Paleoclimate influence on early diagenesis of plant triterpenes in the Dajiuhu peatland, central China

Aromatic derivatives of vascular plant triterpenoids are common in recent and ancient sediments, coal, and petroleum. Understanding their early diagenetic alterations and their relation with environmental conditions can facilitate their applications in paleoenvironmental reconstructions. Here we present a high-resolution record of aromatic triterpenes in a Holocene peat core collected in the Dajiuhu peatland, central China. These aromatic triterpenes are derivatives of plant triterpenoids with oleanane, ursane and lupane carbon skeletons and exist in three different structural groups: aromatic des-A-triterpenes, aromatic pentacyclic triterpenes, and C-ring cleaved aromatic triterpenes. Such a high diversity of aromatic triterpenes in a young peat deposit is compelling evidence for rapid microbial mediation of these important degradation pathways during very early diagenesis. Of particular importance is the occurrence of C-ring cleaved aromatic triterpene and aromatic des-A-triterpenes in the Dajiuhu peat samples, which until now have not been identified in recent sediments. The downcore profile shows that the microbial aromatization process of oleanoids positively correlates with paleoclimate change. During dry or warm intervals, highly aromatized products such as tetraaromatic triterpenes become predominant over their triaromatic homologs. In contrast, triaromatic triterpenes become dominant during wet or cold intervals. In addition, this study provides further evidence to support that the climate pattern in the middle reaches of the Yangtze River is different from that in north China during 13-9.4 ka. These findings suggest that aromatic triterpenes can be valuable tools for Holocene paleoenvironmental reconstructions. (C) 2013 Elsevier Ltd. All rights reserved.