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

Biomarkers were analysed in a surface sediment from La Trinitat saltern pon ds and a Miocene marl from the Northern Appenines. Both are characterised b y enriched delta C-13 values for bulk organic matter and for biomarkers, i. e. heavier than -20 parts per thousand. Exceptions are long-chain C-22-C-34 n-alkanes and C-16-C-20 fatty acids which have values typically lighter th an -20 parts per thousand, suggesting that they are not derived from aquati c organisms but from surrounding terrestrial vegetation. The enriched delta C-13 values for biomarkers of different algae and bacteria suggest that th e local (microbial mat) ecosystem may have been CO2-limited. (C) 2001 Elsev ier Science Ltd. All rights reserved.