Evolution of soils on quaternary reef terraces of Barbados, West Indies

Soils on uplifted Quaternary reef terraces of Barbados, similar to 125,000 to similar to 700,000 yr old, form a ctimo-chronosequence and show changes in physical, chemical, and mineralogical properties with terrace age. Paren t materials are dust derived from the Sahara, volcanic ash from the Lesser Antilles island are, and detrital carbonate from the underlying reef limest one. Although some terrace soils are probably eroded, soils or their remnan ts are redder and more clay-rich with increasing terrace age. Profile-avera ge Al2O3 and Fe2O3 content increases with terrace age, which partially refl ects the increasing clay content, but dithionite-extractable Fe also increa ses with terrace age. Profile-average K2O/TiO2, Na2O/TiO2, and P2O5/TiO2 va lues decrease with terrace age, reflecting the depletion of primary mineral s. Average SiO2/Al2O3 values also decrease with terrace age and reflect not only loss of primary minerals but also evolution of secondary clay mineral s. Although they are not present in any of the parent materials, the younge st terrace soils are dominated by smectite and interstratified kaolinite-sm ectite, which gradually alter to relatively pure kaolinite over similar to 700,000 yr. Comparisons with other tropical islands, where precipitation is higher and rates of dust fall may be lower, show that Barbados soils are l ess weathered than soils of comparable age. It is concluded that many soil properties in tropical regions can be potentially useful relative-age indic ators in Quaternary stratigraphic studies, even when soils are eroded or ch anges in soil morphology are not dramatic. (C) 2001 University of Washingto n.