【作者】 李俊云；

【导师】 谢世友； 李红春；

【作者基本信息】 西南大学 ， 自然地理学， 2007， 硕士

【摘要】 本论文对贵州中西部地区的郑家洞、石将军洞和织金洞三个洞穴水样和碳酸钙沉积物样品的地球化学特征的分析，重点研究了石将军洞的两根鹅管的微量元素变化特征和元素比值（Mg/Ca，Sr/Ca，Mg/Sr）。得出三个洞穴的洞穴水Mg/Sr比平均值分别为1278±411、1155±207、14.0±2.7，安顺洞穴的水样富Mg贫Sr，与织金洞的相反，一方面可能与围岩组成的差别有关，另一方面可能与洞穴地表的植被和土壤覆盖有关。通过织金洞洞穴水和现代碳酸钙沉积物中Sr／Ca比值，计算出K_Sr值为0.04～0.134，平均值为0.073±0.035；K_Mg平均值为0.021±0.010，这些结果对今后利用石笋Mg/Sr比值作为古气候代用指标的研究提供基础数据。石将军洞鹅管SJJ-5，SJJ-6的Mg，Sr含量变化呈反相关关系，Ba，Sr含量呈正相关关系，Fe，Mn的含量变化一致，Mg/Ca、Mg/Sr比值变化受Mg含量的控制，Sr／Ca比值受到鹅管中Sr含量的影响。两根鹅管中的Mg/Sr比值都出现了突变，且变幅比较大，这种变化可能不是由于温度的变化造成的，有可能是由于外界地表土壤和植被的变化所致。鹅管SJJ-5，SJJ-6的Mg/Sr比值与δ¹³C，δ¹⁸O的变化呈相反关系，δ¹⁸O偏轻即降水量增加时期，δ¹³C也随之偏轻，Mg/Sr比值增加，可能该时期为暖湿气候，反之则为冷干型气候。根据元素比值和δ¹³C，δ¹⁸O的变化特征，推测SJJ-5沉积时期的气候为暖湿、冷干交替出现；SJJ-6的，δ¹⁸O、δ¹³C值逐渐偏重，说明该鹅管沉积时期的降水量从老到新逐渐减少，从而导致地表植被也随着发生了较大的变化，同时Mg/Sr比值呈逐步减小的特征，说明Mg/Sr比值能响应外界环境变化。两根鹅管的Mg/Ca、Sr／Ca和Mg/Sr比值与从该洞穴采集的石笋顶部沉积物的相近，可见它们沉积时段具有相似性。鹅管SJJ-5与现代洞穴滴水的Mg/Ca，Sr／Ca比值计算的K_Mg、K_Sr平均值分别为0.00547±0.00629，1.751±0.271，鹅管SJJ-6的K_Mg、K_Sr平均值分别是0.00202±0.00304，1.731±0.173。两根鹅管的K_Sr值与现代沉积物的K_Sr值相差甚远，但与石将军洞石笋顶部沉积物的K_Sr值非常接近，说明石将军洞内采集的样品都不是现代沉积物。通过分析贵州中西部地区洞穴堆积物以及水系的地球化学元素含量及Mg/Ca，Sr／Ca，Mg/Sr比值，计算出石将军洞洞穴沉积物的K_Mg、K_Sr值，并把石将军洞洞穴沉积物元素比值与δ¹³C，δ¹⁸O的变化进行比较，可以看出贵州中西部地区的地表环境如气候，植被等都发生了比较大的变化，这些变化在洞穴沉积物的元素比值中得到很好的反映，因此洞穴沉积物的元素比值可以作为研究贵州中西部地区古环境演变的重要指标。更多还原

