Download Classification of Sedimentary Rocks

SES 4UI - Mr. J. Snyder
Learning Goals
 Student will be able to:
1) Explain the formation of all 3 types of sedimentary
rocks
2) Identify common types of sedimentary rocks.
Success Criteria
 Student will show their understanding by:
1) Understanding term used in Sedimentary rock
formation and identification
2) Explaining the geological environment in which
different sedimentary rocks form.
3) State the uses or importance of common
sedimentary rocks
Before We Start
Rock Identification Lab
Key Concepts
 Immediately following this
 Some of these slides provide
presentation, Students
should study the Rock
Identification Trays that
include sedimentary rocks.
 Samples 10 - 18 are
sedimentary rocks and
include clastic, chemical and
organic sedimentary rocks.
background information that
helps you to understand key
concepts. In order to allow
you to focus on key concepts:
1) Black font is used for key
concepts
2) Red font is used for
background information
 Remember once again -
Looking Deeper
geologists do not learn to
identify rocks just for the sake
of classification!
 A rock will tell the Geologist
the conditions in which the
rock formed! This is a key to
understanding conditions in
the past.
 For example when a geologist
sees this limestone road cut
and its fossils, it tells the
geologist that this region was
once a shallow, warm sea
teeming with ancient marine
creatures. The geologist can
also determine the economic
value of the rocks in that
region.
Sedimentary Rocks
 Rocks composed of particles derived from pre-existing
rocks or by the crystallization of minerals that were
held in solutions.
 A general characteristic of this group is the layering
or stratification.
The Weathering Process
 Terms: weathering
erosion
transport
deposition
lithification
cementation
 Weathering causes rock to be eroded at the earth’s
crust.
 Erosion is both a physical and chemical process.
Chemicals dissolved in water tend to break down the
less resistant minerals (mafic minerals, micas, etc.)
and leave resistant minerals (such as quartz and
feldspar) behind. Fragments of rock eroded from an
outcrop are called clasts.
The Weathering Process
 Terms: weathering
erosion
transport
deposition
lithification
cementation
 Clasts are transported by rivers, streams, wind and
ocean currents
 Eroded sediments are transported and deposited by
water wind and ice. Deposition often occurs far from
the source of the rock. Major rivers can carry
continental sediments and deposit them in oceans
thousands of kilometers downstream.
Erosion
Wind Erosion
Size of clasts and sequence of
deposition
Glacial Erosion
Weathering
 Notice in the figure to
the right that rate that
minerals weather
(break down
chemically) is in the
exact opposite order to
Bowen’s Reaction
series. Basically more
silica-poor minerals
erode more slowly.
 Note: erosion tends to
be a physical process
while weathering is a
chemical process.
Deposition and Cementation
 As water slows down, the largest sediments are
deposited first followed by smaller and smaller
particles. As a result, sedimentary rocks are often
sorted into layers of different sized particles.
 As sediments are deposited in ever thicker layers,
pressure and temperature causes lithification.
 During lithification, water is squeezed out of the
sediments, the grains are compacted together and
then cemented into sedimentary rock. The cement
between the grains is often quartz and calcite.
Sedimentology and Stratigraphy
 These two sciences come together when :
1) Sedimentologists (sedimentary Geologists) identify
rock types in each layer and perhaps their identifying
fossil assemblages
2) Stratigraphers try to trace these layers over (often by
looking at the sequence of layers or again by using
fossil assemblages.
3) Using these sciences together, geologists can date or
find fossils, locate petroleum bearing rocks (and
areas where petroleum is trapped)
Sedimentology and Stratigraphy
The Morrison Formation
is famous because it hosts
some of the best
Dinosaur fossils in the
world.
Classifying Sedimentary Rocks
There are three groups of
sedimentary rocks:
 Clastic
 Chemical
 Organic (Biochemical)
Clastic Sedimentary Rocks
Clastic sedimentary rocks are those composed of rock
fragments that have been cemented together. They are
classified according to the predominant grain size present.
Using this scheme, they can be classified as:
Sediment
Particle Size
Rock Name
conglomerate
(rounded) or breccia
(angular grains)
>256 mm
boulder
64-256 mm
cobble
2-64 mm
pebble
0.0625 – 2 mm
sand
sandstone
0.0039 – 0.0625
mm
<0.0039 mm
silt
siltstone
mud
shale
Clastic Sedimentary Rocks
Conglomerate
Sandstone
Siltstone
(not included in the rock sets)
Breccia
Shale
Further Classification (Not in this course)
 In this course we will stick to the terms above, but
recognize that professional sedimentary geologists
require more precise terms. Prefixes can also be
added to indicate the dominant mineralogy. For
example, a quartz-rich sandstone is a quartzose
sandstone, a feldspar-rich sandstone is an arkose, a
mica-rich sandstone is a micaceous sandstone, and a
lithic-rich sandstone or shale is a greywacke.
 Quartz-rich sandstones are generally older because
they have undergone more erosion and chemical
weathering
Clastic Sedimentary Rock Types
change as you move downstream
 The clasts become smaller as they are transported
downstream – this is due to the fact that the river or
stream becomes slower and loses more energy
 The clasts change shape from more angular to more
rounded as they are transported downstream (due to
abrasion (erosion)
 The clasts become more sorted (the clasts have a more
uniform size) as you move downstream.
1) Clastic Sediment Rocks
Talus slopes
Mtn. Streams
Beaches
Alluvial Fans
Rivers (plains)

