Dune Reddening and Time

Abstract

ABSTRACT Abundant evidence exists that many dune sands become reddened with the passage of time. The process is promoted by warm temperatures, oxidizing conditions, and the periodic presence of moisture. Reddening is due to the gradual weathering of iron oxide and silicate mineral grains; the weathering tends to cause the coatings to become thicker and affects increasing numbers of grains with the passage of time. In addition, evidence suggests that the hematitic grain coatings are resistant to the abrasion associated with eolian transport. It is suggested that the basic requirements for development of hematitic weathering products--warm temperatures, oxidizing conditions, and the occasional presence of moisture--are regularly met in most tropical and sub-tropical dunes, even those in very dry environments, because of the ability of dune sands to absorb and retain rainfall.