Abstract

New exploration data is providing information on the early development of New Zealand's greater Taranaki Basin. The 6,200 km Astrolabe nonexclusive 2D seismic survey, acquired during 2001 over the deepwater extension of the Taranaki Basin from the shelf-edge to the 2000 m isobath, revealed a Cretaceous section, thicker and probably older than any previously known from the Taranaki Basin.

Sequence analysis shows that a major deltaic system, comparable to the Golden Beach and Emperor subgroups of the Gippsland Basin and the Ceduna Delta of the Bight Basin of Australia, built into a restricted seaway during the Late Cretaceous and culminated with deposition of the Rakopi Formation coal measure succession.

Three Cretaceous megasequences are recognised:

• Megasequence A, a synrift succession of possible Early Cretaceous age;

• Megasequence B, a prograding deltaic succession, deposited from 100 to 75 million years ago from the Late Albian to the late Campanian and capped by Rakopi Formation correlatives;

• Megasequence C, a transgressive, nearly parallel-bedded succession equivalent to the North Cape Formation of Taranaki.

The Astrolabe Survey has provided an important link in understanding New Zealand Cretaceous basin development. The recognition of previously unknown Jurassic and Lower Cretaceous synrift successions, together with Upper Cretaceous marginal marine and marine sediments in the deepwater Taranaki Basin allows correlation with south-eastern Australia and gives a better understanding of the development of New Zealand's Canterbury and Great South basins.