…everything looks so old that it belongs to a different world…
Artist Hans Heysen, 1926, Flinders Ranges, South Australia
It is a two hour drive from Port Augusta to the Prairie Hotel at Parachilna in the Flinders Ranges. You head south for a few kilometres, across shimmering salt pans, and then turn east onto the Flinders Ranges Way. The road cuts across plains of wiry grass and grey-leaved shrubs, and winds through a gap in the hills near Saltia, passing over and under the narrow-gauge track of the Pitchi Ritch Railway on the way to Quorn. At Hawker, you leave the Flinders Ranges Way and travel the Outback Highway. From here, it is an hour to Parachilna.
Parachilna is a blink-and-you’ll-miss it town. It was formerly a railway siding — the original town had been established 10 kilometres to the east, at the entrance to Parachilna Gorge, but had been abandoned because of the inconvenience of being so far from the railway line and, more importantly, because the hotel was built at the siding. It was one thing to transport goods to and from the railway, but quite another thing to live that distance from the pub.
The Prairie Hotel opened in 1876. The current building, made of local sandstone, topped by a corrugated iron roof and fronted by a striped awning, was built in 1905. It is a comfortable, welcoming Outback pub with two unusual features — camel on the menu and 560 million-year-old fossils on display.
In 1946, geologist Reginald Sprigg visited the Ediacara Hills, north-west of Parachilna. The hills had been mined for copper in the 1860s and silver in the 1880s, but had been abandoned after a few decades. Sprigg’s job was to investigate the potential for reopening them.
The Ediacara Hills are made of quartzite laid down as fine sand in a shallow sea about 560 million years ago. It weathers in thin sheets that break into flagstones. During his lunch break, Sprigg examined the stones and noticed impressions in them — imprints of jellyfish-like creatures similar to those previously recorded from Newfoundland and the White Sea, but unknown in Australia. He found five new genera and at least five new species preserved as empty shapes in the rocks. In his description of the Ediacara fauna (1947), he wrote that they were ‘among the oldest direct records of animal life in the world’.
But Sprigg was cautious about the age of these fossils. At the time, it was thought that animals arose and diversified in the Cambrian period and older (Precambrian) rocks were devoid of complex life. The Ediacara Hill quartzite was regarded as ‘Eo-Cambrian’, an imprecise term for strata at the junction of the Cambrian and Precambrian periods. The presence of these fossils suggested that the end of the Precambrian and beginning of the Cambrian might have to be pushed back.
The significance of Ediacara was not recognised until 1956, when a fossil imprint was found in indisputably Precambrian rocks in the United Kingdom. (You can read the story of its discovery here.) Since then, these strange, shell-less creatures have been recorded from many sites across the world. The geological time in which they lived is now known as the Ediacaran Period.
In the Flinders Ranges, visitors can travel through 140 million years of Earth history. The rocks are tilted, leaning like books on a shelf. At Brachina Gorge, a dirt road runs for 20 km through the stone library where you can browse the volumes — Life Before Animals, Snowball Earth, The Ediacaran Period, Cambrian Explosion, and The Beauty of Now.
Volume 1: Life Before Animals
You enter the eastern end of Brachina Gorge in the gentle slopes of Enorama Shale (650–645 million years before present), but it’s not until you reach the next formation, Trezona limestone and shale (645–640 mybp), that the earliest fossils become obvious. Stromatolites lie in layered curves in the stone. These structures are formed from mats of single-celled organisms, mostly photosynthetic cyanobacteria, that trap sediment as they grow. Although fossil stromatolites are common, living stromatolites are much rarer. They can be seen in the hyper-saline waters of Hamelin Pool, Western Australia, and (less easily) in freshwater sinkhole lakes in the limestone around Mount Gambier, South Australia.
Volume 2: Snowball Earth
Then come the tillites, rocks composed of glacial deposits (till). The Marinoan glaciation began about 650 million years ago and persisted for 15 million years. At the height of Snowball Earth, about half the world’s oceans were frozen. As they inched their way to the sea, glaciers scraped up and bulldozed rocks and soil, which they dropped as they melted. The Elatina Formation (640–635 mybp) is made up of consolidated till.
After that, things get wild.
Volume 3: The Ediacaran Period
On the banks of Enorama Creek, a short walk from the road along the kangaroo-grazed cliff top, a small round plaque is cemented to the dolomite lying over the Elatina tillite. The dolomite belongs to the Nuccaleena Formation and was laid down in warm shallow water between 635 and 630 million years ago. The plaque is a ‘golden spike’, a reference point that marks the start of a significant geological stage. It says ‘Ediacaran’ and is the only Precambrian golden spike.
For the rest of the drive through Brachina Gorge, the road passes through rock formations of shale, limestone, sandstone, and quartzite, all of marine origin. The Bunyeroo Formation contains a thin layer of much older sharp-edged volcanic rock thrown up when a meteorite smacked into the Eyre Peninsula about 600 million years ago. The spectacular Rawnsley Quartzite (560–550 mybp), which gives Wilpena Pound its dramatic profile, contains the largest array of Ediacaran fossils. You can find them on the underside of weathered slabs — once you get your eye in. That can take a while.
Volume 4: Cambrian Explosion
About 3 km from the western end of the track, you cross into the Cambrian. The sandstone here is textured with marine worm burrows, Another 500 m or so further along, white limestone boulders beside the road are packed with archaeocyathids, a now-extinct group of marine invertebrates that were probably the first reef-building animals. At the end of the drive, the Wirrealpa Limestone shows the results of the Cambrian Explosion frozen for half a billion years. The rocks contain shelled animals — trilobites and brachiopods and tiny molluscs shaped like nightcaps.
Volume 5: The Beauty of Now
Brachina Gorge is both Then and Now. As you travel the road, you are surrounded by ragged walls of red and pink, and ancient river red gums — although not quite as ancient as the hills — that line ephemeral creeks marked out in pebbles and water-worn boulders. Sunlight paints the slopes ochre. Clouds paint them cool lilac. Yellow-footed rock-wallabies negotiate the rugged, fractured cliffs with ease. During the heat of the day, these beautiful animals lie up in caves, but in the late afternoon they come out to feed. In time, they are a long way from the jellyfish of the Ediacara; in space, they are as close as they can be.