Occurrence of a tetraaromatic hopane in the late Holocene peat deposit, central China

Hopanoids are important cell membrane components of many prokaryotes. These compounds are commonly found in sediments and are used as biomarkers for bacteria. During the diagenesis, biological hopanoids can be transformed into geological hopanoids, including aromatic hopanoids. Our understanding of the processes active in the aromatization of hopanoids in young sediments and their paleoenvironmental implications, however, remains somewhat limited. In this study, we report the occurrence of a C25 tetraaromatic hopane in the late Holocene peat horizons at Dajiuhu, central China. Similar fluctuations of a C25 tetraaromatic hopane and diploptene suggest that the latter may be an important precursor for the aromatic hopane in this peat sequence. The concentration of the C25 tetraaromatic hopane is greater in peats deposited between 2.2 and 1.6 ka when other proxies record a wetter climate and the peat water would have been less acidic than in other intervals. The possible mechanisms underlying the relationship between aromatic hopanes and hydrological settings in immature sediments should be considered further in the future.