Geomorphic and cosmogenic nuclide constraints on escarpment evolution in an intraplate setting, Darling Escarpment, Western Australia

Abstract

The~900 km long Darling Scarp in Western Australia is one of the most prominent linear topographic features on Earth. Despite the presence of over-steepened reaches in all westerly flowing streams crossing the scarp, and significant seismic activity within 100 km of the scarp, there is no historical seismicity and no reported evidence for Quaternary tectonic displacements on the underlying Darling Fault. Consequently, it is unclear whether the scarp is a rapidly evolving landform responding to recent tectonic and/or climatic forcing or a more slowly evolving landform. In order to quantify late Quaternary rates of erosion and scarp relief processes, we obtained measurements of the cosmic-ray produced nuclide beryllium-10 ( 10 Be) from outcropping bedrock surfaces along the scarp summit and face, in valley floors, and at stream knickpoints. Erosion rates of bedrock outcrops along the scarp summit surface range from 0·5 to 4·0 m Myr -1. These are in the same range as erosion rates of 2·1 to 3·6 m Myr -1 on the scarp face and similar to river incision rates of 2·6 to 11·0 m Myr -1 from valley floor bedrock straths, indicating that the Darling Scarp is a slowly eroding 'steady state' landform, without any significant contemporary relief production over the last several 100 kyr and possibly several million years. Knickpoint retreat rates determined from 10 Be concentrations at the bases of two knickpoints on small streams incised into the scarp are 36 and 46 m Myr . If these erosion rates were sustained over longer timescales, then associated knickpoints may have initiated in the mid-Tertiary to early Neogene, consistent with early-mid Tertiary marginal uplift. Ongoing maintenance of stream disequilibrium longitudinal profiles is consistent with slow, regional base level lowering associated with recently proposed continental-scale tilting, as opposed to differential uplift along discrete faults. Cosmogenic 10 Be analysis provides a useful tool for interpreting the palaeoseismic history of intraplate near-fault landforms over 10 5 to 10 6 years.

Paleogene Grand Canyon incompatible with Tertiary paleogeography and stratigraphy

“…Kooi and Beaumont (1994) concluded that scarp recession is more likely to occur on scarps that are also drainage divides. There also is evidence that some major scarps do not always undergo the signifi cant degree of lateral retreat originally argued by King (1953), such as the slow evolution of the Darling escarpment of western Australia, proposed by Jakica et al (2011). However, the dramatic "Grand Staircase" physiography of northern Arizona and southeastern Utah demonstrates that regional scarp recession was an important aspect of latest Cretaceous and Cenozoic Colorado Plateau history.…”

Spatial and temporal patterns of Cenozoic dynamic topography around Australia

“…Along the west coast, Pliocene shorelines occur at elevations of up to 75 m with progressively younger shorelines at lower elevations [ Collins and Baxter , ]. Geomorphological investigations of river profiles and cosmogenic dating of the Darling Escarpment suggest that it became emergent during Neogene times [ Jakica et al ., ]. The sign and amplitude of oceanic residual topography along the west coast closely match the inferred uplift of this escarpment.…”

Knickpoint formation, rapid propagation, and landscape response following coastal cliff retreat at the last interglacial sea-level highstand: Kaua'i, Hawai'i

“…In an early application of cosmogenic nuclide dating, Seidl et al (1997) attempted to measure the waterfall retreat rate in Ka'ula'ula Valley, Kaua'i, but the results were largely inconclusive. Since the work of Seidl et al (1997), improvement in cosmogenic nuclide exposure dating methods has proven the technique a valuable tool for measuring long-term rates of both channel incision and knickpoint retreat (e.g., Weissel and Seidl, 1998;Reusser et al, 2004;Righter et al, 2010;Valla et al, 2010;Abbuhl et al, 2011;Jakica et al, 2011;Jansen et al, 2011).…”