Proposal for geological classification and nomenclature of soils: both genetic-descriptive and compositional-mineralogical

Abstract

Numerous systems with detailed classification of soil are in existence. Most of them are based on a variety of complex criteria, such as material type and properties like the amount of organic material, presence of clay layers, and the presence of oxidation or reduction iron-rich horizons, as well as depositional characteristics, its landform morphology and depositional formation processes. Many of these have been developed for use in fields such as agronomy and geotechnics. This paper focuses on the classification of the soil by determining its materials, their origin and the geological processes that shape them, following these basic assumptions: (1) The soil initially comes from the weathering of a parent substrate that can be either sedimentary deposits (for example, alluvial or fluvial) or of any type of rock (igneous, metamorphic or sedimentary), (2) the parent substrate structure is composed by original sequential facies (e.g. foliation, igneous cumulates or stratigraphic intercalation of sedimentary layers), (3) the physical and chemical weathering and the biogenic activity and productivity processes that occur in the soil modify both the original structure and the constituents of the parental substrate, resulting in the formation of new materials, the conservation of others, and the overprint of the sequential facies of the soil (horizons A, B and C) developed on the original parental sequential facies, additionally (4) some materials will be lost from the system and others will be incorporated into it. Finally, a strictly compositional-mineralogical classification of soil is also proposed, which corresponds essentially to the main groups of minerals: silicates, carbonates, phosphates, oxides and hydroxides, sulfates, organic rich matter, nitrates, sulphides, borates, native elements and halides, named in sedimentology as monomaterials, plus the polymaterials or rock fragments (RF). This classification offers an advantage when examining materials that are not genetically linked to the parent substrates, making each soil profile unique, by highlighting the role played by the parental materials in this process. This classification is intended to complement, but not replace any existing soil classification