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Sediments Produced by Living Organisms

White Cliffs Living organisms, from tiny bacteria to huge dinosaurs, are important producers of sedimentary rock, especially the small organisms that exist in vast numbers in the sea.

The high chalk cliffs of Sussex (photo) are almost entirely made up of the remains of creatures (plankton) so small, that you need an electron microscope to see them (photo insert) at all!

The most important rock materials produced by living organisms are: Limestone, Coal, and Petroleum (oil & gas).
Photo credit: DfES

Photo credit: DfES


Limestone is mainly formed from the remains of living organisms. There are many types of limestone, including chalk (above).

In Britain, large areas of limestone were also formed in shallow tropical seas around 350 million years ago. These now form the Mendip hills, the Peak District and the Pennines. The Peak District, was a large atoll, edged by coral reefs surrounding a lagoon, with volcanic islands here and there.

See also: page on Shoreline and Near-shore Environments.


Coal is a black sedimentary rock formed from the remains of trees and other vegetation. Around 300 million years ago, much of Britain was a low-lying delta swamp covered by covered in thick tropical forest (right), now coal seams.

Oil & Gas

Oil & Gas are produced from remains of marine algae that sank to the sea floor. The sediments containing them are heated gently, and the remains “mature “ to form oil & gas. These may be trapped in porous rocks, for example, beneath the North Sea.

Find out more about Britains Offshore Oil and Gas.
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