Objectives Sequence the formation of sedimentary rocks. Formation of Sedimentary Rocks Explain the formation and classification of clastic sediments

Objectives• Sequence the formation of sedimentary rocks.

Formation of Sedimentary Rocks

• Explain the formation and classification of clastic sediments.

• Describe features of sedimentary rocks.

– sediment

– clastic

– deposition

– lithification

– cementation

– bedding

– graded bedding

– cross-bedding

Vocabulary

• When sediments become cemented together, they form sedimentary rocks.

• The formation of sedimentary rocks begins when weathering and erosion produce sediments.

• Sediments are pieces of solid material that have been deposited on Earth’s surface by wind, water, ice, gravity, or chemical precipitation.

Formation of Sedimentary Rocks• Much of Earth’s surface is covered with sediments.


Weathering• Wherever Earth’s crust is exposed at the surface

it is subject to weathering.


• Weathering is a set of physical and chemical processes that break rock into smaller pieces.– Chemical weathering occurs when the minerals in a rock are dissolved or otherwise chemically changed.

– Minerals remain chemically unchanged during physical weathering.

Weathering


Weathering• Clastic describes rock and mineral fragments

produced by weathering and erosion.


• Clastic sediments range in size from huge boulders to microscopic particles.

Erosion and Transport• After rock fragments have been weathered out of

outcrops, they are transported to new locations.


• Erosion is the removal and movement of surface materials from one location to another.

• The four main agents of erosion are wind, moving water, gravity, and glaciers.

• Eroded materials are almost always carried downhill.

Erosion and Transport

Deposition


– Deposition occurs when sediments are laid down on the ground or sink to the bottoms of bodies of water.

– Sediments are deposited when transport stops.

– As water or wind slows down, the largest particles settle out first, then the next-largest, and so on, so that different-sized particles are sorted into layers.

– Since wind can move only small grains, sand dunes are commonly made of fine, well-sorted sand.

– Sediment deposits from glaciers and landslides are not sorted because both move all materials with equal ease.

Erosion and Transport

Burial


– Most sediments are ultimately deposited on Earth in depressions called sedimentary basins.

– These basins may contain layers of sediment that together are more than 8 km thick.

– As more and more sediment is deposited in an area, the bottom layers are subjected to increasing pressure and temperature which causes lithification.

– Lithification includes the physical and chemical processes that transform sediments into sedimentary rocks.

Lithification• Lithification begins as the weight of overlying

sediments forces the sediment grains closer together, causing the physical changes.


• Layers of mud shrink as excess water is squeezed out.

Lithification• Sand resists additional compaction during burial.


• Grain-to-grain contacts in sand form a supporting framework that helps maintain open spaces between the grains.

Lithification• The temperature in Earth’s crust increases with

depth by about 30°C per kilometer.


• Sediments that are buried 3 to 4 km deep experience temperatures that are high enough to start the chemical and mineral changes that cause cementation.

• Cementation occurs when mineral growth cements sediment grains together into solid rock.

Lithification• There are two common types of cementation.


– A new mineral, such as calcite (CaCO3) or iron oxide (Fe2O3) grows between sediment grains as dissolved minerals precipitate out of groundwater.

– Existing mineral grains grow larger as more of the same mineral precipitates from groundwater and crystallizes around them.

Features of Sedimentary Rocks• Bedding, or horizontal layering, is the primary

feature of sedimentary rocks.


• The type of bedding depends upon the method of transport.

• The size of the grains and the material within the bedding depend upon many factors.

Features of Sedimentary Rocks• Graded bedding is bedding in which the particle

sizes become progressively heavier and coarser towards the bottom layers.


• Graded bedding is often observed in marine sedimentary rocks that were deposited by underwater landslides.

Features of Sedimentary Rocks• Cross-bedding is formed as inclined

layers of sediment move forward across a horizontal surface.


Features of Sedimentary Rocks• Small-scale cross-bedding can be observed at

sandy beaches and along sandbars in streams and rivers.


• Most large-scale cross-bedding is formed by migrating sand dunes.

• Small sedimentary features such as ripple marks are also preserved in sedimentary rocks.

