| The abnormal global climate change has severely impact on anthropogenic activities and life. How to utilize the climate change rule and tendency to provide better service for human has become hot topic in scientist research. The star point of modern climate research primary is to study paleo-climate and paleo-environment in geological history. Abundant information about paleo-environment, paleo-climate and Paleolithic culture can be obtained from the red earth in southern China which contains guiding significance for Quaternary terrestrial paleoclimate reconstruction and climate change tendency forecasting. Moreover, it also plays an important role in north and south China comparison on Quaternary paleoclimate and paleo-environment construction.The vermicular red soil, the product of active biological climate effect in geological history, is affected greatly by eluviation which limits traditional higher plants and algae lipids research. However, lipids derived from microorganism are usually deposit on inner soil and are easier to conserve and their structure and composition are sensitive to environment factors, such as temperature, in molecular level for their rapid metabolism and propagation. Currently, microorganism lipids glycerol dialkyl glycerol tetraethers (GDGTs) has gradually become important index in paleoclimate and paleo-environment reconstruction. Thus, how to use laterite microorganism lipids to reconstruct paleoclimate in south red soil needs more research on excavate and determine its paleoclimate significance in south red soil.Researches on south red soil are mainly in four profiles:Guangxi Baise, Zhejiang Changxing, Jiangxi Jiujiang and Anhui Xuancheng. In this paper, 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 characteristic of the microbial lipids, especially GDGTs were investigated by comparative analysis.The distribution of GDGTs from Xuancheng profile shows that:(1) the concentration of bGDGTs is apparently higher than that of iGDGTs, which is totally consistent with the characteristics of GDGTs distribution in laterite. (2) It is apparently showed in MBT and CBT curves 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. (3) The measurement derived PH compare with the equation derived PH shows that the former one represents acid and the later one represents neutral to weak alkaline with PH fluctuate between 7.0 and 8.0, however, they are both acid in surface modern soil. Thus, it could be inferred that the early deposition period of this profile was alkalescency and became acid along with the climate and environment changes. Due to the aeolian deposit in the area which can lead to further infer that laterite in this area is mainly derived from the arid areas in north-western China or alternatively from the dry river sediments in the Middle-Lower reaches of the Yangtze River. (4) There is distinct correlation between BIT and Ri/b indices showing in the comparison of BIT, Ri/b and stalagmite oxygen isotopes curves which can be presumed that it was very dry at 130 ka BP in Xuancheng area. The result shows that microbial lipids GDGTs can reconstruct a high-resolution quantitative paleoclimate in Xuancheng, Anhui province, which has important research significance. |
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