Formation, morphology and classification of colluvial soils: a review

Colluvial soils have received increased attention in different fields of environmental and geoarchaeological research over the past two decades. However, their pedological functions and status as specific soil units have seldom been discussed. The concepts and general understanding of the term colluvial soil' often vary; the definition of this term is vague and thus requires standardization. In this paper we define colluvial soils as soil units that underwent a specific profile development and record characteristics formed by specific processes. We also review and summarize concepts and definitions of colluvial soils in the geosciences, describe their morphology and properties, assess a typical colluvial profile and propose a new definition and inclusion of colluvial soils in soil classification systems. We suggest that colluvial soils should be defined as either (i) colluvisols, which are recent undeveloped soils formed by the periodic rejuvenation of a soil profile because of the accumulation of eroded topsoil or (ii) colluvium-derived soils, which are soils that developed from colluvia that underwent various pedogenetic processes. The proposed criteria for the classification of colluvisols highlight (i) the accumulation of eroded soil material as the primary process in the formation of colluvisols, (ii) their specific terrain positions and (iii) the different types of development of colluvisol profiles.