【Abstract】 We have collected water and carbonate samples from Zhengjia, Shijiangjun and Zhijin caves in central western Guizhou province. The samples have been analyzed for elements including K⁺, Na⁺, Ca²⁺, Mg²⁺, Si²⁺, Ba²⁺, Fe³⁺ and Mn²⁺. We have analyzed the variation of trace elements concentration and Mg/Ca, Sr/Ca, Mg/Sr ratios of two soda straws （SJJ-5, SJJ-6） from Shijiangjun cave. The average Mg/Sr ratios of the cave waters in Zhengjia, Shijiangjun and Zhijin Caves are 1278±411, 1155±207 and 14.0±2.7, respectively. The geochemical feature of cave waters from Zhengjia and Shijiangjun Caves is enriched in Mg²⁺ and depleted in Si²⁺; whereas waters from Zhijin Cave depleted in Mg²⁺ and enriched in Sr²⁺. This feature indicates that not only the bed rocks compositions but also vegetation and soil coverage above the caves affect the Mg/Sr ratios of the cave water. Based on the measurements of Mg/Ca and Sr/Ca ratios in both waters and modern carbonates from Zhijin Cave, we have calculated the co-precipitation coefficient constants for Mg/Ca and Sr/Ca between calcite and water. The K_Sr value changes from 0.04 to 0.134, averaging 0.073±0.035. The average K_Mg ratio is 0.021±0.010. The values provide us the fundamental data for using Mg/Sr ratio as a proxy of paleoclimate reconstruction.There is opposition relationship of Mg and Sr concentration, positive relationship between Ba and Sr concentration, Fe and Mn concentration of soda straw SJJ-5, SJJ-6. The changing of Mg/Ca and Mg/Sr ratio are controlled by the concentration of Mg. The concentration of Sr affects Sr/Ca ratio. Mg/Sr ratio changed obviously during some period. We think that it is not affected by the change of temperature. It may be affected by variation of the soil and vegetation above the cave. The relationship of Mg/Sr ratio andδ¹³C orδ¹⁸O is oppositive. We conclude that the climate was warm and humid when Mg/Sr ratio increased andδ¹⁸O decreased. Based on the variation of Mg/Ca, Sr/Ca, Mg/Sr ratios, we surmise the climate was warm and humid, cold and dry in turn when soda straw SJJ-5 was depositing.δ¹⁸O andδ¹⁸C increased so that we imagine the precipitation decreased gradually since the deposition of SJJ-6 soda-straw. It induced the vegetation above the cave reducing and the soil on the surface being swept. The process reflected in the variation of Mg/Sr ratio and it decreased gradually. We conclude that Mg/Sr ratio of soda straw can reflect the environment changing outside of the cave.Mg/Ca、Sr/Ca and Mg/Sr ratios of the soda straws are similar with those of carbonate samples which are from the top of stalagmites in Shijiangjun cave. It is explained that they deposited at the same phase. The average ratio of K_Mg and K_Sr is 0.00547±0.00629 and 1.751±0.271 in SJJ-5 soda straw, respectively. The average ratio of K_Mg and K_Sr of SJJ-6 soda straw is 0.00202±0.00304, 1.731±0.173, respectively. K_Sr ratios of SJJ-5 and SJJ-6 soda straw are much more than those of modern deposition from the top of stalagmite from Zhijin cave, while they are close to the K_Sr ratios of deposition from the top of stalagmite from Shijiangjun cave. We consider that the speleothem samples collected from Shijiangjun cave are not depositing today.We have argued the geochemical features and Mg/Ca, Sr/Ca, Mg/Sr ratio of the samples from cave water and speleothem in central western Guizhou, calculated K_Mg、K_Sr ratio of the deposition from Shijiangjun cave and compared Mg/Ca, Sr/Ca, Mg/Sr ratio withδ¹³C,δ¹⁸O. We conclude that the climate and vegetation at central western Guizhou province changed largely and trace element ratio can reflect and record the environment change. The ratios including Mg/Ca, Sr/Ca, Mg/Sr are important indexes to study paleoenvironment evolution at at central western Guizhou province.更多还原