Submarine channelforms and fans in the Miocene Moki and Mount Messenger formations, Taranaki Basin, New Zealand

Abstract

Taranaki Basin (New Zealand) contains a Late Cretaceous – Cenozoic sedimentary succession up to 9 kilometres thick. Neogene strata are volumetrically a significant part of the basin fill. During the late-Middle Miocene a new sediment source, arising from the onset of uplift and erosion of the Southern Alps mountain belt, supplied the basin with copious sediment, continuing to the Recent. This resulted in the development of a northwestward prograding shelf-slope wedge within the basin. The Moki and Mount Messenger formations accumulated as sandstone strata within mudstone (Manganui Formation) and display obvious sediment conduits (i.e. canyons, channels and gullies) in seismic reflection profiles. Past studies considered that these conduits pass through submarine fans, while in reality fans occur basinward of the mouths of the sediment conduits. This thesis study leverages seismic reflection data and applies seismic stratigraphy and seismic geomorphology, integrated with analysis of wireline logs, core, and outcrops, to better understand the occurrence of sediment conduits and fans within the Moki and Mount Messenger formations. Results show that in southern Taranaki Basin, increased sediment influx resulted in steepening of the continental slope, changing the morphometrics of sediment conduits. Critical analysis of data generated here forced the dismissal of all published fans associated with these sandstone formations. Rather, two new Late Miocene submarine fans have been mapped in deep-water western Taranaki Basin towards the head of the New Caledonia Basin. New paleogeographic maps for the Middle and Late Miocene have been drawn that display the sediment conduits and new fans.