Analysis of benthic foraminifera in upper Cretaceous through Oligocene bathyal sediments from East Coast, North Island, New Zealand demonstrates that the catastrophic extinction event of intermediate-water (100-1000 m) taxa occurred approximately 58-57 Ma during the latest Paleocene-early Eocene global warming. The following middle Eocene cooling produced stepwise origination events signifying the greatest turnover of the fauna. Most of the extinct species are aerobic forms, whereas the surviving taxa are dysaerobic forms. This interpretation suggests that a change of environment to low oxygen conditions was the main cause of the extinction. Following the extinction event, a dysaerobic fauna occupied the intermediate-water for about one million years. The stepwise appearance of new aerobic species in the middle Eocene indicates a gradual increase of dissolved oxygen in the intermediate-water.
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