Browsing by Author "Chappell, JMA"

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    26Al/10Be dating of an aeolian dust mantle soil in western New South Wales, Australia
    (Elsevier B.V., 2014-08-15) Fisher, A; Fink, D; Chappell, JMA; Melville, MD
    Aeolian dust mantle soils are an important element of many landscapes in south-eastern Australia, though the age of these aeolian deposits has not been radiometrically determined. At Fowlers Gap in western New South Wales, surface cobbles of silcrete and quartz overlie a stone-free, aeolian dust mantle soil, which has a thickness of about 1.6m. The clay-rich aeolian dust deposit in turn lies upon a buried silcrete and quartz stone layer. Modelling in-situ cosmogenic 26Al and 10Be concentrations measured in both the surface quartz stones and in the buried quartz layer of rocks, reveals that each has experienced a complex exposure-burial history. Due to the absence of quartz stones or sand at intermediate depths, our cosmogenic 26Al and 10Be modelling was not able to determine a definitive mechanism of stone pavement formation and stone burial. Various scenarios of stone formation, transport, burial and exhumation were tested that constrain the age of the deposit to range from 0.9±0.2Ma to 1.8±0.2Ma, based largely on different assumptions taken for the time-dependency of the net sedimentation rate. This corresponds with the initiation of the Simpson Desert dune fields and the deflation of lakes in central Australia, which probably responded to the shift to longer-wavelength, larger-amplitude Quaternary glacial cycles at around 1Ma. Sensitivity analyses were carried out to identify those parameters which better constrained model outputs. Within model errors, which largely are the result of analytical errors in measured 26Al and 10Be concentrations, all three competing theories of colluvial wash, upward displacement of stones, and cumulic pedogenesis are possible mechanisms for the formation of the surface stone pavement. © 2020 Elsevier B.V
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    26Al/10Be dating of an aeolian dust mantle soil in western New South Wales, Australia
    (Australian Geosciences Council, 2012-08-05) Fisher, A; Fink, D; Chappell, JMA; Melville, MD
    Aeolian dust mantle soils are an important element of many landscapes in southeastern Australia, though the age of the aeolian deposits has rarely been determined. Measuring 26Al and 10Be in rocks and cobbles buried by an aeolian dust mantle soil at Fowlers Gap in western New South Wales, and modelling their exposure history has revealed the age of the deposit to be 1.1 ± 0.2 Ma, placing increasing aridity at least back to MIS 22, many stages before the MIS 10 increase in aeolian dust observed within Tasman Sea cores. The aeolian age of 1Ma coincides with initiation of the Simpson Desert dunefields and deflation of lakes in central Australia, which likely responded to the shift to longer-wavelength larger-amplitude Quaternary glacial cycles at the mid-Pleistocene Transition. Modelling the 26Al and 10Be exposure history of samples from the surface stone pavement has shown that they have experienced periods of prolonged burial. The simplest explanation for this burial is that the surface cobbles were buried, perhaps episodically, during periods of aeolian deposition, before travelling upwards through the soil to be re-exposed at the new ground surface. Vertical stone movement may have occurred through soil heaving as clay minerals swell and shrink upon wetting and drying, evidence of which is visible in the gilgai-microtopography and horizontal stone sorting (patterned ground) at the site.