A Late Holocene Marine Terrace on the Kidnappers Coast, North Island, New Zealand: Some Implications for Shore Platform Development Processes and Uplift Mechanism

A marine terrace up to 6 m above present mean sea level is preserved along 15 km of the Kidnappers coast, Hawke's Bay, North Island, New Zealand. Radiocarbon dates for 10 shell samples collected from intertidal marine deposits overlying an uplifted shore platform have a total age range of 590 yr (from 2280 ± 50 to 2750 ± 70 yr B.P.). Sample age decreases landward suggesting a small relative sea-level rise, probably as a result of tectonic subsidence prior to uplift. Rates of contemporary shore platform formation preclude the preservation of a marine terrace subjected to constant, aseismic uplift. Preservation of a subhorizontal uplifted shore platform mantled by intertidal marine deposits with in situ fauna is best explained by abrupt coseismic uplift 2300 yr B.P. and preceded by tectonic subsidence. The presence of a single marine terrace does not permit the calculation of past earthquake magnitude or recurrence, but the NNE tilt of the 2300-yr-old marine terrace indicates continued growth of the north-trending late Pleistocene Kidnappers Anticline.