Characterization of Iron-Manganese Concretions in Kentucky Alfisols with Perched Water Tables
Characterization of Iron-Manganese Concretions in Kentucky Alfisols with Perched Water Tables
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DOI：
10.1346/ccmn.1997.0450312
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发表时间：
1997-06
影响因子：
2.2
通讯作者：
Min Zhang;A. Karathanasis
中科院分区：
文献类型：
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作者：
Min Zhang;A. Karathanasis
铁锰结核在肯塔基州内蓝草地区的淋溶土上部很常见。它们的性质和数量似乎与季节性栖息水位以上的粘土质粘层的波动。本研究旨在研究结核的宏观和微观形态、化学和矿物学随大小、颜色和土壤深度的变化。随结核粒度的增大，全Mn、Fe含量增加，SiO2含量降低。黑色结核含有较高的锰，而棕色结核的铁含量较高。结晶锰和铁的氧化物分级与顺序提取程序增加，但无定形锰和铁的结核尺寸下降。针铁矿是通过X射线衍射（XRD）分析鉴定的唯一结晶氧化铁矿物。氧化锰矿物由于其XRD峰的扩散性质和差的结晶度而非常难以检测。土壤薄片的检查表明，限制性粘土层上的土壤层结表现出差异化的织物，尖锐的外部边界和一般的球形。粘土限制层内或岩屑界面上方发现的混凝土通常具有较少的结构组织，较软的基质和扩散的外部边界，由于长期的饱和条件。扫描电子显微镜（SEM）检查表明，结核矩阵，尽管其密度，有许多空腔和广泛的溶解的血浆Fe和Mn可以扩散和沉淀的pathogenic系统。
Iron-manganese concretions are common in upper sola of Alfisols in the Inner Bluegrass Region of Kentucky. Their nature and quantities appear to be related to the fluctuation of seasonal perched water tables above clayey argillic horizons. This study was conducted to examine changes in the macro-and micromorphology, chemistry and mineralogy of concretions as a function of size, color and soil depth. Total Mn and Fe contents increased, while SiO2 decreased with concretion size. Black concretions contained higher Mn, while brown concretions were higher in Fe. Crystalline Mn- and Fe-oxides fractionated with a sequential extraction procedure increased, but amorphous Mn and Fe decreased with concretion size. Goethite was the only crystalline Fe oxide mineral identified by X-ray diffraction (XRD) analysis. Manganese oxide minerals were very difficult to detect due to the diffuse nature of their XRD peaks and poor crystallinity. Examination of soil thin sections showed concretions of soil horizons overlying restrictive clayey layers to exhibit differentiated fabrics, sharp external boundaries and generally spherical shapes. Concretions found within clayey restrictive layers or above lithic interfaces usually had less structural organization, softer matrices and diffuse external boundaries due to longer term saturated conditions. Scanning electron microscopy (SEM) examinations suggested that the concretionary matrix, in spite of its density, has numerous cavities and an extensive micropore system within which dissolved plasmic Fe and Mn can diffuse and precipitate.