Earth Science Notes
SEDIMENTARY ROCKS
Objectives
I can…
• Explain what Sedimentary Rocks are
• Explain the processes that create sediments
and sedimentary rocks
• Classify Sedimentary Rocks.
• Tell the geological history of an area based on
the bedding patterns
Sedimentary Rocks
• Rocks formed from sediments
• Sedimentary rocks often form as layers on the
bottom of a body of water.
Sedimentary Rock Formation
• Sediments are loose materials like small rocks,
minerals, and organic debris.
• Weathering and erosion produce sediments
– Weathering – the breaking down of rocks into bits via
chemical and mechanical means.
– Erosion – the moving of these small bits of rock to a new
location where they are deposited.
Sedimentary Rock Formation
• Weathering and Erosion
Sedimentary Rock Formation
• Sedimentary rocks form from other rocks
• These rocks are compacted and cemented
together.
– Compaction – sediments stick together due to pressure
– Cementation – minerals are deposited between pieces of
sediment – holding it together.
• Lithification  the process by which
sediments can undergo chemical and physical
processes to become sedimentary rocks.
Sedimentary Rock Formation
• Compaction and Cementation
Sedimentary Rock Formation
• Sedimentary rocks display certain characteristics
that allows draw conclusions about the history of
landforms and rock formations.
• One such feature bedding. This is the result of
sediment settling out in large flat areas.
Sedimentary Rock Formation
• STRATIFICATION refers to the way
sediment layers are stacked over each
other, and can occur on the scale of
hundreds of meters. It is a fundamental
feature of sedimentary rocks.
Sedimentary Rock Features
Types of Bedding
• Graded Bedding – size of the
sediments become large the
farther down you go in a rock
layer
– form when a steep pile of
sediment on the sea floor (or
lake floor) suddenly slumps
into a canyon or off a steep
edge.
Sedimentary Rock Features
Types of Bedding
• Cross-Bedding – forms when sand is transported as
sand-dune like bodies, in which sediment is moved
up and eroded along a gentle up-current slope, and
redeposited (avalanching) on the downcurrent slope.
Sedimentary Rock Features
• RIPPLE MARKS are produced by flowing water
or wave action.
Ancient ripples on a sandstone
surface. Ripples are symmetrical and show
"tuning-fork" branches. This indicates to a
geologist that the sandstones were
deposited in an environment with wave
action (nearshore).
Sedimentary Rock Features
• Sedimentary rocks may contain “signs” of life.
Classification of Sedimentary Rocks
Clastic (Detrital) Sedimentary Rocks: sedimentary
rocks made from broken bits of other rocks
• Ex: Conglomerate – large sediments, rounded rocks
• These types of rocks have rounded sediments because
they were near wind and water
• EX: Breccia – large sediments, sediments have sharp
angles
• These types of rocks have jagged sediments because
they were not near wind and water
Detrital Sedimentary Rocks
Conglomerate
Breccia
Classification of Sedimentary Rocks
Chemical Sedimentary Rocks: sedimentary rocks
that form when dissolved minerals come out of
solution.
• Often founds along seas or lakeshores.
• This type of rock is the only form of sedimentary
rock that did not form from preexisting rocks.
– Ex: Limestone (CaCO3) – forms when calcium carbonate comes out of
a solution.
• Limestone is deposited on bottom of lakes and seas.
– Ex: Rock salt – forms when the evaporation of water occurs, leaving
behind the salt
Chemical Sedimentary Rocks
Classification of Sedimentary Rocks
Organic (Biochemical) Sedimentary Rocks:
sedimentary rocks made of once living things
• This type of rock will form when clams, corals, snails,
and mussels die and let their shells accumulate on the
ocean floor.
– Ex: Chalk – made from the shells of organisms.
– Ex: Coal – formed from the decay and compaction of plant
materials.
Organic Sedimentary Rocks
Sedimentary Rocks
Summary
• What makes a rock
Sedimentary?
• Formation of Sedimentary
Rocks
• Classification of Sedimentary
Rocks
– Detrital / Chemical / Organics