Types of fossilization and their characteristics

Fossils are plant or animal remains that have been dead for a long time, which have not reached putrefaction and which, over the years, have become another component of the earth’s crust. Its study, through the geological dating of rocks and phenomena at the planetary level, allows ordering the fossils in geological time , which is the time elapsed since the Earth was formed until today.

The process of fossil formation , called fossilization, is considered a complex natural cycle that depends on: the lack of oxygen, the rapid burial of organisms (generally in hydric sediment) and the paralysis of the decomposition process.

Obviously, there are fossilization processes in which the changes in the composition and structure of the organisms are minimal or scarce, which is why we speak of unaltered fossils (inclusion, mummification, freezing); however, there are also the altered fossils (permineralization, carbonization, replacement) in which there is a drastic structural or chemical transformation. As indicated, fossils can be formed in a number of ways. Here is a brief explanation of how fossils are classified according to their formation .

These are the 3 types of fossilization according to the geological process :

Permineralization or petrification

It is the fossilization process by which the hard parts of an organism, made up of porous material and cavities, are covered with runoff water loaded with dissolved ions (silica, calcium carbonate, phosphates, sulfates, iron oxide) that occupies their interior, being able to cause the disappearance of the internal structure and the formation of crystals that preserve the surface structure of the organism. This type of mineralization, similar to the foundation process, is very common in dinosaur fossils . If these creatures are curious to you, here you can learn about herbivorous dinosaurs: names, types, characteristics and images and here about carnivorous dinosaurs: names, types, characteristics and images.

Print

Printing or compression fossilization, very common in plants, occurs when the remains of organisms are subjected to high temperatures or the high pressures exerted by rocks and other edaphic and subsoil materials.

Inclusion

This fossilization process occurs when organisms become trapped in conservative materials or environments. Depending on the conditions, 3 types of inclusion or embedding can be distinguished :

• Gelification or freezing: it is a fossilization more typical of glacial areas. The glaciations that have occurred on our planet have left numerous organisms preserved in whole (Siberian mammoth) or in part (mammoth hair in permafrost), buried under large layers of ice.
• Mummification: considered a pause in the disintegration process, without becoming a real fossilization, it originates after a massive loss of fluids in the organisms, which prevents the putrefaction of the organisms.
• Trapped in amber or pitch: Amber, which is a fossilized plant resin, preserves the external structure, but not the internal one, of organisms. Within the fossilization in amber it is common to find insects, spiders, frogs and lizards. With pitch, which is a very viscous hydrocarbon, the same thing happens. In general, Pleistocene fossils stand out, such as mammoths , mastodons, wolves, bison, saber-toothed lions , etc.

These are the 5 types of fossilization according to the physical process :

Dislocation

Disarticulation, which involves the separation of the components of the remains of organisms, can take place during the processes of bioturbation, compaction of the sediment or by phosyldiagenesis.

Fragmentation

Fragmentation is a destructive process that is easy to identify in fossils, since it consists of their breaking, caused either by physical impacts or by the action of living beings.

Bioerosion

This process is very common in marine fossils and consists of the removal or decomposition of materials from a hard substrate by the action of organisms. In these ecosystems, bioerosion is caused mainly by mollusks , sponges , crustaceans and fish , among others.

Abrasion

It consists of the erosion or wear of organic remains that end up being fossils through friction with water currents and also with air currents.

Corrosion

Corrosion is triggered by factors that promote chemical degradation and alter the surface of the fossil record.

These are the 5 types of fossilization according to the chemical process :

Carbonation

This type of fossilization is very common and consists of the replacement of hard organic remains by calcite, a mineral composed of calcium carbonate. Since the skeleton of corals is made up mostly of this material, fossilization through this process takes place rapidly.

Carbonification

This fossilization process, which consists of the substitution of organic components for carbon , characterizes the Carboniferous period, and is very common in plant remains and arthropods , due to its cellulose and chitin content, respectively.

Silicification

Sometimes silica is derived from chemicals that allow fossilization, as is the case with chaldedonia. The most common fossils in this process are foraminifera, echinids, ammonites, gastropods, and brachiopods.

Pyritization

In pyritization, the organic parts of shells and skeletons are replaced by marcasite and pyrite, two types of iron sulfides, a product of the combination of sulfuric acid generated by the decomposition of marine organisms under anoxic conditions with the iron present in seawater. .

Phosphating

In this process, very common when there is a certain accumulation of vertebrate remains, the calcium phosphate present in bones and teeth, together with the calcium carbonate in the sediment, favors the formation of fossils.

In addition to the types of fossils mentioned below, through the paleontological trace it is possible to obtain information about the organisms when they were alive. The ichnofossils (fossilized footprints or fossil footprints) can be found indoors, known as coprolites , or on the surface of the stratum, as is the case of dinosaur ichnites .

Bodily

In this type, the fossil preserves its skeleton to a greater extent. We have the example of the frozen mammoth and one closer to us, which we have surely seen at some time, the shells.

Mold

It is the impression or the filling of the fossils after dissolving their organic parts. If we see the shape printed, we speak of an external mold; on the contrary, if we observe that a tracing product of the internal filling of the body has formed, we speak of an internal mold.

Fossil substances or chemical fossils

Fossil substances or chemical fossils can be found in geological materials, which turn out to be substances that were generated by the activity of extinct organisms and were trapped there.

Now that you have learned all this about how fossils are formed and what is the conservation process of fossils naturally , you may be interested in continuing to learn more about what living beings and the planet were like so many millions of years ago. If by now you have learned enough about the types of fossilization and their characteristics , go ahead and discover which is the oldest fossil in the world .

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