Isotropic smectite coatings and spheroids in Holocene volcanic deposits under temperate climate, France
Isotropic smectite coatings and spheroids in Holocene volcanic deposits under temperate climate, France
复制标题
DOI：
10.2136/sssaj1998.03615995006200010037x
复制
发表时间：
1998
影响因子：
2.9
通讯作者：
A. Jongmans;L. Denaix;F. Oort
中科院分区：
文献类型：
--
作者：
A. Jongmans;L. Denaix;F. Oort
在法国中部地块的Puy de la Vache火山下的Hapludand，在全新世过度排水的玄武质火山渣沉积物中观察到各向同性的粘土涂层和球体。这些新形成的粘土织物的形态，化学和矿物学进行了研究，通过光学显微镜和分析扫描和透射电子显微镜。在1至3米的深度在存款的样品的光学显微镜显示薄，各向同性的涂层和球状体内的火山渣碎片囊泡。此外，各向同性的涂层，有时厚达200 μm，覆盖熔渣碎片，在它们之间形成桥梁。各向同性涂层表明沉积后，成壤起源。涂层和球体的内部结构相似。表明他们有共同的遗传关系尽管涂层的各向同性行为通常表明其矿物组成为无定形，但分析电子显微镜显示存在小的（<1 μm）褶皱双八面体层状硅酸盐颗粒，形成蜂窝状图案。定期限制排水条件下，在众多的介孔和微泡孔的火山渣被认为是导致局部和暂时停滞的富硅土壤溶液，因此，有利于smeetite形成，尽管整体渗透性高。由于在3米深的火山渣碎片是不变的，形成的二次粘土涂层被归因于共沉淀的浸出元素的风化释放在上覆的哈普鲁丹。蒙脱石粘土颗粒的小尺寸和随机取向图案以及它们与无定形化合物的偶然关联解释了在偏光显微镜下观察时粘土涂层的各向同性性质。
Isotropic clay coatings and spheroids were observed in Holocene, excessively drained, basaltic scoria deposits underlying a Hapludand at the Puy de la Vache volcano in the Massif Central in France. The morphology, chemistry, and mineralogy of these neoformed clay fabrics were studied by optical microscopy and analytical scanning and transmission electron microscopy. Optical microscopy of samples taken at 1- to 3-m depth in the deposit showed thin, isotropic coatings and spheroids inside vesicles of the scoria fragments. In addition, isotropic coatings, occasionally up to 200 μm thick, covered scoria fragments, forming bridges between them. The isotropic coatings indicated a post-depositional, pedogenic origin. The internal fabric of coatings and spheroids were similar. suggesting a common genetic relationship. Although isotropic behavior of coatings generally points to an amorphous mineralogical composition, analytical electron microscopy showed the presence of small (<1 μm) crinkly dioctahedral phyllosilicate particles, forming a honeycomb pattern. Periodically restricted drainage conditions in the numerous meso- and microvesicular pores of the scoriac were assumed to cause local and temporary stagnation of Si-rich soil solutions and, consequently, to favor smeetite formation despite the overall high permeability. Since scoria fragments at 3-m depth were unaltered, formation of the secondary clay coatings was ascribed to co-precipitation of leached elements liberated by weathering in the overlying Hapludand. The small size and random orientation patterns of the smectite clay particles and their occasional association with amorphous compounds explained the isotropic properties of the clay coatings when observed under the polarizing microscope.