Browsing by Author "Chappell, J"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Building a future on knowledge from the past: what paleo-science can reveal about climate change and its potential impacts in Australia
    (Commonwealth Scientific and Industrial Research Organisation, 2005-06) Harle, KJ; Etheridge, DM; Whetton, P; Jones, R; Hennessy, K; Goodwin, ID; Brooke, BP; van Ommen, TD; Barbetti, M; Barrows, TT; Chappell, J; De Deckker, P; Fink, D; Gagan, MK; Haberle, SG; Heijnis, H; Henderson-Sellers, A; Hesse, PP; Hope, GS; Kershaw, P; Nicholls, N
    In Australia, high quality instrumental climate records only extend back to the late 19th century and therefore only provide us with a brief snapshot of our climate, its mean state and its short-term variability. Palaeo-records extend our knowledge of climate back beyond the instrumental record, providing us with the means of testing and improving our understanding of the nature and impacts of climate change and variability in Australia. There is a vast body of palaeo-records available for the Australian region (including Antarctica), ranging from continuous records of sub-decadal up to millennial scale (such as those derived from tree rings, speleothems, corals, ice cores, and lake and marine sediments) through to discontinuous records representing key periods in time (such as coastal deposits, palaeo-channels, glacial deposits and dunes). These records provide a large array of evidence of past atmospheric, terrestrial and marine environments and their varying interactions through time. There are a number of key ways in which this evidence can, in turn, be used to constrain uncertainties about climate change and its potential impacts in Australia.
  • No Thumbnail Available
    Item
    Eroding Australia: slowly.
    (Elsevier, 2008-07) Heimsath, AM; Chappell, J; Hancock, GR; Fink, D; Fifield, LK
    We use in situ produced 10Be and 26Al to quantify erosion rates across a wide variety of field settings in Australia. Here we present the full suite of data from our diverse studies to provide an overview of how Austalia is eroding, as well as showing how robust this methodology is. Field sites range from several soil-mantled landscapes spanning the passive margin escarpment of southeastern Australia, to rocky, bedrock dominated landscapes in the Flinders Ranges and the Central Australia Outback. Also, in the far north, we examine an undisturbed catchment in the rugged topography of Arnhem Land: Tin Camp Creek. We sample detrital sands draining the landscape in a nested fashion at each of our field sites: from small to large catchments. We also sample across the slopes to quantify point-specific rates of soil production and bedrock erosion. Soil production rates and mechanisms across the escarpment have been presented in previous publications and will be used here to compare with a new, ‘humped’ soil prodction function from the Arnhem Land field site. In the rocky landscapes of the Flinders Ranges and MacDonnell Ranges, we sample the blocky slopes as well as catchment sands to constrain a block failure model for slope retreat. Point specific rates are also compared with detrital rates for Kings Canyon and the Todd River drainage to examine the potential for long-term landscape equilibrium. To conclude we show the first, unequivocal example of a regolith mantled landscape eroding in dynamic equilibrium from the western MacDonnell Range. Rates span an order of magnitude, from about 4 to 40 m/Ma across the escarpment in southeastern Australia. The ‘humped’ soil production function peaks at just over 20 m/Ma under about 30 cm of soil and decreases to less than 5 m/Ma under 70 cm of soil. Rates in the Outback are extremely slow, from less than 1 in places to the distance evidence for equilbrium in the Western MacDonnells, at about 7 m/Ma. These results raise many provocative questions and suggest new directions for quantifying how landscapes evolve. Copyright © 2008 Published by Elsevier Ltd.
  • Thumbnail Image
    Item
    Erosion and the sediment conveyor in central Australia
    (Geological Society of Australia, 2016-02-29) Jansen, JD; Chappell, J; Struck, M; Eccleshall, SV; Fujioka, T; Codilean, AT; Fülöp, RH; Fink, D; Cohen, TJ; Nanson, GC
    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.
  • No Thumbnail Available
    Item
    History of Australian aridity: chronology in the evolution of arid landscapes
    (Geological Society of London, 2010-01-01) Fujioka, T; Chappell, J
    Australian climate and vegetation, known from marine and lacustrine sediments and fossils, varied dramatically throughout the Cenozoic Era, with several warm reversals superimposed on overall drying and cooling. A suite of landforms, including stony deserts, dunefields and playa lakes, formed in response to the advancing aridity but their age generally remained uncertain until fairly recently, owing to a lack of suitable dating methods. Within the last 5 years, the chronology of Late Quaternary fluctuations of lakes, dunes and dust-mantles has been established by luminescence dating methods, and mid-Pleistocene onset of playa conditions in a few closed basins has been estimated using palaeomagnetic reversal chronology. Only recently has it been shown, by cosmogenic isotope dating, that major tracts of arid landforms including the Simpson Desert dunefield, and stony deserts of the Lake Eyre Basin, were formed in early Pleistocene and late Pliocene times, respectively. These landscapes represent a stepwise response to progressive climatic drying and, speculatively, were accompanied by biological adaptations. Recent molecular DNA studies indicate that Australia's arid-adapted species evolved from mesic-adapted ancestors during the Pliocene or earlier, but whether speciation rapidly accompanied the development of stony deserts and other arid geomorphological provinces awaits further studies of arid landscape chronology. © The Geological Society of London 2010
  • Thumbnail Image
    Item
    Tracking the 10Be–26AI source-area signal in sediment-routing systems of arid central Australia
    (European Geosciences Union, 2018-05-07) Struck, M; Jansen, JD; Fujioka, T; Codilean, AT; Fink, D; Fülöp, RH; Wilcken, KM; Price, DM; Kotevski, S; Fifield, LK; Chappell, J
    Sediment-routing systems continuously transfer information and mass from eroding source areas to depositional sinks. Understanding how these systems alter environmental signals is critical when it comes to inferring source-area properties from the sedimentary record. We measure cosmogenic 10Be and 26Al along three large sediment-routing systems (∼ 100 000 km2) in central Australia with the aim of tracking downstream variations in 10Be–26Al inventories and identifying the factors responsible for these variations. By comparing 56 new cosmogenic 10Be and 26Al measurements in stream sediments with matching data (n= 55) from source areas, we show that 10Be–26Al inventories in hillslope bedrock and soils set the benchmark for relative downstream modifications. Lithology is the primary determinant of erosion-rate variations in source areas and despite sediment mixing over hundreds of kilometres downstream, a distinct lithological signal is retained. Post-orogenic ranges yield catchment erosion rates of ∼ 6–11 m Myr−1 and silcrete-dominant areas erode as slow as ∼ 0.2 m Myr−1. 10Be–26Al inventories in stream sediments indicate that cumulative-burial terms increase downstream to mostly ∼ 400–800 kyr and up to ∼ 1.1 Myr. The magnitude of the burial signal correlates with increasing sediment cover downstream and reflects assimilation from storages with long exposure histories, such as alluvial fans, desert pavements, alluvial plains, and aeolian dunes. We propose that the tendency for large alluvial rivers to mask their 10Be–26Al source-area signal differs according to geomorphic setting. Signal preservation is favoured by (i) high sediment supply rates, (ii) high mean runoff, and (iii) a thick sedimentary basin pile. Conversely, signal masking prevails in landscapes of (i) low sediment supply and (ii) juxtaposition of sediment storages with notably different exposure histories. © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 Licence