Sedimentary rocks

choppedspleenMécanique

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Chapter 8

Sedimentary

Rocks Part2



Types of sedimentary rock





Sedimentary structures






Types of
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





Sedimentary

rocks

Chapter 8

Sedimentary rocks



Clastic



sedimentary rocks



Size of clasts (particles)



gravel


bigger than 2 mm
conglomerate




(1/10 inch)
or breccia



sand

sand
-
sized (1/16
-
2)
sandstone



silt, clay

very fine
-
grained (<1/16)
shale,







mudstone,siltstone

common name

size

Detrital rock

See Table 8.3

conglomerate

sandstone

siltstone

shale

clay

silt

sand

gravel

sediments

sedimentary

rocks

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 w/plant remains



shale beds often underlay groundwater


conduits




raw material for brick, tile, pottery, china



shale+limestone= Portland cement



shale may contains fossils, oily organics,
breaks along bedding planes

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



2 types of precipitation






-

chemical






-

biochemical



precipitation

from solution to form “chemical sediments”

See Table 8.4

Chapter 6

Sedimentary rocks



Chemical sedimentary rocks



Limestone



composed primarily of calcite
(calcium carbonate CaCO
3
)



10% of all sedimentary rocks (by
volume)



most abundant
chemical

sedimentary rock



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(CO
3
)
2

Typically formed
secondarily from limestone

Chapter 6

Sedimentary rocks



Chemical sedimentary rocks




coquina (rock of shell fragments): bioclastic

Organic rock of biochemical origin

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

See Box 8.1

Darwin’s theory on atolls (1831)

Chapter 8

Sedimentary rocks



Chemical sedimentary rocks


Common chemical sedimentary rocks


Chert


Made of microcrystalline
silica (SiO
2
)


Varieties include flint and
jasper (banded form is
called agate)


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



ancient seawater basins evaporated and deposited salt

Salt flats, Utah

Death valley, Calif.



sequence of precipitation: carbonate, gypsum
(calcium sulfate), rock salt (halite, NaCl); bitter salts
(potassium and magnesium salts)

Chapter 8

Sedimentary rocks



Chemical sedimentary rocks



Evaporites
-

the story of the Mediterranean

Fig. 8.19

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.

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”)



each layer is unique



deposited horizontally



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


(Physical features)

4. Ripple marks



wavy surfaces in sand: current



ripple marks



tell direction of current because

they are perpendicular to flow

See Fig. 8.8

Sedimentary structures


(Physical features)

5. Mud cracks



sediment alternatively



wet/dry



shallow lakes,


desert basins



flood plains

Some MC questions…


Which of the following sets of processes is written in order of increasing temperature?



A. sedimentation, metamorphism, diagenesis

B. diagenesis, sedimentation, metamorphism

C. sedimentation, diagenesis, metamorphism

D. metamorphism, diagenesis, sedimentation


Some MC questions…


What type of sediments are accumulations of solid fragments produced by weathering?



A. biochemical sediments

B. chemical sediments

C. clastic sediments

D.
all

of the above

Some MC questions…


Which of the following statements about transportation of sediment is
false
?



A. Smaller particles settle faster than larger particles.

B. As a current slows, the largest particles start to settle.

C. Faster currents carry larger particles than slower currents.

D. 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. beach (waves)

B. desert (wind)

C. alluvial (stream)

D. delta (river + tides)


Some MC questions…


Which of the following minerals is
least

likely to occur in a marine evaporite
environment?


A. calcite

B. gypsum

C. halite

D. quartz