Grotzinger • Jordan
Understanding Earth
Sixth Edition
Chapter 5:
SEDIMENTATION:
Rocks Formed by Surface Processes
© 2011 by W. H. Freeman and Company
Chapter 5
Sedimentation:
Rocks Formed by
Surface Processes
About Sedimentation
• Sediments are produced on the Earth’s
surface as a result of weathering.
• Sediments are transported and become
sedimentary rocks after they come to
rest.
• Sedimentary rocks give evidence of
ancient sedimentary environments where
they formed.
Lecture Outline
1. Surface processes of the rock cycle
2. Sedimentary basins: the sinks for
sediments
3. Sedimentary environments
4. Sedimentary structures
5. Burial and diagenesis: from sediment to
rock
Lecture Outline
6. Classification of siliciclastic sediments
and sedimentary rocks
7. Classification of chemical and biological
sediments and sedimentary rocks
1. Surface Processes and the Rock Cycle
Weathering
Physical weathering
Chemical weathering
1. Surface Processes and the Rock Cycle
Processes forming sedimentary rock:
Weathering
Erosion
Transportation
Deposition (sedimentation)
Burial and compaction
Diagenesis
1. Surface Processes and the Rock Cycle
1. Surface Processes and the Rock Cycle
Classification of sediments
Siliciclastic sediments
Chemical sediments
Biological sediments
1. Surface Processes and the Rock Cycle
Current strength and distance of
transport affect:
Size of clastic particles
Sorting of clastic particles
Rounding of clastic particles
1. Surface Processes and the Rock Cycle
Chemical mixing vats:
Oceans
Lakes
Thought questions for this chapter
A geologist is heard to say that a particular sandstone was
derived from a granite. What information could she have
gleaned from the sandstone to support this?
Weathering of the continents has been much more
widespread and intense in the past 10 million years than it
was in earlier times. How might this be borne out in the
sediments that now cover Earth’s surface?
Describe the beach sands that you would expect to be
produced by the beating of waves on a coastal mountain
range consisting largely of basalt.
2. Sedimentary Basins
Sediments tend to accumulate in
depressions in the Earth’s crust.
Depressions are formed by
subsidence.
Sedimentary basins are depressions
filled with thick accumulations of
sediment. They are sinks for
sediment.
2. Sedimentary Basins
Types of sedimentary basins:
Rift basins and thermal
subsidence basins
Flexural basins
Sedimentary basins
form on rifted
continental
margins
3. Sedimentary Environments
Types of environments:
1. Continental
Lake
Alluvial
Desert
Glacier
3. Sedimentary Environments
Types of environments:
2. Shoreline
Delta
Beach
Tidal flats
3. Sedimentary Environments
Types of environments:
3. Marine
Deep sea
Continental shelf
Organic reef
Continental margin
Continental slope
and slope
Sedimentary
Environments
3. Sedimentary Environments
3. Sedimentary Environments
Environments of siliciclastic
sediments:
Continental (alluvial, desert,
lake, and glacial)
Shoreline (deltas, beaches,
and tidal flats)
Marine (shelf, margin, slope,
and deep sea)
3. Sedimentary Environments
Environments of chemical and
biological sediments:
Carbonate deposits (organic
reefs, beaches, shelves,
and tidal flats)
Siliceous environments (deep
sea)
Evaporite environments (lakes)
Thought questions for this chapter
From the base upward, a bedding sequence begins with a
bioclastic limestone, passes upward into a dense
carbonate rock made of carbonate-cementing organisms,
and ends with beds of dolostone. Deduce the possible
sedimentary environments represented by this sequence.
In what sedimentary environment are carbonate muds?
How can you use size and sorting of sediments to
distinguish between sediments deposited in a glacial
environment and those deposited in a desert?
Where are reefs likely to be found?
4. Sedimentary Structures
Sedimentary structures – all kinds
of features in sediments formed at
the time of deposition.
