Deepwater, frontier basins of northwestern New Zealand - Burial history and hydrocarbon maturation

The deepwater basins of northwestern New Zealand offer opportunities for exploration as the quest for oil moves out beyond the continental shelf. Over the last decade the head of the New Caledonia Basin, the Reinga Basin, and the adjacent deepwater parts of the Taranaki and Northland basins have been investigated using geophysical surveys with stratigraphic control from the contiguous Northland and Taranaki basins. The depositional and deformational history of the region can now be deduced, and petroleum generation modelled for each basin. Interpretation of seismic reflection data indicates that the oldest sediments were deposited in a continental margin setting, which underwent extensional faulting in the Cretaceous as the New Zealand sub-continent broke away from Gondwanaland. Sedimentation changed from terrestrial to marine in the Late Cretaceous, and regional subsidence and marine transgression continued into the Paleogene. In the Oligocene the development of the Australian-Pacific plate boundary led to subduction, arc volcanism and increased sedimentation in northern New Zealand. During the Neogene, clastic sediment supply to the Taranaki and Northland Basins was uninterrupted, while clastic sedimentation continued in the Reinga Basin until the Late Miocene when it was replaced with hemipelagic drifts. In the New Caledonia Basin, Neogene sedimentation has been more or less continuous, with a northwestward reduction in clastic component. Two-dimensional burial history and hydrocarbon generation models of the New Caledonia and Reinga basins, using standard source rock parameters, predict that hydrocarbon generation and expulsion has taken place over significantly large areas of the basins. Models also predict oil will be trapped in places where suitable structures exist. The results from modelling indicate that the deepwater, frontier basins of northwestern New Zealand have hydrocarbon potential, and with modem drilling technology are viable petroleum exploration provinces.