Upper cenozoic stratigraphy of South Westland, New Zealand

Abstract

The upper Tertiary sequence in South Westland, exposed along the highly deformed vertical limb of the Coastal Monocline, rests unconformably on pre-Miocene rocks. The oldest unit, Awarua Limestone (Sl), is overlain conformably by the Tititira Formation (Sl-w), a deep-water sequence passing upwards from hemipelagic mudstone through distal and proximal turbidites (Kaipo Member) into a mass-flow conglomerate-sandstone complex (Long Reef Member). The Jackson Formation (?Tt), composed of highly deformed calcareous mudstone and muddy limestone, apparently overlies the Tititira Formation, although the possibility that it may have been emplaced tectonically cannot be discounted. Small intrusions of high-Al, low-K basalt and microgabbro cut the Jackson Formation in the Hope River area. A major unconformity, probably representing uplift and erosion of at least 2500 m, separates the Halfway Formation (Wo-p) from older rocks. The Halfway Formation is exposed only in the area immediately south of Halfway Bluff, although believed to have been much more extensive at the time of deposition, and consists of middle to outer shelf marine sediments (partly slumped into place) resting with slight unconformity on a basal gravel. The overlying Cascade Conglomerate (? late Quaternary) is a complex glacial unit composed of till, lake sediments, and outwash gravel. Flat-lying sequences in Hari Hari-1 and Waiho-1 drillholes to the west of the monociinal axis are similar, although not truncated by unconformities. In comparison with North Zestland, the upper Tertiary succession in South Westland is thicker (progressively thickening and containing an increasing proportion of redeposited beds to the south) and of deeper-water facies. © 1978 Taylor & Francis Group, LLC.