The stratigraphy and structure of the mt bruce area, northern wairarapa, north island, new zealand

Abstract

A sequence of terrestrial and estuarine to upper bathyal sediments of the Mangaoranga Formation accumulated in the Mt Bruce sub-basin during transgression over Torlesse Supergroup rocks during late Miocene (Tongaporutuan) time. The Moles Mudstone is defined as a new member ofthe Mangaoranga Formation; it consists of mudstone, lignite and conglomerate deposited in estuarine conditions. Conglomerate overlying the Moles Mudstone accumulated locally in a fault-angle depression, establishing an alluvial fan adjacent to a coastline, with its more distal parts deposited offshore. Subsequent deposition of progressively finer grained sediments (from sands and silts to muds) records continuing basinal subsidence and a marine transgression across the Mt Bruce area. Upper-bathyal conditions were widespread by late Tongaporutuan time. The folded Miocene sediments are preserved as infaulted outliers within a zone cif dextral shear bounded by the Wellington and Wairarapa Faults. They are unconformably overlain by aggradational river gravels of Pleistocene age. © 1987 Journal of the Royal Society of New Zealand.