Biostratigraphy of Kora-1 offshore well, North Taranaki

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Hayward, B.W.; Strong, C.P. 1993 Biostratigraphy of Kora-1 offshore well, North Taranaki. Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 93/13 ii, 28 p.

Abstract: Kora-1 offshore petroleum exploration well, located in north Taranaki, was drilled to a total depth of 3421 m during November and December, 1987. Bottom-of-hole lies within rocks of the Bartonian Stage. Analysis of foraminifera from 27 cuttings and 13 core or sidewall core samples provided the following biostratigraphy: 0-630 m undated; 630-1300 m Mangapanian-Castlecliffian; 1390-1700 m Waipipian; 1767-1780 m Opoitian; 1780-2580 m undated andesitic volcanics; 2600-2762 m Altonian; 2800-2887 m late Waitakian-Otaian; 2900-2952 m early- mid Waitakian; 3030-3081 m Whaingaroan-Duntroonian; 3105-3195 m early Whaingaroan; 3246.6-3252 m probably Kaiatan-Runangan; 3285-3421 m (T.D.) Bartonian. A time gap may be present between the top of the volcanics and mid/late Opoitian around 1780 m, and a more likely time gap lies between the base of the volcanics (inferred to be Lillburnian) and the mid-Altonian beneath. The foraminiferal assemblages indicate mid bathyal depths from the Bartonian through to-Altonian. The volcanics undoubtedly accumulated at bathyal depths, and are overlain by a transgressive Pliocene sequence that rapidly shallowed to ''shelf'' depths. Kora-1 has remained at ''shelf'' depths (0-200 m) since mid-Waipipian. The subsidence curve for Kora-1, derived by geohistory analysis, suggests rapid early Paleogene subsidence, followed by decreased but consistent subsidence from Hortonian through Altonian and undated volcanics interval. A pulse of further rapid subsidence initiated in the Waipipian continues through to the present day. (auths)