Stratigraphy of the Castlecliffian type section: 10 mid‐Pleistocene sequences from the Wanganui coast, New Zealand

Abstract

The 160 m thick Castlecliff coast section was deposited during the middle Pleistocene (c. 1.07–0.35 Ma) and comprises 10 disconformity‐bound cyclothems or sequences. A typical sequence has three parts: (1) a basal suite of shore face and inner shelf sediments with intertidal and shallow subtidal molluscan faunas, and cross‐bedded, pebbly shell gravels (type A shellbeds); (2) a mid‐cycle shellbed, which contains in situ offshore molluscs in a matrix of muddy fine sandstone or fine sandy siltstone (type B shellbeds); and (3) an upper unit of terrigenous siltstone, either bedded and barren of fossils, or bioturbated and with a sparsely scattered in situ fauna similar to that of the subjacent shellbed. The three parts of each sequence correspond respectively to the transgressive systems tract, mid‐cycle shellbed, and highstand systems tract of the sequence stratigraphic model. Sequence 7 (Kupe Formation, Upper Kai‐Iwi Shellbed, Upper Kai‐Iwi Siltstone) is designated as the type example of the Castlecliff motif. A detailed measured section is presented of the Castlecliff section, with 30 formations designated which correspond to the most significant lithostratigraphic units and to the inferred systems tract interpretation. Where possible, the formational nomenclature follows that of Fleming (21 formations, six with adjusted boundaries). However, three formations represent newly observed units (Mowhanau Formation, Lower Kai‐Iwi Shellbed, Lower Castlecliff Siltstone), and seven other formations are erected on the basis of previously described beds, members or informal units (Rolled Concretion Conglomerate, Tiostrea‐Dosina Bed, Ophiomorpha Sand, Lower Westmere Shellbed, Kaikokopu Formation, Upper Westmere Shellbed, Upper Kai‐Iwi Shellbed). The lithofacies and macrofaunal and microfaunal associations are documented across the section in terms of this lithostratigraphic framework.