Alteration and deformation of fossils

While certain fossils are perfectly preserved and retain their original shape, others have undergone varying degrees of deformation or alteration. The zone in which a fossil was buried may have been subjected to a variety of phenomena including tectonics or metamorphism. Buried in these zones, under the influence of pressure and heat, the fossils and their gangue become deformed or broken. Furthermore, chemical and physical degradations lead to the oxidation and erosion of fossils.

All of these deformations modify the shapes of fossils and make it more complicated for palaeontologists to understand them. Thanks to modern technologies, in particular 3D imaging, it is possible to virtually reconstruct their original morphology.

Arca (Bivalve)
Upper Cretaceous, Turonian
From - 94 to - 90 Ma

• Original organism
• Fragmentation
• Bioerosion
• Abrasion
• Corrosion and dissolution

Different types of fossil deformation

Palaeontologists distinguish deformations due to the compaction of sediment during diagenesis and those caused by tectonic and metamorphic phenomena, associated with pressure and temperature. The intensity of these deformations depends on the nature of the sediments and the shapes of the fossils. These deformations can be brittle or supple (ductile).

• Reference specimen
• Brittle deformation
• Ductile deformation
• Combination: both types of deformation
• Partial: deformation of part of a rock