Abstract—

Knowledge of lithologic discontinuities (LDs) provides important information about sedimentology processes and soil development. The main objective of this research was to evaluate different criteria from the Soil Taxonomy (ST) system to detect LDs in soils of arid and semi-arid regions. For that, five sites in Iran were selected, and several parameters were measured to identify LDs in studied pedons, these were: profile morphology, depth functions of clay-free particle size distribution, clay-free sand to silt ratio, uniformity value index, particle size parameters (mean, sorting, skewness and kurtosis) and particle size mode, morphology of quartz grains and chronological data. Results confirmed that, in some occasions, field evidences (differences in texture, color and parent material that are not the result of pedogenic processes) failed to reveal LDs, laboratory data could show this diagnostic soil characteristic. Also, the results showed that quartz grains morphology revealed a lithologic discontinuity (LD) between the Btk and Cry1 horizons within the pedon at site 1. Skewness and kurtosis parameters and particle size mode of differnt horizons were useful parameters to distinguish and confirm the presence of LD in the soil. Moreover, results showed that the clay-free depth functions of particle size distribution were useful to ascertain the presence of LDs so long, as far as sufficient amounts of the silt and sand fractions were available. Since field evidences were not always clear, the revision of some qualitative rules of the ST system and defining quantitative criteria for an abrupt change in particle size distribution seems necessary to improve its ability for LDs detection.

中文翻译：

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土壤中岩性间断的检测：以伊朗干旱和半干旱地区为例

摘要-

岩性间断（LDs）知识提供了有关沉积学过程和土壤发育的重要信息。这项研究的主要目的是评估土壤分类法（ST）系统中用于检测干旱和半干旱地区土壤中LDs的不同标准。为此，选择了伊朗的五个地点，并测量了几个参数以识别研究的脚踏子中的LD，包括：轮廓形态，无粘土粒径分布的深度函数，无粘土砂土比，均匀度指数，粒度参数（平均值，分选，偏度和峰度）和粒度模式，石英晶粒的形态以及时间数据。结果证实，在某些情况下，现场证据（质地差异，颜色和母体材料（不是成岩过程的结果）无法显示LD，实验室数据可以显示这种诊断性土壤特征。此外，结果表明，石英晶粒的形态揭示了站点1上脚架内Btk和Cry1层之间的岩性不连续性（LD）。偏斜度和峰度参数以及不同层的粒度模式是区分和确认存在的有用参数。 LD在土壤中。此外，结果表明，只要有足够数量的粉砂和砂质组分，粒径分布的无粘土深度函数就可用于确定LDs的存在。由于现场证据并不总是很清楚，