Thermo-Tectonic History of Taranaki Basin (New Zealand) Using Apatite Fission Track Analysis (AFTA)

P. J. J. Kamp, K. A. Hegarty, P. F. Green

The Taranaki basin, which extends offshore between the north and south islands of New Zealand, contains several large gas fields (e.g., Maui field) and smaller oil fields. The Taranaki basin is New Zealand's only productive hydrocarbon basin. The basin trends north-south, is asymmetrical in cross section, and is faulted with up to 7 km of displacement along parts of its eastern margin.

Preliminary results from Apatite Fission Track Analysis (AFTA) reveal the timing and magnitude of basin inversion. Four well cross sections from the southern part of the basin have been used. Initially, basin tectonics and sedimentation were associated with extension and the formation of half-grabens that began in the Late Cretaceous with the breakup of Gondwana. However, most of the observed subsidence and sedimentation resulted from mid-Cenozoic rifting throughout western New Zealand. Following the formation of the modern Australia-Pacific plate boundary during the early Miocene, the southern part of the basin, which lies only 60 km from the Alpine fault in places, was partially inverted. AFTA parameters (apparent age and length) downhole at the Fresne-1 well show a distinct break i slope at 1,100 m depth (currently at 30°C) where the apparent age is 15 Ma for the Late Cretaceous Pakawau Coal Measures. The data indicate that basin inversion began about 15 Ma and was accompanied by the removal of 2-3 km of section. Sedimentation began again in the Taranaki basin during the mid-Pliocene.

The source of the gas and gas condensate in the basin is probably the Eocene coal measures. The maturation history of these beds and the overlying reservoirs was modeled using the constraints from AFTA data. Discrepancies exist between estimates of maximum paleotemperature from AFTA results and from vitrinite reflectance.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.