Fragipan degradation and nodule formation in Glossic Fragiudalfs of the lower Mississippi River Valley.
Fragipan degradation and nodule formation in Glossic Fragiudalfs of the lower Mississippi River Valley.
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DOI：
10.2136/sssaj2000.6451713x
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发表时间：
2000-09
影响因子：
2.9
通讯作者：
D. Lindbo;F. Rhoton;W. Hudnall;N. Smeck;J. Bigham;D. Tyler
中科院分区：
文献类型：
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作者：
D. Lindbo;F. Rhoton;W. Hudnall;N. Smeck;J. Bigham;D. Tyler
Glossic Fragiudalfs包括数百万公顷的农业重要土壤，位于密西西比河下游的粉质高地（主要土地资源区[MLRA] 134）。这些土壤的典型特征是，在距离地表100厘米的地方有一个软质层，上面覆盖着一层5厘米厚或更厚的光滑层，其中包含沿原生坡面的漂白涂层（白色物质），表明软质层已经退化。铁锰结核的浓度也出现在fragipan以上的地平线上。关于结节的原位形态或其与下伏瘤的关系的文献资料有限。本研究的目的是记录(i)结核的剖面分布，（ii）结核形态随深度的变化，以及（iii） fragipans在结核形成中的作用。结核是最常见和最大的直接高于脆弱的地平线。野外和显微形态观察表明，脆性脆性脆性岩基质残留物中形成的结核是Btx物质向E'物质（白垩物质）转化的结果，该物质隔离并包围了脆性脆性岩。作为结核的前体的脆性岩石，其尺寸逐渐减小，铁锰氧化物的浸渍程度越来越高。铁浓度和泥质在结核中的空间关系表明，尽管结核有明显的边界，但结核是在原地形成的，而不是运输的。随着时间的推移，光滑层以脆性层为代价而扩展，形成由铁锰结核和白垩质基质中一些孤立的脆性颗粒组成的层。
Glossic Fragiudalfs comprise several million hectares of agronomically important soils within the silty uplands of the lower Mississippi River Valley (Major Land Resource Area [MLRA] 134). These soils are typified by a fragipan within 100 cm of the surface overlain by a 5-cm-thick, or more, glossic horizon containing bleached coatings (albic material) along primary ped faces, indicating fragipan degradation. Concentrations of Fe-Mn nodules also occur in horizons above the fragipan. There is limited documentation regarding the in situ morphology of the nodules or their relationship to the underlying fragipan. The objectives of this study were to document (i) the profile distribution of nodules, (ii) variations in nodule morphology with depth, and (iii) the role of fragipans in nodule formation. Nodules were most common and largest directly above the fragipan horizons. Field and micromorphological observations suggested the nodules formed in remnants of the brittle fragipan matrix as a result of the conversion of Btx material to E' material (albic material) that isolated and surrounded brittle fragipan peds. The brittle peds that are the precursors to nodules appeared to decrease in size and became more highly impregnated with Fe and Mn oxides with distance above the fragipan. Spatial relationships of Fe concentrations and argillans within the nodules illustrated that the nodules were being formed in place and were not transported despite having distinct borders. With time the glossic horizon expands at the expense of the fragipan, resulting in a horizon consisting of Fe-Mn nodules and a few isolated brittle peds in a matrix of albic material.