Oceans
Delta
Note that as a river moves downstream, its slope decreases and water
velocity decreases. The net effects] is that clasts are more rounded
downstream and are better sorted by size and Mineralogy
2) Chemical Sedimentary Rocks
a) Precipitation of Minerals
 The most common is Limestone, where CaCO3
(calcite) is precipitated in shallow ocean
environments.
 Limestone is very common – it is forming on
continental shelves around the globe.
 Most of southern Ontario is underlain by thick
deposits of limestone, indicating that Ontario was at
the bottom of a shallow sea millions of years ago.
 Fossils are common in Limestone and Dolomite.
 Various limestone samples
Limestone
 Limestone has value as a building material (slabs for
buildings & patios), source of cement , chalk and as
crushed stone for roadways and construction
Limestone quarry for cement Limestone quarry for slabs
Chalk
White Chalk Cliffs of Dover
Limestone building
Limestone gravel quarry
2) Chemical Sedimentary Rocks
a) Precipitation of Minerals
 Dolomite (CaMg(CO3)2) forms (precipitates)
in warm, near shore marine sediments. It looks
very similar to limestone but tends to be harder.
 Chert (SiO2) forms in deep marine areas where
silica precipitates out. Chert is hard to identify
by small samples because it does not show
layering.
 dolomite
chert
Dolomite and Chert
 Dolomite is named after

dolomite
Chert


Dolomite Mountains
in Italy
Flint = black chert
Jasper = red chert

the Dolomite mountains of
Italy.
Dolomite can usually be
distinguished from
Limestone due to a weaker
acid reaction and a harder,
crystalline appearance.
Chert is very hard (7),
since it is made entirely of
silica (SiO2) like quartz
Chert has conchoidal
fracture like glass and
quartz.
Chert comes in other
famous varieties such as
flint (used by Stone Age
humans to make the first
tools) and Jasper.
2) Chemical Sedimentary Rocks
b) Evaporites
 These rocks form when seas dry up or lakes dry up in
arid drainage basins.
 The minerals calcite, halite (NaCl), gypsum
(CaSO4∙2H2O) and potash (mostly KCl) can
precipitate out in layers.
 Halite (NaCl), Gypsum (CaSO4∙2H2O) and potash
(mostly KCl) can form in very thick layers and are
mined for road salt, wallboard and fertilizer
respectively.
Halite
Gypsum
Potash
Salt Mines in Goderich, Ontario
 A vast shallow inland sea covered central N. America 400
million years ago. During periodic drying periods, the sea
would evaporate and vast salt deposits would be produced.
 Most salt is used for roadways in winter.
A chunk of unrefined
salt from Goderich
Inside the Sifto mine
in Goderich
A vast pile of salt from a mine
located below Cleveland, Ohio
Gypsum Mines in Ontario
 The evaporation of seas also produces vast quantities
of Gypsum which is used to make Drywall.
Underground Gypsum mine
in Hagersville, Ont.
Open Pit
Gypsum mine
in Ontario
The largest natural mineral crystals (10
meters long) ever discovered were these
Gypsum crystals in a cavern found in a mine
in Mexico
Potash Mining in Saskatchewan
 Canada is the world’s leading producer of Potash.





