Oceanic palaeoenvironment of the Miocene Fyansford Formation from Fossil Beach,near Mornington,Victoria, interpreted on the basis of Ostracoda

Study of an ostracode assemblage from the Miocene Fyansford Formation near Mornington allows determination of the principal characteristics of the hydrologic environment at that time.

Palaeodepth was upper epibathyal (about 150–250 m). The oxygen minimum zone mostly was weakly demarcated at about O₂ 5 ml/l. Productivity was good and the benthic ostracode microfauna was rich and varied. Occasionally, a sudden and strong increase in productivity occurred which correlated to a rapid and well marked increase in the oxygen minimum zone. Physico-chemical factors, which developed following bacterial breakdown of organic matter that had accumulated on the bottom, are reflected in Bradleya shells by distinct signs of aggradation/degradation. A few allochthonous forms from the nearby continental shelf were transported downwards onto this part of the upper slope. Bottom currents contributed (by furrowing) to the formation of calcareous ‘hard grounds’.

Bradleya morningtonensis n.sp. is described as new.