Genesis and Classification of Nitisols from Volcano-Sedimentary Lithology in Northeastern Brazil

ABSTRACT On the southern coast of Pernambuco State (PE), Brazil, lithotypes of the Cabo Basin (volcanic and sedimentary rocks), in association with the relief, allow the determination of the dynamics of the formation of Nitossolos Háplicos (Nitisols), including those with high levels of exchangeable aluminum. The objective of this study was to evaluate the influence of lithological diversity (basalt and sedimentary siliciclastic rocks) on the morphological, physical, chemical, and mineralogical properties of Nitossolos Háplicos along a slope (P1-summit, P2-backslope, P3-footslope) on the southern coast of PE, in order to consider its genesis and the relation of soil properties to adjacent environments and to evaluate its framing within the Brazilian Soil Classification System (SiBCS). The interaction of lithology/soil permeability and climate indicate significant differences in the mineralogical composition and dynamics of soil chemical elements. The profiles P1 and P2 are subject to monosialitization, ferralitization, and alitization processes. All profiles showed high Fe contents (ferric soils) and clay fractions, consisting primarily of kaolinite, goethite, hematite, and gibbsite, as well as quartz and feldspar in the sand and silt fractions. However, smectite minerals (P3) are probably inherited from the sedimentary source material. In the conglomerate samples, under P3, biotite, muscovite, and plagioclase were identified. Allytic characteristics (P3) are probably associated with the weathering of aluminous smectite minerals. These properties distinguish these soils from adjacent Nitossolos and other Nitossolos in Brazil. For the classification of soils according to SiBCS, considering the high levels of Fe and Al, Nitossolo Háplico distroférrico (P1 and P2) and Nitossolo Háplico alitiférrico (P3) are suggested, and according to the World Reference Base of Soils (WRB), the soils are classified as Ferritic Nitisols.

摘要 巴西伯南布哥州（PE）南部海岸的卡博盆地（Cabo Basin）岩性（火山岩与沉积岩）结合地貌特征，可用于解析哈普利克强风化粘磐土（Nitossolos Háplicos, Nitisols）的形成动力学过程，包括交换性铝含量较高的该类土壤。本研究旨在评估岩性多样性（玄武岩与沉积硅质碎屑岩）对伯南布哥州南部海岸某坡地（P1-坡顶、P2-坡腰、P3-坡脚）上哈普利克强风化粘磐土的形态学、物理学、化学及矿物学特性的影响，以探讨其成土机制，明确土壤特性与相邻环境的关联，并依据巴西土壤分类系统（SiBCS）对其进行归类。岩性、土壤渗透性与气候的相互作用，会对土壤矿物组成及化学元素的迁移转化过程造成显著影响。P1与P2剖面经历了单硅铝化作用、富铁铝化作用及铝化作用。所有剖面均表现出高铁含量（铁质土壤）特征，并含有黏粒组分，其主要矿物成分为高岭石、针铁矿、赤铁矿与三水铝石，砂粒及粉粒组分中还含有石英与长石。但P3剖面中的蒙脱石矿物可能继承自沉积源物质。在P3剖面下方的砾岩样本中，鉴定出黑云母、白云母与斜长石。P3剖面的铝质特性可能源于含铝蒙脱石矿物的风化作用。上述特性将此类土壤与巴西境内相邻的哈普利克强风化粘磐土及其他同类土壤区分开来。依据巴西土壤分类系统（SiBCS）进行土壤分类时，考虑到高铁铝含量，建议将P1、P2划分为腐殖质贫瘠铁质哈普利克强风化粘磐土（Nitossolo Háplico distroférrico），P3划分为富铝铁质哈普利克强风化粘磐土（Nitossolo Háplico alitiférrico）；而依据世界土壤资源参比基础（World Reference Base of Soils, WRB），此类土壤可归类为铁质粘磐土（Ferritic Nitisols）。