许家窑遗址地层时代讨论

许家窑遗址是中国旧石器时代中期的一处重要考古遗址,按照地层古生物学常规判断,其地层为上更新统下部.许家窑遗址是泥河湾盆地乃至东亚地区发现的上更新统包含古人类及古哺乳动物化石和旧石器时代考古遗物最丰富的一个地层剖面.许家窑遗址的古地磁测年的分析存在重大理念误区,其"早更新世晚期至中更新世早中期"的断代结论令人难以置信.

DISCUSSION OF THE AGE OF THE XUJIAYAO PALEOLITHIC SITE,NIHEWAN BASIN

The Xujiayao site in the Nihewan Basin is an important paleoanthropological site in China and in East Asia.A lot of archaeological remains have been unearthed from the deposit at 7.4～12.8 m below the present ground surface.The cultural remains were embedded in fluvial-lacustrine sediments of the "Nihewan beds".The human fossils of the "Xujiayao Man" include 20 bone fragments and teeth and represent more than 10 adult and young individuals that were assigned to archaic Homo sapiens.Over 30,000 stone artifacts were unearthed of the "Xujiayao fauna".The fauna includes:Struthio sp.,Ochotona sp.,Myospalax fontanieri,Microtus brandtioides,Canis lupus,Panthera cf.tigris,Palaeoloxodon cf.naumanni,Coelodenta antiquitatis,Equus perzewalskii,E.hemionus,Sus sp.,Megaloceros ordosianus,Cervus elaphus,C.nippon grayi,Gazella subgutturosa,Spirocerus hsuchayaocus,S.peii,Procapra picticaudata przewalskii,and Bos primigenius.According to biostratigraphic data,the complex of cultural layers should be assigned to the Late Pleistocene and was named the"Xujiayao Formation".It has yielded the most abundant paleoanthropological,Paleolithic and paleontological data in the Nihewan basin.The Xujiayao site was dated to 104~125 ka by the uranium series method.The IRSL age is 60±8~69±8 ka.The assumptions underlying the sampling method used in palaeomagnetic studies in the Nihewan basin have revealed severe inherent problems,including the lack of the Brunhes-Matuyama reverse event.It is therefore difficult to date Late Pleistocene sites using the paleomagnetic method.A paleomagnetic date of the Xujiayao site to the late Early to early Middle Pleistocene,based on the belief of the Brunhes-Matuyama boundary beneath the cultural horizon and the assumption of sedimentary accumulation rates,is not convincing.The paleomagnetic age was calculated from an averaged sedimentary accumulation rate,which assumed the deposition of strata through a constant process in different sections throughout the time of deposition.However,lithostratigraphy of the "Nihewan beds" varies greatly in time and space.The sections sampled for palaeomagnetic analysis vary in thickness and there is no basis for a uniform sedimentation rate among the sections.This means that the averaged sedimentary accumulation rate used in the palaeomagnetic dating is unreasonable.