Submarine Canyons in the Flinders Ranges Point to How Earth's Earliest Complex Life Was Preserved

Rising seas may explain why some of Earth's earliest complex organisms left traces at all. A team led by Adelaide University has mapped the geology of South Australia's Flinders Ranges and reconstructed a shallow ocean that once covered the terrain, and the rocks there now carry the evidence.

"You have to imagine that the Flinders Ranges was under the ocean," associate professor Diego Garcia-Bellido says. Today it's dry, arid country. Hundreds of millions of years ago, it sat beneath water, and the research team set out to work out what that seafloor looked like and how sediment and fossils ended up buried in it.

Canyons under the waves

The strongest clue turned up at Nilpena Ediacara National Park and the Chace Range. Unusual rock formations there pointed to submarine canyons. Garcia-Bellido and colleagues from the university and the South Australian Museum began finding them "all over the Flinders", some up to 280 metres deep and 6 kilometres wide. That's a serious trench system, not a shallow dip in the seabed.

The canyons weren't carved for show. "Canyons were being carved and creating this accommodation space for a lot more sediment," Garcia-Bellido says. In other words, the depressions made room for material to pile up, and that material is what preserved the record.

Flooding and the first complex life

Here's the thing: the team's findings link the canyons to a sea that kept rising. The research focuses on the Ediacaran period, roughly 550 million years ago, "at the time or just before the appearance of the first complex life on the planet".

The team's read is that seawater flooding helped shape the canyons and, in turn, preserved some of the first complex life on the planet. As the canyons filled and sea levels climbed, they left behind shallow shelves. Garcia-Bellido describes what happened next: "What we see is that, as the canyons get filled and the sea level rises, this creates in the shallow shelf an environment that is ideal for the shallow water microbial mat to grow."

"This is where this original Ediacara biota began to grow and actually produce the most diverse assemblage of this pre-animal world."

Why the setting matters

The Ediacaran biota are soft-bodied fossils, first discovered in the Flinders Ranges in 1946. They're hard to read without context. That's why the environment matters so much to the research. "The environment is a very important point of reference; you need to know where these organisms started living, and why they settled there," Garcia-Bellido says.

The same region is also part of an ongoing bid for UNESCO World Heritage recognition, and this kind of fieldwork gives that case a physical record of how the environment shifted. Mapping the canyons and the sediment they trapped doesn't just explain the fossils. It tells researchers where to look for more.

"The fact that this is so important is because we see how animals arrive on this planet, or start developing on this planet," Garcia-Bellido says. "With these studies, we're trying to find more about these very earliest complex forms."

That's the part that sticks with me. "It's glimpsing a world that is probably the most alien we can actually find because we've gone so far back in time that the animals that we see around us today didn't even exist."