通过对汉江上游湖北郧县-郧西段河谷的野外考察,选择前坊村汉江第一级阶地典型的黄土覆盖层剖面进行了深入研究.我们系统进行采样,分选出40～63μm石英颗粒,利用单片再生剂量法(SAR)技术,测得这些样品的光释光(OSL)年龄在2.90±0.15～16.76士0.60ka之间.OSL年龄值与地层深度表现出良好的对应关系.其中,利用释光信号组分拟合得到3种指数组分,发现快速组分达80％以上,且不同积分区间获得的De值处于一个坪区,各测片De值呈正态分布,说明这些风成沉积物晒退比较彻底.结合粒度参数Y值分析,确定这些沉积物属于风成堆积物.利用样品OSL年龄与气候替代指标,结合与秦岭北侧黄土剖面的对比,表明汉江上游河谷第一级阶地的风成堆积物从18.0ka开始堆积形成.自全新世以来受到不同程度的成壤改造作用,形成了与渭河谷地相似的Lt-Lt-So-Ll-MS土壤地层序列.同时发现在1.8ka(200A.D.)前后,汉江上游发生了一期特大古洪水事件.这些研究成果对于深入了解汉江上游水文气候变化具有重要意义.%Geomorphological and sedimentological study was carried out in the upper Hanjiang River Valley. A typical eolian loess-palaeosol profile(QFC-B)was found on the first terrace land near the Qianfang village in the Yunxian reach (32"48'13"N, 110°35'18"E; 161m a. s. 1). After detailed pedo-stratigraphic sub-divisions during the fieldwork, a group of 7 OSL dating samples and another group of 228 sediment samples were collected from the profile systematically. The results of sedimentological analysis showed that the profile was deposited by dust storms and dust falls and palaeosol was developed during the warm-humid period. OSL dating on quartz grains at the size of 40 ~63μm were carried out by using the single aliquot regenerative-dose ( SAR) protocol. The OSL dates of the samples were ranged from 2.90±0.15ka to 16. 76 ±t0. 60ka and the ages changed linearly with the depth change in this profile. A depth-age relationship was therefore established in the profile with the OSL dates in combination with the archaeological dating and the loss-on-ignition and grain size distribution. It showed that the eolian loess was deposited from 18. Oka on the first terrace land along the upper Hanjiang River Valley. The loess( L1 ) was deposited between 18. 0ka and 11. 5 ka under the dry and cold climate during the last glacial. The transitional loess ( Lt) was deposited during 11.5 ~ 8. 5ka during the early Holocene climatic amelioration. During the middle Holocene climatic optimum between 8. 5ka and 3. 1 ka,palaeosol S0(Udic Luvisol)was developed on the eolian dust deposit. This palaeosol S0 was well correlatable to the palaeosol S0( Ustic Luvisol) in the Guanzhong Basin north of the Qinling Mountains. Recent loess L0 was deposited from 3. 1 ka in the cooler and drier climate during the late Holocene. Typical palaeoflood slackwater deposit was identified in the upper part of the profile. It has recorded an extraordinary palaeoflood event occurring in the upper Hanjiang River that was dated to 1. 8ka(200A. D. ). These results are of great importance in understanding the hydro-climatic change in the upper Hanjiang River valley.
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