This page last updated on 01-Feb-2012
Prof. Stephen A. Nelson
Sediment and Sedimentary Rocks
Rivers, oceans, winds, and rain runoff all have the ability to carry the particles washed off of
eroding rocks. Such material, called
, consists of fragments of rocks and minerals.
When the energy of the transporting current is not strong enough to carry these particles, the
particles drop out in the process of
. This type of sedimentary deposition is
referred to as
. Another type of sedimentary deposition occurs when
material is dissolved in water, and chemically precipitates from the water. This type of
sedimentation is referred to as
. A third process can occur, wherein
living organisms extract
ions dissolved in water to make such things as shells and bones.
type of sedimentation is called
The accumulation of plant matter,
such as at the bottom of a swamp, is referred to as
Thus, there are 4
major types of sedimentary rocks:
Clastic Sedimentary Rocks
Chemical Sedimentary Rocks
Biochemical Sedimentary Rocks
Organic Sedimentary Rocks
Clastic Sediments and Sedimentary Rocks
The formation of a clastic sediment and sedimentary rocks involves five processes:
- The first step is transforming solid rock into smaller fragments or dissolved
ions by physical and chemical weathering as discussed in the last lecture.
- Erosion is actually many process which act together to lower the surface of the
In terms of producing sediment, erosion begins the transpiration process by
moving the weathered products from their original location.
This can take place by
gravity (mass wasting events like landslides or rock falls), by running water. by wind, or
by moving ice.
Erosion overlaps with transpiration.
Sediment can be transported by sliding down slopes, being picked up
by the wind, or by being carried by running water in streams, rivers, or ocean currents.
The distance the sediment is transported and the energy of the transporting medium all
leave clues in the final sediment that tell us something about the mode of transportation.
Sediment is deposited when the energy of the transporting medium
becomes too low to continue the transport process. In other words, if the velocity of the
transporting medium becomes too low to transport sediment, the sediment will fall out
and become deposited. The final sediment thus reflects the energy of the transporting
- Lithification is the process that turns sediment into rock. The
first stage of the process is compaction. Compaction occurs as the weight of the
overlying material increases. Compaction forces the grains closer together, reducing pore
space and eliminating some of the contained water. Some of this water may carry mineral
components in solution, and these constituents may later precipitate as new minerals in