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|Title: ||Erosion and the sediment conveyor in central Australia|
|Authors: ||Jansen, JD|
|Issue Date: ||29-Feb-2016|
|Publisher: ||Geological Society of Australia|
|Citation: ||Jansen, J. D., Chappell, J., Struck, M., Eccleshall, S. V., Fujioka, T., Codilean, A. T., Fülöp, R. H., Fink, D., Cohen, T. J., & Nanson. G. C. (2016). Erosion and the sediment conveyor in central Australia. Paper presented at the Neotectonics on the Australian Plate: New Science for Energy, Mineral and Groundwater Systems, and Hazard Assessment Seminar, 26th February to 1st March 2016, Canberra, Australia.|
|Abstract: ||Why are the Neogene sedimentary fills across central Australia generally thin and discontinuous?
One long-standing explanation is that sluggish tectonism and intensified aridity have combined to
suppress rates of erosion and sediment production yielding a landscape crowded with inherited, preMiocene forms. Quantifying rates of sediment production, residence time and transport is possible
with numerous methods, but the recent growth of cosmogenic nuclide (CN) analysis has provided
unprecedented quantitative insights to rates of landscape evolution. Measurements of in situ
produced cosmogenic 10Be and 26Al integrate rates of surface processes over million-year
timescales—the last part of the Neogene in which aridity has strengthened across the continental
interior. We present a compilation of ~600 published and unpublished 10Be and 26Al measurements
from central Australia with a focus on the Neogene Eyre Basin and its periphery.
Outlying and inlying bedrock uplands serve as engines of sediment production via erosion of bedrock.
Surrounding the bedrock outcrops are vast sediment conveyors of varying efficiency and tempo:
hillslopes, pediments, and alluvial fans are interim storage/burial zones for sediment in transit to the
network of low-gradient rivers, dunes, and playas towards base level. Interactions between fluvial and
aeolian processes are especially pertinent to sediment flux in the Eyre Basin. Major rivers such as the
Cooper and Finke traverse dunefields in their lower reaches where quantities of alluvia are
recirculated into dunes and vice versa. Tracking the trajectories of sediment from source-to-sink
(including aeolian recirculation) remains a major challenge, but is central to unravelling the
sedimentary dynamics of central Australia's Neogene basins. Based on the CN compilation we
estimate 1) spatially averaged erosion rates at the scale of a hillslope or river catchment; 2) pointbased erosion rates on bedrock surfaces; 3) residence time of sediment in hillslope regolith and
alluvial fans; and 4) cumulative burial history of sediments in transit.
Catchment-scale erosion rates (n~100) are consistently low (<10 m/Myr) and include some of the
lowest rates ever measured (~0.3 m/Myr); however, a small group of catchments in the Flinders Ras
yield higher erosion rates (~30–60 m/Myr). Bedrock hillslopes (n~200) tend to erode even slower (<5
m/Myr), with a subset of Flinders Ras sites again being the exception (~10–30 m/Myr) and suggesting
the influence of recent tectonism. Several CN depth-profiles measured on hillslopes and alluvial fans
indicate sediment residence times >0.5 Myr, and high-resolution sampling along three hillslopes with
differing morphology (linear, convex, and concave) reveals major variations in sediment production
and transport rates that hint at the long-term evolution. In the rivers, fluvial sediments show a weak
tendency to increase cumulative burial history downstream (1–2 Myr), consistent with the expanding
accommodation space for storage and burial. Dune sediments sampled in the Simpson and Tirari
dunefields (n~16) contain cumulative burial histories (up to 1.5 Myr) similar to that of the intersecting
rivers. This points to an intimate mix of fluvial and aeolian processes in areas approaching base level.
Curiously, these sediments occur in the lowest part of the continent and contain the longest histories
of cumulative burial, yet do not form part of the thickest sedimentary fills in the Eyre Basin.|
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