贵州荔波董哥洞3号石笋的同位素年龄及古气候信息

Isotopic Ages and Paleoclimatic Implications of No.1 Stalagmite from Dongge Cave in Libo

石笋是岩溶记录中最全面、最系统的古气候环境信息库 ,研究表明 ,洞穴内、外环境变化 ,都不同程度地显示在石笋的组成、结构构造、沉积 (生长 )纹层及其层面构造、沉积速率和古气候环境变化等方面。利用洞穴石笋保存的信息重建古环境 ,是近 2 0年来的热门课题之一。当前全球气候变化预测研究中 ,洞穴石笋的高分辨率定年和碳、氧同位素组成的变化规律 ,为这个领域的突破和填补空白作出了重大贡献。本文通过对荔波董哥洞 3号石笋进行热电离质谱 (TIMS)U—系测年及碳氧同位素分析 ,获得了距今 16 .33万年至 9.13万年的古气候信息。石笋在大于 16 .33万年前开始生长 ,9.13万年后停止生长 ,平均沉积速率为 2 .87mm/ 10 0a(未扣出间断时间 ) ,属中更新世的产物。其年龄与δ18O的变化可与深海岩芯V2 8～ 2 38同位素记录所揭示的第五和第六阶段以及与北方离石黄土层 (L2 )和下马兰黄土第一古土壤层 (S1)进行对比。它反映此阶段区内经历了寒冷和温暖 (间夹冷期 )等气候变化 ,与全球古气候变化波动基本一致 。

Stalagmites in cave is the most comprehensive and systemetic paleo climatic environmental information contaimed in karst records. The study has shown the environmental changes in cave and at outside of the cave with the indication of the different degree in the composition of stalagmite, texture or structure, sediment or growth laminates, bedding plane structure, growth rate and environmental changes of paleo climate and so on. The reconstruction paleoenvironment by use of the preserved information in stalagmite is one of the popular project for lastest the 20 years. Under the study of the global climatic changes, high resolution dating and the change law of carbon and oxygen isotopic component of stalagmites in cave have made a great contribution to the breakthrough in the field. A large stalagmite with continuous profile of clear annual growth laminae for studying the paleoclimatic changes were found in Dongge cave of Libo area last year.Because the laminae of stalagmite is mainly composed of calcite, they are suitable to be measured by TIMS U series method to get reliable and high resolution ages compatable with other materials such as lake or marine sediments. Therefore, stalagimte may have vast vistas for geochronology study since the middle Pleistocene Epoch. Paleoclimatic information from 163.3 ka B.P. to 91.3ka B.P. have been obtained through TIMS U series dating ages and carbon and oxygen isotopic analysis to No.3 stalagmite from Dongge cave in Libo. The ages and the change of oxygen isotopic records in Libo area can compare with theⅤ and the Ⅵ stages of oxygen isotopic records of the deep sea cores(or sediments). The results shown that the records of climatic change from 163.3ka B.P. to 91.3ka B.P. in this period in Libo area underweth from the cold period to warm and humid period. It coincides with the wave motion of the global paleoclimatic change, in the meantime, the climatic change of the region also exist.