When a chemical reaction creates a thin film outline of an animal or plant what type of preservation has occurred ?

Carbonization.

Explanation:

Carbonization is a type of preservation of matter that occurs during chemical reactions. In this process, some elements of organic matter are released, such as oxygen, nitrogen and hydrogen. In place of these elements arises a film, a thin carbon film (hence the name carbonization). This type of preservation is common in the fossilization of vegetables, due to liquinine, cellulose, chitin and keratin.

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