A multifaceted study of the offshore Titihaoa-1 drillhole and a Neogene accretionary slope basin, Hikurangi subduction margin

Abstract

This paper presents a reappraisal of datasets from Titihaoa-1, an offshore petroleum exploration drillhole that intersects a ∼2740 m-thick Holocene to early-middle Miocene sedimentary succession in the Titihaoa Sub-basin, part of the Hikurangi accretionary wedge. The well provides an important datapoint in the offshore southern Hikurangi subduction margin. We present new and revised foraminiferal biostratigraphic and paleoenvironmental interpretations that help to constrain age, depositional paleo-water depths, sedimentation rates, and oceanicity. Analysis of open-hole wireline and image-log datasets, combined with analogues from nearby outcrops, provide an improved understanding of the sedimentary architecture, depositional systems, and present-day in-situ stress at the drillhole site. The succession within Titihaoa-1 comprises a shallowing-upward succession of thin-bedded lower- to middle-bathyal turbidites, overlain by mudstone-dominated lithofacies deposited in the middle- to upper-bathyal and mid-shelf environments. The geological history and stratigraphic trends within the Titihaoa Sub-basin are analogous to other Neogene accretionary wedge basins within the Hikurangi Margin.