Basement structure and sediment thickness beneath the continental shelf of the Hauraki Gulf and offshore Coromandel region, New Zealand

Abstract

The basement structure and sedimentary history of the continental shelf east of the northern section of North Island, New Zealand, is interpreted from geophysical data collected by petroleum companies. Interpretation of magnetic data shows the basement to be composed of both igneous and nonigneous rocks in the vicinity of the Coromandel Peninsula and Great Barrier Island; further north the basement is almost entirely nonigneous. From seismic reflection data, basement in the region can be seen to have undergone extension, being faulted into a series of fault-angle depressions and grabens. Sea-floor expression indicating continued development of the fault-angle depressions is found locally, especially in the Tauranga Harbour — Cuvier Island region. Outside the Hauraki Gulf, the sedimentary section overlying basement is separated into two units by an unconformity of unknown age. The lower unit is probably late Tertiary — Quaternary sediments and the upper unit is probably late Quaternary sediments. Within the Hauraki Gulf, the poor quality of seismic reflection data precludes analysis of the sedimentary section.