Bedding (stratification)
Cross-bedding
Graded bedding
Ripples
Bioturbation structures
Crossbedding
Ripples – modern and ancient
Bioturbation Structures
4. Sedimentary Structures
Bedding sequences – vertically
stacked layers of sedimentary rock
with different types of sedimentary
structures in each layer.
Example of a Bedding Sequence
Thought questions for this chapter
You are looking at a cross section of rippled sandstone.
What sedimentary structure would tell you the direction of
current that deposited the sand?
You discover a bedding sequence that has a conglomerate
at the base; grades upward into sandstone and then to a
shale; and finally, at the top, grades to a limestone. What
changes in the sediment source area would have been
responsible for this sequence?
5. Burial and Diagenesis
Burial is the preservation of
sediments within a sedimentary
basin.
Diagenesis is the physical and
chemical change that converts
sediments to sedimentary rocks.
5. Burial and Diagenesis
Lithification includes:
Compaction
Cementation
Thought questions for this chapter
If you drilled one oil well into the bottom of a sedimentary
basin that is 1 km deep and another that is 5 km deep,
which would have the higher pressures and
temperatures? Oil turns into natural gas at high basin
temperatures. In which well would you expect to find
more natural gas?
6. Classification of Siliciclastic Sediments
and Sedimentary Rocks
Classification of sediments by
particle size
Classification of sedimentary
rocks by texture and composition
6. Classification of Siliciclastic Sediments
and Sedimentary Rocks
6. Classification of Siliciclastic Sediments
and Sedimentary Rocks
Four major compositional groups
of siliciclastic sediments:
Arkose
Lithic
Quartz arenite
Graywacke
7. Classification of Chemical
and Biological Sediments,
Sedimentary Rocks
Chemical sedimentary rocks
Limestone
Chert
Organics
Phosphorite
7. Classification of Chemical
and Biological Sediments,
Sedimentary rocks
Biological sedimentary rocks
Dolostone
Iron formation
Evaporite
Organic Reef Development
Organic Reef Rock
7. Classification of Chemical
and Biological Sediments,
Sedimentary Rocks
Carbonate sediments and rocks
Evaporite sediments and rocks
Other sediments and rocks
7. Classification of Chemical
and Biological Sediments,
Sedimentary Rocks
Carbonate sediments and rocks
Limestones
Dolostones
7. Classification of Chemical
and Biological Sediments,
Sedimentary Rocks
Evaporite sediments and rocks
Marine
Non-marine
7. Classification of Chemical
and Biological Sediments,
Sedimentary Rocks
Other sediments and rocks
Siliceous
Phosphorite
Iron oxide
Coal and peat
Thought questions for this chapter
What role do organisms play in the origin of some types of
limestone?
A bay is separated from the open ocean by a narrow,
shallow inlet. What kind of sediment would you expect to
find on the floor of the bay if the climate were warm and
arid? What kind of sediment would you find if the climate
were cool and humid?
How are chert and limestone similar in origin? Discuss
the roles of biological versus chemical processes.
Key terms and concepts
Arkose
Bedding sequence
Bioclastic sediment
Biological sediment
Bioturbation
Carbonate rock
Carbonate sediment
Cementation
Chemical sediment
Chemical weathering
Chert
Clay
Claystone
Coal
Compaction
Key terms and concepts
Conglomerate
Continental shelf
Cross-bedding
Crude oil
Diagenesis
Dolostone
Evaporite rock
Evaporite sediment
Flexural basin
Foraminifera
Graded bedding
Gravel
Graywacke
Iron formation
Limestone
Key terms and concepts
Lithic sandstone
Lithification
Mud
Mudstone
Natural gas
Oil
Organic sedimentary rock
Peat
Phosphorite
Physical weathering
Porosity
Quartz arenite
Reef
Rift basin
Ripple
Key terms and concepts
Salinity
Sand
Sandstone
Sedimentary basin
Sedimentary environment
Sedimentary structure
Shale
Siliciclastic sediments
Silt
Siltstone
Sorting
Subsidence
Terrigenous sediment
Thermal subsidence basin