The Virtual Petrified Wood Museum.  Dedicated to the Exhibition and Educational Study of Permineralized Plant Material
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Compressions & Carbonization
Carbonized Insects
Carbonized Insects
(Insect Compressions)
Green River Formation
Cenozoic; Paleogene; Eocene
Kemmerer, Wyoming
Slab 6 cm x 4 cm

When organisms become trapped and squeezed between sediments they may form compressions. Larger organisms can be distorted by compression. However, good fossils of leaves and insects are often formed by compression.

Insect and plant compression retain organic material. The organic matter making up the body of the organism may be altered during decay and rock formation. The distillation of volatile compounds and the polymerization of lipids chemically transform the organic structures and leave a thin film. The thin, dark, film is made of stable, polymerized carbon molecules that remain after more volatile and unstable compounds get dissolved away, hence the name carbonization. Thus, a compression fossil may represent a type of carbonization. The thin carbon layer on a plant compression is known as a phytoleim (Cleal & Thomas, 2009, p. 4).

As organisms are squeezed into compressions they may form an imprint or impression. When siltstone is split along bedding planes both a compression and impression may be revealed. Compressions often show the external surface of an organism flattened in a two dimensional fashion. Impressions often represent a negative imprint of a compression. The compression retains altered tissues composed mainly of carbon. If the layer of carbon is lost on the compression through weatherning or further diagenesis then it is known as an impression (Cleal & Thomas, 2009, p. 4).

Insects and leaves preserved in the Eocene aged Florissant beds of Colorado are often carbonized. It is believed that leaves and insects became entangled in diatom mucus mats (formed by aggregates of diatoms under stress). Insects and leaves were incorporated into layers of sediments and volcanic ash at the bottom of lake Florissant. Many of these insects and leaves decomposed leaving imprints. As the sediments compacted and hardened into shale the imprints became impression fossils. Some organisms only partially decayed retaining a dark colored carbon residue to become compression fossils (carbonization). Many insects have their wings preserved as impressions and their bodies as dark compressions. Compressions are often flattened, having a two-dimensional appearance. However, the preservation in diatom layers allows some organisms to retain their three-dimensional character. Some insects are found with organs and appendages. Some leaves can be found with internal structures (Meyer, 2003, pp. 35-37).

Feathers are often preserved through carbonization. It is believed that the carbon residue is the result of feather degrading bacteria. An analysis of a Cretaceous aged fossil feather showing a banded color pattern from Brazil produced interesting results. The light areas of the feather represented an impression (no organic residue). The dark areas, representing a compression, consisted of 1-2 micrometer oblate carbonaceous bodies. These objects turned out to be carbonized melanosomes; molecules that were responsible for the original feather color. The fact that the structure of the melanosomes is preserved opens up the possibility of determining the original feather color (Vinther, J., 2008, p. 522).

Most fossils found in coal deposits are compressed and carbonized or coalified. Coal balls are the exception and are discussed in our permineralization article. Plant and animal remains may also be Charcoalified or Fusainized. Many believe that fusainized organisms are transformed to charcoal by ancient forest fires. Although evidence of fire is associated with some fusainized plant tissues there are exceptions. Some fusainized remains preserve cuticle and resins, which does not seem consistent with an origin that includes fire (Schopf, 1975, p. 45). Fusainized remains are three-dimensional and may be replicated to the cell level by carbon (Grimaldi & Engel, 2005, pp. 49-50).

Carbonized Cone
Pinaceae Family.
Arcen, Netherlands
Maas River Sediments Quarry in
Germany East of Arcen
6 cm long x 3.5 cm wide

Carbonized Walnut Fruit
Juglans tephrodes

Arcen, Netherlands
Maas River Sediments Quarry in
Germany East of Arcen

5 cm long x 3 cm wide

Fish Compression
Priscacara serrata

Green River Formation
Wyoming, USA
20 cm long

Leaf & Seed Compression
Cedrelospermum sp.

Randecker Maar Esslingen, Germany
Leaf 4 cm long, Seed 1 cm long

Cone & Needle Compression
Metasequoia glyptostroboides

Muddy Creek Formation
Beaverhead County, Montana
cone and stem 5 cm long

Eurypterus Compression
Eurypterus remipes

Fiddler Green Formation
Phelps Member
Upper Silurian
Herkimer Co., New York
Specimen is 13 cm long

Coalified Fern Seeds
Seeds from Seed Fern in Bituminous Coal
Trigonocarpus sp.
Collected in Maryland/Pennsylvania Area
5 to 6 cm in length

Fusainized Wood
Lithocarpus sp.
Location Unknown
4 cm diameter

Fusainized Wood View 2
Lithocarpus sp.
Unknown Location
4 cm wide x 7 cm long


Cleal C.J. & Thomas, B.A. (2009). Introduction to Plant Fossils. United Kingdom: Cambridge University Press.

Grimaldi, D. & Engel, M.S., (2005). Evolution of the Insects. New York: Cambridge University Press.

Meyer, H.W., (2003). The Fossils of Florissant. Washington: Smithsonian Books.

Thompson, I. (1982). National Audubon Society Field Guide to Fossils. New York: Alfred A. Knopf.

Schopf, J.M. (1975). Modes of Fossil Preservation. Review of Palaeobotany and Palynology, vol 20: pp. 27-53.

Vinther J., Briggs, D.E.G, Prum, R.O., & Saranathan, G. (2008). The Colour of Fossil Feathers. Biology Letters, vol 4: 522-525.

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