摘要
通过对桂林周边3个洞穴的3个石笋进行^(210)Pb测试,分别计算出3个石笋的沉积速率:盘龙洞石笋PL-4的平均沉积速率为0.042mm/a,茅茅头大岩石笋DY-2的平均沉积速率为0.731mm/a,住岩石笋ZY-5的平均沉积速率为0.029mm/a;另外,通过滴水实验验证了石笋正在沉积,且茅茅头大岩沉积速率较大,盘龙洞和住岩沉积速率较小。通过与其他地区石笋以及对3个洞穴石笋之间的初始^(210)Pb放射性比活度的比较,发现桂林地区石笋初始^(210)Pb放射性比活度低,主要是受制于桂林特殊的地质背景和地理环境;而3个洞穴由于洞穴封闭条件、石笋沉积速率、滴水点等差异,石笋的初始^(210)Pb放射性比活度也表现出差异。
Three stalagmites,collected from three caves which are located very close to the border district of Guilin city, Guangxi Province in China,had 210Pb test. The climatic conditions（ subtropical monsoon climate： trenchant climate with dry and wet two seasons） , geological background （ the limestone strata of Upper Devonian Rongxian Group） and ecological environment（ thin overlying soil layer with high vegetation cover） of the three caves are similar. The three caves are Maomaotou Dayan（25°18＇34.3＂N,110°16＇26.9＂E） ,Panlong cave（24°57＇39.4＂N,110°21 ＇17.4＂E） ,and Zhuyan cave （25°15 ＇32.0＂1＇~, 110°21 ＇35.4＂E ） , and are located in the north, south and east of Guilin respectively. The stalagmites of DY-2,PL-4 and ZY-5 were collected from November 27 to 29, 2009. The DY-2 stalagmite was collected from Maomaotou Dayan, which is about 10 centimeters long, with integral color appearing white and has good crystallinityas well as more porosity when the stalasgmite is cut. 25 effective data were obtained from these tests. PL4 stalagmite was collected from Panlong cave, and is about 8.8 centimeters long. The stalagmite surface of Panlong cave is white, with integral color appearing cyan, and densified, well homogeneous as well as less poros laminae. Seven valid data were obtained. Afterwards ZY-5 stalagmite was collected from Zhuyan cave, and is 11 centimeters long, with the integral color of the stalagmite appearing white. Fifteen valid date were obtained. Moreover,the laminaes of the three stalagmites are densified, homogeneous, presenting regular repeatability, but without obvious hiatus, and there was dripping water above the stalagmites when samples were collected. By calculating the deposition rate of the three stalagmites separately： the average deposition rate of PL-d stalagmite in Panlong cave is for 0. 042mm/a, the average deposition rate of DY-2 stalagmite in Maomaotou Dayan is measured for 0. 731mm/a,while the average deposition rate of ZY-5 stalagmite in Zhuyan cave is for 0. 029mm/a,which has been verified through the dripping water experiment, and the deposition rate of Maomaotou Dayan is bigger than those of Panlong and Zhuyan caves. The initial 2~~pb specific radioactivity of the three stalagmites are 7. 931_＋ 0. 366dpm/g（ 0 - 2mm ） of PL-d stalagmite, 2. 491 _＋ 0. 164dpm/g （ 0 - 2mm ） of DY-2 stalagmite and 0. 691 ＋ 0. 076dpm/g（0- 2mm）of ZY-5 stalagmite respectively,which is far below the initial 210Pb specific radioactivity of other cave deposits in China and other countries and mainly relate to Guilin caves developed in single,Marine,low dissolution rate and low U level limestone,where the overlying soil layer is thin and has absorption capacity, and relatively high vegetation cover and strong enrichment function as well as stable crust. Furthermore, the closed conditions, stalagmites deposition rate, dripping water sites, etc. caused the initial 210pb specific radioactivity difference among the three caves.
出处
《第四纪研究》
CAS
CSCD
北大核心
2011年第5期883-890,共8页
Quaternary Sciences
基金
国土资源部地质调查项目"岩溶动力系统与碳循环"(批准号:1212010911062)
国家自然科学基金项目(批准号:40902053)
重庆市科委院上基金资助项目"重庆典型岩溶地下河系统污染的形成
演变机制及防控对策"(批准号:CSTC
2010BC7004)资助
