Development, Composition and Age of Indurated Sand Layers in the Late Quaternary Coastal Deposits of Northern Moreton Bay, Queensland

Brief description

Indurated sand is commonly found in Quaternary coastal deposits in a range of temperate and tropical environments. These horizons can record past regionally significant phases of soil development. Also, their lower hydraulic conductivity can produce locally perched water tables and they have been regarded as a potential source of iron in coastal waterways. Samples were analysed from exposures in sand mine pits at Beachmere and in the bank of an estuarine channel at Bells Creek in southeast Queensland. In these samples cements coat grains and usually partially infill interstitial pores. Distinctive cement forms are produced by different constituents that are dominantly kaolinite, amorphous organic-rich complexes or a mix of clay and amorphous material. Trace metal concentrations in the cements are lower than previously reported for soils and modern estuarine sediments in the region. Large-scale exposures at Beachmere reveal that in addition to the podzolisation process, mineral and amorphous organic-rich cements also precipitate from groundwater that preferentially flows through the poorly sorted coarser sediments. OSL and TL ages for the deposits examined indicate that induration occurs over long periods of time, 100,000 ? 70,000 years. Only incipient induration has developed over the last 16,000 ? 2,600 years. The degree of induration, however, is not always proportional with age and is strongly influenced by the texture of the deposits, with gravely sands (OSL age 76,700 ?6,500 yr) exhibiting a greater degree of induration than an adjacent medium to coarse sand (98,000 ?9,900 yr).

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