Channel Country - landform
The Channel Country Bioregion is a region of extensive stream systems draining to Lake Eyre. Multiple river channels, very wide floodplains and large waterholes crisscross this subdued landscape of gibber plain, low stony rises and dunefields.
Tertiary and Quaternary sediments form the extensive stony plains between low tablelands and mesas of Mesozoic sandstones. The climate is extremely arid and the vegetation sparse. Floods are infrequent but, when they occur, major events trigger huge breeding and growth responses in the biota.
Geology and geomorphology
The NSW part of the bioregion is atypical geologically in that it contains three small areas of older bedrock at the core of the Mt Arrowsmith - Tibooburra Ranges. These outcrops of late pre-Cambrian and Cambrian rocks reflect a ridge of high bedrock running from Mt Koonenberry to Tibooburra that separates two parts of the Great Australian Basin; the Lake Frome embayment in the east and the Bulloo embayment in the west.
The Tibooburra granodiorite has weathered to low hills covered with rounded boulders or tors, with low ridges of resistant quartz veins.
Marginal to the basement rocks, the Mesozoic and Tertiary sediments form a series of tablelands and mesas with shallow stony soils and prominent low cliff lines of silicified sandstones. Claystones underlie the lower slopes.
Drainage from the hills runs into the Simpson-Strzelecki Dunefields Bioregion on the west and into the Bulloo Overflow on the east. The Bulloo Overflow is a complex of terminal channels, floodplains and lake basins of the Bulloo River. It is dominated by Quaternary sediments of clays in the channels and lakes and sand reworked by wind into lunettes, sand sheets and some dunes.
This area of deposition was the source for sand that is now in the Bulloo Dunefield subregion (Simpson-Strzelecki Dunefields Bioregion) and the Ursino Sandplains subregion (Mulga Lands Bioregion).
Important features of this bioregion include the following:
- the rounded tors of granodiorite on the hills combined with the tableland scarps, extensive surface cover of rounded siliceous pebbles (gibber), and contour banding on the downs country, make these landscapes unusual in arid NSW;
- the Bulloo Overflow is an important ephemeral wetland in the extreme arid zone, and the lunettes on the lakes contain important evidence of climate change and human occupation; and
- several areas of basement rocks in the ranges have supported small goldfields in the late nineteenth century and retain heritage structures associated with mining.
Soil development is limited to shallow, stony, gritty loams on the bedrock hills. On the Cretaceous sediments, yellow-brown to brown loams with stony surfaces are common on the sandstones, and sticky grey-green clays with high carbonate and gypsum content, or shallow stony texture contrast soils are found on the claystones on the lower slopes.
Most slopes are contour banded with areas of stony soil alternating with deeper stone-free brown loams.
In floodout areas from the ranges, brown loamy clays occur with thin patches of red sand and low dunes marginal to the creeks. In the Bulloo Overflow, grey cracking clays, often saline, are the norm for the fluvial areas, with pale red sands and earthy sands in the sandplains to the east.
Soils and sediment on the lunettes are more complex and similar to those on lunettes in the Menindee Lakes.
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Page last updated: 27 February 2011