安徽宣城红土微生物GDGTs分布特征及其古环境意义
Distributions and Paleo-Environment Implications of Microbial GDGTs from Red Earth Profile in Xuancheng, Anhui Province

中国南方更新世红土是古气候环境变化研究非常重要的载体之一,红土微生物类脂分子是其古气候环境研究的有效指 标,但其在红土中的古气候意义需要更进一步的挖掘和明确.选取处于气候变化敏感地带并且已有很好年代学基础的安徽宣 城红土剖面进行详细的野外调查和系统的样品采集,利用改善后的碱式水解法提取红土微生物类脂分子,通过对比分析、比 较印证等方法对其中的甘油二烷基链甘油四醚(glyceroldialkylglyceroltetraethers,简称GDGTs)进行系统研究.宣城剖面 GDGTs分布特征显示:剖面下部各指标呈旋回性变化、而上部相对稳定,表明形成初期环境比较动荡,而后期成土环境相对稳 定;土壤pH 为7.0~8.0,推测其物源主要来源于北方干旱区或长江中下游干涸河滩沉积;BIT 指标反映宣城地区在130ka BP左右气候极为干旱.结果表明,红土中微生物类脂物GDGTs能够定量、高分辨率地重建安徽宣城的古气候环境,具有重要 的研究意义.
Abundant information about paleo-environment, paleo-climate and paleolithic culture can be obtained from the red earth in southern China. However, the vermicular paleoso1 is proposed to be incapable of interpretating the origina1 information about the past climate and envrionment changes owing to the intensive pedogenesis in the tropica1-subtropica1 area. Therefore, previous studies on bio-climatic approaches including po11en, spore fossils and phytoliths are also believed to be not suitable for such kind of stratigraphy. Despite that some studies show the microbia1 molecular fossils are usefu1 in the paleo-environment re- construction, but their implications in red earth need to be further exp1ored and confirmed. It is necessary to introduce some new methods to extract the detailed bio1ogica1 information in the red earth. In this study, we co11ected red earth samples from the Xuancheng section, Anhui Province in the Middle-Lower Reaches of the Yangtze River, which is we11-dated and sensitive to climate change. Microbia1 lipids in the red earth are extracted by emp1oying alkaline hydrolysis combined with the field survey andthelaboratory investigation. The characteristics of the microbia1 lipids, especia11y glycero1 dialky1 glycero1 tetraethers (GDGTs) are investigated. The distributions of GDGTs from the Xuancheng profile show that a11 GDGT-derived proxies in the 1ower 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 thelater soi1 environment was relatively stable. The CBT-inferred soi1 pH ranges from7.0 to8.0, indicating that the soi1 parent materia1 likely comes from the arid areas in north- western China or alternatively from the dry river sediments in the Middle-Lower Reaches of the Yangtze River. The1ow BIT values suggest that it was very dry at130 ka BP in the Xuancheng region