Barkly Karst Region
(Queensland & Northern Territory)
Background
The Barkly Karst Region is an area of tropical arid to semi-arid karst that extends from northwest Queensland into the Northern Territory, Australia. The climate is tropical monsoon, with pronounced wet and dry seasons.
The karst is hosted by the carbonate rocks of the Cambro-Ordivician Georgina Basin. The Camooweal Dolomite occupies most of the centre of the basin while a number of limestone units occur around the margins. Karst development has been retarded by the arid climate, and also by the extensive cover of heavy black clay soils. These clays pond the rainfall (which occurs as intense storms separated by hot sunny periods) in surface hollows (Gilgae) so that infiltration into the carbonate rocks only occurs locally.
At the northeast edge of the region the rocks have been dissected and we get much stronger relief, with incised gorges and extensive karren-fields.
Click here for details of the Lawn Hill Gorge area
Further reading
GRIMES, K.G., 1988: The Barkly Karst Region, North-west Queensland. 17th Australian Speleological Federation Conference, Proceedings. pp 16-24.
See also
For photos of Micro-karren and etchings in the Barkly Karst click on the following links.
Microkarren in the region.
Etchings on the Camooweal dolomite.
Selected photographs and diagrams
To view full size images, click on the displayed image.
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Map showing the main part of the Barkly Karst Region.
LH = Lawn Hill, C = Camooweal, MI = Mount Isa, B = Boulia.
The dashed purple line is the boundary between arid (south) and semi-arid (north) climates.
The blue-purple area is labeled "Limestone" - but is actually dolomite for most of the basin.
The yellow area of "cover" is mostly a thick impermeable clay soil.
Red circles are major karst features: caves or large collapse dolines.
The main cluster of known caves is in the Camooweal area. Additional caves have recently been found southeast of Mount Isa.
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Typical vegetation cover on the dolomite outcrops is open woodland Img00180.jpg
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Stereopair of a dolomite outcrop (view cross-eyed) Fine etchings such as these are common. 15 cm Ball-point pen for scale. IMG00176.jpg
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The Georgina River flows only during the wet season. Here, north of Camooweal, we see the dry channel and three collapse dolines. The one in the channel has been clogged with alluvial clay and now holds water. The two other dolines are connected by a cave and the right hand one takes flood waters from the river via a small overflow channel (see below). Local information is that it takes several days for the cave to fill up after the river starts flooding into it. IMG00196.jpg
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Ground view of Barwidgee Doline, which takes flood waters from the Georgina River via the channel in the background. IMG00175.jpg
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Dolines in the Camooweal Region
In the Camooweal region we can recognise an evolutionary sequence in the dolines.
From youngest to oldest we see:
Small vertical entrances into caves, Large collapse dolines above cave chambers, Degraded dolines in which soil mounds are starting to clog the floor, Completly clogged dolines that may hold permanent water and finally broad shallow clay pans that are barely recognisable as karst features.
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The entrance to Niggle Cave is a tight squeeze into a shaft hidden in the rubble in the foreground. IMG00194.jpg
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A large collapse doline above a major cave chamber
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This collapse doline has a central mound of soil that has been washed in from the surrounding country. The margins however are still clean and water percolates rapidly through the rubble there into the underlying cave. IMG00192.jpg
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Eventually the soil mound completely clogs the doline floor and a permanent lake can form IMG00193.jpg
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Finally the doline becomes completely degraded and only a broad shallow pan remains, with a circle of trees. IMG00195.jpg
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The Caves
The Caves at Camooweal a widely spaced, but include some large multi-level systems.
Cave Levels
Are the cave levels formed at old water tables, or do they reflect preferential solution of soluble beds?
The Camooweal Dolomite is flat-lying so we cannot be sure. However some beds certainly seem to be very soluble, as shown below.
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Stereopair of soluble bed in Kalkadoon Cave (view cross-eyed) This bed has been intensly dissolved to leave a fine spongework. View is about 15 cm wide IMG00182.jpg
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Cave life
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Stutgarids (related to centipedes) such as these are normally fast running. This one must have been sick as it stood still long enough for me to take both photos of the stereopair! Its body is about 20 mm long. StutgarR.jpg
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