Abstract

This paper deals with soil genesis and distribution of Ni and Cr in soils formed along a toposequence of mainly ultramafic rocks in an aridic soil moisture regime in Northeastern Iran. Three pedons in the summit (Xeric Haplogypsids), backslope (Lithic Xeric Torriorthents), and footslope (Lithic Calcigypsids) of a toposequence were described and sampled. Hornblende was the main mineral of the parent materials, while chlorite and albite were the associated minerals. The calcic and gypsic horizons were the diagnostic horizons in shallow solums of the studied pedons. Despite the low amount of Ca in the parent materials, the Ca/Mg ratio in the soils reached to 33, owing to the high amount of carbonates and gypsum with aeolian origin. Released iron from the ferromagnesian minerals has created a brown color in the soil groundmass. The amount of Fe_d (CBD-extractable Fe) in the studied soils (3.5 to 6.8 g kg^–1) was significantly lower than soils formed in humid areas. Iron oxides features were as nodule in the groundmass, coating, and hypocoating in carbonate nodules and voids, as well as coating along microcracks of coarse fragments. The total amount of Ni and Cr in the parent materials was 106–1485 and 244–2653 mg kg^–1, respectively. The aqua-regia extractable concentrations of Ni and Cr in the soil layers varied from 52.6 to 191.8 and from 35.2 to 127 mg kg^–1, respectively. Fe_d, Ni, and Cr concentrations and the presence of chlorite reflect the nature of ultramafic rocks. On the other hand, high amount of gypsum, carbonates, and silt contents, presence of mica and palygorskite in the clay fraction, and high values of Ca/Mg ratio in the studied soils were the evidence of aeolian addition.

中文翻译：

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干旱气候下超镁铁质土壤拓扑序列中镍、铬的成因及分布

摘要

本文研究了伊朗东北部干旱土壤水分条件下沿主要超镁铁质岩石的拓扑序列形成的土壤中 Ni 和 Cr 的土壤成因和分布。描述并采样了拓扑序列的山顶（Xeric Haplogypsids），后坡（Lithic Xeric Torriorthents）和山脚（Lithic Calcigypsids）中的三个踏板。角闪石是母质的主要矿物，绿泥石和钠长石是伴生矿物。钙质层和石膏层是所研究地基浅层土壤的诊断层。尽管母质中的 Ca 含量较低，但由于风成源的碳酸盐和石膏含量较高，土壤中的 Ca/Mg 比达到了 33。铁镁矿物释放的铁在土壤基质中形成棕色。铁的量_{研究土壤中的d}（CBD 可提取铁）（3.5 至 6.8 g kg ^–1）明显低于潮湿地区形成的土壤。铁氧化物的特征是在基体中的结核，碳酸盐结核和空隙中的涂层和低涂层，以及沿着粗碎片的微裂纹的涂层。母材中 Ni 和 Cr 的总量分别为 106-1485 和 244-2653 mg kg ^-1。土壤层中 Ni 和 Cr 的王水可提取浓度分别为 52.6 至 191.8 和 35.2 至 127 mg kg ^-1。美联储_{_}、Ni 和 Cr 浓度以及绿泥石的存在反映了超镁铁质岩的性质。另一方面，高含量的石膏、碳酸盐和淤泥含量，粘土部分中云母和坡缕石的存在，以及所研究土壤中的高 Ca/Mg 比值是风成添加的证据。