Sediments and Sedimentary
Rocks
Chapter 5
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Concepts you will need to know for the
exams
Weathering
Erosion
Transportation
Sorting
Angularity
Sedimentary environments,
Cross-bedding (sedimentary structures)
Bioturbation, bedding sequences, diagenesis
Classes of sediments and sedimentary rock:
-based on grain size
-based on chemical composition, e.g.,
carbonate rocks ("carbonates") and evaporitic rocks
("evaporites")
Lecture Outline
1. Sedimentary rocks
2. Your sedimentary environment and Burial
Diagenesis
3. Interpretation of clastic texture
4. Sedimentary structures
5. Sedimentary Rock classification
1. Sedimentary Rocks
•Cover most of the land surface and
seafloor
•Your physical geography determines the
dominant process at work in the
sedimentary rock cycle
•e.g. (1) Mountains => weathering and/or
erosion
•e.g., (2) Southern Louisiana =>
•e.g., (3) offshore Louisiana =>
1. Sedimentary Rocks
•Cover most of the land surface and
seafloor
•Your physical geography determines the
dominant process at work in the
sedimentary rock cycle
•e.g. (1) Mountains => weathering and/or
erosion
•e.g., (2) Southern Louisiana =>
transportation or deposition or erosion
•e.g., (3) offshore Louisiana =>
1. Sedimentary Rocks
•Cover most of the land surface and
seafloor
•Your physical geography determines the
dominant process at work in the
sedimentary rock cycle
•e.g. (1) Mountains => weathering and/or
erosion
•e.g., (2) Southern Louisiana =>
transportation or deposition or erosion
•e.g., (3) offshore Louisiana => erosion or
sedimentation
erosion
weathering
transportation
Erosion includes BOTH weathering and transportation
Sedimentary rocks are typically
layered, (although layering is not
diagnostic of only sedimentary rocks)
Lecture Outline
1. Sedimentary rocks; surface processes
2. Your sedimentary environment and Burial
and diagenesis
3. Interpretation of clastic texture
4. Sedimentary structures
5. Sedimentary Rock classification
A sedimentary environment is a
geographic location that has a
peculiar combination of geological
processes
Walther’s Rule (1894)
“The different (sedimentary) rocks
(types) were formed beside each
other in space, but in a crustal profile
we see them lying on top of each
other….”
Bedding sequences--are successions of rock ( in
a vertical profile) that help
geologists work out the
past environment
Lateral associations
Vertical stacking
http://www.mines.unr.edu/geology/faculty/jthomepage/GEOL
_202_files/10%20depmodel%20%2712.pdf
Mount Sharp, Mars– What type of
sedimentary environment created these
layer geometries?
Where do you live?
•What dominant
sedimentary process is at
work where you live?
http://sedimentlog.blogspot.com/
If deposition is the dominant process, e.g.,
offshore Lousiana then rocks are in the
process of being formed:
Diagnesis includes
(1) compaction = volume loss (mechanical
squeezing)
and is accompanied by dewatering (= water
loss) (by chemical or physical means)
(2) changes in mineral composition (chemical
process with heat and or fluids)
(3) cementation (physical)
If a sediment eventually becomes a rock we
say it is lithified.
DIAGENESIS
compaction
DIAGENESIS
compaction
dewatering
DIAGENESIS
compaction
dewatering
Cementation &
mineral
changes
Lecture Outline
1. Sedimentary rocks; surface processes
2. Your sedimentary environment and Burial
and diagenesis
3. Interpretation of clastic texture
4. Sedimentary structures
5. Chemical and biological classification
Geological FUZZY rules
for determining degree of
weathering and transport a
rock or sediment has
experienced respectively
(1) Product composition
(2) Degree of sorting
•Sorting is a measure of how similar grain sizes
are within a sediment or rock and tells us about
the relative strength of the current before it
dropped (deposited) it cargo.
•In a current of water or air, the larger and
denser grains fall faster than the smaller
grains. That is, for the same density, size
determines settling velocity.
(3) Angularity or roundness
(antonym) is a measure of the
distance of transportation
Which of the following
sediment characteristics is
best used to determine
former current speed?
1. sorting
2. angularity or roundness
3. diagenesis
Lecture Outline
1. Sedimentary rocks; surface processes
2. Your sedimentary environment and Burial
and diagenesis
3. Interpretation of clastic texture
4. Sedimentary structures
5. Chemical and biological classification
Cross-bedding
Cross-bedding: sets of bedded material
within rock layers that are inclined at
angles as large as 35 degrees from the
horizontal. These latter indicate windblown conditions in either a desert or a
beach.
2 directions of
fluid movement
Fossil example of the past activity of organisms
mixing sediment --- an example of fossil
BIOTURBATION
Lecture Outline
1. Sedimentary rocks; surface processes
2. Your sedimentary environment and Burial
and diagenesis
3. Interpretation of clastic texture
4. Sedimentary structures
5. Sedimentary Rock classification
Three types of sedimentary
Rocks
•Clastic
•Biochemical
•Chemical
Major Classes of sediments
and sedimentary rocks
For clastic sedimentary rocks there is a
classification scheme based on the SIZE of their
clasts, (or rock fragments) that comprise them.
Clst size indicates ancient relative current velocity
weak moderate
>=1.8 km/hr (strong currents)
MOBILE SEISMIC LABORATORY
Radio
antenna
240-channel Sercel 388 radiotelemetric seismic acquisition system
Electricalmechanically
detonated surface
seismic shear
17th St Canal Breach
W
E
~6m
sand
N
S
~16 m
sand
~6-9.00 a.m., Aug. 29, 2005
(Adapted from
Rogers et al.,
2008;
What type of sediment is
peat?
1. chemical
2. clastic
3. biological
The End of Chapter 5