Transcript Sedimentary rocks

Earth Systems 3209 – Unit 3
The Rock Cycle
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Why study sedimentary rocks? Economic use, fossils and
earths history.
5% of Earths crust is sedimentary rock.
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75% of Earths surface is sedimentary rock.
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Sedimentary Processes
Formed from sediments of pre-existing rocks
(i.e. metamorphic, igneous or sedimentary).
 Created by the processes of WEATHERING
(i.e. break-up) and EROSION (i.e. removal
and transportation).
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 Weathering (Two Types: Chemical and
Mechanical)
 Erosion (Agents: water, ice, and wind)
 Aided by gravity, sediments travel to bodies of water
where they are deposited (i.e. come to rest). Over
geological time, sediments transform into sedimentary
rock.
Sedimentary Processes
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Sediments are formed into rock by the process of
LITHIFICATION, which includes two subprocesses:
 Compaction: pressure from the burial of sediments
solidifies material into rock. This results in reduced
porosity and permeability. (Note: effective with small grain
sizes)
 Cementation: minerals precipitate out (i.e. crystallize) of
circulating ground water, which cements sediments
together (SiO2, CaCO3, FeO3)
Cementation and Compaction
Sediment Particles
Can anyone give examples of sedimentary rocks?
Cement
Coal
Sandstone
Breccia
Conglomerate
Shale
Rock Salt
Siltstone
Gypsum
Limestone
Coquina
Dolomite
Chaulk
CLASSES of Sedimentary Rocks
 Clastic (also called detrital):
 (e.g., shale, siltstone, sandstone, conglomerate, breccia)
 Formed from mechanical weathering
 Classified based on particle size (and particle shape)
 Chemical:
 Evaporites (e.g., rock salt, gypsum, sylvite)
 Precipitates (e.g., compact limestone, travertine, dolomite,
chert)
 Chemical weathering – dissolving of chemicals
 Biochemical
 (e.g., coquina, chert, coal, coral limestone, chaulk)
 Accumulation of living material – i.e. organic remains
Clastic Characteristics:
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Clastic rocks are classified based on grain size (e.g.,
shale - clay, siltstone - silt, sandstone - sand) with
the exception of Breccia (angular gravel particles),
and conglomerate (rounded gravel particles), which
are classified based on grain shape.
Grain Shape (rounded, angular)
Sorting (well sorted, poorly sorted) DOES NOT APPLY TO
CHEMICAL OR BIOCHEMICAL, BUT IT DOES APPLY TO CLASTICS!
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Cementation (e.g., siliceous, calcareous, or iron
oxide)
Porosity (pore space - % of open space or holes)
Permeability (communication or interconnectiveness
between pore space – Darcy’s)
What can we tell from grain size/shape?
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Grain size decreases with decreasing current velocity
(i.e. decreasing energy). In general, larger grain sizes are
closer to the source of weathering. Smaller grain sizes are
further from the source of weathering.
The roundness of grains increases with increasing
distance from the source of weathering. Angular grains
have not traveled far from the source.
High Velocity
Low Velocity
Breccia, Conglomerate  Sandstone  Siltstone  Shale
HORRIZONTAL SORTING (COARSE TO FINE FROM LEFT TO RIGHT)
Clastic Depositional Environments AND
Rocks
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Fluvial (Rivers/streams) – Conglomerate, Breccia,
Sandstone, Siltstone, Shale
Lagoonal/Bays – Siltstone, Shale
Beaches – Conglomerate, Sandstone
Deep Marine – Involves turbidites (Conglomerate,
Sandstone, Siltstone, Shale), but is dominated by
chemical sedimentary rocks.
Shallow Marine – Conglomerate, Sandstone,
Siltstone, Shale
Fluvial
Beach
Fluvial
Shallow
Marine
Turbidites
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Deep marine sedimentary rocks resulting from
underwater avalanches. Characterised by graded
bedding - fining upwards sequences of conglomerate at
the bottom, followed by sandstone, siltstone and shale.
Chemical Sedimentary Rocks
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Chemical:
1) Evaporites (e.g., halite, gypsum, sylvite)
 NOTE THAT THE ABOVE ARE THE RESULT OF THE
EVAPORATION OF WATER.
2) Precipitates (e.g., compact limestone, travertine,
dolomite, nodular chert)
 DUE TO CHANGES IN ENVIRONMENTAL CONIDITONS
(E.G., TEMPERATURE CHANGE, CHEMICAL CHANGE,
CONCENTRATION CHANGE).
 Chemical weathering – dissolving of chemicals
Chemical Sedimentary rocks
Chemical Depositional Environments:
1. Shallow Marine (e.g., gypsum, halite, sylvite,
limestone and dolomite)
2. Deep Marine (e.g., limestone, dolomite and
nodular chert)
3. Cave - Stalactites and stalagmites
Stalactites are icicle-like pendants that hang from the
ceiling. Water seeps through cracks in the ceiling of
the cave.
Stalagmites form from the floor.
The precipitated limestone that makes up stalactites
and stalagmites is called travertine.
Stalactites and Stalagmites
Biochemical Sedimentary Rocks
Coquina – forms from the build-up, compaction, and
cementation of shells from dead organisms (mostly on
beaches).
 Chaulk – forms from the accumulation, compaction, and
cementation of microscopic marine organisms such as
formaminifera (i.e. deep marine)
 Chert – forms from the accumulation of microscopic marine
organisms, such as radiolaria and diatoms, that form a very
hard rock consisting of microcrystalline silica. Examples of
chert include jasper, flint, and agate (i.e. deep marine)
 Coral limestone – accumulations of coral can be compacted
and cemented into coral limestone (i.e. shallow marine)
 Coal – formed form the accumulation of plant material, which
is buried and chemically altered over millions of years.
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What are corals?
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Corals are examples of organisms that are
capable of creating large quantities of marine
limestone from their shells and external skeletons
which are composed of calcium carbonate.
The Formation of Coal - Swamps
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There are 4 stages of coal formation:
1) Peat – earliest stage of plant accumulation. Contains
large amounts of volatiles. (PEAT IS NOT A ROCK).
(VOLATILES – E.G., CARBON DIOXIDE, WATER).
2) Lignite – decreased levels of volatiles. It is classified
as a sedimentary rock.
3) Bituminous – higher grade of coal than lignite. It is
classified as a sedimentary rock.
4) Anthracite – final stage of coal formation. It is
classified as a metamorphic rock due to heat, pressure,
and hot chemical fluids. It burns cleaner than other
stages of coal due to less volatiles present. Small
amount available world-wide.
Increasing
Grade
Four Stages of Coal Formation
Peat
Lignite
Bituminous
Anthracite
Biochemical Sedimentary Rocks
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Depositional Environments
Swamp – Coal
Shallow Marine – Coquina, Limestone (Coral)
Beach – Coquina
Deep Marine – Chaulk, Chert
Think about the concept of systems. How do
biochemical sedimentary rocks and coral
represent a dynamic interaction of the
spheres?
Core Lab 3 – Sedimentary Rocks
Review:
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Concept Map for rocks
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Next class – Metamorphic Rocks