贵州荔波董歌洞较老石笋ICP-MS~(230)Th测年研究及古气候应用

石笋记录研究的进展与测年技术的发展密不可分,测年新技术的突破不断推动利用石笋重建古气候研究的飞速前进。在利用石笋进行古气候重建过程中,建立精确的时标是首要条件。通过对较老(>250ka)石笋的ICP-MS230Th测年研究,发现贵州荔波董歌洞D6、D7、D9石笋具有比较连续的高分辨记录,最老年龄超过400ka,通过230Th测年数据的分析为建立我国西南地区500ka以来标准剖面打下基础;对董歌洞3根大型石笋135个230Th年龄数据及生长速率的分析研究,发现石笋生长速率在大尺度的变化上与海洋沉积SPECMAP曲线δ18O记录有很好的负相关关系,并与北纬25°夏季太阳辐射能量变化曲线呈一定的正相关关系,石笋生长速率的变化在间冰期处于高值,而在冰期时为低值,在间冰期和冰期转化阶段生长速率呈跳跃式变化。通过生长速率变化分析表明,石笋生长速率记录了过去突变冷暖事件的变化,因此可以作为一个有意义的环境记录替代指标来研究古降水及古气候变化。

RESEARCH ON OLD STALAGMITES BY ICP-MS230 Th DATING AND PALEOCLIMATE RECONSTRUCTION IN DONGGE CAVE,LIBO,GUIZHOU

Advances in the research of stalagmites keep pace with the development of dating techniques,because new dating techniques aid paleoclimate reconstruction.Therefore,a precise chronology is the key for paleoclimate reconstruction based on stalagmites.Our study on old stalagmites(>250ka) using the ICP-MS 230 Th dating method shows that stalagmite D6,D7,D9 of the Dongge Cave contain continuous and high resolution paleoclimate since 400ka ago.The 230 Th data serve as a standard for paleoclimate study in southwestern China for the last 500ka.This paper focuses on the relationship between stalagmite growth rate and paleoclimate reconstruction based on 135 precise ICP-MS 230 Th analyses of three big stalagmites in the Dongge Cave in southwestern China.The growth rate of stalagmites is negatively correlated with the δ 18 O record of SPECMAP and positively correlated with summer insolation at 25°N.Stalagmite growth rate was high in interglacial intervals,low in glacial periods,and more variable in transitional periods.Based on these results,we suggest that stalagmite growth rate may record changes in abrupt cold and warm events and thus could provide a useful proxy for long term records of paleoprecipitation and paleoclimate.