Sedimentary Rocks

Rock formed from layered sediments that pile up and squeeze together, providing clues to the earth’s past.

Vocabulary Sediments: particles carried away by erosion. Erosion: Process by which smaller particles of rock are

displaced by moving water, wind, or ice. Deposition: The build-up of sediments on the bottom of

lakes, valleys, and the oceans. Compaction: Sedimentary rock process where the water is

squeezed out of the spaces, and the particles of sediment pack tightly together.

 

Cementation: The process of sediment spaces filling and

binding together with minerals.

Formation of Sedimentary Rocks How do sedimentary rocks form?

1. Breakdown of earth

Forces from water, wind, ice, and pollution break down the existing rock on the surface.

Four steps form sedimentary rocks.

2. Erosion

Moving water transports these sediments to lakes or oceans…this process is called erosion.

3. Deposition

• These sediments settle to the bottom of the water when the current slows.

• Over time the sediments build up.

4. Compaction & Cementation

• Over very long periods of time the sediments continue to build up forming layers on top of layers.

• Pressure from the stack of sediment hardens lower, older layers, forming sedimentary rock.

• A thin film of minerals around the sediments fills all spaces and binding together the particles (cementation).

Classification of Sedimentary Rock

ESRT page 7

Classification of Sedimentary

Sedimentary rocks are grouped according to composition and texture.

1. Clastic Rock

2. Organic Rock

3. Chemical Rock

Clastic Rock • Particles of rock and mineral grains

compact and cement together.

• Grain size (and shape) determines type of clastic rock.

Organic Rock

• Sedimentary rock formed from living things or their remains.

Coal Example:

• When plants in a swamp die, they form layers of dead plants.

• These layers build up and harden into peat.

• The peat is buried under sediments and over long periods of time the pressure forms coal.

Organic Rock on ESRT

Organic Rock

Limestone Example:

• Ocean organisms such as coral and clams have hard outer coverings made of calcite.

• When these organisms die, they fall to the bottom of the ocean, and build up in layers.

• Over time the fragments compact and cement together, forming limestone.

Chemical Rock

• When minerals come out of solution and crystallize.

• These are also known as evaporites or chemical precipitates.