Critical re-assessment of Middle and Late Miocene submarine fans in offshore southern and western Taranaki Basin, New Zealand, to update the paleogeography

Abstract

The purpose of this paper is (i) to re-assess the presence of submarine fan systems of Middle and Late Miocene age (Moki and Mount Messenger formations) previously mapped on the continental slope in offshore southern and central Taranaki Basin, New Zealand, and (ii), to demonstrate the occurrence of two newly mapped Late Miocene submarine fans in the deep-water part of offshore western Taranaki Basin, based on accepted seismic stratigraphic criteria for submarine fans. In our work we have found that the fans previously mapped amongst canyons and channels in the Moki and Mount Messenger formations on the upper and middle continental slope in southern and central Taranaki Basin do not fulfil established stratal criteria for submarine fan deposits. Moreover, detuning of 3D seismic reflection volumes for the Moki and Mount Messenger formation intervals ahead of amplitude attribute extraction, shows that the strata previously mapped as submarine fans based on amplitude alone, are merely artifacts of bed thickness. The two new fans systems of Late Miocene age that we map here, both attributed to the Mount Messenger Formation, principally comprise mudstone and represent a minor proportion of the Late Miocene succession that accumulated in southern and central parts of the basin. Our remapping of slope canyons and channels in the southern part of the basin and the identification of the two new fan systems in the western part of the basin are embodied in three new paloegeographic maps for the Middle and Late Miocene development of Taranaki Basin. A modern analogue for the two new Late Miocene fans in Taranaki Basin is the Hikurangi Fan at the terminus of the Hikurangi Channel, located outboard of the modern subduction zone of the Hikurangi margin along Eastern North Island. The new Taranaki Basin deep-water fans documented here, may have significance for hydrocarbon exploration in deep water parts of Taranaki Basin, which is largely unexplored.