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Chapter 6a
Sedimentary Rocks:
Environments & Processes
PowerPoint Presentation
Stan Hatfield . SW Illinois College
PowerPoint Presentation
Ken
Pinzke . SW Illinois College
Stan Hatfield . Southwestern Illinois College
Charles
Henderson
. University
Calgary
Ken
Pinzke . Southwestern
Illinoisof
College
Charles
Henderson
. University of
Calgary
Tark
Hamilton
. Camosun
College
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6-1
What is a sedimentary rock?
Sedimentary rocks are products of mechanical
and chemical weathering
They account for about 5 percent (by volume) of
Earth’s outer 16 kilometres
Contain evidence of past environments
• Sediment transport directions
• Macro- , Micro- & Trace fossils, evolution, time &
changing ecologies
• Stable isotope records of past sea water & climates
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6-2
What is a sedimentary rock?
Sedimentary rocks are important for economic
considerations because they may contain:
• Coal
• Petroleum and natural gas
• Limestone for cement
• Gypsum for plaster & sheetrock
• Salt for roads & chemicals
• KCl in evaporites & Apatite in phosphate rock for
fertilizers
• Sources of iron, aluminum, and manganese
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Lithification: Turning Sediment into
Sedimentary Rock
Many changes occur to sediment after it is deposited
Compaction
Reduction or recycling of organic compounds
Dewatering
Cementation
Recrystallization
Diagenesis – all of the chemical, physical, and biological
changes that take place after sediments are deposited,
but prior to metamorphism
• Occurs within the upper few kilometres of Earth’s crust at
temperatures generally less than 200ºC
• Clays persist in sediments (Micas form in Metamorphism)
• Reduction of porosity & permeability
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Lithification: Turning Sediment into
Sedimentary Rock
Diagenesis Includes:
Recrystallization –
• Pressure Solution: grains dissolve at corners
• Infilling of porosity
• Development of more stable minerals from less
stable ones: Plagioclase  Clay + Calcite
Lithification • Unconsolidated sediments are transformed into
solid sedimentary rock by compaction and
cementation
– Cements include calcite, silica, clays, zeolites, iron oxide,
pyrite
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Types of Sedimentary Rocks
Sediment originates from mechanical and/or
chemical weathering
Rock types are based on the source of the
material
• Detrital sedimentary rocks – transported sediment
as solid particles, earlier rocks & minerals
• Chemical sedimentary rocks – sediment that was
once in solution
• Biochemical sedimentary rocks – sediment formed
or shed from living organisms
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Detrital (Clastic) Sedimentary Rocks
The chief constituents of detrital sedimentary
rocks include components shed from weathering
on land (terrigenous debris):
• Clay minerals: kaolinite, illite, chlorite, smectite
• Quartz & Chert
• Feldspars (Kspar >> Plagioclase)
• Micas: Muscovite, Vermiculite, Chlorite,
Serpentine
Particle size is used to distinguish among the
various types of detrital rocks
• Boulders, cobbles, gravel, sand, silt, clay
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Detrital Sedimentary Rocks
Particle
size
important
inCanada
the classification
of detrital sedimentary rocks.
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Detrital Sedimentary Rocks
Shale and other Mudrocks (Argillite, Wackes)
• ~60% of all sedimentary rocks, best fossil records!
• Frequently organic rich and the source rocks for
hydrocarbons
• Mud-sized particles in thin layers that are commonly
referred to as laminae
• Deposited as a result of gradual settling in quiet
environments: floodplains, deep lakes, deep ocean basins
• Shale exhibits fissility (splits into thin layers) and mudrock
does not (sometimes bioturation or mixing destroys layers)
• Siltstone consists of silt-sized particles as well as mud
• Most common sedimentary rock, but often inconspicuous
because they weather recessively and are covered by veg!
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Detrital Sedimentary Rocks
Shale
is a Pearson
type of
mudrock.
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Inc.
shale above contains plant fossils.
