Semi-Arid/Arid Zone Calcretes: A Review

The methods and concepts required for understanding the properties and genesis of semi-arid/arid zone calcretes are described. Calcretes are near-surface terrestrial, secondary calcium carbonate accumulations in soil profiles, bedrocks, and sediment. They commonly occur in both Quaternary and pre-Quaternary continental and marginal marine sequences and are of value in palaeoenvironmental and palaeoclimatic interpretation. Without pretending to be comprehensive, the present review provides a brief coverage of the aspects of calcrete classification, profiles, maturity, hydrological setting, micromorphology, cathodoluminescence signatures, mineralogy and chemistry, mode of introduction of carbonates, and the environments and rates of calcrete formation. Additional aspects include the climatic/palaeoclimatic implications of calcretes, the use of stable isotopic compositions of calcretes for palaeoenvironmental interpretation and calcrete dating. Through its interdisciplinary character, the study of calcretes improves our understanding of the evolution of Quaternary landscapes and can be potentially applied to the stratigraphie record from the Early Proterozoic onwards—the time of the first occurrence of calcretes.