Changes in quaternary oceanographic bottom conditions as documented by foraminifera in sediment cores from the slope of the exmouth plateau (off Western Australia)

Benthonic foraminifera from 15 surface- and 70 core-sediment samples (three cores) from the Western Australian continental margin (Exmouth Plateau) were quantitatively investigated. As far as possible, the occurrences of the species were correlated with the recent oceanographic conditions especially as related to water depths. The sampled sites are separated from the Australian Shelf by the Montebello Trough so that the taphocoenoses cannot become adulterated by foraminifera from the shelf. Only 1% or less of the foraminifera are benthonic species. The benthonic foraminiferal faunas of the surface sediment samples from 3800 to 1700 m are composed of about the same deep-water species as described from southeastern Indian Ocean basins by Corliss (1979a). They differ from one another only because different species dominate the faunas dependent on different water depth and/or water mass. Above 1700 m the character of the benthonic foraminiferal fauna is slowly changing from abyssal to bathyal. Downcore the benthonic foraminifera show marked changes in abundance patterns, which partly parallel the changes which can be observed with the “cool” and “warm” indicating planktonic foraminifera, partly show regular phase displacement with these changes. The different abundances of the same species in a core from, for instance, 3000 m or from 2000 m water depth, respectively, prevent a direct correlation between the cores. It also proved impossible to correlate the changes in the frequency patterns of certain species to certain paleo-oceanographic conditions. Examples for this are given.