Kyle J. Bland

High-level stratigraphic scheme for New Zealand rocks

We formally introduce 14 new high-level stratigraphic names to augment existing names and to hierarchically organise all of New Zealands onland and offshore Cambrian–Holocene rocks and unconsolidated deposits. The two highest-level units are Austral Superprovince (new) and Zealandia Megasequence (new). These encompass all stratigraphic units of the countrys Cambrian–Early Cretaceous basement rocks and Late Cretaceous–Holocene cover rocks and sediments, respectively. Most high-level constituents of the Austral Superprovince are in current and common usage: Eastern and Western Provinces consist of 12 tectonostratigraphic terranes, 10 igneous suites, 5 batholiths and Haast Schist. Ferrar, Tarpaulin and Jaquiery suites (new) have been added to existing plutonic suites to describe all known compositional variation in the Tuhua Intrusives. Zealandia Megasequence consists of five predominantly sedimentary, partly unconformity-bounded units and one igneous unit. Momotu and Haerenga supergroups (new) comprise lowermost rift to passive margin (terrestrial to marine transgressive) rock units. Waka Supergroup (new) includes rocks related to maximum marine flooding linked to passive margin culmination in the east and onset of new tectonic subsidence in the west. Māui and Pākihi supergroups (new) comprise marine to terrestrial regressive rock and sediment units deposited during Neogene plate convergence. Rūaumoko Volcanic Region (new) is introduced to include all igneous rocks of the Zealandia Megasequence and contains the geochemically differentiated Whakaari, Horomaka and Te Raupua supersuites (new). Our new scheme, Litho2014, provides a complete, high-level stratigraphic classification for the continental crust of the New Zealand region.

Paleogeography of the Taranaki Basin region during the latest Eocene–Early Miocene and implications for the ‘total drowning’ of Zealandia

Latest Eocene–earliest Miocene strata in the subsurface of the Taranaki Basin provide important new regional paleogeographic and tectonic constraints not available from outcrop. Six paleogeographic maps of the Taranaki Basin region have been produced utilising extensive well, seismic reflection and outcrop data. These record three broad periods of sedimentation characterised by (1) variable transgression and initial deformation (c. 40–30 Ma); (2) maximum transgression with moderate deformation (c. 30–21 Ma); and (3) regression with accelerated deformation (< 21 Ma). Local sedimentation patterns were influenced by reverse faulting, producing depocentres and topographic highs adjacent to the Taranaki Fault System. Reverse faulting commenced as early as c. 40 Ma and may signify the onset of subduction beneath the North Island. In common with other parts of New Zealand, the region reached maximum marine inundation in the Waitakian (c. 23 Ma). However, the deposition of thick clastic sediments in eastern parts of Taranaki Basin, coupled with ongoing tectonism, suggests the presence of land throughout the Oligocene and Early Miocene, and is inconsistent with total Oligocene drowning of Zealandia.

Pegasus Basin, eastern New Zealand: A stratigraphic record of subsidence and subduction, ancient and modern

The stratigraphic architecture of a thick (c. 9000 m) Albian–Recent sedimentary succession within the Pegasus Basin is presented here, based primarily on interpretation of the New Zealand Governments ‘PEG09’ 2D reconnaissance seismic survey. The basin lies immediately east and outboard of the Hikurangi subduction zone, and formed mainly because of Neogene downwarping of the underlying Pacific Plate near the transition from subduction to oblique-slip faulting. The basin fill is little deformed by the Neogene–Recent convergent margin tectonics that pervasively deform the adjacent East Coast Basin. Four large-scale tectonostratigraphic units are differentiated: (1) metasedimentary ‘basement’ rocks, deposited and accreted within the Gondwana Mesozoic accretionary wedge; (2) Early Cretaceous Large Igneous Province crust of the Hikurangi Plateau; (3) non-accreted ‘cover’ strata, incorporating rocks age-equivalent to the youngest parts of the Gondwana accretionary wedge, plus the overlying Late Cretaceous and Paleogene rocks deposited during thermal subsidence; and (4) Neogene–Recent strata deposited since the renewal of subduction beneath eastern North Island. The pre-Neogene geology illustrated by the seismic data describes the Mesozoic subduction along the Gondwana margin, ‘frozen’ at the time when active subduction accretion ceased at c. 110–105 Ma. The geology of Pegasus Basin also provides an insight into the much-debated relationship between ‘basement’ and ‘cover’ rocks in the East Coast Basin. This study is also relevant to the assessment of the petroleum potential of the basin, which is currently held under licence.

A fossil rhombosoleid flounder (Pleuronectiformes) from the Late Pliocene of Te Pohue, eastern North Island, New Zealand

Abstract A fossil skeleton of a rhombosoleid flounder is described for the first time. It was discovered in shallow marine-deposited strata of the Titiokura Formation (Waipipian Stage) from Te Pohue in western Hawkes Bay, North Island, New Zealand. Anatomical comparison with extant flatfishes present in New Zealand waters suggests this fossil can be considered as a representative of Pelotretis flavilatus, the endemic New Zealand lemon sole. This species occurs today in shallow coastal waters around New Zealand to depths of 100 m, in habitats consistent with palaeoenvironmental reconstructions of the Te Pohue area during the Late Pliocene.