A molecular isotopic study of 13C-enriched organic matter in evaporitic deposits : recognition of CO2-limited ecosystems

Abstract Biomarkers were analysed in a surface sediment from La Trinitat saltern ponds and a Miocene marl from the Northern Appenines. Both are characterised by enriched δ 13 C values for bulk organic matter and for biomarkers, i.e. heavier than −20‰. Exceptions are long-chain C 22 –C 34 n -alkanes and C 16 –C 20 fatty acids which have values typically lighter than −20‰, suggesting that they are not derived from aquatic organisms but from surrounding terrestrial vegetation. The enriched δ 13 C values for biomarkers of different algae and bacteria suggest that the local (microbial mat) ecosystem may have been CO 2 -limited.