摘要
选择位于黄土高原东南缘的渭南剖面和中部的西峰剖面末次间冰期以来的黄土-古土壤序列,研究了黄土颜色(亮度和红度)变化的时空特征及其主要控制因素。结果表明,黄土的亮度变化主要与铁氧化物、有机质、碳酸盐的含量有关,三者的影响依次减弱,而红度变化则主要受控于铁氧化物的种类和含量。值得注意的是,渭南剖面的红度变化与亮度和磁化率记录在L2/S1过渡时段明显不一致,表明单一的磁化率或颜色指标(红度)在重建夏季风强度时都有一定的局限性。尽管磁化率和红度变化受控的铁氧化物不同,但两者都同风化成壤关系密切,本文综合考虑两个指标,通过对磁化率和红度标准化,提出一个新的Stack指标,用于反演末次间冰期以来夏季风的演化,为深入理解东亚夏季风演化尤其是倒数第二次冰消期夏季风的增强特征提供了新的线索。
Two loess-paleosol sequences at the Weinan and Xifeng sections spanning the last climatic cycle were investigated to better understand the spatial and temporal variations of the soil color （e.g., lightness and redness） and their major controlling factors. Our results show that lightness and redness are significantly different between loess and paleosols layers, with relatively low lightness values and high redness values in the paleosol layers. Variations in the lightness are strongly linked to the concentrations of iron oxides, organic matter and calcium carbonate. Relative impacts of these factors on the lightness decrease gradually from iron oxides and organic matter to calcium carbonate. By contrast, the redness is dominantly controlled by types （e.g., goethite and hematite） and concentrations of iron oxides. It is noteworthy that during the transition of L2 to S1, changes in the magnetic susceptibility and lightness differ significantly from that of the redness, implying that either magnetic susceptibility or redness has limitations for inferring the summer monsoon intensity. While variations in the magnetic susceptibility and redness are controlled by different magnetic minerals, these two proxies are closely associated with post-depositional processes such as chemical weathering and pedogenesis. Here we combine these two indicators by normalizing each proxy and averaging as a stacked summer monsoon index and interpret this proxy as the most indicative of summer monsoon variability. This new proxy provides a new clue to better understanding the summer monsoon variation, in particular the pattern of the summer monsoon strengthening during the penultimate deglaciation.
出处
《地球化学》
CAS
CSCD
北大核心
2010年第5期447-455,共9页
Geochimica
关键词
中国黄土
亮度
红度
磁化率
夏季风
Chinese loess
lightness
redness
magnetic susceptibility
summer monsoon
