Rock-like minerals seep in over time and replace the organic tissue that was originally there. The formation of a rock-like fossil from silica, calcite, or pyrite. This fossilisation technique can be used to preserve both hard and soft tissue. The vast majority of bone and wood fossils have already been mineralized.
2. Mold and Cast
Sedimentary rocks have the ability to preserve an exact replica of a plant or animal. The hollow depression that is left behind after an organism is buried in sediment, and then dissolved by underground water, is referred to as a mould. The mould retains only the structure and markings of the organisms from which it originated. It does not disclose the underlying structure internally. The hollow depression is filled with minerals or sediment, which then forms a cast.
In an environment with a low oxygen content, fine sediments can enclose fragile matter such as leaves. After some amount of time has passed, the organism’s liquid and gaseous components will be forced out by the pressure, leaving behind only a trace amount of carbon. Other elements like oxygen, hydrogen and nitrogen are removed.
4. Trace Fossils
The imprints of extinct animals, such as those found in rocks, are what give rise to the formation of fossils.
i) Tracks: Tracks are the footprints of animals that were made in the soft sediment that later hardened into sedimentary rock.
ii) Burrows: Burrows are animal tracks that were made in soft sediment that eventually hardened into sedimentary rock.
The remains of fossil dung (faeces) and the contents of the stomach found in soft sediment that would later harden into sedimentary rocks. Drooping that has been fossilised can provide information about the feeding behaviour of extinct animals, and as a result, it can be of significant importance.
Original remains may be frozen or stored in amber to ensure their preservation (tree sap). Amber and ice both prevent the organisms from decomposing over time (oxygen free environment). Even the soft parts, which typically decompose and disappear, have been preserved despite the fact that the entire animal has been preserved.
When an organism passes away, the more rigid parts of its body sink to the bottom of the ocean floor, where they are eventually covered by sediment. The process of sedimentation continues unabated, which results in the formation of fossils.
8. Natural Molds
In the mud or on the sand, organisms leave behind impressions. These imprints eventually become stone as they continue to harden (Figure 1). These imprints that have become solid over time are referred to as natural moulds.
9. Mummified Plants
Vertical pressure is applied to plants or plant fragments in order to achieve compression. These plants are known as mummified specimens.
There is a process of mineral precipitation, which is followed by mineral infiltration of the cell wall. Several different types of mineral elements, such as silica, calcium carbonate, and magnesium carbonate, are responsible for triggering the process. These minerals dissolve the brittle parts of the rock and replace them.