Ironsand in continental shelf sediments off western New Zealand—a synopsis

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Abstract
The ironsand component (ilmenite, titanomagnetite, and/or magnetite) of surficial sediments on New Zealand's western continental shelf is highest on the inner-middle shelf between Auckland and Taranaki where the mean concentration is x 0304; = 3.85% by weight. Sediments off Westland and Nelson contain only x 0304; = 0.17% ironsand. The subsurface distribution of ironsand, as revealed in piston cores, resembles that at the surface except that subsurface concentrations are markedly lower (e.g., x 0304; = 0.77% for Auckland-Taranaki) Textural and compositional data from the Auckland-Taranaki shelf suggest ironsand was originally concentrated under littoral conditions during the Holocene transgression and was dispersed north and southeast of the main primary source, the Egmont volcanics. The ironsand and host sediment are now approaching equilibrium with the modern hydraulic regime of waves and storm-induced currents and, therefore, are regarded as palimpsest. Any ironsand concentrated on the Westland-Nelson shelf during a lower stand of sealevel is now covered by ironsand-poor modern sediment; the Auckland-Taranaki shelf has a far lower modern sediment supply and, thus, the ironsand has remained exposed.

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