DEFINITION OF BIOGENIC SEDIMENT

Sediments that are produced directly

by the physiological activities of plants or animals. Rocks

derived from biogenic sediments include both subaqueous

and subaerial varieties. Coal is a biogenic rock, produced by

the burial, heating and compression of terrestrial organic

remains, including peat that typically forms in swampy environments.

Lime muds and shell accumulations produce

micritic limestone and shelly limestone, both of which are

biogenic rocks. Coral reefs produce a variety of biogenic

rocks, including coralline limestone and accumulations of

reef organisms that may form packstones and coralline breccias.

The benthic environment also hosts biogenic sediments,

including calcareous and siliceous oozes that form by the

gradual rain of shells of deceased planktonic organisms.

In many sedimentary environments, sediments with biogenic,

clastic, or chemical origins are altered in some way by

living organisms. Biogenic structures include a variety of markings

left by animals, but not the skeletal remains of the organisms

themselves. Bioturbation is a process whereby organisms

may churn, stir up, or otherwise disrupt previously deposited

sediment. Other biogenic trace fossils or ichnofossils include

burrows left by worms and organisms that bury themselves

beneath the sediment/water interface, tracks or footprints left

on a subaqueous or subaerial surface, or borings left in solid

surfaces. The types of trace fossils present in a rock can be

used to learn about the sedimentary environment of deposition,

rates of deposition, and as paleocurrent indicators.

See also BENTHIC; HYDROCARBONS; LIMESTONE; SEDIMENTARY

ROCKS.

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