• If a rippled surface is buried gently by more sediment without being disturbed, it might later be preserved in solid rock.

Features of Sedimentary Rocks

Evidence of Past Life


– Fossils are probably the best-known features of sedimentary rocks.

– Fossils are the preserved remains, impressions, or any other evidence of once-living organisms.

– Fossils are of great interest to Earth scientists because fossils provide evidence of the types of organisms that lived in the distant past, the environments that existed in the past, and how organisms have changed over time.

Section Assessment

1. Match the following terms with their definitions.

___ clastic

___ deposition

___ lithification

___ bedding


A. horizontal layering of sedimentary rocks

B. the physical and chemical processes that transform sediments into sedimentary rocks

C. rock and mineral fragments produced by weathering and erosion

D. occurs when sediments are laid down on the ground or sink to the bottoms of bodies of water

C

D

B

A

Section Assessment

2. How is cross-bedding formed?


Cross-bedding is formed as inclined layers of sediment move forward across a horizontal surface.

________ Cementation is a form of lithification.

________ During deposition, the largest particles end up in the top layer.

________ Graded bedding is often observed in marine sedimentary rocks.

________ Clastic sediments can range in size from microscopic particles to huge boulders.

Section Assessment

3. Identify whether the following statements are true or false.


true

false

true

true

Objectives• Describe the types of clastic sedimentary rocks.

• Explain how chemical sedimentary rocks form.

• Describe organic sedimentary rocks.

• Recognize the importance of sedimentary rocks.

– clastic sedimentary rock

– porosity

– evaporite

Vocabulary

Types of Sedimentary Rocks

Types of Sedimentary Rocks• The classification of sedimentary rocks is based

on how they were formed.


• There are three main groups of sedimentary rocks: clastic, organic, and chemical.



Clastic Sedimentary Rocks• Clastic sedimentary rocks, the most common

type of sedimentary rocks, are formed from the abundant deposits of loose sediments found on Earth’s surface.


• Clastic sedimentary rocks are further classified according to the sizes of their particles.

Clastic Sedimentary Rocks

Course-Grained Clastics


– Sedimentary rocks consisting of gravel-sized rock and mineral fragments are classified as coarse-grained clastics.

– Conglomerates are coarse-grained sedimentary rocks that have rounded particles, whereas breccias contain angular fragments.

– Conglomerates, such as gravel, are transported by high-energy flows of water and it becomes abraded and rounded as the particles scrape against one another.

– The angularity of particles in breccias indicates that the sediments did not have time to become rounded.


Medium-Grained Clastics


– Sedimentary rocks that contain sand-sized rock and mineral fragments are classified as medium-grained clastic rocks.

– Sandstone is formed when these medium-sized sediments are buried and lithified.

– Sandstone has high porosity of up to 30 percent.

– Porosity is the percentage of open spaces between grains in a rock.

– Sandstone layers are valuable as underground reservoirs of oil, natural gas, and groundwater.


Fine-Grained Clastics


– Sedimentary rocks consisting of silt and mud are called siltstone and mudstone.

– Siltstone is mostly composed of silt-sized grains, while shale is composed mostly of silt and clay-sized particles.

– Shale has very low porosity and often forms barriers that hinder the movement of groundwater and oil.

Chemical Sedimentary Rocks• During chemical weathering, minerals can be

dissolved and carried into lakes and oceans.


• As water evaporates from the lakes and oceans, the dissolved minerals are left behind.

• In arid regions, high evaporation rates can increase the concentration of dissolved minerals in bodies of water.

Chemical Sedimentary Rocks

Rocks Formed from Evaporation


– When the concentration of dissolved minerals in a body of water reaches saturation, crystal grains precipitate out of solution and settle to the bottom.

– Evaporites are the layers of chemical sedimentary rocks that form as a result of the precipitation of crystal grains.

– Evaporites most commonly form in arid regions, in oceans and in drainage basins on continents that have low water flow.

– The three most common evaporite minerals are calcite (CaCO3), halite (NaCl), and gypsum (CaSO4).


Rocks Formed from Evaporation



Organic Sedimentary Rocks


– Organic sedimentary rocks are formed from the remains of once-living things.

