沙漠边缘厚层黄土上部光释光测年的初步研究  

OPTICALLY STIMULATED LUMINESCENCE DATING OF UPPER PART OF A THICK LOESS SECTION AT CAOXIAN NEAR THE NORTHERN DESERT OF CHINA

作　　者：覃金堂[1] 周力平[1] 

机构地区：[1]北京大学地理学院地表过程分析与模拟教育部重点实验室,北京100871

出　　处：《第四纪研究》2007年第4期546-552,共7页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:90411017和49925307)资助

摘　　要：对处于中国西北黄土高原沙漠边缘曹岘厚层黄土剖面上部进行了光释光年代初步研究。实验结果表明,45～63μm石英颗粒的光释光信号以快组分为主,适合应用单片再生剂量法(SAR)测年。在自然和再生剂量预热温度为260℃持续10秒,检测剂量预热温度为160℃持续0秒的条件下,石英单片再生剂量法获得的光释光年龄随样品深度而增加。但是,剖面底部S1古土壤和L2顶部黄土样品的光释光年龄仅为69·1±5·5ka和72·0±4·6ka,表现出30%～50%的年龄低估。利用多片再生剂量法(MAR)得到的年龄与SAR方法所得年龄无显著差异,即出现了类似的年龄低估现象。在20·1～18·8ka时段内,该剖面的沉积速率超过500cm/ka。末次冰盛期的寒冷气候,与沙漠的距离以及近邻黄河的地貌特点共同造成了如此高的沉积速率。OSL dating method is applied to a thick loess section at Caoxian, Gansu which is located in the northwestern part of the Loess Plateau and close to the northern desert. Eight samples for OSL dating collected from upper 45m of the profile were studied. The 45～63μm quartz fraction was extracted by sieving and chemical treatment. OSL signals of these samples are dominated by a fast component. Preheat plateau is identified for a young sample in the range from 180℃ to 260℃. A monotonic increasing equivalent dose with preheat temperature is observed for a relatively old sample. Nevertheless, a successful dose recovery test indicates the usefulness of the experimental condition of 260℃ preheat combined with a cut-heat of 160℃. This preheat strategy is applied to all samples except the young one at the depth of 50cm, which is. measured with a preheat temperature of 220℃. The OSL ages obtained by the single aliquot regenerative-dose （SAR） protocol exhibit an increase with depth. However, the samples from S1 and upper L2 yield OSL dates of 69. 1 ± 5.5ka and 72. 0 ±4. 6ka respectively, which seem to have underestimated their true ages by 30%～50%. The results seem to suggest that when OSL dating is performed on Chinese loess samples from S1 or earlier, the obtained OSL dates may suffer significant age underestimation even though the internal checks of SAR protocol are robust and the growth curve does not suffer from dose saturation. The OSL ages obtained by the sensitivity corrected multiple aliquots regenerative （MAR） protocol are indistinguishable from those by the SAR. Dust accumulation rate derived from the OSL ages of the uppermost part of the section exceeded 500cm/ka during 20. 1 ～ 18. 8ka. This is attributed to the very cold climatic condition during the last glacial maximum. Other factors such as the proximity to the northern desert source and the potential availability of sand from the Yellow River may have also contributed to the high accumulation rate of loess at the site.

关 键 词：曹岘 黄土 光释光 沉积速率 

分 类 号：P533[天文地球—古生物学与地层学] P941.74[天文地球—地质学]