A review of Wanganui Basin, New Zealand: global reference section for shallow marine, Plio–Pleistocene (2.5–0 Ma) cyclostratigraphy

Abstract

Wanganui Basin, New Zealand, contains one of the most complete late Neogene marine stratigraphic records in the world. The ca. 2 km thick basin-fill for the last ca. 2.5 Ma comprises 47 superposed cyclothems which correspond to successive 5th (100 ka) and 6th (41 ka) order glacio-eustatic, sea-level fluctuations on the palaeo-New Zealand shelf since oxygen isotope stage 100. Stages 100 to 5 are represented by marine cyclothems, whereas stages 17 to 3 are represented by a suite of coeval and younger uplifted marine terrace sequences. Additionally, a predominantly glacial loess stratigraphy exists for isotope stages 12–2. The presence of interbedded tephras and an established paleomagnetic stratigraphy allows the development of an integrated cyclostratigraphy for Wanganui Basin which correlates closely with the global oxygen isotope scale. In all except two cases (cycles 12 and 36), individual unconformity-bound cyclothems (sequences) represent a single glacial/interglacial couplet of Milankovitch frequency. Lithologic and faunal variation within the cyclothems corresponds closely to that predicted by the sequence stratigraphic model. Each cyclothem generally contains a transgressive systems tract, a mid-cycle condensed shellbed, a highstand systems tract, and often a regressive systems tract. Six common cyclothem motifs are inferred to represent deposition in shelf locations between the highstand and lowstand shorelines, viz. the Hawera, Maxwell, Turakina, Seafield, Castlecliff, and Rangitikei motifs. A seventh type, the Nukumaru motif, includes coquina limestone and represents deposition in shoreface and very shallow water marine environments.