– The most abundant organic sedimentary rock is limestone, which is composed primarily of calcite.

– Calcite comes from the calcium carbonate that some organisms use to make their shells.

– Calcium carbonate precipitates out of the water and crystallizes between the grains of carbonate sediment to form limestone.

– Limestone is common in shallow water environments.


Organic Sedimentary Rocks


– Another type of organic sedimentary rock, coal, forms from the remains of plant material.

– Over long periods of time, thick layers of vegetation slowly accumulate in swamps and coastal areas and are buried and compressed.

– Coal is composed almost entirely of carbon and can be burned for fuel.

Importance of Sedimentary Rocks• The characteristic textures and features of

sedimentary rocks provide a geologic “snapshot” of surface conditions in Earth’s past.


• By considering all of this information, geologists can better understand how geologic changes occur over time.

Importance of Sedimentary Rocks

Energy Resources


– The study of sedimentary rocks has great practical value because many of the natural resources used by humans come from sedimentary rocks.

– Oil, natural gas, coal, uranium, phosphate, and iron are found in sedimentary rocks.

– Limestone is processed to make cement for the construction industry.

– Sandstone and limestone are often cut into blocks for use in walls and buildings.

Section Assessment

1. What is porosity and how is it a valuable characteristic?


Porosity is the percentage of open spaces between grains in a rock. It is a valuable characteristic because a rock with high porosity, such as sandstone, can be an underground reservoir for oil, natural gas, and groundwater.

Section Assessment


2. The following are which type of sedimentary rock?___ coal

___ sandstone

___ limestone

___ shale

___ conglomerate

___ rock gypsum

___ breccia

A. clastic

B. chemical

C. organic

D. A and B

E. B and C

C

A

E

A

A

B

A

Section Assessment

3. What are the three most common evaporite minerals?


The three most common evaporite minerals are calcite (CaCO3), halite (NaCl), and gypsum (CaSO4).

Objectives• Compare and contrast the different types and

causes of metamorphism.

• Distinguish among metamorphic textures.

• Explain how mineral and compositional changes occur during metamorphism.

• Understand how rocks continuously change from one type to another in the rock cycle.

Metamorphic Rocks

– regional metamorphism

– contact metamorphism

– hydrothermal metamorphism

– foliated

– nonfoliated

– porphyroblast

– rock cycle

Vocabulary

Metamorphic Rocks

Causes of Metamorphism• Metamorphic rock forms when high temperature

and pressure combine to alter the texture, mineralogy, or chemical composition of a rock without melting it.

Metamorphic Rocks

• The high temperatures ultimately are derived from Earth’s internal heat.

• The high pressures can be generated in two ways:– From vertical pressure caused by the weight of overlying rock

– From the compressive forces generated as rocks are deformed during mountain building

Types of Metamorphism• Different combinations of temperature and

pressure result in different types of metamorphism.

Metamorphic Rocks

• Large belts of regional metamorphism are produced when high temperature and pressure affect large regions of Earth’s crust.

• Regional metamorphism can be low grade, intermediate grade, and high grade.

• The grade of regional metamorphism reflects the relative intensity of temperature and pressure.

Types of Metamorphism

Metamorphic Rocks

Types of Metamorphism• Geologists have

divided the regional metamorphic belt that has been mapped in the northeastern United States belt into zones based upon the mineral groups found in the rocks.

Metamorphic Rocks

Types of Metamorphism• Knowing the

temperatures that certain areas experienced when rocks were forming can help geologists locate economically valuable metamorphic minerals.

Metamorphic Rocks

Types of Metamorphism• Some key minerals are used to map

metamorphic zones.

Metamorphic Rocks

Types of Metamorphism• A local effect called contact metamorphism

occurs when molten rocks, such as those in an igneous intrusion, come in contact with solid rock.

Metamorphic Rocks

• High temperature and moderate-to-low pressure form the mineral assemblages that are characteristic of contactmetamorphism.

Types of Metamorphism• Because temperature decreases with distance

from an intrusion, metamorphic effects also decrease with distance.

