汉江上游安康东段古洪水事件光释光测年研究

OSL Dating of the Palaeoflood Events in the Ankang East Reach in the Upper Hanjiang River Valley

通过对汉江上游峡谷广泛的野外考察,结合系统采样和粒度成分与磁化率测试分析,证明汉江上游安康东段第一级阶地黄土质覆盖层剖面夹有两组典型的古洪水滞流沉积层,其记录了两期特大古洪水事件.本文在该河段选择两个剖面进行系统采样,对其进行了年代学研究.应用单片再生法（SAR）技术获得其光释光年龄值,结合地层和高分辨率气候变化记录对比分析,确定第一期古洪水事件发生在12700～12500 a BP之间,对应于晚冰期Bolling-Allerod向着Younger Dryas转折的时期,第二期古洪水事件发生在1000～900 a BP,对应于我国历史上北宋时代的气候恶化时期.这表明汉江上游古洪水事件的发生与气候恶化转折密切相关.由于季风气候状态不稳定,降水变率增大,导致特大洪水与干旱事件皆有发生.

Based on the paleohydrological investigation and sampling in the upper Hanjiang River valley,and analysis of grain sizes and magnetic susceptibility,it has been identified that two sets of typical paleoflood slackwater deposits found to occur along the riverbanks in the Ankang east reach record two super-large paleoflood events.Samples were collected from two profiles for dating.OSL age was obtained using SAR technology （Single Aliquot Regenerative-dose）.Combined with analysis of the strata and high-resolution weather change records,the first paleoflood event occurred between 12700 and 12500 a BP,corresponding to a period transiting from Bolling-Allerod to Younger Dryas.The second paleoflood event occurred at 1000～900 a BP,corresponding to a climate worsening period in late period of the North Song Dynasty（A.D.1100～ 1000）.This indicates that occurrence of paleofloods along the Hangjiang River was closely related to climate worsening.High instability of monsoon climate resulted in great variation of precipitation,which might cause flood and droughts to happen frequently.