Geoscience Reference
In-Depth Information
Appendix A5: Fossils
Table A5.1
Modes of fossil preservation.
Mode of preservation
Explanation
Examples
Preservation of the original material
(duripartic)
Due either to the chemical
composition of the original
material, and/or to special
characteristics of the depositional
environment. Original
characteristics are well preserved
and can be used for a range of
geochemical environmental
proxies
Natural mummifi cation
(Figure 5.3a); insects in
amber
Chemical alteration
of the fossil:
permineralization
Cell walls of the original organism
remain more or less unaltered
Ammonites with their
original aragonitic shell
petrifaction
All the original material is
replaced by minerals. Several
phases of mineralization may be
present
Figure 5.3b
Casts and moulds
Mould refers to the sedimentary
deposits that show the internal or
external form of the fossil after the
soft parts have decayed. Cast
refers to fossils where the hard
parts (e.g. shell) have been
replaced.
Figures A5.2, 5.3c, 5.6
Impressions
Two-dimensional remains of where
a fossil has been in contact with
the rock. The term impression is
also given to a leaf fossil where
the organic remains have been
oxidized away leaving only a
'mould' of the original leaf
surface.
Figure 5.3d
