Group nomenclature of late oligocene and early miocene rocks in Auckland and northland, New Zealand; and an Akarana supergroup

Abstract

Recent mapping of late Oligocene and early Miocene rocks in Auckland and Northland has lead to a re-appraisal of group nomenclature. Rocks of Ballance's western Waitakere Magmatic Arc are assigned to the new Waitakere Group. Rocks of the eastern Northland Magmatic Arc are assigned to an expanded version of Skinner's new Coromandel Group. Between the two Arcs the rocks of the marine interarc basin are divided into three Groups: Waitemata Group (revised so as to transfer the Manukau Breccias to the Waitakere Group), centred around the central flysch body of Auckland, Hay's Otaua Group for marine sediments underlying the Waitakere Group at Hokianga, and Leitch's unpublished Parengarenga Group for a marine sequence at North Cape. Constituent subgroups and formations are listed. Because of their close genetic links as the rock record of the early phases of evolution of the New Zealand Magmatic Arc, the five groups are linked, together with underlying and overlying. Chaos-breccia units (Ballance and Sporli's west Northland Allochthone, and Kear and Waterhouse's Onerahi Chaos-breccia, respectively), in a new Akarana Supergroup.