Mass balance of soil evolution on late Quaternary marine terraces in coastal Oregon

Mass-balance analysis was used to quantify elemental losses, gains and transformations for a soil chronosequence developed on elevated marine terraces in south-coastal Oregon. The four soils analyzed in the study range in age from 80 ka to greater than 250 ka and are Inceptisols, Spodosols and Ultisols. Dominant soil-forming processes include (1) desilication and loss of base cations from the solum, (2) redistribution of iron and aluminum from surface to subsurface horizons, (3) transformation of iron and aluminum from sand and silt-size fractions to secondary clay and crystalline sesquioxide fractions, and (4) accumulation of organic matter. Silica represents the largest mass loss of any element from the system and varies from -6.48 g/cm(2) (11% loss from solum compared to original amount of Si in parent material) to -42.99 g/cm(2) (22%) with increasing terrace age. Losses of silica from the sand-size fraction over time (2% to 17%) are accompanied by increases of silica in the clay-size fraction. Base cations represent only a small portion of the soil mass but up to 53% (-0.09 g/cm(2)) of the sodium present in the parent material is lost due to weathering and leaching. Iron and aluminum are redistributed within the sola of younger terraces, during podzolization, but are lost from the older soils due to intense weathering and leaching over time. The majority of iron is transformed from the sand and silt-size fractions to the crystalline sesquioxide fraction. In contrast, the majority of aluminum lost from the sand and silt-size fractions is transformed to the clay-size fraction. (C) 1998 Elsevier Science B.V. All rights reserved.