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Compressions
& Carbonization
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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.
Pliocene-Pleistocene
Arcen, Netherlands
Maas River Sediments Quarry in
Germany East of Arcen
6 cm long x 3.5 cm wide
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Carbonized
Walnut Fruit
Juglans tephrodes
Pliocene-Pleistocene
Arcen, Netherlands
Maas River Sediments Quarry in
Germany East of Arcen
5 cm long x 3 cm wide
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Fish
Compression
Priscacara serrata
Green River Formation
Eocene
Wyoming, USA
20 cm long
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Leaf
& Seed Compression
Cedrelospermum sp.
Miocene
Randecker Maar Esslingen, Germany
Leaf 4 cm long, Seed 1 cm long |
Cone
& Needle Compression
Metasequoia glyptostroboides
Muddy Creek Formation
Oligocene
Beaverhead County, Montana
cone and stem 5 cm long
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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
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Fusainized Wood View 2
Lithocarpus sp.
Unknown Location
4 cm wide x 7 cm long |
Bibliography
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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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