ANOXIA DURING DEPOSITION OF MARLS

Marls from the evaporitic Mulhouse basin (Oligocene; Alsace, France) c ontain alkyl porphyrins dominated by nickel-complexed species. The pre sence in high relative abundance of a range of components with carbon numbers up to C37 indicates that anaerobic photosynthetic bacteria mad e a significant contribution to the photosynthetic community in the pa laeoenvironment and. in turn. that anoxic conditions extended into the photic zone of a stratified water column. Further evidence is given b y the assignment, by HPLC coinjection with a standard, of a C34 compon ent with the same carbon skeleton as one of the bacteriochlorophylls d of such bacteria. Significant differences in the nickel and vanadyl p orphyrin distributions in one of the samples examined appear to result from changes in the depositional environment which are recorded with a stratigraphic resolution below that sampled, or indicate derivation of these two porphyrin pools from different parts of the water column.