First of all a catch-up left over from our geological excursion in April.

Avid readers will recall that we were last sighted visiting the pinnacles and stromatolites around Cervantes. We then hopped further up the coast to Kalbarri, about 600km north of Perth. Our visit coincided with a mass emergence of bush flies following unseasonal rain. I have never seen so many flies, literally millions and probably many billions. Extraordinary; harmless but very irritating. The only comfortable way to venture outside is in a full head net, with long sleeves and trousers:

Even the locals dress like this, even shopping in town or out jogging.

The Kalbarri area is composed of rocks of the Tumblagooda sandstone which is of Lower Ordovician age, laid down 400-500 million years ago. Dating it is difficult because like many Australian sedimentary rocks it has been little disturbed since deposition. There is no volcanic intrusion (easily dated) and datable body fossils are almost entirely absent, but after much debate the age seems reasonably secure now at about 440mya. These sandstones are interpreted as being deposited by high energy braided streams, probably disgorging onto tidal sandflats. This was evidently going on for quite a while because these rocks, over a very large area, are 1400m thick! 

Here is scenery at the gorge of the Kalbarri River, caused by a Miocene (23-5 mya) uplift of about 60m; note the headnet again:

In some places trace fossils (fossils where the maker is unknown) are abundan or, in the jargon, the rocks are intensely bioturbated. These are skolithos, typically marine and believed to be worm burrows:

The difficulty in dating these rocks matters rather a lot, because they contain what are believed to be the world’s oldest terrestrial animal tracks so far discovered.

And here they are:

These are the tracks of a very early arthropod, a euthycarcinoid. It had eleven pairs of legs and was well over a metre long. The really interesting thing, though, is that it was walking along a shoreline, out of the water. The tracks clearly show that they were made in wet sand in the open air and not under water. And the lack of body marks means that it was walking up on its legs with its considerable body held clear of the substrate. And this is so early in terrestrial life’s history that there were almost no land plants - just a few algae, liverworts and mosses. The higher plants had not yet evolved! I find this in particular quite extraordinary - these very large amphibious arthropods had the entire surface of the land almost to themselves, it seems.

Well worth coming to Australia to see, I reckon; though it was abundantly plain that no-one else visiting this tourist hotspot while we were there had the faintest idea what they were missing.