石笋中稀土元素含量的测定及气候环境意义

首次采用经过改良的外标法校正数据的ICP-MS方法对石笋中的稀土元素含量进行了测定。结果表明,该方法可以用于测定石笋中含量很低的稀土元素,尤其是对含量相对较高的轻稀土元素如La、Ce可以获得较精确的数据。对采集于四川东北部诺水河溶洞群的石笋SJ3的分析结果显示,在相对温暖湿润时期的石笋沉积中稀土元素含量明显增加。可能的原因包括:(1)温暖湿润的气候条件有利于土壤和岩石的化学风化及稀土元素的活化;(2)温暖湿润的气候条件下地下水动力加强,使得地下水中稀土元素的载体(有机质、铁锰胶体和颗粒物质等)增多。因此,石笋沉积中的稀土元素可以用于研究上覆土壤和岩石的化学风化和地下水水文演化。

Determination of rare earth elements in a stalagmite and their paleoclimatic and paleoenvironmental significance

The content of rare earth elements in a stalagmite was tentatively measured by the improved ICP-MS method which was suggested by Eggins et al.(1997).It is found that the data are generally acceptable.The precisions of the data for light rare earth element La and Ce,which is expressed as the relative standard deviation,are high enough and comparable with that commonly obtained by ICP-MS method for trace element analysis.Variations of the rare earth element content in SJ3,a stalagmite which was sampled from Nuoshuihe Karstic Beauty Spot,northeastern Sichuan,are climatically related.The layers precipitated under relatively warm and humid climate are obviously enriched in rare earth elements.The possible mechanisms for this include:(1)warm and humid climate would strengthen the chemical weathering of the earth surface and increase the activation of rare earth elements,and(2)warm and humid climate would lead to a stronger groundwater dynamics and in turn,lead to higher contents of organic material,Fe-Mn colloid and particle in groundwater.All of these are important carriers for rare earth element transportation in groundwater.Rare earth elements in stalagmite are useful for tracking the chemical weathering of the overlying soil of karstic cave and the hydrodynamic of groundwater.