Earth Materials Unit: Sedimentary Rocks
and Processes
Maybe One Day…
Text: Chapters Five and Six
Lab: Laboratory Six
Name________________________________
Geology 12: Sedimentary Rock
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Sedimentary Rocks and Processes
Purpose: To classify sedimentary rocks and features
by their physical and chemical properties.
-By the end of this unit, students are expected to be
able to:
1. Outline the origin and process of sedimentary rock
formation.
2. Contrast clastic sediments with chemical
(precipitate or biochemical) sediments and the rocks
they become.
3. Describe the features of, and identify, the
following sedimentary rocks:
Conglomerate
Limestone
Breccia
Chert
Sandstone
Gypsum
Siltstone
Rock Salt
Shale
Coal
4. Diagram and describe the following sedimentary features and use them to reconstruct hypothetical
sedimentary environments:
a) Sedimentary structures: Stratification, crossbedding, ripple marks, mud cracks, graded bedding, varves.
b) Particle size, shape and sorting.
c) Fossils and organic structures
Geology 12: Sedimentary Rock
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Geology 12: Sedimentary Rocks and Processes
Part A: What is a Sedimentary Rock?
-Sedimentary rock is rock that is composed of sediments.
-Sediments are loose grains and chemical residues of rocks and
minerals, and of plants and animals.
-Sediments are formed from parent materials at a source
location. At the source, the parent material is weathered (broken
up or dissolved) into sediments or aqueous solutions.
-The weathered material is eroded (removed from its source) and
transported some distance, and then deposited.
-The weathered material is then lithified (hardened into rock by
pressure and/or cementation), or precipitates from solution.
*95% of the earth’s crust is composed of crystalline rock (igneous or metamorphic). However,
sedimentary rock is the most common rock at or near Earth’s surface!
Part B: Sedimentary Rock Formation
-Using the paragraph above, name the four basic steps in sedimentary rock formation:
a) ___________________________________________________________________________________
b)___________________________________________________________________________________
c) ___________________________________________________________________________________
d)___________________________________________________________________________________
*In the following pages, we will explore each of these steps:
Step 1: Weathering Processes
-Weathering is the chemical or physical breakdown of Earth’s
materials.
1. Mechanical (or Physical) Weathering
-Mechanical weathering is the _____________________________
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-Types of mechanical weathering include:
a) Frost Wedging _________________________________________
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-What types of sediments and debris features are formed through
frost wedging?
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Geology 12: Sedimentary Rock
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-In what environment would frost wedging be very prominent?
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-Where would frost wedging not be found?
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b) Thermal Expansion and Contraction
-How can heat cause rocks to be broken down?
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-In what environment would thermal expansion be very prominent?
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c) Pressure Release
-Describe how an exfoliation dome is created:
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-Exfoliation is a big concern in underground mining as it can result in rock
bursts.
d) Biotic Weathering
-How can living organisms cause weathering?
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2. Chemical Weathering
Chemical weathering is the breakdown of rocks and minerals by chemical
alteration of the parent material.
-How does the product of chemical weathering differ from that of mechanical
weathering?
________________________________________________________________
-Water is the most important agent in chemical weathering as it is a universal
solvent and its chemical activity is increased by the addition of small amounts of
dissolved materials. It plays a leading role in the three major types of chemical
weathering:
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a) Dissolution
-Some minerals (such as Halite) dissolve easily in pure water, but most minerals are
insoluble. However, water containing acid (H+ ions) is a much more efficient
weathering agent.
-What are three sources for H+ ions?
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-For example, Calcite (Limestone, Marble) is a mineral dissolved completely by
acidic water. No new minerals are created through this reaction!
b) Hydrolysis
-Reaction of acidic water with silicate minerals (Feldspars,
Quartz) that changes the silicate structure of the mineral
and results in the production of ions and clay minerals.
c) Oxidation
-Oxygen combines with iron to form oxides (Hematite
and Limonite).
-What type of minerals would be most affected?
_____________________________________________
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-Why does oxidation occur more quickly in the presence of water?
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Geology 12: Sedimentary Rock
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*Chemical Weathering Produces:
a) Changes to the internal structure of minerals:
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b) Physical changes to rocks:
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*Rates of Chemical Weathering are Affected by:
a) Rock Characteristics
-Mineral Composition:
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-Physical Characteristics: Why would fractures or particle size affect
the rate of weathering?
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b) Climate: What type of climate would promote greater chemical
weathering?
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c) Differential Weathering
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*Mechanical and chemical weathering occur at the same time and can work in concert:
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Step 2: Erosion and Sedimentary Depositional
Environments
-Erosion is the movement of weathered materials from its
source to depositional environment.
-What are some processes of erosion?
