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

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 δ13C values for bulk organic matter and for biomarkers, i.e. heavier than −20‰. Exceptions are long-chain C22–C34 n-alkanes and C16–C20 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 δ13C values for biomarkers of different algae and bacteria suggest that the local (microbial mat) ecosystem may have been CO2-limited.