Abstract
Abstract The Middle Miocene (Altonian-Waiauan) sequence at Waikawau (Mokau-Mohakatino Groups), totalling c. 350 m thick, sits directly on Mesozoic basement rocks or rarely on local Oligocene Te Kuiti Group. It comprises four newly defined formations. Nukuhakari Formation is dominated by hemipelagic slope mudstones and some turbidites; Tirua Formation comprises redeposited calcareous sandstone/sandy limestone sheets, frequently thoroughly bioturbated, formed in broad, shallow channels on an upper to mid-continental slope carbonate apron; Ngarupupu Formation consists of variably volcaniclastic sandstones and mudstones deposited from sediment gravity flows on the mid- to outer regions of deep-marine, coalescing, volcaniclastic fan-aprons; and Waikaretu Formation is dominated by fine nonvolcaniclastic sandstones deposited by sand-rich, high-concentration turbidity currents at bathyal depths. Two petrofacies occur, suggesting two distinct sediment provenances: Nukuhakari and Waikaretu Formations have a Mesozoi...
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