New palaeoenvironmental and palaeoceanographical interpretations of the Miocene Wuk Wuk Marl and Bairnsdale Limestone using ostracod microfossils

For the first time, fossilised ostracod assemblages have been reported from the 9-7 million-year-old sedimentary rock layers known as the Upper Wuk Wuk Marl and Bairnsdale Limestone from Bairnsdale, Victoria. These layers represent stacked ancient seabeds, which yield information on past environments and oceanographic conditions. The assemblages provide data for new interpretations about early Late Miocene ancient continental shelf environments in the Gippsland region and ocean current circulation patterns. One key finding was the recognition of an earlier than previously thought influence of the Antarctic Circumpolar Current (ACC) on south eastern (SE) Australian marine realms.

About 600-750 ostracods were obtained each from two Upper Wuk Wuk Marl and two Bairnsdale Limestone samples from different Bairnsdale District rock exposures. The interpretations were made analysing ostracod assemblage comparative diversity, population age structures and fossil preservation characteristics, as well as through the consideration of abundant and/or ecologically significant taxa.

These fossil ostracod faunas gave new insights into the past continental shelf position of sampled sites, past local wave or current intensity, past (warmer) maritime conditions, and the past confluence of cool and warm water currents, as well as the likely past presence of seagrass meadows, and a weak coastal upwelling system. The occurrences of the Tasmanocypris dartnalli species group within these early Late Miocene outcrops provides evidence for an earlier than previously recorded influence of the ACC in southern Australia.