Presenter: Alysha Johsnon (University of Wollongong)

Description:
The Tasmantid Seamount Chain, off the east coast of Australia, comprises at least twenty age-progressive seamounts, guyots and carbonate reefs. The chain is associated with northward migration of the Australian Plate over a stationary hotspot extending from the youngest volcano in the south (~6.5 Ma) to the oldest (>30 Ma) in the north. Multibeam echosounding (MBES) undertaken aboard Schmidt Ocean Institute's research vessel Falkor (voyages FK201228, FK210206) has augmented existing bathymetric data held within Geoscience Australia's AusSeabed database. The newly collected high-resolution bathymetry covers ~75,000km² of seafloor and enables morphologic assessment of terraces, carbonate reefs, mass-wasting structures and tectonic features. Geospatial analysis, when combined with existing seismic and dredge data, reveals contrasting morphologies between guyots and carbonate reefs. These include complex carbonate summits on Cato Reef, Fraser and Recorder seamounts, differing from the erosive summits on the younger Barco, Taupo and Gasycone guyots. The oldest volcanoes in this chain, Kenn, Wreck and Cato reefs, sit upon elevated older continental crust with modern reef growth at present-day sea level. Fraser Seamount and all volcanoes south of it erupted onto young oceanic lithosphere and have since progressively subsided below sea level. Multiple sets of terraces and reefs characterise the geomorphology of the Kenn, Wreck, Cato, Fraser and Recorder volcanic pedestals. Thus, the high-resolution bathymetry captures the latitudinal variation of carbonate reefs, seamounts and guyots, as these volcanoes have transitioned from non-reef-forming to reef-forming seas, in contrast to the well-studied Hawaiian chain.