Geological Controls on Oil and Gas Occurrence in Taranaki Basin, New Zealand

KING, P. R., and J. M. BEGGS, DSIR Geology & Geophysics, Lower Hutt, New Zealand

Taranaki basin contains all the commercial oil and gas fields in New Zealand as well as several marginal and subeconomic accumulations. The basin has a polyphase tectonic history, with different phases controlling specific aspects of hydrocarbon occurrence.

Basin formation began with oblique rifting in the mid-Late Cretaceous. Principal petroleum source rocks are coal measures deposited in southern, central, and eastern parts of the basin during the rift and immediate postrift phase. In the Latest Cretaceous and early Cenozoic, the Taranaki basin was part of a western passive margin bordering proto-New Zealand, a large region of thinned continental crust separating from Australia and Antarctica. Clastic sediment supply to the basin progressively diminished as the sea transgressed the land to the south and east. Coastal and fluvial sandstones deposited during this phase are major petroleum reservoirs; a late Eocene turbidite reservoir in the north contains a noncommercial accumulation.

In the mid-Cenozoic, the modern plate boundary began to propagate through New Zealand. In initial response, the Taranaki basin evolved into a submerged foreland basin. A recent significant oil discovery is reservoired in fractured limestones deposited in the foredeep. Taranaki basin Neogene development is characterized by structure reactivation, eversion, overthrusting, and differential subsidence along its eastern margin and in the south. Mountain building adjacent to the basin caused an increase in clastic sediment supply and concomitant regression, during which some minor reservoirs were deposited. However, the major significance of the Neogene tectonic phase lies in the formation of all proven traps, and in maturation of source rocks with increasing burial.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)