Episode 5: What's Under your Paddocks? Soil Horizons and Parent Material with Tim Overheu

Thanks, Leonie.

Right.

First question.

I recently had a chat with Richard Bell and he was talking to me about parent material and saying that while we are discussing parent material and the soil that comes from that parent material, the parent material in WA is old, but the soil, in his opinion, is young and changing because of that biological part.

Western Australia is actually regarded as a very stable state geologically.

You know, we have the Yilgarn Craton.

And the thing that's different about Western Australia is that we had no kind of volcanic period in between, and then we had this marine regression, then sand blew in over the top, we get a little bit of siltstone, and that's about it for Western Australia.

And so when it comes to, you know, parent material, a lot of our landscape is very old, you know, parched sediment, you know, rock outcrops and various other bits and pieces.

We've had some faulting and we've had some uplift and we've had some shear zones and other things like that sort of, influences the hydrology in the landscape but its soil forms from rock and as the rock breaks down they call it soil weathering and in some instances it can be very slow.

The drivers, Richard's correct, the drivers are biology.

I'd also like to think geochemistry and moisture and water in the landscape as well.

There are different theories out there about, you know, rocks rolling down hill slopes called colluvium.

But then we do have some areas in Western Australia where our soil formation is relatively young because it's a rejuvenated landscape.

So it's all about geomorphology and physiography and those sorts of things and erosive and stripping and deposition.

Let's take an area like we've got the zone of rejuvenated drainage is what it's known in the Avon Basin.

And it's actually had a lot of material that's been deposited because of the Swan River, for example.

And when you look at those soils and a lot of that landscape, they've got most often quite beautiful red-brown sorts of colours.

And that's a fairly recent type sort of a development.

There is a hypothesis out there about our protease seed plants and root exudates actually manipulating the soil or manipulating the parent material to suit the roots of the plants.

So the plants are just another plant trying to survive.

And with that, it's actually changing the soil in situ, and so that's more of a biological process.

In some instances, we open up a soil profile And you can see, you know, blotches of reds and browns and yellows in there.

Some people think that's, you know, recent modelling.

That's a modelling thing that they call.

In a lot of occasions, it could be relict.