What is sedimentation?

The Blue Lias. A cliff made out of layers of mud, sand and limestone near Lyme Regis, UK. (MichaelMaggs, Wikimedia)

The Blue Lias. A cliff made out of layers of mud, sand and limestone near Lyme Regis, UK. (MichaelMaggs, Wikimedia)

Sedimentation is very important. Without it we wouldn’t have any dinosaur fossils. It is the building up of layers of small particles like sand or mud. The easiest place to see this is the beach. A beach is made up of lots of sand which have been deposited, or left behind, by the sea.

Sand and mud come from inland. Rivers erode them from the land and bring them towards the sea. As the water slows, it can’t carry as much and so sand and mud are dropped. The bigger the grain of sand, the sooner it is dropped.

If you look at a cliff, you will often see layers which make the cliff look like a layer cake. These layers are caused by sedimentation. Over a long period of time, the grains of sand and mud build up and up, forming the layers.

Fossils are found in these layers. The quicker bones are buried, the more chance they will be saved from scavenging animals and damage by weather.

The sea, rivers and lakes are the best depositors of sand and mud and dinosaurs are found where there used to be a sea, lake or river. But big glaciers also carry grains and the air can also carry very small grains.

A land-slide, where mud and rock fall down a mountain of a sand dune can also save the bones of a dinosaur. One famous fossil called ‘The Fighting Dinosaurs’ is two dinosaurs entwined as though they are fighting. Palaeontologists think that the Velociraptor was hunting the other dinosaur, Protoceratops when a sand dune collapsed on both, killing them and preserving their bones.