A THICK LATE MIOCENE TO EARLY PLIOCENE PROGRADATIONAL CONTINENTAL MARGIN SUCCESSION CONTAINING 41 KA SHELFAL SEQUENCES IN NEW ZEALAND (TARANAKI BASIN)

The stratigraphic succession exposed in onshore Taranaki Basin, western North Island, New Zealand, contains a succession of shelfal cyclothemic strata recording Milankovitch-scale (obliquity, 41 ka, 6th-order) glacio-eustatic sea-level fluctuations throughout the Late Miocene to Early Pliocene.

This study has documented the sequence stratigraphic architecture of the Matemateaonga Formation, which is an ~1100 m-thick succession of strongly cyclothemic, unconformity bounded shelfal strata of Late Miocene (Late Messinian) to Early Pliocene (Early Zanclean) age (c. 5.5-4.7 Ma). This succession accumulated chiefly in shoreface to mid-shelf environments, and formed as a result of the interplay between climatically-driven 6th-order (41 ka) eustatic sea-level changes, high rates of tectonically driven basin subsidence, and high rates of sediment flux derived from denudation of the Southern Alps located to the south. The sequences comprise a shellbed (TST), siliciclastic siltstone (HST) and siliciclastic sandstone (RST) lithofacies. These sequences have an architecture that is fundamentally the same as those of Pleistocene age, which we have previously described from Wanganui Basin, New Zealand.

A chronology for this succession has been built up from micro- and macrofaunal biostratigraphy integrated with a magnetostratigraphy correlated to the geomagnetic polarity time scale (GPTS). The Matemateaonga Formation provides a quality record of glacio-eustatic sea level changes during the Late Miocene - Early Pliocene superimposed on a tectonically-driven 3rd-order cycle of Middle Miocene to Early Pliocene age.

The Matemateaonga Formation and sequences within it have been geologically mapped at 1:50 000 scale over ~1500 km² of the eastern Taranaki Peninsula region, and placed within a 3rd-order progradational continental margin succession. Underlying parts of this succession contain continental slope and basin-floor facies, the whole succession having been passively uplifted and eroded during the Pleistocene.