Burial of Sediments

Sediments originate from weathering and erosion of rocks on land. Most of this sediment eventually gets transported and deposited in the sea, near river mouths or further offshore, as can be seen in this satellite photo of the Mississippi delta, USA.

As the Mississippi delta builds outward into the sea, sediments that were once deposited offshore get buried beneath sediments laid down on the delta top. The older layers get buried beneath newer ones.

N. Sea Rift 140 million years ago. Diagram from UK Offshore Oil & Gas

Sediments cannot continue to build up indefinitely unless the surface on which they are deposited is slowly sinking – areas where this is happening are sometimes called Sedimentary Basins.

An example of a sedimentary basin is the North Sea. This began to form over 250 million years ago due to stretching and thinning of the Earth’s crust. As deposition continued over millions of years, thousands of metres of sediment have built up on the sinking sea floor.

Cross-section through the rocks beneath part of the North Sea. Large arrows show the crust being pulled apart, small arrows show fault movement.