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.
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