Metamorphic Rocks

• Contact metamorphism from extrusive igneous rocks is limited to thin zones.

Types of Metamorphism• Hydrothermal metamorphism occurs when very

hot water reacts with rock and alters its chemistry and mineralogy.

Metamorphic Rocks

• Hydrothermal fluids can dissolve some minerals, break down others, and deposit new minerals.

• Hydrothermal metamorphism is common around igneous intrusions and near active volcanoes.

Metamorphic Textures• Metamorphic rocks are classified into two

textural groups: foliated and nonfoliated.

Metamorphic Rocks

– Foliated metamorphic rocks are characterized by wavy layers and bands of minerals.

– High pressure during metamorphism causes minerals with flat or needlelike crystals to form with their long axes perpendicular to the pressure.

Metamorphic Textures– Nonfoliated metamorphic rocks lack mineral

grains with long axes in one direction.

Metamorphic Rocks

– Nonfoliated rocks are composed mainly of minerals that form with blocky crystal shapes.

– Quartzite and marble are two common examples of nonfoliated rocks.

Metamorphic Textures

Porphyroblasts

Metamorphic Rocks

– Under certain conditions, new metamorphic minerals can grow quite large while the surrounding minerals remain small.

– Porphyroblasts are large crystals, which can range in size from a few millimeters to a few centimeters.

– Porphyroblasts are found in areas of both contact and regional metamorphism.

Mineral Changes• Minerals are stable at certain temperatures and

crystallize from magma at different temperatures.

Metamorphic Rocks

• During metamorphism, the minerals in a rock change into new minerals that are stable under the new temperature and pressure conditions.

• Minerals that change in this way are said to undergo solid-state alterations.

Compositional Changes• When hot fluids migrate in and out of the rock

during metamorphism the original composition of the rock can change.

Metamorphic Rocks

• Chemical changes are especially common during contact metamorphism near igneous intrusions.

• Valuable ore deposits of gold, copper, zinc, tungsten, and lead are formed through the invasion of hydrothermal fluids.

The Rock Cycle• Metamorphic rocks are formed by the changing

of other rocks.

Metamorphic Rocks

• Any rock can be changed into any other type of rock.

• The rock cycle is the continuous changing and remaking of rocks.

Other Possible Paths• There is more than one path in the rock cycle.

Metamorphic Rocks

• The rocks of Earth’s crust are constantly being recycled from one type to another.

• The processes that help shape Earth’s landscapes are also part of the rock cycle.

Section Assessment

1. Match the following terms with their definitions.

___ foliated

___ nonfoliated

___ porphyroblasts

___ rock cycle

Metamorphic Rocks

A. metamorphic rocks that lack grains with their long axes in one direction

B. the continuous changing and remaking of rocks

C. metamorphic rock with wavy layers and bands of minerals

D. large crystals in metamorphic rocks that are surrounded by smaller crystals

C

A

D

B

Section Assessment

2. Identify what causes each type of metamorphism.

___ regional

___ contact

___ hydrothermal

Metamorphic Rocks

B

D

A

A. very hot water reacts with rock and alters its chemistry and mineralogy

B. high temperatures and pressures affect large areas of Earth’s crust

C. molten lava hardens on Earth’s surface

D. molten rocks come in contact with solid rock

Section Assessment

Metamorphic Rocks

3. How can sedimentary rocks skip the metamorphic and igneous stages in the rock cycle?

Rocks can take many different paths through the rock cycle. If a sedimentary rock is raised through uplifting and exposed to weathering and erosion it breaks into sediments, possibly to be reformed into new sedimentary rock.

Chapter Resources Menu

Chapter Resources Menu

Study Guide

Section 6.1

Section 6.2

Section 6.3

Chapter Assessment

Image Bank

Section 6.1 Main Ideas• The processes of weathering, erosion, deposition, burial, and

lithification form sedimentary rocks.

Section 6.1 Study Guide

• Clastic sediments are rock and mineral fragments produced by weathering and erosion. They are classified based on particle size.

• Sediments are lithified into rock by the processes of compaction and cementation.

• Sedimentary rocks can contain depositional features such as horizontal bedding, cross-bedding, and ripple marks.

