Deck 6: Weathering, Soil, and Sedimentary Rocks

Question 1

How does loss of soil fertility exacerbate soil erosion?

Answer 1

Loss of fertility reduces the amount of plant cover and thus increases temperature due to loss of the cooling effects of plants and excess water. Without binding, irrigation, and aeration of soil by plants, soil becomes exposed and hardened and thus rendering them more susceptible to large losses as a result of sheet runoff.

Question 2

Briefly explain why water is such an important agent in chemical weathering.

Answer 2

Water is a universal solvent because of the asymmetrical shape of the molecule and the difference in charge between the two sides of the molecule. The negative side of the water molecule attracts positive ions from a mineral, and the positive side attracts negative ions, which effectively results in the eventual dissolution of the mineral.

Question 3

How do detrital sedimentary rocks differ from chemical sedimentary rocks?

Answer 3

Detrital sedimentary rocks are made from the fragments of preexisting rocks. The cement may be new material, but otherwise the material forming them predates the formation of the rock. Chemical sedimentary rocks precipitate from a solution; they are made of new material that forms for that rock. Detrital sedimentary rocks form as a result of mechanical or physical weathering in comparison with chemical sedimentary rocks that precipitate from an aqueous solution.

Question 4

Briefly explain the sequence in which a soil develops.

Question 5

Explain why the ferromagnesian minerals most susceptible to chemical weathering are those formed early in the continuous branch of Bowen's reaction series.

Question 6

Explain how fossils, and especially microfossils, can be used to help determine ancient depositional environments.

Question 7

What processes lead to soil degradation?

Question 8

How are oil and gas trapped in rock strata? What are these traps called?

Question 9

How do soils that form in humid regions differ from soils that form in semi-arid regions in the environments in which they form and in their basic characteristics?

Question 10

Briefly explain how hydrolysis results in the weathering of some minerals along with an example.

Question 11

What factors led to the development of the Dust Bowl during the 1930s in the United States?

Question 12

List the agricultural practices that reduce the rate of soil erosion, and explain why each does so.

Question 13

Briefly explain the process of differential weathering.

Question 14

Explain why understanding the depositional environments of sedimentary rocks are sometimes economically important.

Question 15

What are the four major types of coal, and which is the most valuable?

Question 16

Carbon dioxide levels in the atmosphere are rising due to the burning of fossil fuels. How might this increased level of carbon dioxide affect rates of weathering?

Question 17

Briefly explain how coal forms.

Question 18

Briefly explain why the study of sedimentary environments is important in the study of historical geology.

Question 19

Explain why and give two examples of how climate is more effective in determining soil type than is parent rock type.

Question 20

What are some ways in which fossils are useful?

Question 21

Why do small particles weather more rapidly than large particles?

Question 22

Under what conditions do carbonates form?

Question 23

List some ways in which organisms contribute to mechanical weathering.

Question 24

In what climatic conditions is frost action most effective?

Question 25

What are the two most common cements in sedimentary rocks?

Question 26

Briefly explain how dolostone is formed.

Question 27

How does mechanical weathering differ from chemical weathering?

Question 28

What are the requirements for a rock body to serve as a reservoir rock for hydrocarbons?

Question 29

What are soil horizons? What are the designations of the soil horizons?

Question 30

How does weathering differ from erosion?

Question 31

What are the major factors that control the rate of chemical weathering?

Question 32

What is soil made of?

Question 33

What is an example of an evaporite sedimentary rock?

Question 34

What are some of the characteristics of sedimentary rocks that are used in determining the depositional environment represented by a facies?

Question 35

How does graded bedding form?

Question 36

How does regolith differ from soil?

Question 37

What constitutes a chemical sediment?

Question 38

What two sedimentary structures can be useful in determining ancient current directions?

Question 39

What is a marine transgression? What are the sedimentary facies associated with a marine transgression?

Question 40

List the three important chemical processes involved in chemical weathering.

Question 41

Soils that are a result of intense weathering and are typically found in the tropics are ____________________ soils.

Question 42

Sedimentary deposits formed by wind tend to be very ____________________ sorted.

Question 43

____________________ form when layers are deposited at an angle to the surface and the layers dip in direction of ____________________.

Question 44

The most important factor controlling soil formation is ____________________.

Question 45

____________________ erosion occurs when water carves small channels into a soil bed.

Question 46

____________________ is an essential component of soil as it provides nutrients to plants and increases the ability of the soil to retain ____________________.

Question 47

A(n) ____________________ occurs when the sea advances landward.

Question 48

The basis for classifying detrital sediments and their rocks is ____________________.

Question 49

Rock units with sheetlike geometry were most likely deposited during marine ____________________ or ____________________.

