In this case the fossil consists of original material, albeit in a geochemically altered state.
This chemical change is an expression of diagenesis.
For permineralization to occur, the organism must become covered by sediment soon after death or soon after the initial decay process.
The degree to which the remains are decayed when covered determines the later details of the fossil.
to dinosaurs and trees, many meters long and weighing many tons.
A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates.
In 2014, Mary Schweitzer and her colleagues reported the presence of iron particles (goethite-a Fe O(OH)) associated with soft tissues recovered from dinosaur fossils.
Based on various experiments that studied the interaction of iron in haemoglobin with blood vessel tissue they proposed that solution hypoxia coupled with iron chelation enhances the stability and preservation of soft tissue and provides the basis for an explanation for the unforeseen preservation of fossil soft tissues.
Some fossils are biochemical and are called chemofossils or biosignatures.
Permineralization is a process of fossilization that occurs when an organism is buried.
For this reason, one term covers the two modes of preservation: adpression.
Because of their antiquity, an unexpected exception to the alteration of an organism's tissues by chemical reduction of the complex organic molecules during fossilization has been the discovery of soft tissue in dinosaur fossils, including blood vessels, and the isolation of proteins and evidence for DNA fragments.
In many cases, however, compressions and impressions occur together.