High-level stratigraphic scheme for New Zealand rocks

Abstract

We formally introduce 14 new high-level stratigraphic names to augment existing names and to hierarchically organise all of New Zealand's 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 country's 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.Keywords: igneous rocks; metamorphic rocks; New Zealand; Zealandia; sedimentary rocks; stratigraphy; tectonics Introduction It has been 40 years since Carter et al. (1974) proposed a tripartite high-level stratigraphic nomenclature for New Zealand rocks. Their Kaikoura, Rangitata and Tuhua sequences were broad, unconformity-bounded stratigraphic units, with the Rangitata Sequence being subdivided into formal assemblages and zones. Following revisions to the International Stratigraphic Guide, Carter (1988) amended the sequences to synthems.The high-level nomenclature of Carter et al. (1974) and Carter (1988) has not been widely adopted. The orogenies, assemblages, zones, sequences and synthems proposed for New Zealand's Cambrian-Early Cretaceous basement rocks were supplanted by a different, stable and well-used classification based on provinces, terranes and batholiths ( Fig. 1; e.g. Coombs et al. 1976;Tulloch 1988). Carter (1988 defined the Kaikoura Synthem to encompass Late Cretaceous-Holocene cover strata in eastern South Island which he divided into five formal groups onshore, four of which he correlated to informal seismic sequences offshore. While Carter's (1988) use of offshore seismic stratigraphy and his concepts for developing a 'lumping rather than splitting' approach were...

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“…The input wavelet used for the generation of the synthetic seismic and a seismic trace from the seabed is shown below. The ages of stratigraphic horizons interpreted in this study are defined and placed into the regional framework of Mortimer et al (2014). See Figure 1 for well location.…”

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