Who could have imagined that iron-rich rocks, commonly associated with rust, could preserve fossils with such remarkable precision? In Australia, the McGraths Flat site is transforming our understanding of the preservation of traces of ancient life.
Located in the Central Tablelands of New South Wales in Australia, the McGraths Flat site dates back to the Miocene, a period marked by the rise of many modern life forms. Although arid today, the region was once covered by a dense tropical rainforest. Researchers have uncovered an extraordinary fossil record there, preserved in rocks of a striking red color.
The rocks at McGraths Flat are characterized by their goethite composition, a mineral containing iron. This material allowed for the remarkable preservation of plants, insects, spiders, fish, and even feathers. The details are so precise that pigment cells in fish eyes or internal organs of insects become discernible.
Typically, the best-preserved fossils come from shale, sandstone, or volcanic ash, as at the Messel Pit in Germany or the Burgess Shale in Canada. These sites rapidly buried organisms under fine sediments. In contrast, iron-rich rocks were considered less favorable for the preservation of terrestrial life, which makes the McGraths Flat discovery particularly unexpected.
A recent study published in
Gondwana Research details the formation of this site. During the Miocene, iron leached from weathering basalt was transported by acidic groundwater to an ancient river meander. On site, it was deposited as ultrafine sediments, coating dead organisms and replicating their structures down to the cellular level, thanks to microscopic iron particles.
This discovery offers new avenues for paleontology. By targeting areas with fine-grained ferricretes, ancient warm and humid climates, and suitable geology, scientists can now search for other comparable sites around the globe. Red rocks could thus reveal other pages of Earth's life history, beyond traditional deposits.
McGraths Flat thus reveals that the conditions for fossil preservation are more diverse than previously estimated. Future advances in the knowledge of ancient terrestrial life may well emerge from these iron-rich rocks, long overlooked, providing a fresh perspective on our natural heritage.