Distributions and Paleo-Environment Implications of Microbial GDGTs from Red Earth Profile in Xuancheng, Anhui Province

Abundant information about paleo-environment, paleo-climate and paleolithic culture can be obtained from the red earth in southern China. However, the vermicular paleosol is proposed to be incapable of interpretating the original information about the past climate and envrionment changes owing to the intensive pedogenesis in the tropical-subtropical area. Therefore, previous studies on bio-climatic approaches including pollen, spore fossils and phytoliths are also believed to be not suitable for such kind of stratigraphy. Despite that some studies show the microbial molecular fossils are useful in the paleo-environment reconstruction, but their implications in red earth need to be further explored and confirmed. It is necessary to introduce some new methods to extract the detailed biological information in the red earth. In this study, we collected red earth samples from the Xuancheng section, Anhui Province in the Middle-Lower Reaches of the Yangtze River, which is well-dated and sensitive to climate change. Microbial lipids in the red earth are extracted by employing alkaline hydrolysis combined with the field survey and the laboratory investigation. The characteristics of the microbial lipids, especially glycerol dialkyl glycerol tetraethers (GDGTs) are investigated. The distributions of GDGTs from the Xuancheng profile show that all GDGT-derived proxies in the lower part of profile fluctuates frequently, whereas they are relatively stable in the upper part, which indicates that the paleo-environment changed frequently during the early period of this profile but the later soil environment was relatively stable. The CBT-inferred soil pH ranges from 7.0 to 8.0, indicating that the soil parent material likely comes from the arid areas in northwestern China or alternatively from the dry river sediments in the Middle-Lower Reaches of the Yangtze River. The low BIT values suggest that it was very dry at 130 ka BP in the Xuancheng region.