泥河湾盆地东坡遗址ESR年代学初步研究

ESR DATING OF DONGPO PALEOLITHIC SITE IN THE NIHEWAN BASIN OF CHINA

中国泥河湾盆地以发育我国北方晚新生代湖相地层和数目众多的古人类文化遗址而闻名于世，是研究中国北方第四纪地质与环境、新旧石器和早期人类演化的一个关键地区。东坡遗址是泥河湾遗址之一，形成时代一直没有确定。根据古地磁和区域地质等分析，初步认为东坡遗址形成时代不早于距今780ka。本文利用石英Ti心ESR法对泥河湾东谷坨剖面B／M界限样品进行了测量，年龄为750±88ka，这表明利用该方法对泥河湾层水相沉积物进行测年是可行的。我们利用同样方法和参数对东坡遗址进行ESR年代学研究，结果表明东坡遗址文化层的形成时代为距今304±12ka到333±23ka，平均年龄为321±15ka。

The Nihewan Basin is located at about 150km west of Beijing,in the Sanggan River drainage, Hebei Province in Northern China. It had experienced environment changes including development of a lake,lake size variations, incision of valley, erosion, alluvial and aeolian deposition, etc. which in the point of view of environment change resembles the Olduvai Gorge in Tanzania. The Nihewan Basin yields Late Cenozoic lacustrine and fluvial strata, named the Nihewan beds,which are among the best preserved Quaternary strata in East Asia,making the basin an important area for the interdisciplinary study of Quaternary geology, palaeoenvironment, palaeontology, geochronology,and Palaeolithic archaeology. A great number of Paleolithic sites, with abundant fossil mammals and stone artifacts, have been discovered from the basin. These sites contain critical information for early human adaptability to high northern latitudes in East Asia. However,the ages of many sites have been determined currently only by magnetostratigraphical method, a chronological framework for all sites hasn＇t been available yet. The Dongpo site was excavated in 1999, It lies 800m east of the Hutouliang Village at approximately 40~10＇N latitude and 114~29＇E longitude. The 15 -20cm thick culture layer is about 40cm below the ground surface. Stone artefacts were discovered in the cuhare layer, which lacks animal fossils. Preliminary magnetostratigraphic analysis indicates that its sedimentary sequence is of normal polarity and may be correlated to the Brunhes normal chron. However,the paleomagnetic method failed to precisely date its age,only roughly estimated the age of younger than 780ka. Electron spin resonance （ESR） dating is applied in this paper to determine the age of the Dongpo site. We eolleeted three samples（DP01 ,DP02,and DP03）from the culture layer of the site at the buried depth 0.45cm, 0.50em,and 0. 55cm, respectively. A previously dated sample （DGT02） collected near the Brunhes/Matuyama （B/M） boundary at a buried depth of about 5m from the Donggutuo site, which was analyzed as a referenee using the same method and parameters. Our dating result of the Donggutuo sample collected from the B/M boundary is 750 ＋ 88ka. It suggests that the sample was totally bleached before deposition and it is thus feasible to use quartz Ti-centre ESR signal to evaluate the age of lacustrine and fluvial sediments of this area. The ages of three culture layer samples collected from the Dongpo site are 325 ±24ka,304 ± 12ka and 333 ± 23ka, respectively,with the average age of about 321 ± 15ka.