Neogene stratigraphic architecture and tectonic evolution of Wanganui, King Country, and eastern Taranaki Basins, New Zealand

Abstract

Analysis of the stratigraphic architecture of the fills of Wanganui, King Country, and eastern Taranaki Basins reveals the occurrence of five 2nd order Late Paleocene and Neogene sequences of tectonic origin. The oldest is the late Eocene‐Oligocene Te Kuiti Sequence, followed by the early‐early Miocene (Otaian) Mahoenui Sequence, followed by the late‐early Miocene (Altonian) Mokau Sequence, all three in King Country Basin. The fourth is the middle Miocene to early Pliocene Whangamomona Sequence, and the fifth is the middle Pliocene‐Pleistocene Rangitikei Sequence, both represented in the three basins. Higher order sequences (4th, 5th, 6th) with a eustatic origin occur particularly within the Whangamomona and Rangitikei Sequences, particularly those of 6th order with 41 000 yr periodicity. The base of each 2nd order sequence is marked by marine flooding and represents a discrete phase in basin development. The Te Kuiti Sequence accumulated in non‐marine and shelf environments, whereas the Mahoenui Sequence accumulated mostly at bathyal depths; no regressive deposits are evident, having been eroded during subsequent uplift. The Mokau Sequence comprises shoreface and non‐marine deposits including coal measures. The Whangamomona Sequence accumulated during extensive flooding of King Country Basin and collapse of the eastern margin of Taranaki Basin. It has a thin retrogressive part (Otunui Formation) and a thick progradational component (Mount Messenger to Matemateaonga Formations). The latter component represents the northward progradation of a continental margin wedge through Wanganui and King Country Basins. The Rangitikei Sequence is marked by extensive flooding at its base (Tangahoe Mudstone) and reflects the pull‐down of the main Wanganui Basin depocentre. This sequence comprises a second progradational margin wedge, which migrated on two fronts, one northward through Wanganui Basin into King Country Basin, and a second west of the Patea‐Tongaporutu High, through the Toru Trough into the Central and Northern Grabens of Taranaki Basin and on to the Western Platform as the Giant Foresets Formation, thereby building up the modern shelf and slope. All five sequences are erosionally truncated, with up to 2100 m of exhumation that affected much of central North Island. The Pliocene timing of the start of erosion, together with its pattern, point to long wavelength deformation of the crust driven from the upper mantle consequent upon migration of the late Miocene andesitic volcanic arc from northern Taranaki Basin into Taupo Volcanic Zone.