Brown Under and Green on Top

A few months ago I took this photograph at a site I was working on (located mid-way between The Channon and Dunoon). It was a cold spring day with strong cold winds and rain threatening. I love the cold weather, it seems to make you feel more alive! Anyway, I thought it would be a good photo to share since it shows several attributes of our landscape and how  it was formed.

The south side of the valley between The Channon and Dunoon

Firstly the background geology. Where the photo is taken from is on a hill made from rock of the Walloon Coal Measures within a larger steep sided valley. The sides of the Valley are two rock formations more resistant to erosion which is the Miocene aged Lismore Basalt (not visible in the picture) and the Kangaroo Creek Sandstone (Cliffs of which can be in the picture). Here the Lismore Basalt overlies the Late Jurassic aged Kangaroo Creek Sandstone which in turn overlies the Jurassic Walloon Coal Measures. I’ve done some earlier posts which describe the nature of the Kangaroo Creek Sandstone and Walloon Coal Measures, just click on the respective link for more.

Rocky Creek runs through the valley today and it is the action of that creek that formed the valley. The creek must have cut through the lavas of the Lismore Basalt and eventually cut through the Kangaroo Creek Sandstone. Once it was through these hard layers it had an easier task of cutting into the softer and finer grained sediments of the Walloon Coal Measures. It is also possible there is some underlying structural control such as folding or doming but I’m not confident of the extent of this.

The top of the ridge in the photo shows a wet sclerophyll vegetation type, an open forest which contains many Eucalypt species reflecting the Kangaroo Creek Sandstones poor nutrient soils and rapid drainage. Also the ridge is quite exposed to direct sunlight and desiccating winds. Below the cliffs the Walloon Coal Measures start and here is found dry rainforest type vegetation reflecting the better, more nutrient rich and finer grained soils that are developed on the Walloon Coal Measures. The nearby Basalts also have the same vegetation type and in places approach wet rainforest especially in gullys and protected places.

In addition the picture shows the indirect and direct effect of Australians on the environment. The indirect effect is weeds. Many of the bright green trees in the middle of the picture are Camphor Laurel (Cinnamomam camphora) loving the dry rainforest environment. Right in the foreground is Wild Tobacco Bush (Solanum mauritianum) overtaking some of the grazing country. But you will also see a line of dead trees which is part of a successful effort to reclaim the weedy forest into quality native vegetation. The dead trees are poisoned Camphor Laurel with many hectares of forest in this area regenerated by staff working for the local water authority in an ongoing rehabilitation project.

Note that the stratigraphy of the Kangaroo Creek Sandstone has been recently revised since this blog post. See the this post for details.