THE MID-CASTLECLIFFIAN MANGATUNA FORMATION OF THE GISBORNE DISTRICT, NORTH-ISLAND, NEW-ZEALAND

The type area of the mid-Castlecliffian Mangatuna Formation is describ ed and three members are proposed. The formation unconformably overlie s marine Pliocene strata in an area of Quaternary uplift at Gisborne, eastern North Island, New Zealand. The strata dip <5 degrees towards t he northwest and were at least 120 m thick (top eroded) near Calhome S tation, where the Calhome (oldest), Matokitoki, and Town Hill Members are mapped. The Calhome Member is composed of nonmarine siltstone, tep hras, and minor sandstone and gravel, whereas the lower part of the Ma tokitoki Member, formed of gravel, represents the deposits of a mid-Ca stlecliffian? braided Waipaoa River. The Town Hill Member contains non marine and estuarine molluscs and at one locality fossil tree trunks. At the commencement of deposition of the formation there was, locally, substantial mid-Castlecliffian (mid-Pleistocene) relief of at least 7 0 m, including the north-trending Valley Road Hill, Mangatuna Ridge, a nd Calhome valley. This relief was buried by the time the Town Hill Me mber was deposited. The presence of Matokitoki Member within the Calho me valley implies that the ancient Waipaoa River flowed along the nort hern margin of the Poverty Bay flats. A mid-Castlecliffian age for the formation is deducted largely from nanofossils.