摘要
目前通用的前处理方法难以从石膏岩中有效提取足量粘土矿物进行测试分析，针对这一技术问题，本研究改进了原有的粘土矿物分析前处理方法，采用新的试剂乙二胺四乙酸二钠（以下简称EDTA）溶解石膏岩，释放其中所含的粘土矿物，有效提高石膏岩中粘土矿物的提取能力。本文以位于青藏高原东北缘西宁盆地塔山剖面（36.5°N，101.8°E） 始新世祁家川组、洪沟组和马哈拉沟组的9个石膏岩样品为研究对象，通过详细对比试验确定了EDTA的溶解条件，明确了采用EDTA提取石膏岩中粘土矿物的实验流程和方法，并探讨了溶解过程对粘土矿物的影响。实验结果表明，EDTA对石膏岩的最佳溶解条件为：温度=100℃、pH=10~12、浓度=0.32mol/L，改进后的前处理方法提取粘土矿物质量是原来的1~25倍，且不破坏粘土矿物的晶型结构。使用EDTA溶解法提取9个样品中的粘土矿物经X射线衍射分析结果表明，西宁盆地始新世石膏岩样品中粘土矿物含量以伊利石为主（62%~90%），含少量绿泥石（3%~17%），蒙脱石（含伊蒙混层矿物）含量变化较大（0~35 %）。粘土矿物组合特征反应该区域始新世以干旱气候为主，盆地内石膏岩地层形成时期的气候环境可能存在一定程度的干湿波动现象。
Gypsum rocks are widely distributed in the Cenozoic basins of China and are important for Cenozoic paleoclimate reconstructions. Analysis of the clay minerals found within gypsum can provide an excellent paleoclimate proxy, but, typically, not enough of the clay fraction can be easily extracted with the commonly used pretreatment. To solve this technical problem, we have improved the standard method by using EDTA（ethylenediaminetetraacetic acid）instead of acetic acid, which can dissolve gypsum and release the clay minerals. In this study, 9 samples were collected for a comparison of methods. The samples are from the Eocene gypsum/gypsiferous layers of Qijiachuan, Honggou and Mahalagou Formations in Tashan section（36.5°N, 101.8°E）, which thickness was about 350m, located in Xining Basin, Qinghai Province, Northwest China. The lithology of Qijiachuan Formation is white gypsum, red/red brown mudstone, brown gypsiferous siltstone; the lithology of Honggou Formation is gray white/gray green gypsum, dark brown mudstone/siltstone, gray green gypsiferous mudstone/siltstone; the lithology of Mahalagou Formation is gray/gray white gypsum, red mudstone, gray yellow/gray green sandstone/siltstone, gray white gypsiferous clay stone/siltstone/sandstone. In this study, EDTA was used to dissolve gypsum and release the clay minerals under several different conditions. The dissolution variables include the pH （7~13）, acid concentration（0.32mol/L, 0.2mol/L, and 0.1mol/L）and temperature（21℃, 60℃, and 100℃）were divided into 9 tests with pH gradient （7~13）（in Table 1）. The experimental results indicate that the most suitable conditions for EDTA dissolution are at 100℃, at a pH of 10~12 with 0.32mol/L of EDTA. Under these conditions quantity of clay minerals was 1~25 times high as with the standard method. The impacts of EDTA dissolution on the clay mineral structure were assessed through comparison X-ray diffraction （XRD） patterns of EDTA as well as acetic acid pretreatment. XRD analyses indicate that there is no destruction of clay structure when using the EDTA dissolution method. The results of the XRD analyses show that the studied samples are composed of 62 % ~90 % Illite, 3 % ~17 % chlorite and 0~35 % smectite（I/S）. The characteristics of the clay mineral assemblages indicate that the paleoclimate was dominantly arid in Xining Basin during Eocene, whereas the large variation of smectite content suggests fluctuations between relatively humid and arid conditions. Therefore, when studying the paleoclimatic significance of gypsum layers in Cenozoic sedimentary basins in Northwest China, the lithology and a comprehensive analysis of the environmental indicators, such as clay mineral, should be combined for more accurate interpretations.
出处
《第四纪研究》
CAS
CSCD
北大核心
2016年第4期926-934,共9页
Quaternary Sciences
基金
国家自然科学基金面上项目（批准号：41172159）、国家自然科学基金重点项目（批准号：41430531）和中国科学院战略性先导科技专项（B类）“青藏高原多层圈相互作用及其资源环境效应”项目（批准号：XDB03020500）共同资助致谢感谢吴海斌、林雅婷、祝淑雅、任祥斌和杨帆等参与了野外采样工作
感谢GreigA.Paterson对英文摘要部分的修改完善
感谢审稿专家和编辑部老师提出的建设性修改意见.
