Structure and evolution of the South Wanganui Basin, New Zealand

Abstract

Abstract The South Wangartui Basin lies in central New Zealand between the South Taranaki Graben and the axial ranges of the North Island. Hili the area of the basin lies offshore beneath northern Cook Strait and the South Taranaki Bight. Four thousand kilometres of CRP seismic reflection profiles, resulting from petroleum exploration in the basin and adjacent areas, have been interpreted to determine the structure and evolution of the basin. The basin is a broad half-graben trending NNE. It contains up to 4000 m of marine Plio-Pleistocene sediments and has developed by progressive subsidence and onlap to the south combined with emergence and offlap in the north. Most of the subsidence occurred during the late Pliocene and early Pleistocene when the depocentres were aligned along the southern continuation of the Taupo Graben trend. The western boundary of the basin is formed by basement highs oriented en echelon and bounded by major pre-Pliocene wrench faults (Flaxmore, Manaia, and Taranaki Faults). The eastern boundary of the basin is marked by NNE-trending probable wrench faults related to basement block movements during Plio-Pleistocene sedimentation. Together with a set of northeast-trending faults across the basin, the boundary faults show a regional pattern of divergent and dextral wrench deformation. To the north the transition to the older North Wanganui Basin is not clear. To the south the Pleistocene sediments onlap the basement rocks of Marlborough Sounds.