The Cretaceous stratigraphy of the Southern Hawke's Bay-Wairarapa region

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Crampton, J.S. 1997 The Cretaceous stratigraphy of the Southern Hawke's Bay-Wairarapa region. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 97/08 4, 92 p.

Abstract: Post-Torlesse Cretaceous rocks of the southern Hawke's Bay-Wairarapa region occupy two north-northeast-trending, elongate, fault-bounded, tectonostratigraphic domains, the Western and Eastern Sub-belts of the Eastern Deformed Belt. On the Eastern Sub-belt, Motuan Torlesse basement is overlain, with marked unconformity, by at least 1300 m of Motuan to Ngaterian sedimentary melange (Gentle Annie formation) grading up into thin-bedded sandstone-mudstone and massive mudstone (Springhill Formation). Glauconic Arowhanan sandstone and mudstone are present locally. These strata are overlain unconformably by approximately 300 m of glauconic Piripauan-Haumurian sedimentary breccia, sandstone, and mudstone (Tangaruhe Formation). On the Western Sub-belt, in contrast, the entire interval from the Ngaterian to the Haumurian is preserved as an unbroken succession at least 1300 m thick, of dominantly thick-bedded sandstone, conglomerate and lesser mudstone (Glenburn Formation). Basement has not been identified on the Western Sub-belt, although it may be represented, in part, by small fault-bounded slivers of Urutawan to Motuan submarine volcanics. On both sub-belts, these successions are overlain conformably by relatively uniform Haumurian shale (Whangai Formation). This twofold tectonostratigraphic subdivision of Cretaceous strata occurs also on Raukumara Peninsula and the Western Sub-belt at least extends into Marlborough. In the Motuan, the Western Sub-belt is inferred to have been one or more upper trench slope basins formed during the final stages of subduction along the Pacific margin of Gondwanaland. In the south, extension during the Motuan and Ngaterian, related to the incipient rifting of New Zealand from Australia and Antarctica, was marked by normal faulting and alkaline volcanism, whereas in the north, compression continued into the Raukumara Epoch. Rapid basin infilling during the Clarence Epoch was followed, from Arowhanan to Piripauan times, by deposition at outer shelf depths of thick sedimentary successions in some areas, deposition of condensed sequences elsewhere and, locally, erosion. The Eastern sub-belt records continuous deposition, under tectonically stable conditions, from Motuan to Haumurian times on one or more prograding submarine fan(s) in the oceanic trench formed during the final stages of subduction on the Pacific margin of Gondwanaland. From the Haumurian onwards, uniform conditions of sedimentation were established across both sub-belts of the Eastern Deformed Belt. (auth)