Hypergypsic Soil Micromorphology and Landscape Relationships in Northeastern Spain

There are not many studies of hypergypsic soils and terminology describing these soils continues to develop. Hypergypsic is here applied to soils having gypsum as a major component, often more than 50%, whereas the term gypsiferous is used for soils with any amount of gypsum. The soils described here developed from gyprock, under a semiarid climate (xeric soil moisture regime). Water tables are below possible capillary rise to the soil surface and the soils do not contain salts more soluble than gypsum. Micromorphology and geomorphic positions of the soils were used to describe and relate the weathering and landscape processes. We developed models to explain the occurrence and distribution of the different kinds of gypsum. Mudflows are an important process of gypsum mobilization. Massive microcrystalline gypsum horizons are related to the gyprock weathering and mudflow deposits. Pedogenic, sand-size sparite crystals were identified in pedofeatures named queras, and can form surface horizons. Two kinds of gypsic fabric (lenticular and microgypsic) result from the studied gypsification processes. The introduction of the hypergypsic diagnostic horizon to the taxonomic classification system would be helpful for the accurate classification of these soils.Peer reviewe