Transient landscape dynamics across the Southeastern Australian Escarpment

Abstract

Passive margin escarpments provide some of the best examples for large-scale transient landscape evolution. Despite the relative simplicity of their geological setting, when compared with active orogenic systems, many open questions exist concerning their modes and rates of evolution. We use catchment wide denudation rates calculated from cosmogenic nuclides concentrations and high resolution topographic analysis to constrain landscape dynamics across the South Eastern Australian Escarpment. We determined denudation rates of ∼15 mm/ka in the lowlands at the foot of the escarpment and of ∼10 mm/ka in the highlands, while catchment draining the escarpment face display rates in the 20-60 mm/ka range. These denudation rates along a passive margin escarpment are among the highest in the world and show greater sensitivity to topographic gradients when compared to other passive margin settings. We interpret this situation as resulting from the intermediate precipitation regime of our study area, as opposed to drier or wetter settings, where hillslope processes can be inhibited due to water availability or deep weathering profiles and vegetation feedbacks, respectively. Combined with the extraction of topographic metrics across the escarpment, these rates allow us to constrain efficiency coefficients for fluvial incision and hillslope diffusion that are similar to other independent estimates in this region.

26Al/10Be ratios reveal the source of river sediments in the Kimberley, NW Australia

“…The escarpment wall 10 Be concentrations predicted by our model can also be used to estimate long-term horizontal retreat rates for the vertical rock faces of the Carson Escarpment in CRSG-1 and CRSG-2. Although these rates are comparable with those obtained for horizontal escarpment retreat elsewhere in Australia (e.g., Nott et al, 1996a;Godard et al, 2019), they should be treated as upper limits given that the model assumes steady-state erosion and does not consider the episodic spalling of meter-sized blocks, which would further reduce the effective nuclide production rates to be lower than 0.5, in turn yielding lower erosion rates. Although these rates are comparable with those obtained for horizontal escarpment retreat elsewhere in Australia (e.g., Nott et al, 1996a;Godard et al, 2019), they should be treated as upper limits given that the model assumes steady-state erosion and does not consider the episodic spalling of meter-sized blocks, which would further reduce the effective nuclide production rates to be lower than 0.5, in turn yielding lower erosion rates.…”

“…Using equation (3) with a production rate half that for non-shielded open exposure (and assuming mean plateau erosion rate of 1 m.My -1 ), we calculate retreat rates of 174 ± 30 m.Myr -1 and 85 ± 7 m.Myr -1 , respectively. Although these rates are comparable with those obtained for horizontal escarpment retreat elsewhere in Australia (e.g., Nott et al, 1996a;Godard et al, 2019), they should be treated as upper limits given that the model assumes steady-state erosion and does not consider the episodic spalling of meter-sized blocks, which would further reduce the effective nuclide production rates to be lower than 0.5, in turn yielding lower erosion rates. Further, it should be noted that unlike passive margin escarpments that are first order continental-scale topographic features in the landscape, the vertical escarpments found on the Kimberley plateausuch as the Carson Escarpmentare lithologically controlled topographic features of a much smaller scale.…”

“…Previous studies employing CRNs on Australian landscapes have focused on mechanisms of soil production (Heimsath et al, 2001;Heimsath et al, 2009), desert morphology and the onset of aridity (Fujioka et al, 2005;Fujioka et al, 2009), quantifying hillslope processes and sediment transport (Struck et al, 2018a(Struck et al, , 2018b, and studying the age of archaeological sites (Pillans and Fifield, 2013). Studies quantifying denudation rates on the basin scale have been few, with notable recent examples including work done in the Flinders Ranges of South Australia (e.g., Quigley et al, 2007;Bestland et al, 2016) and along the basins draining the eastern board of the Great Dividing Range (Nichols et al, 2014;Croke et al, 2015;Godard et al, 2019).…”

Hillslope denudation and morphologic response across a rock uplift gradient

“…These measurements will then allow to compute a non dimensional erosion rate E * according to equation 6. We use the approach presented by Hurst et al (2012) and Grieve et al (2016a), which we implemented into the GRASS GIS environment (Neteler et al, 2012) and R scripting language (R Core Team, 2018), as described in Godard et al (2019) ( figure 4).…”

“…Only a handful of studies have actually attempted to reconcile CRN-based denudation data with topographic metrics extracted from High Resolution DTMs into a GTL-based physical framework (e.g. DiBiase et al, 2012;Hurst et al, 2012Hurst et al, , 2013bGodard et al, 2016Godard et al, , 2019Neely et al, 2019).…”