PERMINERALIZATION OF FOSSILS: WHAT IT CONSISTS OF AND PROCESS - BIOLOGY - 2025

The permineralization is one of the mechanisms fossilization, ie the formation of fossils. In addition, there are other mechanisms of fossilization: carbonization, casts, replacement and crystallization.

Fossils are the bodily remains of beings that existed in the past, in addition to a set of their activities during their existence: footprints or traces, burrows, eggs, feces, etc. They are generally found forming parts of sedimentary rocks and in a petrified state.

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Fossils can be made of hard parts -bones, teeth, corals, shells- or soft parts -leaves, stems, seeds, muscles, bird feathers, skins, etc.-. However, there is a classification of them: fossil imprint, ichnofossils, casts, mummification and inclusion.

In fossil imprinting the organism decomposes on a clay or silt surface, leaving its imprint or imprint. The ichnofossils show the tracks that animals left when moving on a soft surface. This surface hardens to form sedimentary rocks.

In molds, the decomposing organisms are covered by the soil. Later, the organism degrades, leaving a mold in the sedimentary rock that contains it. Finally, in mummification and inclusion, the organic matter does not decompose completely, but retains many of its characteristics.

What is permineralization?

Permineralization occurs when a decomposing organism is covered by sludge. There, the organisms come into contact with mineral-rich groundwater.

Subsequently, the minerals are deposited on the surfaces, cavities or pores of bones, shells, etc., impregnating these structures.

This process preserves the hard structures of the fossils and in some cases the soft structures, avoiding their deformation. In this process the fossils acquire greater consistency and weight. Additionally, fossils undergo a color change, as they take on the color of minerals.

Sometimes the mineral substance present in decomposing organisms is replaced by other minerals, the most common being calcite, pyrite and silica. This last mineral is the one that plays an important role.

It can happen that the organic material is replaced, partially or totally by minerals. The organic material that remains is embedded in a mineral matrix.

In dinosaurs

Minerals form a crystallized mold on the porous walls of shells, bones, or vegetables. This can maintain the shape of a plant's leaves and preserve them over time. The same occurs with dinosaur bones, which through permineralization can preserve their cellular structure.

When dinosaurs die, they can undergo a dehydration process, leaving only their outer covering, which is known as leather. This occurs during a process known as mummification. Finally, permineralization occurs that preserves the aforementioned structure.

Organisms can decompose completely leaving an empty space. Subsequently, there is a mineral deposition that preserves the external form of the decomposed organism.

Process

In permineralization, there is a deposit of minerals inside the cell of decomposing organisms. The mineral-laden water penetrates into the pores of the organic tissues, depositing the minerals in them in the form of crystals.

The process continues to reach the cellular light, leaving the cell wall in its original form covered by crystals, formed by the deposition of minerals from the water.

The minerals silica, calcite and pyrite are frequently involved in the fossilization mediated by permineralization.

Silicification

Water containing silica enters the cells of a decomposing organism, which undergoes dehydration. This generates the formation of opal crystals that create a mold of the interior of the body.

Among the silica fossils, those of foraminifera, echinids, ammonites, brachiopods, gastropods, bacteria and algae are frequent. It is also worth mentioning the xyloid jaspers from the fossilization of tree trunks and branches.

Silicification allows the knowledge of the environment in which the fossils were formed.

Carbonation

It is a process that consists of the removal of organic matter petrified by calcium carbonate, specifically as the mineral calcite. This is in fact the one that is most found in sedimentary rocks.

Corals have a rapid fossilization and an almost total conservation of details. Also many mollusk fossils have their shells formed by calcium carbonate in the form of aragonite. This then transforms into calcite, the most stable form of calcium carbonate.

The fossilization of plants and their tissues involves the formation of so-called carbon balls. These are a calcareous permineralization of the peat by calcium and magnesium carbonates.

They are produced when carbonate enters the cells of an organism. Coal balls produce information about plants from the Upper Carboniferous period.

Pyritization

This form of permineralization occurs when organic matter decomposes in an oxygen-poor environment, which produces sulfuric acid that reacts with iron salts in marine waters to produce iron sulfides (pyrite and marquesite).

Iron sulfides can displace carbonate shell material when there is low carbonate saturation in the surrounding water.

When pyrite remains unchanged, fossils have a metallic appearance, but pyrite, and especially marquesite, can oxidize and be destroyed in the presence of the atmosphere.

Plants can undergo pyritization in clay soil, but to a lesser degree than in seawater.

Examples of permineralization

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-Dinosaur fossils comprising bones, teeth, footprints, eggs, skins, and tails.

-Fossils of the ammonite a mollusk that originally had a shell of aragonite, an original form of calcium carbonate, replaced by pyrite. It existed in the Mesozoic period.

-The Petrified Forest National Park in Arizona (United States), product of silicification.

-In White Cliffs, Australia, entire skeletons of animals have been permineralized with opal, a silicate.

-Fossil of Devonochites sp., A Devonian brachiopod permineralized with calcite and externally with pyrite.

References

1. What is permineralization? Taken from ucmp.berkeley.edu
2. Mireia Querol Rovira. (January 25, 2016). Knowing Fossils and Their Age. Taken from: allyouneedisbiology.wordpress.com
3. Murcian Paleontological Cultural Association. (2011). Chemical processes of fossilization. Taken from: servicios.educarm.es
4. Wikipedia. (2018). Petrifaction. Taken from: en.wikipedia.org
5. Meanings. (2018).Permineralization (nd). Taken from: meanings.com
6. Casal, Gabriel A., Nillni, Adriana M., Valle, Mauro N., González Svoboda, Ezequiel, & Tiedemann, Celina. (2017). Permineralization in dinosaur remains preserved in overflow deposits of the Bajo Barreal Formation (Upper Cretaceous), central Patagonia, Argentina. Mexican Journal of Geological Sciences, 34 (1), 12-24. Recovered from: scielo.org.mx