The preservational mode of the Doushantuo formation

Doushantuo Formation

The Doushantuo Formation is a Lagerstätte in Guizhou Province, China that is notable for being one of the oldest fossil beds to contain highly preserved fossils...

involves very early phosphatisation on a cellular level - with cells being replaced by phosphate before they degrade.

Occurrence

The mode of preservation is typically found in shallow, high energy waters, as lenses of phosphate in carbonate rocks. Its occurrence is assisted by high concentrations of phosphate, which are presumably led to precipitate around the degradation products of cells and cell walls.

What is preserved

Cells are preserved at a cellular level, with arguments that sub-cellular structures may even represent cell nuclei.

Bias

Although the preservational window is open pretty continually from about through most of the Cambrian, it tends to preserve microscopic things, such as embryos and bacteria.