青海兴海上新世砂岩中膨胀性粘土矿物种属的厘定及光谱学特征

利用X射线衍射(XRD)和傅里叶红外吸收光谱(FTIR)深入研究了青海羊曲剖面砂岩中膨胀性粘土矿物的具体种属和光谱学特征。XRD结果表明，砂岩中粘土矿物以膨胀性粘土矿物为主，含量在97 %以上。样品006面网在1.534  和1.498 均存在明显的衍射峰，表明可能同时含有二八面体和三八面体结构膨胀性粘土矿物。进一步的Li+-300 ℃加热后甘油饱和实验结果显示，大部分样品膨胀性粘土矿物001衍射峰塌陷至9.3～9.9，少数样品膨胀至 ～18 ，表明膨胀性粘土矿物以蒙皂石为主，部分样品含少量皂石。蒙皂石由于部分Li+进入八面体层间，平衡了由于Mg替代Al造成的电价不平衡，从而使得蒙皂石不膨胀。FTIR结果表明，膨胀性粘土矿物同时含有吸附水和结构水，与X射线衍射结果一致。样品在913和842 cm-1出现吸收峰，表明膨胀性粘土矿物八面体层间以Al—Al和Al—Mg为主;部分样品含有Al—Fe(吸收谱峰880 cm-1)，指示其为二八面体结构。膨胀性粘土矿物中同时含有Si—O以及Al—O—Si振动峰，表明四面体只有部分Al取代Si。XRD和FTIR均指示研究样品与贝得石和绿脱石有不一样的光谱学特征，而与蒙皂石极为吻合。本研究能有效对膨胀性粘土矿物具体种属进行厘定，对粘土矿物学揭示沉积物物源和气候环境信息具有重要的作用。

Species Determination and Spectral Characteristics of Swelling Clay Minerals in the Pliocene Sandstones in Xinghai,Qinghai

X-ray diffraction (XRD) and Fourier infrared absorption spectroscopy (FTIR) were conducted to deepen our research on specific species and spectral characteristics of swelling clay minerals in the Pliocene sandstones in Xinghai, Qinghai province. XRD results show that swelling clay minerals are dominant clay minerals in the sandstones, which can be up to 97% in percentage. XRD patterns show 060 reflections of the samples occur both remarkably at 1.534  and 1.498 , indicating the samples contain physical mixtures of trioctahedral and dioctahedral swelling clay minerals, respectively. Further treatment of Li-300 ℃ heat and glycerol saturation shows the swelling clay minerals collapse to 9.3～9.9  with a partial expansion to ～18 . This indicates the swelling clay minerals dominate montmorillonite and contain minor saponite. The montmorillonite shows no swelling after Li-300 ℃ heat and glycerol saturation because of Li+ inserting into the octahedral layers, which balances the layer charge caused by the substitution of Mg to Al. FTIR results show the samples are composed of a kind of phyllosilicate with absorbed and structural water, which is in agreement with the results of XRD. Absorbed peaks at 913, 842, 880 cm-1, corresponding to OH associated with Al—Al, Al—Mg, and Al—Fe pairs, further indicates the minerals are dominant dioctahedron in structure. Meanwhile, absorbed peaks at 625 and 519 cm-1, corresponding to coupled Si—O and Al—O—Si deformation, indicates parts of Si is replaced by Al in tetrahedron. The spectral characteristics of the samples are against the presence of beidellite and nontronite based on the results of XRD and FTIR, while demonstrating an existence of montmorillonite. This study, to distinguish the specific species of swelling clay species in clay minerals, would be of great importance when using clay mineralogy to interpret provenance and climatic information.