The Ash That Recorded a Continent's First Breath: South Australia's Ediacaran Tumblagooda Sandstone

Somewhere on the western edge of South Australia, a slab of sandstone bears the oldest known footprints on the continent—not of feet, but of bellies. The Tumblagooda Sandstone, exposed along the Murchison River gorge near Kalbarri, preserves the crawling traces of animals that moved across tidal flats 550 million years ago, when Australia was still part of Gondwana and life had only just begun to walk.

The Sandstone That Held a Secret

The Tumblagooda Sandstone is a thick sequence of red and white quartz arenite, deposited in a shallow marine environment during the late Ediacaran Period. It outcrops across the southern Carnarvon Basin, but its most dramatic exposure lies in the gorges carved by the Murchison River, where 80-metre cliffs reveal layer after layer of ripple-marked sand.

The rock itself is unremarkable—clean, well-sorted sand that once formed tidal flats and river deltas. What makes it extraordinary is what the sand preserved. On the undersides of many bedding planes are impressions that look like the trails of slugs: sinuous ridges, paired grooves, and sets of parallel scratches. These are trace fossils, the preserved evidence of animal movement, and they are among the oldest on Earth.

The creatures that made them were bilaterians—animals with a front and back, left and right, that could move through sediment in a directed way. They left behind burrows and grazing trails that geologists call Rusophycus and Cruziana, names that describe the distinctive bilobed shapes. These traces predate most body fossils, which is why they matter: they record behaviour, not just anatomy.

A Coastline Before Bones

When the Tumblagooda Sandstone was deposited, the Ediacaran world was coming to an end. The soft-bodied organisms of the Ediacara biota—frond-like Rangea, disc-shaped Dickinsonia—still lived in deeper waters offshore. But on the tidal flats of this ancient shoreline, a different kind of life was stirring.

The trace-makers were arthropod-like animals, perhaps early relatives of trilobites, though they lived before trilobites had evolved hard shells. They crawled through wet sand, searching for organic matter, leaving behind trackways that recorded their passage in three dimensions. When the next tide covered the flats with fresh sand, the burrows were infilled and cast, preserving the negative space of the animal's body.

A single trail in the Tumblagooda Sandstone can record the shape of a creature that no longer exists, moving across a shoreline that no longer exists, in a world that no longer exists.

These trace fossils are not unique to Australia—similar Ediacaran traces occur in Namibia, Brazil, and the White Sea region of Russia. But the Tumblagooda Sandstone preserves them on a scale and clarity that is rare. Some bedding planes at Kalbarri are covered with hundreds of trails, cross-cutting each other like the scribbles of an ancient hand.

What the Traces Tell Us

The Tumblagooda trace fossils reveal something specific about the pace of early animal evolution. The Ediacaran Period (635–541 million years ago) saw the first appearance of complex multicellular life. For most of that time, animals were sessile or moved slowly through the water column. The Tumblagooda traces, dated to around 550 million years ago, show that by the late Ediacaran, animals were actively burrowing into sediment—a behaviour that had profound consequences.

Burrowing aerates the seafloor, mixes nutrients, and changes the chemistry of sediments. Before burrowing evolved, microbial mats covered most shallow marine sediments, binding them into firm, leathery surfaces. The first burrowers broke those mats apart, opening new niches and accelerating the nutrient cycle. Some palaeontologists argue that this "agitation of the seafloor" was a necessary precondition for the Cambrian explosion, the rapid diversification of animal life that began just a few million years later.

The Tumblagooda Sandstone preserves this transition. Below the trace-bearing layers, the rock shows evidence of microbial mats—wrinkle structures and desiccation cracks that formed on undisturbed surfaces. Above them, the mats disappear, replaced by bioturbated sediment that records the activity of burrowing animals. The shift happens within a single vertical section, a few metres of rock that capture a revolution in how life interacted with the planet.

A Quiet Archive

Today, the Murchison River gorge is a tourist destination, visited for its dramatic red cliffs and the river that winds through them. Most visitors see the landscape, not the history written in it. But the sandstone beneath their feet holds the record of the first animals to move across a continent—not walking, exactly, but crawling, inch by inch, through wet sand on a shoreline that has long since vanished.

The Tumblagooda Sandstone is not a flashy rock. It contains no gold, no gemstones, no dramatic fossils of giant creatures. It is simply sand, compacted and cemented over half a billion years, and it happens to preserve the moment when life on Earth began to move with purpose. That is enough.