Abstract The Waikawau region occupies a critical position near the junction between onland North Wanganui Basin and mainly offshore Taranaki Basin, affording a unique, albeit narrow, onshore “window” into a portion of the mainly offshore geology in North Taranaki Graben of Taranaki Basin. The sedimentary geology at Waikawau has previously been ascribed to the Middle Miocene Mohakatino Group, and undifferentiated as to formations. Although probable correlations with formations in both the Mohakatino and Mokau Groups elsewhere can be made, four new formations are defined and their distribution presented in a geological map. The lowermost, the Nukuhakari Formation, is dominated by Altonian to upper Lillburnian-Waiauan, massive, blue-grey calcareous mudstone, which either overlies localised Oligocene Te Kuiti Group strata, or, more commonly, onlaps Mesozoic basement rocks. Nukuhakari Formation correlates partly with Mokau Group, but mainly represents time missing in a prominent unconformity in Mokau-Mohakatin...