Australia: The Land Where Time Began
Sturt's Stony Desert
Sturt's Stony Desert is situated in northeastern South Australia. This desert and adjacent areas are covered by a layer of siliceous stones resulting from the breakdown of the silcrete capping of the area.
is a “gibber desert”, one characterised by a covering of closely-spaced,
glazed stones. Throughout the area of gibber deserts there a scattered
flat-topped sandstone hills. These
hills are capped by a layer of hard, chalcedonised sandstone, which is much more
resistant to weathering than the underlying sandstone. As cracks are formed in
it erosion finally breaks through to the underlying sandstone which is worn away and slumps to the plain below, taking its piece of cap with it. The
pieces of cap material are slowly rounded and glazed by windblown sand. The sand
in between the “gibbers” is removed by wind and the occasional flood, which
causes the gibbers, which are not removed so easily, to accumulate and become more
The breakdown product of the silcrete are stones with a conchodial fracture (with concave faces), very sharp edges being formed at the intersection of the faces on the individual stones. The local Aboriginal people used these stones as pre-formed blades for tool making, They caused a lot of problems for the hooves of the horses on Charles Sturt's expedition. The silcrete capped plateaux the stones derive from are either flat-topped or concave upwards. Coarse angular stone debris covers the slopes of these plateaux, the layer of purplish stones coming to cover the surface of the plain as the slopes of the plateaux are eroded away from beneath them.
The alluvium in the valley floors where the gibber plains have been dissected by erosion, having derived from the clay that underlies the silcrete capping, is a creamy colour. The stony rises between have irregular, concentric patterns that appear from the air to be formed of rings of fine debris that has washed down the slopes (Twidale & Campbell, 2005).
There are not many fixed dunes in this desert, with some irregular mobile forms. According to Sturt's account from 1840, there were on every side 'stupendous and almost unsurmountable sand ridges of a fiery red'. Most of the sand from this area has now been moved from the area, having been accumulating in depressions between the plateaux that are strewn with gibbers or carried further downwind to lowlands where it has been incorporated into vast dunefileds. Burke & Wills wrote of their 1861-62 expedition, between the dunes and near residual rises and uplands, especially those with a silcrete capping, the ground is covered 'with sharp dark brown stones that were terrible to walk on'.
Small patches of gibbers also occur in the other deserts, but not to the extent they occur in Stuart's Stony desert.
|Author: M.H.Monroe Email: firstname.lastname@example.org Sources & Further reading|