豫西鸡冠洞洞穴水及现代沉积物Mg,Sr和Ba记录及其意义

摘要

Speleothems contain a number of suitable proxies reconstructing climate environmental changes, which is a top topic in current research.Due to the variety of sources and complex factors,trace elements are less frequently used than the oxygen isotopes in climate studies.However,they are used to reveal the groundwater runoff in the epikarst overlying the cave with the process and the surface environment.Induc-tively coupled plasma mass spectrometry (ICP-MS)and inductively coupled plasma optical emission spec-trometry(ICP-OES)have been used to analyse the trace elements of Ca、Mg、Sr and Ba in cave water and ac-tive formations in Jiguan Cave during December,2009 and August,2013.Jiguan Cave (33°46′N,111°34′E) is located in Luanchuan county,western Henan Province,which is north of the Qinling ranges-Huaihe River and southeast of Loess Plateau,while at the foot of the northern watershed of the Yangtze River and the Yellow River.It main exposed rocks are Sinian chlorite marbles.Located in the typical east Asian monsoonal zone,the Jiguan Cave area is typically has cold/dry winters and warm/wet summers.More than 50 % of the total annual precipitation occurs in summer.The mean annual temperature and precipitation recorded at a nearby meteorological station are 12.1±0.9 ℃ and 846±181 mm (1957-2009)respectively.In the paper, trace elements such as Ca,Mg,Sr and Ba in cave water and active formations collected in Jiguan Cave were analyzed with ICP-MS and ICP-OES.The Mg/Ca,Sr/Ca and Ba/Ca of cave water varied between 0.2-0.8, (1.2-6.0)×10-3 and (0.3-2.0)×10-3 respectively.Mg/Ca can respond to the environment outside the cave faithfully.The wet-dry condition of the karst system is suggested as the dominant controller of Mg/Ca ratios in cave pool water and underground rivers,whereas the Sr/Ca and Ba/Ca may have nothing to do with precipitation and temperature.The Mg/Ca,Sr/Ca and Ba/Ca ratios in active speleothems varied between (9-50)×10-3 ,(0.1-1.2)×10-3 and (0.8-3.2)×10-3 respectively.Corresponding to that of the water, the opposite trend was observed in Sr/Ca,Ba/Ca and Mg/Ca ratios.This opposite trend may have been in-fluenced by atmospheric dust and surface soil,but there are still unexplained phenomenons worth further re-search.The co-precipitation coefficient constants for Mg/Ca and Sr/Ca between modern carbonate and water were calculated,giving a KSr value of 0.02-0.18 and KMg value of 0.01-0.03.Positive correlation between KMg and cave temperature is faint.%采用电感耦合等离子体质谱仪(ICP-MS)和电感耦合等离子体光谱仪(ICP-OES)对2009年12月-2013年8月采自河南省栾川县鸡冠洞洞穴水(滴水、池水及地下河水)和现代碳酸盐沉积物的 Ca、Mg、Sr和 Ba 微量元素地球化学指标进行了分析。结果显示：(1)鸡冠洞洞穴水的 Mg/Ca对地表环境的干湿条件变化响应迅速,具体表现为池水和地下河水 Mg/Ca旱季高而雨季低,而 Sr/Ca 和Ba/Ca的变化与降水和气温的关系并不明显；(2)鸡冠洞现代沉积物的 Mg/Ca 变化与滴水有着良好的对应关系,但现代沉积物的 Sr/Ca和 Ba/Ca可能受大气粉尘活动和地表土壤的影响,变化趋势与 Mg/Ca 相反；(3)鸡冠洞碳酸盐岩与岩溶水间 Sr/Ca和 Mg/Ca的分配系数KSr值在0.02~0.18之间,KMg值在0.01~0.03之间,KMg值与洞穴温度的正相关关系不明显。