A guide to paleoenvironmental assessment using New Zealand Cenozoic foraminiferal faunas

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Hayward, B.W. 1986 A guide to paleoenvironmental assessment using New Zealand Cenozoic foraminiferal faunas. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report PAL 109. 73 p.

Abstract: For decades fossil foraminifera have been the dominant method used in dating New Zealand Cenozoic sedimentary rocks, but their potential usefulness in paleoenvironmental assessments has lagged well behind. The general cause has been the complexity of interrelated factors that influence foraminiferal distributions and the lack of documentation on known distributions and on methods to use in paleoenvironmental analysis. Fortunately, most geological problems do not require paleoenvironmental assessments in terms of each of these determining factors individually, Of significance to the geologist are paleodepth and sometimes oceanicity, water turbulence, bottom oxygen concentration, salinity and paleotemperature. Assessments of these are all possible with our present level of knowledge, although limits of accuracy vary. For example paleodepth estimates in shallow water (less than 100 m) are far more accurate than those in deep water (greater than 500 m).Planktic foraminiferal percentage, maximum size, encrustration, diversity, coiling ratios and taxonomic composition can be used to give direct assessments of oceanicity and paleotemperature and may also give an indication of paleodepth.Benthic foraminiferal diversity and suborder composition may provide a general guide to paleodepth or salinity, but taxonomic composition gives the most detailed information of all the methods available. Charts and tables are presented giving approximate ranges of many New Zealand Cenozoic benthic genera and species, in terms of depth, salinity, water turbulence, bottom oxygen concentration and temperature.Post-mortem faunal changes can affect paleoenvironmental assessments, but the recognition of reworking and current or mass transport of benthics may be useful in paleogeographic studies.A technique for rapid paleoenvironmental assessment is suggested. It involves a quick estimate of planktic percentage (oceancity), benthic suborder composition and the dominant benthic taxa (paleodepth, water turbulence, salinity). This may be supplemented by the identification of rarer benthics with restricted paleoenvironmental ranges.