Traditionally, the most exceptionally well-preserved fossil sites are from rocks dominated by shale, sandstone, limestone, or volcanic ash. Consider Germany’s Messel Pit or Canada’s Burgess Shale. At these sites, fine-grained sediments rapidly buried organisms, under unique conditions that allowed the exceptional preservation of soft tissues, not just hard parts. Messel Pit preserves ~47 million-year-old fur, feathers, and skin outlines, while the Burgess Shale contains soft tissues from some of Earth’s earliest animal life dating back 500 million years.
Sedimentary rocks made entirely of iron, on the other hand, are the last place you’d expect to find such well-preserved remains of land-based animal and plant life. Iron-rich sedimentary rocks are predominantly known from banded iron formations (BIFs) that are massive iron deposits laid down over two billion years ago in Earth’s ancient oxygen-depleted oceans, long before complex animal and plant life evolved. In more recent history, iron is considered a mere weathering product, forming rust on the continents when exposed to our oxygen-rich atmosphere. Just look at Australia’s iconic red rocked outback landscape that preserves these million- to billion-year-old features. Yet, the recent discovery of McGraths Flat defies these expectations.