Xinxin Wang, Xianyu Huang, Dirk Sachse, Yu Hu, Jiantao Xue, Philip A. Meyers

• Knowledge of the possible impacts of early diagenesis on lipid biomarkers in geologic settings is important for robust applications of lipid proxies for paleoclimate reconstructions. In this study, molecular distributions and carbon isotopic compositions of lipids were compared in two particle-size fractions (<0.3 mm and >0.3 mm) of twelve surface peat samples collected from Dajiuhu peatland, central China. The average chain length (ACL) values of long-chain n-alkanes, n-fatty alcohols, n-fatty acids and n-alkan-2-ones show no significant differences between the finer and coarser fractions. In contrast, the carbon preference index values of long-chain n-alkanes, n-fatty alcohols and n-alkan-2-ones have relatively smaller values in the finer fractions than in the coarser ones. Stanols were also more abundant in the finer fractions. In addition, the delta C-13 values of odd-numbered n-alkanes (C-23-C-33) were generally less negative in the finer fractions. Our results indicate that (1) the finer fractions probably experienced strongerKnowledge of the possible impacts of early diagenesis on lipid biomarkers in geologic settings is important for robust applications of lipid proxies for paleoclimate reconstructions. In this study, molecular distributions and carbon isotopic compositions of lipids were compared in two particle-size fractions (<0.3 mm and >0.3 mm) of twelve surface peat samples collected from Dajiuhu peatland, central China. The average chain length (ACL) values of long-chain n-alkanes, n-fatty alcohols, n-fatty acids and n-alkan-2-ones show no significant differences between the finer and coarser fractions. In contrast, the carbon preference index values of long-chain n-alkanes, n-fatty alcohols and n-alkan-2-ones have relatively smaller values in the finer fractions than in the coarser ones. Stanols were also more abundant in the finer fractions. In addition, the delta C-13 values of odd-numbered n-alkanes (C-23-C-33) were generally less negative in the finer fractions. Our results indicate that (1) the finer fractions probably experienced stronger degradation than the coarser fractions; (2) the less negative delta(CC)-C-13 values of odd-numbered n-alkanes (C-23-C-33) in the finer fractions were largely a result of greater heterotrophic reworking during degradation; (3) ACL values of long-chain n-alkyl lipids (n-alkanes, n-fatty alcohols and n-fatty acids, n-alkan-2-ones) appear to be reliable proxies to trace lipid sources and their associated paleoenvironmental signals in peat deposits.…