Chapter 8
Sedimentary
Rocks Part2
 Types of sedimentary rock
 Sedimentary structures
Types of
sedimentary
rocks
Sedimentary
rocks
• Sediment originates from mechanical
and/or chemical weathering
• Rock types are based on the source of the
material
• Clastic rocks – transported sediment as
solid particles
• Chemical/Biochemical rocks – sediment
that was once in solution
Chapter 8 Sedimentary rocks
 Clastic
sedimentary rocks
Size of clasts (particles)
common name
 gravel
size
bigger than 2 mm
(1/10 inch)
 sand
 silt, clay
See Table 8.3
sand-sized (1/16-2)
very fine-grained (<1/16)
Detrital rock
conglomerate
or breccia
sandstone
shale,
mudstone,siltstone
sediments
gravel
sand
silt
clay
sedimentary
rocks
conglomerate
sandstone
siltstone
shale
Chapter 8 Sedimentary rocks
 Clastic sedimentary rocks
Siltstone, Mudstone & Shale
 silt & clay-sized particles (clay, silt),
particles too small to identify w/ eye
 over 1/2 of all sedimentary rocks
 deposited in quiet (slow moving) water
- deep ocean & continental slope
- lakes
- floodplains (siltstone)
 shale beds often underlay groundwater
conduits
 shale may contains fossils, oily organics,
breaks along bedding planes
 raw material for brick, tile, pottery, china
 shale+limestone= Portland cement
Shale w/plant remains
Chapter 8 Sedimentary rocks
 Clastic sedimentary rocks
Sandstone
 composed of sand grains
 2nd most abundant sedimentary rock
 deposited by moderate currents:
- rivers & deltas
- beaches
- wind (sand dunes)
 mostly quartz (strong & chemically stable, but may
also contain volcanic rock)
See Fig. 8.15 for major groups of sandstone
Chapter 8 Sedimentary rocks
 Clastic sedimentary rocks
Sandstone
 sorting
degree of similarity in particle size
Chapter 8 Sedimentary rocks
Clastic sedimentary rocks
Sandstone
 shape
degree of roundedness
Chapter 8 Sedimentary rocks
 Clastic sedimentary rocks
Conglomerate
 composed mostly of gravel
pebbles to boulders
 poorly sorted
 deposited by strong, turbulent currents:
- big flooding rivers
- steep streams (near mountains)
- glaciers
Chapter 8 Sedimentary rocks
 Clastic sedimentary rocks
Breccia
 conglomerate with angular grains
 didn’t travel far
Chapter 8 Sedimentary rocks
 Chemical
sedimentary rocks
 derived from material carried in solution to lakes/seas
 precipitation from solution to form “chemical sediments”
 2 types of precipitation
- chemical
- biochemical
See Table 8.4
Chapter 6 Sedimentary rocks
 Chemical sedimentary rocks
Limestone
 10% of all sedimentary rocks (by
volume)
 most abundant chemical
sedimentary rock
 composed primarily of calcite
(calcium carbonate CaCO3)
 Marine biochemical limestones form as coral reefs,
coquina (broken shells), and chalk (microscopic
organisms)
 Inorganic limestones include travertine (caves) and
oolitic limestone (tropical beach environment)
 Dolostone: dolomite=CaMg(CO3)2 Typically formed
secondarily from limestone
Chapter 6 Sedimentary rocks
 Chemical sedimentary rocks
Organic rock of biochemical origin
 coquina (rock of shell fragments): bioclastic
Chapter 6 Sedimentary rocks
 Chemical sedimentary rocks
Fossiliferous limestone
Coral reef
Limestone cliff
(Guadalupe Mountains
Natl Park, TX)
• How to build a carbonate platform
See Figure story 8.16
• How to build an atoll
Darwin’s theory on atolls (1831)
See Box 8.1
Chapter 8 Sedimentary rocks
 Chemical sedimentary rocks
Common chemical sedimentary rocks
•Chert
Made of microcrystalline
silica (SiO2)
Agate
Varieties include flint and
jasper (banded form is
called agate)
Chapter 8 Sedimentary rocks
 Chemical sedimentary rocks
Evaporites
 water evaporates and triggers the deposition of salts
 sequence of precipitation: calcite (calcium
carbonate), gypsum (calcium sulfate), rock salt (halite,
NaCl); bitter salts (potassium and magnesium salts)
(a) calcite
Chapter 8 Sedimentary rocks
 Chemical sedimentary rocks
Evaporites
 water evaporates and triggers the deposition of salts
 sequence of precipitation: carbonate, gypsum
(calcium sulfate), rock salt (halite, NaCl); bitter salts
(potassium and magnesium salts)
 ancient seawater basins evaporated and deposited salt
Salt flats, Utah
Death valley, Calif.
Chapter 8 Sedimentary rocks
 Chemical sedimentary rocks
Evaporites- the story of the Mediterranean
During the Miocene, lower sea
level almost shut down the inflow
of Atlantic surface water into the
Mediterranean over the Strait of
Gibraltar. Evaporation removed
vast quantities of water and left
behind evaporative sediments that
underlay the sediments in the
Mediterranean today.
Fig. 8.19
Chapter 8 Sedimentary rocks
 Chemical sedimentary rocks
Coal
 buried and compacted plant material
 different kinds of coal, depending on formation process
Sedimentary structures
(Physical features)
1. Layers (bedding, or “strata”)
2. Cross-bedding
3. Graded beds
4. Ripple marks
5. Mud cracks
Sedimentary structures
(Physical features)
1. Layers (bedding, or “strata”)
 deposited horizontally
 each layer is unique
 separated by bedding planes
Sedimentary structures
(Physical features)
2. Cross-bedding
 tilted bedding
 commonly ancient sand dunes
 river deltas, flow channels
Sedimentary structures
(Physical features)
3. Graded beds
 particles within a layer
gradually change:
coarse at bottom
 fine at top

 rapid deposition from
water w/ varying sed. sizes
Colorado River
Sedimentary structures
4. Ripple marks
 wavy surfaces in sand: current
ripple marks
 tell direction of current because
they are perpendicular to flow
See Fig. 8.8
(Physical features)
Sedimentary structures
5. Mud cracks
 sediment alternatively
wet/dry
 shallow lakes,
desert basins
 flood plains
(Physical features)
Some MC questions…
Which of the following sets of processes is written in order of increasing temperature?
A.
B.
C.
D.
sedimentation, metamorphism, diagenesis
diagenesis, sedimentation, metamorphism
sedimentation, diagenesis, metamorphism
metamorphism, diagenesis, sedimentation
Some MC questions…
What type of sediments are accumulations of solid fragments produced by weathering?
A.
B.
C.
D.
biochemical sediments
chemical sediments
clastic sediments
all of the above
Some MC questions…
Which of the following statements about transportation of sediment is false?
A.
B.
C.
D.
Smaller particles settle faster than larger particles.
As a current slows, the largest particles start to settle.
Faster currents carry larger particles than slower currents.
Rivers and ocean currents move much more material than do air currents.
Some MC questions…
In what type of environment did the ripples depicted above most likely form?
A.
B.
C.
D.
beach (waves)
desert (wind)
alluvial (stream)
delta (river + tides)
Some MC questions…
Which of the following minerals is least likely to occur in a marine evaporite
environment?
A.
B.
C.
D.
calcite
gypsum
halite
quartz