Biostratigraphic dating in the Tamar Graben

MRT has published a new report weighing the evidence for using plant fossils to provide accurate dating of sedimentary units in Tasmaina's Tamar Valley.

Plant fossils preserved in sediments in the Tamar Graben are a natural archive of past environments in the Tamar Valley at, and to the north of, Launceston over the past 70 million years (Ma) – a period of geologic time during which Tasmania evolved from a promontory of mainland Australia separated from Antarctica by rift valleys (Southern Margin Rift System), into an island over 2500 km north of the ‘ice’ continent. Like most Late Cretaceous–Neogene sites in inland central, southern, and western Tasmania, the geohistory of this graben is based on a combination of isotopically dated basalts and/or the stratigraphic distribution of fossil pollen and spores (miospores) preserved in fluvio-lacustrine sediments. The biostratigraphic age control for such sites however, assumes that the age range of these miospores in geologic time is the more or less the same as in the offshore Gippsland and Bass basins in Bass Strait.

In this recently published collaborative report, the above assumption is tested in the Tamar Graben by comparing the age ranges of fossil pollen and spore species (morphospecies) preserved in nine boreholes, with their age ranges in the offshore Gippsland and Bass basins.