A placic horizon is a thin soil layer that is cemented or indurated by Fe, Mn, and/or Al compounds as well as by organic matter. The placic horizon is a hard, continuous, and nearly impermeable and impenetrable horizon that retards the vertical leaching of water and inhibits the growth of roots. Placic horizons can develop under different climates and in various ways. However, we do not fully understand the interactions between lithology and pedogenesis that might promote placic horizon formation. Therefore, to shed light on the mechanisms of placic genesis, we used an applied multiproxy approach (electrical resistivity tomography – ERT, XRD, 57Fe Mössbauer spectroscopy, bulk geochemistry, soil micromorphology and 14C dating) for three soils developed from sandstone–mudstone parent materials in mountainous areas of SW Poland, to shed light on the mechanisms of placic horizon genesis. The ERT inversion models and soil survey data indicate lithic discontinuities in the profiles. Soil micromorphology data confirmed that a placic horizons formed slightly below the discontinuity. Radiocarbon ages of the placic horizon span from 2.2 to 4.8 ka and suggest that more humid conditions were favorable for the formation of a placic horizon, which aligns with our mineralogical results. Ferrihydrite is the major Fe oxyhydroxide in the placic horizon. Micromorphological data showed that after the formation of the placic horizon, a phase of clay migration might have occurred, while later, podzolisation took over as the main soil-forming process. This sequence shows that thin iron pans can develop independently of other processes and can exist (at least some of them) before the development of a spodic horizon. A placic horizon causes severe hydrological changes in the topsoil and subsurface horizons. Thus, water stagnation in the soil transforms it into a Stagnosol or Planosol and it’s responsible for the evolution of local plant communities and the ecosystem.

中文翻译：

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温带气候土壤中 placic 层位的形成 – 岩性和土壤发生的相互作用 （Stołowe Mts， SW Poland）


层位是被 Fe、Mn 和/或 Al 化合物以及有机物胶结或硬化的薄土层。地平线是一个坚硬的、连续的、几乎不透水和无法穿透的地平线，它阻碍了水的垂直浸出并抑制了根的生长。Placic 层位可以在不同的气候下以各种方式发展。然而，我们并不完全了解岩性和土壤发生之间的相互作用，这可能会促进 Placic 层位的形成。因此，为了阐明沉积物的成因机制，我们对波兰西南山区由砂岩-泥岩母质发育而成的三种土壤使用了应用多代理方法（电阻率断层扫描 - ERT、XRD、57Fe Mössbauer 光谱、块状地球化学、土壤微形态学和 14C 测年），以阐明沉积层发生机制。ERT 反演模型和土壤调查数据表明剖面中存在岩层不连续性。土壤微形态数据证实，在不连续面略下方形成了一个 placic 层位。Placic 层位的放射性碳年龄跨度为 2.2 至 4.8 ka，这表明更潮湿的条件有利于形成 Placic 层位，这与我们的矿物学结果一致。水铁矿是钙层中主要的氢氧化铁。微观形态数据表明，在板层形成后，可能发生了粘土迁移阶段，而后来，灰化成为主要的土壤形成过程。这个序列表明，薄铁锅可以独立于其他过程发展，并且可以在 spodic 层位发展之前存在（至少其中一些）。 地层会导致表层土壤和地下层发生严重的水文变化。因此，土壤中的水分滞留会将其转化为 Stagnosol 或 Planosol，它负责当地植物群落和生态系统的进化。