Digital Inquiry: Sedimentary Rock

Last updated 7 months ago

11 questions

VIDEO: Rocks and Minerals
Click the link to learn how each is formed. Focus on the formation of sedimentary rock.

What gets put down in layers?

What happens after it is deposited in layers?

INTERACTIVE: HOW ARE SEDIMENTARY ROCKS FORMED?

Sedimentary rocks form on or near Earth’s surface. Eroded particles of rock are transported by wind, water, and ice and deposited on dry land, on the beds of rivers and lakes, or in the seas. Over years, these pieces of rock, or sediments, are pressed together by the weight of new deposits on top of them and cement together to form rocks.

Layers of rock:
   Sedimentary rock forms in layers called strata.

River:
   A river carries sediments, which are produced through the process of weathering (breaking down of rocks).

Seabed:
   Sediments or fragments of rock may be deposited on the seabed.

Glacier:
   A glacier picks up and transports pieces of rock.

What happens to sediments?

TEXT: A TRIP TO THE COLORADO PLATEAU
The Colorado Plateau was lifted many thousands of feet, mostly straight up, from an ancient sea bed. After that, millions of years of weathering (breaking down) and erosion (moving) by the Colorado River left high river cliffs. The exposed surface of the cliffs shows the formation of many layers of sedimentary rock.

On a hard bedrock, layers of sediments (matter that settles to the bottom) built up over millions of years. Each layer of sediment depends on whether the area was covered with a sea, dry land, or shallow muddy shore. The layers are: greenish shale from seas, tan sandstone from sandy shores, yellow-gray limestone from the remains of sea creatures, red iron- rich layers of left by muddy flood zones, and more greenish sandstone when the area was covered by a deep sea. Between wet times, a sandy desert blew across wide areas, laying down the Coconino Sandstone layer. Great pressure from layers above pressed the layers together. Along the Colorado River, you can see that deposition (laying down) of
sediments, compaction (pressing together), and cementation (sticking together) forms sedimentary rock.

What is deposition?

What is compaction?

What is cementation?

GUIDE: SEDIMENTARY ROCKS
Read the text and view the images about sedimentary rocks.
Pay attention about deposition, compaction, and cementation.

Sedimentary rocks
The grains in sedimentary rocks are arranged in layers. The oldest layers are at the bottom and the youngest layers are at the top.

Chalk, limestone, shale, and sandstone are all examples of sedimentary rocks. All these different sedimentary rocks are formed from the broken remains of other rocks that become joined together.

There are five processes that make a sedimentary rock:
transport → deposition → sedimentation → compaction → cementation

Transport
Sedimentary rocks are formed by the action of water. A river carries pieces of broken rock as it flows along. This is transport.

Deposition and sedimentation
When the river reaches a lake or the sea, these rocks settle to the bottom - the rocks are deposited. Layers of rocks build up in a process called deposition. These layers are called sediments. This process is called sedimentation.

Compaction and cementation
The weight of the sediments on top squashes the sediments at the bottom in a process called compaction. This squeezes out the water from between the pieces of rock and crystals of different salts form. The crystals stick the pieces of rock together. This process is called cementation.

Uses of sedimentary rocks
Sedimentary rocks are often used as building materials.

For example:

sandstone is easy to shape into blocks so has been used to make building stones for walls for centuries
limestone is also used for building stones for walls because it is hard and lasts for many years without being worn away

Did you know?
Sedimentary rock may contain fossils of animals and plants trapped in the sediments as the rock was formed.

What is deposition?

What is compaction?

What is cementation?

ANIMATION: SEDIMENTARY ROCK LAYERS

Scientists are able to ‘read’ layers of sedimentary rock by using a technique called relative dating. This animated video demonstrates how sedimentary rock features, like the cliffs near Whanganui, were formed, stacked, eroded and tilted by tectonic movement before new rocks were formed on top.

What changes did you observe?

Sedimentary rock is formed over a long period of _________.  Small pieces of rocks called ______________ are carried away and deposited in ___________ .  

Over time, more and more layers of sediments form, __________________ on the layers below.  

The weight of the layers squeezes the sediments together during the process known as _______________.  As the water is squeezed out, crystals form. The sediments stick together. This process is called ________________.

Sedimentary rock is formed.