Characteristics and significance of some humate-cemented sands (humicretes) at Cape Flattery, Queensland, Australia

Abstract

Humate-cemented sands (humicretes) are exposed at several locations along the foreshore and in gullies near Cape Flattery, North Queensland, Australia. Three broad types of humate accumulation are recognized: (a) pedogenetic; (b) groundwater; and (c) aquatic. Pedogenetic and groundwater humicretes usually have a grain-supported fabric in which quartz represents > 99% of the framework grains. Hand specimens of humicrete are brittle but disintegrate rapidly in 0.1 N-NaOH. Concentration of humate is considered to have occurred by vertically and laterally migrating groundwater, while induration has probably been caused by irreversible drying of the humic substances during periods of seasonal water-table lowering. Radiocarbon dating of an in situ root embedded in indurated humate near Cape Flattery has indicated a ‘background’ age of > 48000 C–14 years.