_______________________________________________
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-Sediments can come in a variety of sizes and shapes
and can be classified as:
a) Detrital Sediments _________________________
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b) Chemical Sediments ________________________
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-Would you expect to find angular and very poorly sorted sediments close to or far away from their parent
material?
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-Sorting and rounding become more prominent the further sediments are transported.
-Transported sediments are eventually deposited in three main environments. Take your own notes from
text 141 to 144.
a) Continental
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b) Transitional
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c) Marine
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Step 3: Lithification
-Finally, after being deposited sediments can be transformed into
sedimentary rock by lithification, which involves two processes:
1. Compaction __________________________________________
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2. Cementation Precipitation of minerals onto the sediments,
eventually filling the pore space and joining sediments together.
-What are the most common mineral cements?
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-Most sedimentary rocks are formed through lithification, but
some are products of crystal growth and are called evaporates.
We will explore these later in the package.
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-Which of the rocks below was transported the farthest from its source? How do you know?
-Which of the rocks below was deposited deeper in an ocean or lake? How do you know?
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Part C: Types of Sedimentary Rocks
Detrital Sedimentary Rocks
- Detritial sedimentary rocks are separated from Chemical and
Biochemical Sedimentary Rocks as they are composed of:
_______________________________________________________
-Detrital rocks are also called Siliclastic because their main constituents
are: a) ____________________; b) ___________________
-This rock category is divided into different rock types according to
grain/sediment size (examine Lab Book Figure 6.3 on page 131).
-What can grain size reveal about the depositional environment?
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-Take your own notes on the different types of Detrital Sedimentary rocks:
a) Mudstone (Claystone, Shale, Siltstone)
Particle Size: ___________________________________________________________
Depositional Environment: ________________________________________________
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Strength: __________________________________________________
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Breakage: _________________________________________________
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Other Characteristics: ________________________________________
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b) Sandstone (Quartz, Arkose, Wacke)
Particle Size: _________________________________________________________________________
Depositional Environment: ______________________________________________________________
Sorting: ______________________________________________________________________________
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Roundness____________________________________________________________________________
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Composition__________________________________________________________________________
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Types:
i) Quartz Sandstone: ______________________________________________
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ii) Arkose Sandstone: _____________________________________________
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iii) Wacke Sandstone: __________________________________________________________________
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*The Folk Classification System for Sedimentary Rocks takes the ratio of mud to sand very seriously…
Geology 12: Sedimentary Rock
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c) Conglomerate and Breccia
Particle Size:__________________________________________________________________________
-Compare and contrast Conglomerate and Breccia depositional environments as revealed by their
constituent particles:
_____________________________________________________________________________________
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Chemical Sedimentary Rocks
-Are the product of materials carried in solution when it precipitates to form
chemical sediments.
-Precipitation occurs as a product of evaporation (crystalline texture) and the
chemical activity of organisms like corals (clastic texture).
a) Limestone
Composition: ____________________________________________________
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Formation Process: _______________________________________________
Types:
i) Organic Limestone: _____________________________________________
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ii) Inorganic Limestone: ___________________________________________
_______________________________________________________________
_______________________________________________________________
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Geology 12: Sedimentary Rock
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b) Chert (Flint, Jasper, Agate)
Composition: _________________________________________________________________________
Formation Process: _____________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
d) Evaporites
-Evaporation results in the precipitation of minerals
(halite, gypsum) out of solution.
Coal
-Take your own notes on coal formation from text
pages 155 to 166.
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Part D: Reading the Rock Record
-The rocks making up Earth’s crust form the only record of prehistory.
-Sedimentary rocks are very valuable as they contain evidence of the environment at the type of
deposition as their properties result from the physical, chemical and biological processes that existed.
-Additionally, the structures that sedimentary rocks form and the fossils they contain can provide further
information.
Sedimentary Structures
A sedimentary structure is any feature in sedimentary
rock formed at or shorty after deposition.
a) Strata or Beds: ____________________________
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b) Bedding Planes: ___________________________
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c) Cross-Bedding: ________________________________
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Animation 1, Animation 2
-What direction was the current/wind moving in the various
strata?
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d) Graded Bedding: ______________________________
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-What type of environment does graded bedding form in?
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-Commonly associated with turbidity currents (an
underwater flow of sediments and water with a greater
density than sediment free water) or storms.
e) Ripple Marks: _____________________
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-What are the differences between Current
Ripple Marks and Oscillation (Wave)
Ripple Marks?
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-In what direction was the current flowing in the image below?
-What type of sedimentary rock is most likely to show ripple marks? _____________________________
f) Mud Cracks: ________________________________________________________________________
Mudstone from the Cambrian period
g) Varves: Annual layers of rocks deposited by galcier melt.
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