The Stuart Range is a low upland in central

South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...

, extending about with a north-west to south-east alignment and passing within to the south-east of

Coober Pedy Coober Pedy () is a town in northern South Australia, north of Adelaide on the Stuart Highway. The town is sometimes referred to as the "opal capital of the world" because of the quantity of precious opals that are mined there. A blower truck ...

Name

The range is named after

John McDouall Stuart John McDouall Stuart (7 September 18155 June 1866), often referred to as simply "McDouall Stuart", was a Scottish explorer and one of the most accomplished of all Australia's inland explorers. Stuart led the first successful expedition to tra ...

, the first European explorer to pass through the area, in 1858.

Formation

During the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

and

Tertiary Tertiary (from Latin, meaning 'third' or 'of the third degree/order..') may refer to: * Tertiary period, an obsolete geologic period spanning from 66 to 2.6 million years ago * Tertiary (chemistry), a term describing bonding patterns in organic ch ...

, central Australia experienced crustal compression resulting in very broad, low-amplitude folding, and the Stuart Range formed on a basement upwarp. Underlying the Stuart Range, the folded sediments include the Early Cretaceous (Aptian-Albian)

Bulldog Shale The Bulldog Shale is a formation of Early Cretaceous age (Aptian to Albian stages) that forms part of the Marree Subgroup of the Rolling Downs Group, located in the Eromanga Basin of South Australia, Queensland and New South Wales. Description ...

, consisting of grey marine mudstones. Where the Bulldog Shale has been exposed at the surface for long periods it has been subjected to deep

chemical weathering Weathering is the deterioration of rocks, soils and minerals (as well as wood and artificial materials) through contact with water, atmospheric gases, sunlight, and biological organisms. It occurs ''in situ'' (on-site, with little or no movem ...

, resulting in bleaching and the "multi-hued, picturesque colouration" found in the Arckaringa-Stuart Range landscape. The prolonged chemical weathering also dissolved silica which, transported through the

regolith Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestria ...

by the movement of groundwater, precipitated as the ambient conditions changed, forming ''

silcrete Silcrete is an indurated (resists crumbling or powdering) soil duricrust formed when surface soil, sand, and gravel are cemented by dissolved silica. The formation of silcrete is similar to that of calcrete, formed by calcium carbonate, and ferri ...

'' (a type of ''

duricrust Duricrust is a hard layer on or near the surface of soil. Duricrusts can range in thickness from a few millimeters or centimeters to several meters. It is a general term (not to be confused with duripan) for a zone of chemical precipitation and ...

)'', with the silica forming a secondary cement binding the sediment grains into sheets of hard, indurated rock, generally parallel to the land surface. This occurred at deeper levels, at the intersection with the groundwater table (forming ''groundwater silcrete''), or close to the surface, within the soil profile (forming ''pedogenic silcrete''). Groundwater silcretes typically formed in more localised, topographically lower settings such as valley bottoms and slopes, whereas pedogenic silcrete tended to form extensive sheets over very large areas. Over long periods of time, as the landscape was lowered further by weathering and erosion, the silcrete became exposed at the surface as a lag gravel, an armoured carapace of ''gibbers'' (also known as a ''

desert pavement A desert pavement, also called reg (in western Sahara), serir (in eastern Sahara), gibber (in Australia), or saï (in central Asia) is a desert surface covered with closely packed, interlocking angular or rounded rock fragments of pebble and ...

''), protecting the weaker regolith below from mechanical erosion. The resulting landscapes are relatively flat, undulating plains with low relief. Throughout the Tertiary the Stuart Range has been an important palaeodrainage divide, between the Eucla and

Lake Eyre basin The Lake Eyre basin ( ) is a drainage basin that covers just under one-sixth of all Australia. It is the largest endorheic basin in Australia and amongst the largest in the world, covering about , including much of inland Queensland, large port ...

s.Callan, R.A., Sheard, M.J., Benbow, M.C. & Belperio, A.P.: Alluvial fans and piedmont slope deposits. In: Drexel & Preiss (1995) pp. 242-3. In places where fluvial erosion has been more active, gullies have dissected the palaeosurface of the upland, forming a characteristic tableland topography where a continuing process of

scarp retreat Scarp retreat is a geological process through which the location of an escarpment changes over time. Typically the cliff is undermined, rocks fall and form a Scree, talus slope, the talus is chemically or mechanically Weathering, weathered and th ...

leaves behind mesas and buttes, which persist until their residual silcrete capping is finally lost.

Notes

References

* Drexel, J.F. & Preiss, W.V. (Eds., 1995): The geology of South Australia. Vol.2, The Phanerozoic. South Australia Geological Survey, ''Bulletin'' 54. {{ISBN, 978-0-7308-0621-9 Mountain ranges of South Australia Far North (South Australia)