• Fossils are the remains or other evidence of once-living things that are preserved in sedimentary rocks.

Section 6.2 Main Ideas• There are three main classes of sedimentary rocks: clastic,

which are formed from clastic sediments; chemical, which are formed from minerals precipitated from water; and organic, which are formed from the remains of once-living things.

• Clastic sedimentary rocks are classified by particle size and shape.

• Evaporites are chemical sedimentary rocks that form primarily in restricted ocean basins in regions with high evaporation rates.

• Limestone, composed primarily of calcite, is the most abundant organic sedimentary rock. Coal is another organic sedimentary rock.

• Sedimentary rocks provide geologists with information about surface conditions that existed in Earth’s past.


Section 6.3 Main Ideas• Metamorphic rocks are formed when existing rocks are

subjected to high temperature and pressure, which cause changes in the rocks’ textures, mineralogy, and composition.

• The three main types of metamorphism are regional, contact, and hydrothermal.

• Metamorphic rocks are divided into two textural groups: foliated and nonfoliated.

• During metamorphism, minerals change into new minerals that are stable under the conditions of temperature and pressure at which they formed.

• The rock cycle is the set of processes whereby rocks continuously change into other types of rock.


1. What is it called when sediments are laid down on the ground or sink to the bottoms of bodies of water?

a. erosion c. deposition

b. transport d. lithification

Multiple Choice

Chapter Assessment

Erosion is the removal of surface. Transport is the movement of eroded materials from one location to another. Lithification is the chemical and physical processes that transform sediments into sedimentary rocks.

2. Oil and natural gas reserves will most likely be found in what type of rock?

a. sandstone c. limestone

b. shale d. gypsum

Sandstone has a high porosity, or percentage of open spaces between the grains of the rock. Porosities of sandstone can be as high as 30 percent.

Multiple Choice

Chapter Assessment

Multiple Choice

3. What are the chemical sedimentary rocks that form as a result of crystal grains precipitating out of a solution called?

a. porphyroblasts c. clastic

b. evaporites d. sediments

Chapter Assessment

Evaporite refers to the evaporation that helps a solution (body of water) become supersaturated. When a solution is supersaturated, crystal grains can precipitate out and collect at the bottom where they become evaporite sedimentary rock.

Multiple Choice

4. Which of the following is an example of a nonfoliated metamorphic rock?

a. schist c. gneiss

b. slate d. quartzite

Chapter Assessment

Unlike foliated rocks, nonfoliated metamorphic rocks lack mineral grains with long axis in one direction. Schist, slate, and gneiss are all foliated rocks.

Multiple Choice

5. What is the horizontal layering that is a primary characteristic in sedimentary rocks called?

a. bedding c. metamorphism

b. cementation d. ripple marks

Chapter Assessment

Bedding can range from a millimeter thick layer of shale to sandstone deposits several meters thick. The type of bedding depends upon the method of transport.

Short Answer

6. What are the three grades of regional metamorphism and how do they relate to temperature and pressure?

Chapter Assessment

The three grades of regional metamorphism are low grade, intermediate grade, and high grade. The grade of regional metamorphism reflects the relative intensity of temperature and pressure, with low grade metamorphism reflecting the lowest temperature and pressure.

Short Answer

7. What is the geological significance of sedimentary rocks in relation to Earth’s past?

Chapter Assessment

The characteristics of textures and features in sedimentary rocks, such as cross-bedding, ripple marks, layering, and fossils, provide a geologic “snapshot” of surface conditions in Earth’s past.

True or False

8. Identify whether the following statements are true or false. ______ Contact metamorphism is a local effect.

______ Clastic sediments are created through a metamorphic process.

______ Cementation is part of the lithification process.

______ Coal forms from the remains of plant material.

______ Hydrothermal metamorphism does not alter the

chemistry or mineralogy of a rock.

Chapter Assessment

true

false

true

true

false

Image Bank

Chapter 6 Images

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Chapter 6 Images

Image Bank

Chapter 6 Images

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Objectives Sequence the formation of sedimentary rocks. Formation of Sedimentary Rocks Explain the formation and classification of clastic sediments