Sedimentary Rocks
Origins and Characteristics
Today’s
Today
s goal
Formation of Sedimentary Rocks
Types of sedimentary rocks
Sedimentary structures
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Sedimentary Rocks
< 10% of crustal rocks
Cover 70% of the continental surfaces
Why are Sedimentary Rocks important in
engineering?
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Origin of Sedimentary Rocks
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Weathering forms clasts
_________ leads to transportation of clasts
Clasts can then be deposited
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Origin of Sedimentary Rocks
4. Particles are converted into rock via Diagenesis
 Lithification
 compaction
 cementation
 Natural cements include calcite, silica, and
iron oxide
 Recrystallization – development of more stable
minerals from less stable ones
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Origin of Sedimentary Rocks
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Sedimentary Rock Types
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Textures: size and arrangement of particles
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Rock types are based on the source of the
material
Detrital sedimentary rocks
 Chemical sedimentary
y rocks
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Detrital Sedimentary Rocks
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Clast
Matrix
Cement
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Detrital Sedimentary Rocks
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Shale and other Mudrocks
Clay to silt-size
silt size particles deposited in thin
layers (laminae)
 Deposited by gradual settling from quiet
water
 Siltstone
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Detrital Sedimentary Rocks
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Sandstone
Composed of sand
sand-size
size particles
 Quartz (durable) is the dominant mineral
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Detrital Sedimentary Rocks
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Conglomerate and breccia
Particles greater than 2mm in diameter
 Conglomerate
 Breccia
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Detrital Sedimentary Rocks
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Particle size and
environment
Rounding, sorting,
composition and
maturity
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Environment??
1. Sandstone
2. Siltstone
3. Breccia
4 Conglomerate
4.
5. Shale
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Chemical Sedimentary Rocks
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Precipitation of calcium carbonate material
occurs in two ways
Inorganic processes
 Organic processes (biochemical origin)
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Forms __________ rock
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Chemical Sedimentary Rocks
Coral reef
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Chemical Sedimentary Rocks
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Chemical Sedimentary Rocks
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Where would the rocks form?
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Chemical Sedimentary Rocks
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Travertine
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Dolostone: typically formed
from limestone when
magnesium replaces some
calcium
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Chemical Sedimentary Rocks
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Evaporites: minerals that precipitate due to
evaporation of a body of water
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Includes: halite, gypsum
Chert:
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Organic Sedimentary Rocks
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Coal
Stages in coal formation:
1. Accumulation of plant
material (often in swamps)
2. Partial decomposition
into peat
3. Shallow burial forming lignite
4 Deeper burial forming
4.
bituminous coal
5. Metamorphism forms
anthracite coal
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Organic Rocks
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Formation of coal
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Sedimentary Rock Types
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Sedimentary Rocks – what are these?
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A
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D
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E
C
Sedimentary Structures
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Clues to what environment the rock was
deposited in
Bedding planes:
Laminae:
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Sedimentary Structures
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Cross-bedding: inclined layers formed from
g
g wavelike bedforms
migrating
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Sedimentary Structures
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Sedimentary Structures
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Graded beds – form from
rapid deposition from water
 coarse material settles
first
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Sedimentary Structures
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Ripple marks – small waves of sand that are
formed by currents (asymmetric) or waves
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Mud cracks – shrinkage on exposure to air
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Summary
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Sedimentary rocks can have a clastic (detrital),
chemical, biochemical or organic origin
The grain size, rounding, composition can tell us
about the maturity of the rock (how far it has been
transported)
Sedimentary structures provide clues to what
environment
i
t the
th rockk was formed
f
d in
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Questions?
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