Geoscience Reference
In-Depth Information
leaves could quickly be buried by flood debris before they could
decay or be scavenged. In fact, many of the well-known dinosaurs from
North America and other parts of the world, including
Tyrannosaurus
and
Triceratops,
come from sedimentary rocks formed in these kinds
of environments.
Lakes also form in depressions on the floodplain, and they tend to
accumulate their own distinctive layers of sediment. Away from
where streams feed into the lake, thin layers of muddy clay, which
floated far out into the lake before settling down through the water, are
formed on the bottom. These thin layers, called laminations, often
form finely striped rocks once the sediment is compacted, and this
kind of rock is found in many ancient sequences of rocks. This envi-
ronment also provides excellent conditions for the preservation of not
only fish and other animals that live in the lake, but also vegetation
and carcasses of dead animals that float out into the lake. The fine
mud that settles out of the water can bury these remains quickly and
preserve skeletons in which almost every bone remains in a natural,
lifelike position. Often, the water at the bottom of a lake is depleted
in oxygen, which reduces the number of bacteria and scavengers
that destroy sunken carcasses, and in these instances, soft tissues such
as hair, muscles, and internal organs stand a better chance of being pre-
served. Ancient lake sediments have produced some of the most
exquisitely preserved fossil specimens of dinosaurs, insects, plants, and
Diagram showing features in floodplain environment.
