Researchers have discovered an extraordinary fossil site in the red rocks of McGraths Flat, located in the central tablelands of New South Wales, Australia. This site, dating to the Miocene epoch between 11 million and 16 million years ago, has revealed remarkable details about an ancient rainforest ecosystem.
Traditionally, well-preserved fossils are associated with fine-grained sedimentary rocks such as shale or sandstone. However, the fossils at McGraths Flat are found within rocks composed entirely of goethite, an iron-rich mineral. This unexpected setting has led palaeontologists and geologists from the Australian Museum Research Institute to challenge existing theories regarding the conditions necessary for exceptional fossil preservation.
Unlike traditional fossil sites, which rapidly bury organisms in fine sediments, McGraths Flat”s unique iron-rich composition has preserved a diverse range of organisms, including plants, insects, fish, and feathers, with astonishing clarity. The iron content has enabled the preservation of intricate details, such as individual pigment cells in fish eyes and delicate structures in insects and spiders.
McGraths Flat is primarily made up of a very fine-grained rock known as ferricrete, which consists almost entirely of microscopic iron-oxyhydroxide particles. When organisms died and were buried, these tiny particles infiltrated every cell, resulting in remarkably well-preserved soft tissue fossils. The findings from this site offer a rare glimpse into terrestrial life, which has been difficult to capture in fossil records.
The formation of McGraths Flat began during the Miocene when iron leached from weathering basalt under a warm and humid rainforest environment. Acidic groundwater transported the dissolved iron, which settled in an oxbow lake, creating ultra-fine iron-oxyhydroxide sediment that coated and preserved the soft tissues of dead organisms.
This new understanding of how McGraths Flat formed may serve as a blueprint for discovering similar fossil sites globally, highlighting the importance of seeking very fine-grained ferricrete in specific geological settings.
As scientists continue to explore this unique fossil site, they acknowledge the traditional custodians of the land, the Wiradjuri Nation, whose heritage is intertwined with the history of this extraordinary location.
The study”s findings have been published in the journal Gondwana Research, marking a significant advancement in the comprehension of ancient terrestrial ecosystems.
