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Late Eocene perturbations: Foraminiferal biofacies and evolutionary overturn, southern Australia


  • Brian McGowran


Abundance patterns of planktonic and benthic foraminifera in profiles of neritic successions at high southern paleolatitudes show evidence that they represent systemic stratigraphic signals from the global ocean. In an interval correlated with upper Zone P15 and Zone P16, long-distance correlations can be made on benthic Sphaeroidina and the aragonitic Robertinacea. Among the plankton, increased numbers of Globigerinatheka alternate with high abundances of Chiloguembelina and increased numbers of Pseudohastigerina, especially during an Hantkenina ingression. Those alternations indicate environmental fluctuations in the upper part of the water column, just as alternations in Cibicididae/Uvigerinidae ratios give similar signals from the benthic communities. The fluctuations are considered to be directly or indirectly linked to available oxygen. Several local neritic events can be correlated with oceanic events, and on the basis of those correlations the suggestion of a stratified ocean during Zone P16 is supported. Near the end of Zone P16 there is a major benthic species overturn and disappearance or weakening of signals of water column stratification and restricted bottom water circulation. I conclude that local events such as species overturn, biofacies spikes, and a brief regression (the Chinaman Gully regression at about the end of Zone P16) are of global significance as part of the stepwise configuration of the Terminal Eocene Event.

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