HOLOCENE SHORELINE DEPOSITIONAL PROCESSES AT POVERTY BAY, A TECTONICALLY ACTIVE AREA, NORTHEASTERN NORTH-ISLAND, NEW-ZEALAND

Holocene depositional processes at Poverty Bay have been affected by: (1) tectonism; (2) sea level response to climate change; (3) fluvial processes responding to: (1) and (2), severe storms and volcanic eruptions. The height distribution of radiocarbon dated beach and estuarine shells and wood, show that during the Holocene relative uplift of the land has occurred at the northeastern margin of the Poverty Bay flats, while subsidence has occurred at the southwestern margin. Three Holocene tectonic subregions are distinguished at the Poverty Bay flats coast; a northern (Gisborne-Wainui) uplift area, a central (Makaraka-Awapuni) static pivotal area and a southern (Patutahi-Muriwai) downdrop area. Periods of significant fluvial upstream degradation into gravel terrace deposits and downstream gravel aggradation are dated at ca, late last glaciation, 12,000-9000 and 7000-5000 BP. The 12,000-9000 BP gravel deposits show tilting to the southwest. Major erosion and infilling events also occurred at ca. 1700 and 300 BP. Holocene marine transgression and progradation shoreline locations are mapped and the coastal processes are reviewed in terms of the tectonic, fluvial and eustatic sea level influences.