Cryptic abundance of long-chain iso and anteiso alkanes in the Dajiuhu peat deposit, central China

Long chain 2-methyl and 3-methyl alkanes occur widely in modern plants and in recent and ancient sediments, but their presence in peat deposits has not been reported. Here, we document an early Holocene enrichment of long chain 2-methyl alkanes in the Dajiuhu peat deposit, accompanied by traces of 3-methyl alkanes. The 2-methyl alkanes showed a strong odd/even predominance and were dominated by C-27 and C-29 homologs. Their delta C-13 values were 5-7 parts per thousand less negative than those of the n-alkanes with the same carbon numbers. Our previous paleoenvironmental reconstruction for this peat sequence indicated that the interval enriched in long chain 2-methyl alkanes corresponded to a period with a very wet climate. Although not resolved, possible sources of the long chain 2-methyl alkanes with relatively enriched C-13 composition include submerged aquatic plants utilizing bicarbonate or heterotrophic microbes in the peatland and its catchment. (C) 2013 Elsevier Ltd. All rights reserved.