- GeoRef, Copyright 2004, American Geological Institute. Reference includes data supplied by Institute of Geological and Nuclear Sciences (SIRIS), Lower Hutt, New Zealand
The 103 documented Paleogene planktonic foraminifera from 21 New Zealand sections which were previously divided into 14 zones have been further subdivided into 26 subzones and a correlation is attempted with Trinidad. A correlation of the following Austral regions is also made: 9 southern Australian sequences, a composite New Zealand sequence based on 21 sections, 4 deep-sea cores from the South Pacific, and 2 sequences from Argentina and 1 from Chile. A detailed examination is undertaken of the Upper Eocene-Lower Oligocene faunas in order to determine the accurate placement of the Eocene-Oligocene boundary. Although there are a number of taxa common to the Boreal, Tropical-subtropical, and Austral belts, some of their extinction levels appear to be diachronous. A record drop in sea-water temperature of 9 degrees C from oxygen isotope analyses in the Upper Eocene of New Zealand effectively reduced species diversity and was the probable cause of the diachronous nature of the initial appearances and extinctions. It is postulated that the cooling probably began in Antarctica in the Upper Eocene, spreading northwards to the New Zealand region, then the cooling affected the already potentially cooler Boreal region in the lowermost Oligocene and finally lowered the temperature of the warmer Tropical-subtropical Belt later in the Lower Oligocene. A time sequential paleo-biogeographic model of the Upper Eocene-Lower Oligocene planktonic foraminifera is presented.