Geology of the Eastern Taranaki Basin margin between 38 ° 00 ' S and 39 ° 00 ' S North Island, New Zealand

Abstract

Study of seismic sections from the eastern Taranaki Basin margin between 38 ° 00 ' S and 39 ° 00 ' S has allowed recognition of seismostratigraphic datums including acoustic basement and the Tikorangi Horizon. Correlation of these and less continuous reflective events to oil exploration wells and outcrop has revealed stratigraphic and structural trends, and enabled a complex history of faulting about this basin margin to be recognised. The data suggest a multiphase history for the basin margin. Fault control on deposition of the Upper Cretaceous Pakawau Group and early Tertiary Kapuni Group sediments appears likely. Peneplanation during the Oligocene was followed by almost complete submergence of the eastern Taranaki Basin margin, and gave way in the early Miocene to compression which resulted in the folding of shallow sediments and the stacking of thrust wedges along a linear fault zone less than 10 km wide. Multistorey stacking in the Internal Thrust Zone has been largely destroyed by erosion, with the products deposited within an entirely autochthonous marine foreland. Localised and episodic oblique - slip faulting on steeply dipping basement faults appears to have limited the width of the westward - directed contractional fault regime. These basement faults are likely to coexist with a different tectonic regime at depth. The west Waikato volcanicity (3.3 M.y.BP) appears restricted within the Internal Thrust Fault Zone to areas adjacent to early branch thrust fault intersections. These faults define the northern margin of a dominantly vertical zone of compression and continuing uplift. Structural history is controlled by the Australia - Pacific plate boundary. Timing of the transition from Tasman Sea rifting to compression remains uncertain. In this region oblique convergence on Alpine fault trends appears to be confined to the early Miocene.