Neogene lithostratigraphy of southern Wairarapa

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SR_1997-036-pdf
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Crundwell, M.P. 1997 Neogene lithostratigraphy of southern Wairarapa. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 97/36 57 p.

Abstract: The primary objective of this report is to formalise the poorly documented lithostratigraphy of the middle Miocene rocks within the Wainuioru Valley, southern Wairarapa, and integrate the new units with the lithostratigraphic nomenclature of Vella & Briggs (1971). The work was carried out as part of the Institute of Geological & Nuclear Sciences' Cretaceous-Cenozoic Basin Studies Programme for the East Coast region. Marked changes in lithofacies, stratigraphic content and thickness within Neogene rocks of southern Wairarapa delineate two sedimentary belts with different depositional and tectonic histories: an eastern sedimentary belt, comprised of small often discrete basins, with locally developed successions of heterogeneous conglomerate, well-bedded sandstone, algal limestone, thick turbidite sequences and hemipelagic mudstone, contained within the Annedale Group; and a western belt, characterised by a widespread often cyclic succession of well-bedded barnacle-rich coquina, shell-rich sandstone and massive often monotonous mudstone, contained within the Palliser and Onoke groups. Annedale Group was proposed by Johnston (1975, 1980) for well-bedded sediments of early to middle Miocene age that crop-out in the Tinui-Awatoitoi district of northeast Wairarapa. Johnston included two formations within the group, the deep-water Whakataki Formation and the shallow-water Takiritini Formation. Palliser Group was proposed by Vella & Briggs (1971) for a transgressive late Miocene sequence that onlaps basement rocks of the Aorangi Range. The group is amended in this report to include all middle and late Miocene strata associated with a major transgressive phase of sedimentation within the western sedimentary belt of southern Wairarapa. Seven formations are included in the amended Palliser Group. Only the late Miocene Hurupi Formation (Vella, 1954) and Bells Creek Mudstone (Vella & Briggs, 1971) have been described previously. New names introduced here for the older formations are: Tattons Sandstone, Ngaumu Mudstone, Karamu Sandstone, Bankview Mudstone and Putangirua Conglomerate. Onoke Group was mapped by Vella & Briggs (1971) to include six formations: shallow-water sandstones and limestones (Clay Creek Limestone, Makara Greensand, Haurangi Limestone and Bull Creek Limestone), and deep-water mudstones and minor sandstones (Mangaopari Mudstone and Greycliffs Formation. Beu (1995) included the Pukenui and Castlepoint limestone formations in the Onoke Group. The Onoke Group is separated from the underlying Palliser Group by a regional unconformity, associated with the Makara Greensand. To make the Onoke Group more useful for regional mapping, this report proposes that: Clay Creek Limestone, Haurangi Limestone, Bull Creek Limestone and Greycliffs Formation are downgraded to members within Mangaopari Mudstone; and Makara Greensand is redefined to include both shallow-water greensands and deep-water glauconitic mudstones and phosphorites. (auth)