Mass-balance interpretation of a soil chronosequence provides a means of quantifying elemental addition, removal, and transformation that occur in soils from a flight of marine terraces in northern California. Six soil profiles that range in age from several to 240,000 yr are developed in unconsolidated, sandy- marine, and eolian parent material deposited on bedrock marine platforms. Soil evolution is dominated by (1) open-system depletion of Si, Ca, Mg, K, and Na; (2) open-system enrichment of P in surface soil horizons; (3) relative immobility of Fe and Al; and (4) transformation of Fe, Si, and Al in the parent material to secondary clay minerals and sesquioxides. Net mass losses of bases and Si are generally uniform with depth and substantial—in some cases approaching 100%; however, the rate of loss of each element differs markedly, causing the ranking of each by relative abundance to shift with time. Loss of Si from the sand fraction by dissolution and particle-size diminution, from ∼100% to <35% over 240 ky, mirrors a similar gain in the silt (from ∼2% to 30%-50%) and clay (from ∼0% to ∼20%) size fractions. The Fe originally present in the sand fraction decreases from >80% to <10%, whereas the amount of Fe present in the clay and crystal-line oxyhydroxide fractions increases to 25% and 70%, respectively. Aluminum originally present in the sand fraction decreases from >90% to <10% concurrently with an increase of AI in the organic sesquioxide and clay phases, to 10% and 50%, respectively, while only minor increases occur in the nonorganic sesquioxide phases.

First Page Preview

First page PDF preview
You do not currently have access to this article.