Imma Perfetto
Cosmos science journalist
Small iron-rich nodules decorating the world-famous Pinnacles in Western Australia have finally allowed researchers to date the formation of these striking landforms to about 100,000 years ago.
The Pinnacles are made up of thousands of limestone formations up to 5m tall and 2m wide, spaced 1.5 to 5m apart in Nambung National Park on the coast of WA about 200km north of the state capital, Perth.
They are a type of karst landscape which make up 15% of the ice-free surface of the Earth. Water forms these landscapes by dissolving susceptible rocks, such as limestone, dolomite, and gypsum, leaving behind empty spaces within the rock.
As these processes are most effective during humid climate phases, karst formations offer crucial insights into ancient climates and environments. However, they have been extremely challenging to accurately date, precisely because they are defined by a lack of rock.
In their new study published in Science Advances, the researchers dated iron-rich nodules, or ferricretes. These became cemented to the sides and bases of the pinnacles during the intense period of karstification which formed them.
Study co-author Martin Danišík, an associate professor at Western Australia’s Curtin University, says the nodules acted as “geological clocks,” trapping helium from the consistent radioactive decay of tiny quantities of naturally occurring uranium and thorium.
“Measuring this helium provides a precise record of when the nodules formed,” Danišík says. “The innovative dating techniques developed in this study reveal the nodules date back about 100,000 years, highlighting an exceptionally wet climate period.”
This period was the wettest experienced by the area in the past half-million years.
Co-author Dr Matej Lipar of the Research Centre of the Slovenian Academy of Sciences and Arts (ZRC SAZU) says this is distinct from other regions in Australia and far removed from Western Australia’s current Mediterranean climate.
“An abundance of water during this time caused the limestone to dissolve, forming the distinctive pillars of the Pinnacles and creating the ideal environment for the iron nodules to develop,” Lipar says.
Study co-author Associate Professor Milo Barham, also from Curtin University, says that being able to reconstruct past climate changes is important given the context it provides to understanding human evolution and ecosystems more broadly amid dramatic climate fluctuations over the past 3 million years.
“This new knowledge will enhance our understanding of global environments and ecosystems, helping us prepare for, and mitigate the impacts of, a warming planet,” says Barham.
