Revised Oligo-Miocene stratigraphy of the Murray Basin, southeast Australia

Abstract

This paper reconciles the outcrop and subsurface Oligo-Miocene marine stratigraphy of the Murray Basin to arrive at a basin-wide correlation. The initial open-marine transgressive marl and clay facies of the basin belong to the Ettrick Formation, a unit that is also laterally equivalent to the calcisiltite and calcarenite that are present on the surface and in the subsurface in the basin. Since this unit is lithologically indistinguishable from the previously identified Victorian Oligocene to Middle Miocene Winnambool Formation, we suggest that the latter unit be replaced as a stratigraphic unit in the basin. The majority of outcropping units in South Australia can be recognised lithostratigraphically in the subsurface of Victoria. The calcisiltite, calcarenite, marl and clay of the lower and upper Mannum, the Finniss, Glenforslan, Bryant Creek and Pata Formations can be distinguished in the Victorian Lower to Middle Miocene Duddo Limestone. Our work suggests that the lithostratigraphic unit the Duddo Limestone can also be replaced as a stratigraphic unit in the region. Direct correlation to the outcropping detailed stratigraphy in South Australia has been achieved across into Victoria for the first time. The correlations will allow a better understanding of the geometry of the Oligo-Miocene strata in the Murray Basin allowing improved hydrostratigraphy. It will also form the basis for ongoing palaeoenvironmental and palaeoceanographic studies in the area.