Guide to Fossils -Fossilization Process 2

Fossilization Process 2


Fossils are abundant in cliffs of Dover. This article is part two the fossilization series is part of our Guide to Fossils. 

Fossilisation can happen through many processes and one is through compression –impression. In this case the fossils are formed through chemical reduction of complex organic molecules which form the tissues of an organism. The fossils have original material in a geochemically altered state. The leftover is a carbonaceous film called phytoleim which results in compression. Generally the phytoleim is lost and what remains is an impression of the organism in the rock causing an impression fossil. Generally compressions and impressions occur together. When a rock breaks open the phytoleim will have an attachment to one part and the counterpart would be only an impression.

Carbonisation is another process where carbonaceous films, which are thin coatings and predominantly made of the element carbon. These carbon residual sheets form a silhouette of the original organism and are formed when soft tissues of organisms which are made largely of organic carbon face reducing conditions during diagenesis.

Bioimmuration is another process where, the skeletal organisms overgrow or else subsumes another organism, while preserving the latter or preserving an impression of it within the skeleton. Generally it is a sessile skeletal organism which is either a oyster or a bryozoan which grows along a substrate. At times the bioimmured organism is soft bodied and is then preserved as an external mold. It could also occur that an organism settles on the top of a living skeletal organism which grows upwards, while preserving the settler in its skeleton.

The process of fossilisation is extremely rare and it is only a small fraction of animals and plant which turn into fossils. These fossils are formed and preserved for millions of years and is embedded in rocks. The fossilisation scenarios are just a few of the many possible processes which turn living organisms into rock like material. Fossilisation is brought about by the steps of decay transport and burial. It is important to note that most organisms turn out to be fossils when they are changed through various means. The heat and pressure when being buried in sediment could cause tissues of organisms to release hydrogen and oxygen , leaving a residue of carbon. This process can yield a detailed carbon impression of the organism which is dead in sedimentary rock.