摘要
文章报道了贵州羊子坡洞一支长约18.6cm、宽约5cm石笋研究的结果。对石笋分别作了210Pb、铀系质谱测年和显微镜下数沉积年轮方法定年;石笋的灰度和碳同位素结果可相互印证,表明其记录是连续可靠的。测年结果显示此石笋保存了从8629年前至今(1999年)的气候变化,而发生在大约130年前(1869A.D.)各代用指标数值的大幅度变化尤其引人注目,其石笋的灰度、同位素和岩性的变化尺度之大以至于不可能单纯从气候变化方面来解释。进一步的深入研究和野外实地调查揭示出,这些急剧变化是由发生在当时一历史事件所产生的植被破坏及树木灰烬微粒被带入洞中而造成的。能谱扫描电镜的结果也证实了此层树木灰烬微粒的存在。此研究表明洞穴石笋具有记录人类活动的能力。
This article reports on the study of an active stalagmite 18.6cm long and ca. 5cm wide that was recovered 180m into Yangzipo Cave, about 30km southwest of Guiyang City, the capital of Guizhou Province in Southern China in December 1999. The stalagmite was cut into two halves along the central growth axis with a band saw, and four large （51mm × 76mm） thin sections were cut so as to minimize the loss of petrographic information. The pertographic study was conducted under a Leitz Laborlux 12 Pol Petrographic Microscope in the University of Georgia Sedimentary Petrography Lab and the Laboratory for Speleothem Studies. Thin section analysis revealed 125 annual layers in the upper 4. 1cm of the stalagmite. The layers could be identified by detrital grains at the top of each layer. Because of the change in petrography and the convergence of the very thin layers, layer counting was difficult to continue further down. Thin section studies also showed that the basal one-fourth of the formation is predominantly aragonite while the upper, darker three-fourth section is largely calcite. The presence of aragonite is the result of deposition in relatively dry or evaporative conditions at higher saturation states, and calcite is considered as the result of precipitation in wetter conditions at lower precipitation rates and saturation states. After polishing and wetting to enhance color differences, one exposed surface was photographed. This photo was scanned at 600 dpi, and gray-scale brightness was measured along the central growth axis in 8-bit format （bright white = 255; black = zero） using software for image analysis. Several dating methods including ^210Pb dating of 4 samples at the Skidaway Institute of Oceanography, University of Georgia, and thermal ionization mass spectrometry （TIMS） U-series dating of 14 samples at the Department of Geology and Geophysics, University of Minnesota, USA, and annul layers counting were applied to obtain a reliable and accurate age for it. ^210Pb analysis and annual layer cou
出处
《第四纪研究》
CAS
CSCD
北大核心
2006年第5期808-813,共6页
Quaternary Sciences
基金
美国国家自然科学研究项目(编号:0002433)
伊龙大学教师研究与发展基金项目资助~~
关键词
洞穴石笋
历史事件
人类活动
stalagmite, historical event, human activities
