柴达木盆地东北部3500年树轮定年年表的初步建立

A 3500-YEAR MASTER TREE-RING DATING CHRONOLOGY FROM THE NORTHEASTERN PART OF THE QAIDAM BASIN

利用柴达木盆地东北部山地上生长的活树,尚未倒伏的死树和山前洪积扇上古墓中保存的椁木、棺木和封土柏木,在树轮年代学交叉定年技术的支持下,建立了该区长达3500年的树轮定年年表。最长的活树样本可追溯到公元404年,古木样本覆盖的时段是公元前1580年～公元793年,而死树样本覆盖了公元130～1794年。3种样本在时间上具有很长的重叠时段,为建立长定年年表提供了可行。样本间能够很好地交叉定年。此外,古木和死树在重叠时段轮宽变化的相关系数是0·51,死树和活树的是0·41,并且古木和活树的是0·61。这种极显著的相关关系说明建立长定年年表是可能的。将程序COFECHA为每个活树样点保存的定年序列、古木的定年序列和死树的定年序列放在一起,再运行程序COFECHA,就建立了一个基于621棵树的样本量组成的总定年年表。该年表的取材完全独立于已发表的都兰年表,在时间上比都兰年表向前延伸了近1000年,使其能够达到商、周朝代。与调整后的都兰年表对比,发现两者在公元前328年～公元2000年之间完全能够交叉定年。文章所建的树轮定年年表是国内目前最长的连续年表,它可为我国西北干旱-半干旱区树轮长序列的定年提供标尺。

A master ring-width dating chronology for the last 3500 years was developed by cross-dating well-replicated samples from different sources at 26 sites distributed over a region almost 200km across in the northeastern part of the Qaidam Basin in Northwestern China. The materials came from living trees, dead trees still standing on the slopes, and archaeological woods such as trunks and wooden coffins from the tombs of the Tang Dynasty situated on the alluvial fans in the study area. The longest core from living trees was dated back to 404A. D., and the time span covered by the archaeological woods is from 1580BC to 793A. D. The specimens from the dead trees covered the period of A. D. 130 to 1794. The overlaps in time among the three types of samples are long enough to support the development of a high-quality long chronology for the study area. We found that cross-dating could be performed well among specimens of different sources and highly significant correlation coefficients were present among three types of samples for their overlaping periods, i. e., 0.51 between the archaeological woods and dead trees, 0.41 between the dead and living trees, and 0.61 between the archaeological woods and living trees, respectively. This suggests that it is possible to establish a master chronology for the study area. Using the master dating series produced by the program COFECHA for each site of the living trees, for all the dated archaeological woods and specimens from dead trees, a master dating chronology using specimens from 621 trees from the study area was developed by COFECHA again. This long chronology is not only independent of the published Dulan chronology, but also more than 1000 years longer, reaching to the time of Shang and Zhou Dynasties. After two missing rings were added to the Dulan chronology, these two chronologies are cross-dated very well for the common period of 328BC ～2000A. D. This is by far the longest tree ring dating chronology in China, which can be used as a reference for ring-width dating for trees from the arid and semi-arid regions of Northwest China.