‘Drowning continent’: research confirms complex history of Perth’s coastline

New research from Curtin University exploring the complex evolution of Western Australia’s two iconic landmarks traces their evolution over thousands of years and offers a glimpse into their future.

Researchers from the School of Earth and Planetary Sciences’ Mineral Systems Timescales Group traced changes along Perth’s coastline, waterways and even the ocean floor to track changes that have occurred as sea levels rise tens of meters over millennia. Sediment samples were collected from multiple locations.

Lead researcher Dr. Andreas Sammetzer said the survey’s dive team discovered a specific type of mineral grain offshore, revealing the complex geological history of Rottnest Island (Wadjemup in Noongar) and the Swan River (Durbar Elligan). was confirmed.

A distinct group of ancient grains off Rottnest Island has been dated to be up to 3.6 billion years old.

These same grains can be traced back to the current Swan River estuary and the tributaries of the River Avon that transported and deposited them thousands of years ago.

The article “When rivers meet oceans: Transport and origins in long-lived estuaries” was published in Basin Research.

“Perth is on the edge of a submerged continent,” Dr Zametzer said.

“Rottnest Island was the tip of a peninsula until about 6,500 years ago, similar to what we see in the Shark Bay area, and it remains part of the sunken continental margin, so there is a large area between Perth and Rottnest. The depth of the ocean rarely exceeds 20 m in most places.

“We also now know for certain that the mouth of the Swan River was once north of where Rottnest is today.”

Dr Zametzer said researchers were surprised to find mineral particles transported by ancient rivers so far out to sea.

“We expected the grain to be eroded and washed away because it was in a very turbulent, high-energy environment of waves and tides,” he says.

“But the river’s distinctive mineral signatures are still there, despite thousands of years of sea-level fluctuations and shelf reworking.

“We have preserved traces of this river system offshore, confirming the history of the coast.”

Dr Zametzer said it was important to know how coastlines had adapted and changed in the past to understand what rising sea levels would mean in the future.

“As sea levels continue to rise rapidly, it’s quite shocking to think about how fast geological processes are actually happening.”