Dune phases in the Otaki-Te Horo area (New Zealand): a geomorphic history

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Optical dating, sedimentological analysis and soil profile development have been used to develop a chronology for, and an understanding of, the geomorphic evolution of the Holocene coastal plain between Otaki and Te Horo, North Island of New Zealand. The coastal plain has prograded 0·48 m a−1 since sea-levels reached their post-glacial maximum 6500 years ago. Dune development on the plain, which is dependent on the supply of sediment suitable for dune building, has been episodic. Three periods of dune activity have been identified - the Foxton, Motuiti and Waitarere phases - the last two of which are believed to have resulted from anthropogenic activities. The dunes north of the Otaki River and south of Mangaone Stream are typical of a coastal dune system that extends from Patea in the north to Paekakariki in the south. However, this system is disrupted by the Otaki River and the gravels it delivers to the coastal zone. Immediately south of the river mouth the dunes are significantly smaller, coarser, and contain significantly more magnetic material. The character of the landforms is the result of: the reworking of the last glacial deposits; ongoing coastal progradation; variation in the input of sediment suitable for dune formation; the change in beach character because of gravel input; and the position of the Otaki River mouth.

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