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渭河咸阳段全新世古洪水事件光释光测年研究

ISSN号：1000-0550
期刊名称：沉积学报
时间：2012
页码：346-355
分类：P331[天文地球—水文科学;水利工程—水文学及水资源;天文地球—地球物理学]
作者机构：[1]陕西师范大学旅游与环境学院,西安710062, [2]黔东南民族职业技术学院,贵州凯里556000
相关基金：国家自然科学基金重点项目（批准号：41030637 40930103）; 教育部博士点基金项目（编号：20110202130002）; 中央高校基本科研业务费专项基金（编号：GK200902020）资助致谢野外采样和实验测试得到赵梅、杨凌同学的热情帮助,两位匿名审稿专家和编辑部提出了有益建议,在此一并致谢.
相关项目：我国北方沙地末次冰期以来干湿变化、地表响应及驱动机制

关键词：古洪水事件, 光释光测年, 全新世, 滞流沉积物, 渭河, palaeoflood slackwater, OSL dating, Holocene, palaeoflood slackwater deposits, Weihe River

中文摘要：

古洪水水文学研究是全球气候变化研究的前沿课题,确定古洪水事件的年代是古洪水研究的重要内容之一。对渭河流域进行深入的野外考察,在中游咸阳段阶地发现全新世黄土—古土壤层里夹有古洪水滞流沉积层,表明该地层记录了古洪水事件发生的信息。在该剖面采集光释光样品,分离提取40～63μm石英颗粒成分,应用单片再生剂量法（SAR）进行红外后蓝光（Post—IR OSL）释光测量,获得了9个OSL年龄值。结果表明由古洪水滞流沉积层记录的特大古洪水事件发生在3 200～2 800 a B.P.之间。结合沉积样品系列的磁化率和粒度成分等气候替代性指标分析,揭示了在全新世中期向晚期转折过渡时期,渭河流域处于气候向干旱化发展的转型期,气候变化剧烈,大气系统不稳定,降水变率增大等,是导致特大洪水多发的主要原因。这也是渭河流域气候水文系统对于全球性气候恶化响应的结果。

英文摘要：

Through deeply field survey,a Holocene loess-soil profile with interbedded flood slackwater deposits（SWD） was found in Xianyang of the middle reaches of the Weihe River,which recorded the information of palaeoflood events.In order to achieve OSL ages,9 luminescence samples were collected and post-IR OSL measurements were used with single-aliquot regenerative-dose（SAR） protocol.Grain-size distribution and magnetic susceptibility were also analysed so as to research the occurrence and cause of palaeoflood.The result shows that the fast component is dominant in OSL signals of quartz grains（40~63 μm）,which is suitale for post-IR OSL measurements.For all dating measurements,preheat temperature of each natural or regenerated dose of young samples and older samples were 260℃ and 240℃,respectively;and the cutheat was set to 220℃.OSL ages increases with depth and conform to layer where were collected except individual ages underestimated. At the NSC site,the layer of flood slackwater deposits（SWD） with horizontal bedding、silty clay-like and sallow colour,was in the depth of 95~110 cm,which has typical characteristic of SWD.This flood deposit involve 3 flood depositional layers,indicate of at least 3 palaeoflood evevts occured.The average of low-frequency magnetic susceptibility of paleosoil was 133.62 10-8 m3.kg-1,was the highest in this profile,while the value of SWD layer was 113.68 10-8m3.kg-1 which was much higher than Malan loess,but lower in paleosoil layer.Grain-size distribution of SWD layer was dominated by silt,the content of silt was 59.43% and clay was 38.107%,the content of sand（0.05 mm）was the least that was 3.32%.The curve of sand（0.05 mm） in the SWD layer present a small peak.The dating results show that the extreme palaeofloods occurred 3.0~3.2 ka.According to the analysis of all the result,extraordinary floods occurred 3 200~3 000 a B.P.in the Weihe river,the period of flood occurred frequently.Three flood depositional layers indicates that each of the slackwater deposit

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