Question 50

____________________ ripple marks form in response to wind or water moving in one direction.

Question 51

Soils that form on granite in Arizona are different from soils that form on granite in Virginia because ____________________ is different.

Question 52

The chemical weathering process that produces most of the red, yellow, and brown colors seen in soils and many sedimentary rocks is called ____________________.

Question 53

The actions of ______ and ______ are responsible for the erosion of most soils.

Question 54

___________________ is fundamental to the origin of sediments and sedimentary rocks

Question 55

The two major types of sediments that may become sedimentary rocks are ____________________ and ____________________.

Question 56

A vertical sequence of a(n) ____________________ facies shows an offshore facies superposed on nearshore facies.

Question 57

Sediment becomes sedimentary rock by the process known as ____________________, which involves the ____________________ of grains, loss of water, and ____________________ whereby material is precipitated in pore spaces and binds grains together.

Question 58

_____________ traps form as rocks are deformed by folding, fracturing, or both.

Question 59

A(n) ____________________ soil forms where the parent material has weathered, whereas ____________________ soil develops from eroded material that was weathered at another location.

Question 60

The rocks on the bottom of a pile of sedimentary rocks are ____________________ in age than the rocks above them.

Question 61

Detrital sediments and rocks are classified by:

A) mineral composition.
B) grain size.
C) the conditions in which they formed.
D) mineral composition and grain size.
E) composition, origin, and texture.

Question 62

Graded bedding forms when:

A) erosion planes off a portion of the sea bottom.
B) sediment is deposited on a steep slope or grade.
C) turbidity currents initially deposit coarse sediment then fine sediment.
D) cross-bedding is truncated.
E) turbidity currents deposit first fine sediment followed by coarse sediment.

Question 63

Mechanical weathering produces no change in the chemical composition of the parent rock.

Question 64

Hydrocarbons can be widespread in sedimentary rock, but reservoirs are formed by:

A) porous and permeable beds bounded on all sides by impermeable rock.
B) large cavities, such as cave systems in limestone reefs.
C) structural traps.
D) porous and permeable beds bounded on all sides by impermeable rock AND structural traps.
E) all of these

Question 65

The presence of mud cracks in a sedimentary rock is a sign that the rock was deposited:

A) in a region that was drying.
B) in a region that was under water.
C) in a desert.
D) beneath a glacier.
E) in a sand dune.

Question 66

If all of the grains in a sedimentary rock are about the same size, shape, and composition, the rock can be characterized as:

A) cemented.
B) compacted.
C) cross-bedded.
D) graded.
E) well sorted.

Question 67

Which coal contains the most carbon and generates most energy when burning?

A) lignite
B) anthracite
C) bituminous
D) peat
E) subbituminous

Question 68

The designation of sediment grain size, from largest to smallest, is:

A) clay, silt, sand, gravel.
B) gravel, sand, silt, clay.
C) gravel, silt, sand, clay.
D) clay, sand, gravel, silt.
E) silt, clay, gravel, sand.

Question 69

Sorting is a result of:

A) transportation of sediment by wind.
B) transportation of sediment by running water.
C) selective transport and deposition.
D) transportation of sediment by ice.
E) precipitation of minerals from seawater.

Question 70

The properties used to describe detrital sediment are:

A) size.
B) sorting.
C) rounding.
D) size and rounding.
E) size, sorting, and rounding.

Question 71

A rock may be subjected to either mechanical or chemical weathering, but never both at the same time.

Question 72

Chemical weathering is most effective when conditions are warm and arid.

Question 73

Humus:

A) is the material always comprising the topmost soil horizon.
B) is dark, organic-rich material formed by bacterial decay.
C) is leaf-litter.
D) must include sediments.
E) none of the above

Question 74

Clay particles are important to soil development because they allow water and gases to enter soil.

Question 75

A well-sorted sediment might consist of:

A) small grains of a variety of sizes (diameters).
B) large grains all of approximately the same size (diameter).
C) grains of moderate but different dimensions (diameters).
D) predominantly round grains.
E) predominantly smooth grains.

Question 76

Erosion is the:

A) movement of weathered material from its source site.
B) decomposition of rock.
C) disintegration of rock.
D) weathering of and transportation of sediment.
E) disintegration of soil.

Question 77

Ancient current directions can be determined by:

A) wave-formed ripple marks.
B) cross-bedding.
C) graded bedding.
D) mud cracks.
E) all of the above

Question 78

Sediments are classified as:

A) detrital, clastic, and chemical.
B) detrital and clastic.
C) detrital and chemical.
D) particulate and crystalline.
E) organic, particulate, and crystalline.

Question 79

Frost wedging in the mountains produces talus.

Question 80

Chemical sedimentary rocks generally have an interlocking grain texture called:

A) clastic.
B) porphyritic.
C) particulate.
D) crystalline.
E) detrital.