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 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 than -20 parts per thousand, suggesting that they are not derived from aquatic organisms but from surrounding terrestrial vegetation. The enriched delta C-13 values for biomarkers of different algae and bacteria suggest that the local (microbial mat) ecosystem may have been CO2-limited. (C) 2001 Elsevier Science Ltd. All rights reserved.