Mistaken Point Ecological Reserve
In normal conditions, when marine organisms die, only bones, shells, and other hard parts are preserved as fossils. The soft-bodied creatures at Mistaken Point lived millions of years before animals developed skeletons, but the imprints of their soft tissues were preserved in place on the muddy sea floor when they were suddenly buried by repeated volcanic ash-falls. The volcanic ash layers contain zircon, which makes it possible for geologists to accurately date the different fossil layers. Fossils of similar age are found in Russia and Australia, but the variety found at Mistaken Point make the site unique.So, it sounds like repeated volcanic ash-falls that settled to the ocean floor.