Cretaceous-Cenozoic geology and petroleum systems of the East Coast region, New Zealand

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Field, B.D.; Uruski, C.I.; Beu, A.G.; Browne, G.H.; Crampton, J.S.; Funnell, R.H.; Killops, S.D.; Laird, M.; Mazengarb, C.; Morgans, H.E.G.; Rait, G.J.; Smale, D.; Strong, C.P. 1997 Cretaceous-Cenozoic geology and petroleum systems of the East Coast region, New Zealand. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences monograph 19 2 v.

Abstract: The East Coast region is an area of about 75,000 square km, about half of which is offshore, extending from East Cape in the northeast to Kaikoura in the southwest, a distance of more than 500 km. The region straddles the active Hikurangi subduction margin between the Australian and Pacific plates. The stratigraphic succession consists of three elements: (1) Cretaceous rocks ranging from paralic sandstones to bathyal mudstones and flysch deposited in a variety of compressional and extensional tectonic settings prior to and during rifting from Australia; (2) latest Cretaceous and Paleogene rocks, mainly mudstone and micrite, reflecting post-rift foundering of the New Zealand region; (3) Miocene rocks dominated by bathyal flysch and mudstone but punctuated by neritic sands and limestones, and Pliocene rocks characterised by alternating siliciclastics and coarse bioclastic limestones. Good seismic data cover much of the offshore part of the region, but are generally of poorer quality and coverage onshore. Cretaceous structures are dominantly compressional onshore in the north and extensional offshore and in the south. There are few Paleogene structures, reflecting a passive margin phase. Numerous oil and gas seeps demonstrate the region's petroleum potential, and significant gas was found in the two offshore wells drilled. Potential reservoir units are terrestrial fan and alluvial conglomerates, paralic and shelfal sand bodies, slope channel systems, bathyal fan deposits, shallow marine limestones and units with secondary fracture porosity. Maturation modelling indicates considerable variability in the timing of generation and expulsion within the basin. The East Coast region has proven hydrocarbon generation, good reservoir units and large closures, and the timing of expulsion is favourable in many areas. The region warrants further exploration. (auth/EB)