Heilbronn, Kelly1, González-Álvarez, Ignacio2 and Klump, Jens2
1Geosciences, College of Science and Engineering, James Cook University, Townsville, Queensland, Australia. 2CSIRO, Mineral Resources, Discovery Program, Kensington, Western Australia, Australia
Landscape features (e.g. paleovalleys) result from the interaction of geology, climate, sea-level changes, sedimentary dynamics and tectonism though time. The Digital Elevation Model (DEM) in SW Australia displays a dendritic to sub-dendritic pattern, interpreted as the surface expression of large buried paleovalleys that cut across geological provinces within the Yilgarn Craton. These paleovalley patterns terminate at the southern boundary of the Yilgarn Craton and are not traceable into the Albany-Fraser Orogen. Paleovally traces which existed in the Albany-Fraser region were later removed. The separation of Australia from Antarctica (Cretaceous) resulted in the deposition of large volumes of eroded sediment from the Albany-Fraser region into the Bremer Sub-basin. Any final traces of paleovalleys from within the Albany-Fraser region were later eliminated due to erosional action of transgression-regression cycles. The Yilgarn Craton, however, has preserved traces of paleovalley due to lack of sea-level influence, and a landscape evolution dominated by river systems.
The dendritic pattern of the large paleovalleys in SW Australia is similar to modern glacial dominated valleys. This observation supports that paleovalleys in SW Australia were carved by glaciers before the breakup of Gondwana, during the Carboniferous-Permian glaciation when ice sheets progressed NNW from Antarctica towards Australia, over the Albany-Fraser Orogen and into the Yilgarn Craton. Additionally, some paleovalleys exhibit unusual morphologies displaying tributaries that narrow downstream and divert abruptly from the overall NNW drainage trend. These peculiar paleovalleys are up to 6 km wide upstream. This study links these unusual morphologies, such as the sudden directional changes from overall NNW drainage trend, with underlying Archean basement architecture. We related magnetic data with DEM sub-products (Multi-resolution Valley Bottom Flatness map (MrVBF), Gallant and Dowling, 2003), revealing that linear features in the magnetics correlate with these unusual paleovalley features in the MrVBF map. This supports that basement structures influenced the narrower width and abrupt change in water flow direction of these paleovalleys when they were active, and were fundamental in the drainage and landscape development of this part of Australia.
Kelly Heilbronn is a PhD Candidate at James Cook University working on the Mesozoic tectonic evolution offshore eastern Australia. Kelly completed an internship with CSIRO in 2018 under supervision of Dr Ignacio González-Álvarez and Dr Jens Klump focusing on the evolution of southwestern Australian paleovalleys from the Palaeozoic until today.