四川广汉三星堆遗址四号祭祀坑的碳十四年代研究

2020年,广汉三星堆遗址新发现祭祀坑的田野考古发掘工作正式启动,为解决祭祀坑的年代问题,四川省文物考古研究院委托国家文物局考古研究中心与北京大学考古文博学院考古年代学联合实验室对四号祭祀坑开展了碳十四年代研究,得到6个碳十四年代数据,经过贝叶斯统计树轮校正计算得到其埋藏年代有95.4%的概率落在距今3148—2966年的时间范围之内,属商代晚期。

AMS Radiocarbon Dating of K4 Sacrificial Pit at Sanxingdui Site in Guanghan City,Sichuan Province

The first two sacrificial pits,K1 and K2 at Sanxingdui site were discovered in 1986.A great quantity of jade,gold,bronze and ivory artefacts was found from the two pits.The way of burial and the diversity of the wares are unique and never seen before in China.Because of the poor preserving condition of the radiocarbon dating samples,it is difficult to get enough amount of carbon component to produce reliable radiocarbon age of the pits byβ-counting radiocarbon dating method at that time.The issues related to the function and the age of sacrificial pits at Sanxingdui site became a hot topic in the academic circles since then.After more than 30 years,the new discoveries of 6 sacrificial pits near K1 and K2 have been excavated since 2020,which shed the light on solving the problems.Multidisciplinary researches are carried out during the excavation.The AMS radiocarbon dating method is applied to get the absolute ages of the 6 pits.The chronological researches about K4,one of 6 pits,is discussed in this paper.There is thick layer deposition of bamboo charcoal mixed with clay above the elephant tusks and there are many artefacts found within or under this layer.It shows that the burnt bamboo and the artefacts were buried simultaneously,which means that bamboo charcoal can be used for radiocarbon dating in order to get the age of K4 pit.Animal bones and elephant tusks excavated from K4 couldn’t be used for radiocarbon dating because all the bones and tusks were burnt before deposition and there is not enough collagen protein preserved.15 samples were collected from K4 pit which are mixtures of clay with small pieces of bamboo charcoal and fragments of burnt animal bones.Samples were screened carefully in the lab and only bamboo charcoal pieces were selected from those mixtures.After the pretreatment protocol of bamboo charcoal,6 graphite samples were prepared under the reduction of H2 with Fe powder as catalyst.The radiocarbon measurement were carried out by the compact accelerator mass spectrometry at Peking University.6 radiocarbon ages were produced and all are consistent with each other in 2σ.The calendar ages were calculated by Bayesian statistical analysis with the tree ring calibration curve 2020.The result of the calibrated age of K4 falls in the range of 3148-2966 cal.BP with 95.4%probability.If compared with the chronology of dynasties in early China,it could be concluded that K4 was buried during late Shang period.