Fossilization

Dad, how does one become fossil ?

Let us take the case of a brachiopod. It dies and fall on the sea-bed. Its organic remainders, either are dispersed, or eaten by the necrophagous. Only the inorganic part, the shell, is preserved. It will become more or less worn down by the jolts of waves and the frictions with rollers, sand and various remains of shells. Little by little the sediments will cover this shell of the brachiopod. The process will continue during million years. With time, the sediments will harden and the shells will be petrified. The deposits thus emerged and formed, will be exposed, as well to the rain as to the sun, the wind and the frost. Little by little, they will be planed by erosion and will release their invaluable contents: the fossilized brachiopod.

(Have a look to the beside animation).

A short animation...


 

...about the fossilization of a brachiopod.

More about fossilization and epigeny

Builders

Richthofenidae or Coralliopsidae of Permian age (about 260 m.y.) were real reef builders, a little in the style of Cretaceous rudistes.

Lumachella of brachiopods

Some sedimentary deposits called "Lumachella" - are full of living organisms of the same type. This photo shows a mass of Callovian Rhynchonella in a Lumachella limestone.

Russian dolls ?

By looking at this image attentively, you can distinguish a fossil Rhynchonella inside a fossil Terebratula. Being given that the latter belongs to the group of the microphagous and is not ravenous thus, that it have to swallow his cousin, "the accident" seems to have occurred postmortem.

Brachiopods and petrology

Brachiopods are found in many sedimentary rocks (limestones, sandstone, clays...) and sometimes in metamorphic rocks.

Pyritisized Spirifer in a slate

Brachiopods and geology Click here

Area of turbulences

This shell was buried in very agitated marine environment, which explains its separation. Normally, the two valves of a brachiopod only seldom dissociate.

Glossary

Rudistes : peculiarly-shaped, inequivalve bivalvia molluscs (Jurassic - Cretaceous),

Microphagous : to live on small preys.
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