![]() |
||||||||||||||
Australia: The Land Where Time Began |
||||||||||||||
Strzelecki &
Tirari Deserts in Australia – Characterisation of Aeolian Sediments Aeolian sediments are a major source of potential
palaeoenvironmental information in arid environments that are dominated
by desert dunes. However, it is unclear to what extent the sedimentology
of dunes can be used in the reconstruction of palaeoenvironments. In
this paper Fitzsimmons, Magee & Amos present the results of their
assessment of the value of dune sediments as indicators of
palaeoenvironments by investigating the sedimentological characteristics
of linear dunes in the Strzelecki and Tirari Deserts of central
Australia. To characterise the sediment that occurs within the
dunefields of the region they used thin section microscopy, analysis of
particle size and X-ray diffractometry (XRD) mineralogy, and examined
the stratigraphic record in the context of the preservation of dunes and
the reworking of sediment. They found that to reconstruct environmental
change from the past in the dunefields of the desert purely on the basis
of sedimentological evidence is rarely possible. Limited
palaeoenvironmental information is, however, preserved within the
sediments in dunes with which it is possibly to combine additional arid
zone proxies and geochronological techniques to enable reconstruction of
conditions in the past that is most reliable. The most informative and unambiguous
palaeoenvironmental indicators within dune sediments are provided by
palaeosols which act as markers of relative environmental stability.
Pedogenic carbonates and gypsum, and illuviated clays in the form of
coating on grains, characterise palaeosols. For the reconstruction of
palaeoenvironments a critical consideration is the potential for
incomplete stratigraphic preservation within dunes, the preservation of
palaeosols, however, indicates that in this region the dunes have not
been reworked completely. Important evidence for pedogenesis is provided
by the coatings on grains when they are intact, and for aeolian
reworking when they are partially abraded. Across the region studied
abraded cutans are ubiquitous. In the Strzelecki and Tirari Deserts
mineralogy of linear dunes is dominated by quartz, with minor feldspar
and clay minerals, the latter of which is in the form of on grain
coatings and aggregates. It is indicated by the occurrence at several
sites of intact sand-sized aggregates that are composed of clay and silt
particles that incipient rather than peak aridity, and may, within this
geomorphic context, indicate reduced discharges of streams. A regional
bias is shown by grain size, though it is most likely that silt-sized
material has been deposited as long-travelled dust. The regional grain
size characteristics, together with the local occurrence of rock
fragments and high feldspar content, suggest that the sediments are
derived mostly from local sources. Fitzsimmons, K. E., J. W. Magee and K. J. Amos
(2009). "Characterisation
of aeolian sediments from the Strzelecki and Tirari Deserts, Australia:
Implications for reconstructing palaeoenvironmental conditions."
Sedimentary Geology 218(1–4): 61-73.
|
|
|||||||||||||
|
||||||||||||||
Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |