Transcript Sedimentary Rocks

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
Four steps form sedimentary rocks.
Forces from water, wind, ice, and pollution
break down the existing rock on the
surface.
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.