New England Tableland - landform
The New England Tableland Bioregion is a stepped plateau of hills and plains with elevations between 600 and 1500m on Permian sedimentary rocks, intrusive granites and extensive Tertiary basalts. Rainfall, temperature and soils change with topography and bedrock, and the vegetation is very diverse with a high degree of endemism.
Geology and geomorphology
The New England fold belt in the northeast of the state is composed of sedimentary rocks of Carboniferous and Permian age that were extensively faulted during a period of rapid continental plate movement associated with granite intrusions in the late Carboniferous. Much of the bedrock is now overlain by Tertiary basalt flows rarely exceeding 100m in thickness that lie on river gravels and sands or on lake sediments. As the basalt erodes the sands are exposed and have been mined for the sapphires, diamonds, gold and tin ore that they contain.
The geology has a strong influence on topography. The eastern edge of the bioregion is at the Great Escarpment where coastal streams have cut deep gorges below the plateau. The granite country is steep with abundant boulder outcrops and rounded tors. The basalt country is more planar, except around former eruption centres that form high peaks and the individual basalt flows are seen as distinct levels across the plains.
The basalts disrupted former drainage patterns and today the pre-basalt topography has been inverted with former valley floors, becoming ridge crests and hills. Large swamps and lagoons such as Llangothlin were partly created by these topographic changes.
During the Quaternary, colder climates had a major impact on vegetation patterns and allowed the formation of wind-blown lunettes on the eastern margins of the lagoons. Sediment in the lagoon floor preserves a pollen record of these changes.
Important features include the following:
- the Great Escarpment with deep rugged gorges such as Apsley Gorge, and steep bouldery slopes on granite on the Moonbi Range;
- granite tor landscapes in many areas throughout the bioregion;
- scree slopes from high rocky peaks such as Ben Lomond may reflect cold climates of the past;
- disrupted drainage patterns and evidence of the development of a new system after the basalt eruptions;
- shallow swamps and lagoons such as Llangothlin and Mother of Ducks Lagoon contain valuable Quaternary pollen records in their sediments;
- pseudo-karst landforms occur in granite boulder streams; and
- heritage features associated with extensive mining of gold, tin and gemstones using techniques that were not common elsewhere in the state.
Siliceous sands derived from granites are found among rock outcrops. Red earths and mellow texture contrast soils of relatively low fertility and poor structure are widespread across the bioregion and are prone to erosion. Soils with increased organic matter occur in swampy sedgelands in valleys. These soils support a variety of open forests and woodlands.
In basalt areas, shallow stony loams are found on steep areas and deep, red brown and brown to black, fertile, well-structured loams are found on flatter slopes. Soils are sometimes waterlogged in valley floors. Siliceous sands and red earths occur on associated Tertiary sands and gravels.
Harsh texture contrast soils in the bioregion derived from Permian sedimentary rocks are generally yellow, thinner and stonier on steep slopes. Some areas of slightly saline soils also occur.
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Page last updated: 27 February 2011