Pliocene foraminiferal environments in Hawke Bay-1 well

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Scott, G.H.; Crundwell, M.P. 1994 Pliocene foraminiferal environments in Hawke Bay-1 well. Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 94/19 27 p.

Abstract: Census data, standardized by weight, on foraminifera from 34 cuttings samples (Nukumaruan - upper Opoitian Stages, Pliocene) between 460 m and 1120 m in Hawke Bay- 1 well are used to interpret depositional environments. The site was at middle bathyal depths between 460 m and - 720 m (Nukumanian - Mangapanian), except for a shallowing excursion at 620 m. Transported shallow shelf taxa are present. High benthic productivity events at 460 m and particularly 620 m and 700 m are associated with spikes of Euuvigerina pygmea and indicate high nutrient flux and/or oxygen depletion; they might be related to cool episodes. There was a substantial (?200 - 400 m) decrease in depth at c. 720 m which is reflected in assemblage composition. The site moved up to uppermost bathyal - outer shelf depths and into sheltered neritic water. Low frequencies of both benthic and planktic specimens in the vicinity of 800 - 900 m (Waipipian) may be due to rapid sedimentation. Between 980 m and 1060 m (Waipipian - upper Opoitian) there is a conspicuous zone of high benthic frequencies, especially of Euuvigerina miozea, and indication of stressed foraminiferal environments. The episode may reflect movement through an oxygen minimum zone near the continental margin. Below 1060 m (upper Opoitian) the site moved into more open water and possibly deepened, although still within the outer shelf - uppermost bathyal zones. (auths)