巴丹吉林沙漠湖泊年轻沉积物14C测年初步研究

A Preliminary Study of AMS 14C Dating of Young Lacustrine Sediments in the Badain Jaran Desert

中文关键词:  AMS¹⁴C测年  碳库效应  ²¹⁰Pb_uns测年  巴丹吉林沙漠湖泊

英文关键词::AMS ¹⁴C  Reservoir Effect  ²¹⁰Pbuns dating  The Badain Jaran desert

中文摘要:

      沙漠湖泊沉积物是研究气候环境变化的珍贵材料,湖泊岩芯年代学研究是重建古气候和古环境的基础和前提,然而其年代的测定存在诸多困难,尤其是年轻湖泊沉积物测年一直是当前地质年代学研究的难题。¹⁴C测年作为一种传统的测年方法已被广泛应用于各类湖泊年轻沉积物的年代测定。巴丹吉林沙漠湖泊年轻沉积物能否利用¹⁴C方法进行测年,其可靠性如何,需进行研究和验证。选择巴丹吉林沙漠腹地的两支岩芯(BR-1和YD-1),对其进行了¹⁴C测年,并与已有的²¹⁰Pb_uns及其推算年代进行了对比。结果表明:1)沙漠湖泊中的植物残体来源存在较大的随机性,可能是原有的更老沉积层中的植物残体的再沉积,测年结果偏老约1000年。2)湖泊岩芯中有机沉积物样品的年代结果基本符合沉积规律,但受硬水效应的影响,其年代整体偏老400~900年。3)与²¹⁰Pb_uns年代对比,两种不同测年物质所测得的年代均存在不同程度的偏老现象,表明岩芯所在湖泊¹⁴C年龄受多种因素影响,总体存在很大的不确定性。在测年材料极为稀缺的沙漠丘间湖区,利用岩芯中的植物残体、沉积物有机质进行¹⁴C测年,可能受老沉积层中测年材料再沉积、湖水碳库效应等因素的影响,¹⁴C年代存在诸多不确定性。因此,在对巴丹吉林沙漠丘间湖泊年轻沉积物测年研究过程中应谨慎运用。

英文摘要:

      :Lacustrine sediments in the desert provide valuable archives for studying the climate and environment changes, the research of its chronology is the basis and prerequisite for the reconstruction of paleoclimate and paleoenvironment, however, there are lots of difficulties in dating the lacustrine sediments, especially the dating of young lacustrine sediments is a difficult problem in current geochronology. ¹⁴C dating, as a kind of traditional dating method, has been widely applied in all kinds of young lacustrine sediment. Further study and validation of the reliability and applicability of the young lacustrine sediments AMS¹⁴ C dating in the Badain Jaran Desert are required. Two sediment cores(BR-1&YD-1)in the inter-dune lakes of the Badain Jaran desert hinterland were chosen to make a comparison study between the AMS ¹⁴C dating and ²¹⁰Pb_uns dating. The results show that:(1) For the great randomness of the source of plant residues in desert lakes or the redeposition of the plant residues which come from the older stratum, the results of plant residues samples are about 1000 years older than what they actually are. (2) The results of organic sediment samples basically conform to the sedimentological law, but affected by the “hard water” effect, it is 400~900 years older than what they actually are. (3) Compared with the results of ²¹⁰Pb_uns dating, the AMS¹⁴C ages of the two materials are older, shows that the AMS¹⁴C ages of the lake sediment cores in the Badain Jaran desert are affected by several factors and overall there is a big uncertainty. When the plant residues and the organic sediments which come from the inter-dune lakes of the Badain Jaran desert are used to date, it may be affected by the redeposition of the plant residues which come from the older stratum or the Reservoir Effect. All these factors will lead to a big uncertainty, consequently, more caution should be paid to the AMS¹⁴C dating of young lacustrine sediments in the inter-dune of Badain Jaran desert which is lack of dating materials.