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南昌市厚田沙地风沙沉积记录的末次冰期气候变化特征

Climatic Characteristics Changes Recorded by Eolian Deposition in the Houtian Desert of Nanchang during the Last Glacial Period

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【Author in Chinese】 王志刚

【Supervisor】 李志文

【Author's Information】 东华理工大学, 地理学, 2018, 硕士

【Abstract in Chinese】 位于南昌市南部的新建区,广泛分布着由沙丘砂—古土壤叠覆堆积组成的沉积序列。这套风沙-风尘堆积,蕴含着丰富的古气候信息,是研究鄱阳湖南部亚热带季风湿润区古环境研究的重要载体。在野外调查的基础上,选择位于新建区南部的厚田剖面进行工作,通过光释光测年、土壤粒度以及磁化率特征等手段,反演末次冰期的气候变化特征及其与东亚季风的关系。研究发现其沉积序列由3层沙丘砂和3层砂质古土壤组成,顶部与底部的OSL年代为14.9ka和77ka BP,表明为末次冰期的产物。依据OSL年代和粒度分析结果,得出结论如下:1)厚田剖面的末次冰期地层可划分为HTS4(77-57.1ka BP)、HTS3c(57.1-49.7ka BP)、HTS3b(49.7-36.8ka BP)、HTS3a(36.8-26.5ka BP)、HTS2(26.5-14.9ka BP)五个阶段。2)以粒径-标准偏差法与主成分因子分析法提取敏感粒度,12.619-20μm含量与平均粒径和黏粒含量呈正相关,400-563.667μm含量与平均粒径和黏粒含量呈负相关,经比对反映冬季风强度的敏感粒径为400-563.667μm;反映夏季风强度的敏感粒径为12.619-20μm。3)平均粒径、磁化率、黏粒含量、敏感粒度在剖面上呈现明显的峰谷交替变化,暖阶段基本同步于葫芦洞石笋记录的夏季风强盛期、磁化率的高值和65°N天文辐射总量的高峰,揭示出HTS3c、HTS3a、HTS2早期为温暖期,砂质古土壤发育;冷阶段对应于古里雅冰芯δ18O记录的冬季风强盛期、平均粒径的粗值和65°N天文辐射总量的低值,揭示出HTS4、HTS3b、HTS2晚期为寒冷期,沙丘砂发育。这些结果表明,厚田剖面末次冰期的气候变化存在万年尺度的气候波动,是太阳辐射总量和东亚季风共同影响下的结果。

【Abstract】 The series of sedimentary sequences superimposed by dunes sand-paleosol is widely distributed in the southern part of Nanchang,Xinjian District.Based on the field investigation,we use optical stimulated luminescence dating,soil particle size and magnetic susceptibility which inverted the characteristics of the last glacial period and its relationship with the East Asian monsoon.Then we found the Houtian section mainly consists of the alternating deposition of 3 layers of dune sands and paleosol,and its top and bottom age is 14.9-77 ka BP,which is the product of the last glaciation.According to the analysis of the contents of grain size and OSL chronology,we got the conclusion as follows:1)The strata of the last glacial in the Houtian section can be divided into five stages,as HTS4(77-57.1ka BP),HTS3c(57.1-49.7ka BP),HTS3b(49.7-36.8ka BP),HTS3a(36.8-26.5ka BP),HTS2(26.5-14.9ka BP).2)The two results extracted by particle size-standard deviation method and principal component factor analysis showed that 12.619-20μm is positively correlated with Mean particle size and clay content,400-563.667μm is negatively correlated with Mean particle size and clay content,inspected that the indicator particle size of winter monsoon is400-563.667μm and the indicator particle size of summer monsoon is 12.619-20μm.3)The Mean particle size,clay content,susceptibility and sensitive particle size shows remarkable variations in alternation of peaks and valleys.The warm periods mainly correspond to strong summer monsoon indicated by stalagmite in Hulu Cave in China,as well as the peak of total amount of astronomical insolation at 65°N in July and susceptibility,which reveals that the sand-paleosol is developed in the warm period of HTS3 c,HTS3a and early HTS2.And cold periods mainly correspond to weak summer monsoon indicated by Guliya ice core in the West Kunlun Mountains,as well as the valley of total amount of astronomical insolation at 65°N in July,which reveals that the dunes sand is developed inthe cold period of HTS4,HTS3 b and late HTS2.The climate changes in the Houtian section during the Last Glacial period has a climate fluctuation of ten thousand years,which probably results from the mutual impact of total amount of insolation and East Asian monsoon.

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