Almost all of it is mined near Esterhazy, Sask.
Potash forms from the extreme evaporation of sea water
(Potash is precipitated after Halite).
Potash is mostly composed of KCl (Sylvite) , but also
includes K2CO3 and K2SO4.
Underground and solution mining is used. Solution
mining (also used for salt and sulfur) is done by injecting
hot water to dissolve the salt, pumping it to the surface and
evaporating out the solid.
Potash is used as fertilizer, providing K which is an
essential nutrient in plant growth - it stimulates early
growth, increases protein production,
improves the efficiency of water use, hardiness and disease
resistance.
Potash Mining in Saskatchewan
 The USA
Potash (KCl) looks like
red Halite (NaCl) but has
a bitter taste.
Solution Potash
Mining
Underground Potash
Mining
and Israel
have vast
evaporation
ponds for
production
of Potash
 (see below)
3) Organic Sedimentary Rocks
 These rocks form from organic processes or are the
remains of living skeletons.
1) Coal - The remains of organic materials die in anoxic
(low O2 environments) such as bogs or marshes
where the plants cannot be decomposed. These
marshy areas are buried and compacted. Millions of
years of burial, compaction and pressure required to
turn “peat” into coal.
2) Limestone - the skeletons of marine organisms form
vast limestone deposits or former coral reefs are
converted into limestone formations.
Coal
Formation
Coal Mining
 Note the size of these massive open-pit operations. North
America, especially the USA, has massive deposits - enough to
fuel electricity consumption for centuries - but at the cost of
high air pollution and acid rain (SO2) and massive CO2
emissions. China’s modern industrial advance (and terrible airpollution problems) are fueled mostly by their vast coal deposits.
Historical Coal Mining
 Coal fueled the
Industrial Revolution
of the 1800’s. Many
operations were
underground mines
(Great Britain, Nova
Scotia). Today, openpit and mountain-top
removal operations
produce the most coal.
Notice that the thickness of the coal seam does not allow the miners to stand up.
Imagine your back after a day of work. Small Pit Ponies were bred to haul coal
carts. Notice the supports used to prevent cave-ins (an ever-present danger ). In
Nova Scotia, the coal seams ran out underneath the ocean.
Modern Coal Mining
 In the USA (Appalachia), coal layers are
exposed for mining by removing entire
mountain tops. Environmental damage
is substantial as waste rock is dumped
into valleys.
Organic Limestone
 Many invertebrate organisms form CaCO3 shells (corals,
clams, snails, etc). However the most important group are
the microscopic diatoms (more commonly known to us as
phytoplankton).
 When diatoms die, there skeletons sink to the bottom of
the ocean (usually shallow continental shelves). Over
millions of years these diatoms form thick layered deposits
of limestone. Diatoms are responsible for most limestone
deposits.
 Since chalk is a pure form of limestone, your teacher is
basically smearing the skeletons of dead marine organisms
on the blackboard.
Limestone Reefs
 Limestone reefs are made almost entirely of fossil
corals which can be seen on close inspection.
 These reefs often host petroleum deposits.