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Detrital Sedimentary Rocks
Sandstone
-20% of sedimentary rocks are sandstone; second
only to mudrocks in abundance
-Composed of sand-sized particles
-Forms in a variety of environments and
transported by wind and water
-Sorting, shape, and composition of the grains can
be used to interpret the rock’s history
-Quartz is the predominant mineral in mature or
long system sediments because it is so durable
-Feldspars & Rock Fragments are abundant in
younger immature sediments
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Detrital Sedimentary Rocks
Quartz sandstone (bottom) and wind-blown layers of sandstone (above) from Zion
National
Park
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Canada
Inc.(Jurassic Desert!).
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Detrital Sedimentary Rocks
Conglomerate and breccia
– Both are largely composed of particles > 2mm
– Indicative of high energy currents or steep slopes
– Conglomerate consists primarily of rounded gravels
– Grain supported have been sorted, winnowed,
redeposited
– Matrix supported usually just deposited once as a
thick slurry or debris flow
– Breccia is composed largely of large angular particles
– Less sedimentary transport
– May result from avalanche or talus in mountainous
terrain
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Detrital Sedimentary Rocks
Conglomerate
is composed
primarily
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of rounded gravel-size particles.6-14
Detrital Sedimentary Rocks
Breccia
composed
ofInc.
angular
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gravel-sized particles.
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Chemical Sedimentary Rocks
Consist of precipitated material that was once in
solution
Precipitation of material occurs in two ways
• Inorganic processes (precipitation, crystallization
from solution in briny or saturated fluids)
• Organic processes (biochemical origin)
– Clams grow shells
– Calcareous algae
– Wood in bayous, oxbow lakes
– Fish poop on shelf!
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Chemical Sedimentary Rocks
Common chemical sedimentary rocks
• Limestone
– Most abundant chemical rock; 10% of all sedimentary
rocks
– Composed chiefly of the mineral calcite (CaCO3)
– Marine biochemical limestones form as coral reefs,
coquina (broken shells; also called bioclastic
grainstone), and chalk (microscopic organisms)
– Inorganic limestones include travertine and oolitic
limestone (comprises small spherical grains or ooids
formed in high wave-energy environments)
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Chemical Sedimentary Rocks
Bioclastic
limestone
shell
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fragments of biochemical origin.
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Chemical Sedimentary Rocks
But Reefs form in the Tropics?
Modern
coral
reefEducation
(A) and
Paleozoic
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Canada
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fossil reef in Arctic Canada (B). 6-19
Chemical Sedimentary Rocks
Common chemical sedimentary rocks
• Dolostone
– Typically formed secondarily from limestone when
magnesium replaces some calcium
• Chert
– Made of microcrystalline silica (SiO2)
– Occurs as nodules in limestone and as tabular layers
(siliceous organisms like diatoms and radiolarians often
provide silica related to chert origin)
– Varieties include flint and jasper (banded form is called
agate)
– Banded Iron Formation (Hematite & Jasper) from
Precambrian evolution of cyanobacteria  Free O2
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Banded Iron Formation
Precambrian between 3.8 and 1.7 Ga (Archean)
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Chemical Sedimentary Rocks
Common chemical sedimentary rocks
• Evaporites
– Evaporation triggers deposition of chemical precipitates
– Examples include rock salt (NaCl) and rock gypsum
(CaSO4.2H2O), anhydrite (CaSO4), sylvite (KCl; potash,
which is used as a fertilizer)
• Phosphate Rock
– Phosphate Rock is apatite rich marine sediment also
used as fertilizer
– Forms on sediment starved shelves
– Upwelling and biological activity exceeds clastic input
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Chemical Sedimentary Rocks
Common chemical sedimentary rocks
• Coal
– Different from other rocks because it is composed
of organic material
– Stages in coal formation (in order)
– 1. Accumulation of plant material (often in
swamps)
– 2. Partial decomposition into peat
– 3. Shallow burial forming lignite
– 4. Deeper burial forming bituminous coal
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Chemical Sedimentary Rocks
Successive
stagesInc.
in
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the formation of coal.
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End of
Chapter 6a
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