Deck 6: Weathering, Soil, and Sedimentary Rocks

Question 1

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

Answer 1

Rock strata that can trap oil and gas are known as stratigraphic traps.A reservoir rock has an overlying cap rock,and it is the difference between the rock types that traps the hydrocarbons.Structural traps result when rocks are deformed by folding,fracturing,or both.The hydrocarbons migrate to the tops of these structures.These require only a good reservoir rock to hold the oil and gas.

Question 2

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?

Answer 2

Soils that form in semi-arid regions contain less organic matter than the soils of more humid areas,so horizon A is lighter colored and contains more unstable minerals because of less intense chemical weathering.Calcium carbonate precipitates in horizon B,forming caliche,as soil water evaporates.Soils that form in humid regions have most of the soluble minerals are leached from horizon A,but that horizon contains abundant organic matter.Aluminum-rich clays and iron oxides tend to accumulate in horizon B.

Question 3

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

Answer 3

It is relatively easy to distinguish between marine and terrestrial organisms,based on a comparison with their living counterparts.Strong invertebrate shells usually indicate a high-energy environment,such as the intertidal zone;deep-sea fossils are microscopic and fragile.Marine microfossils are particularly important because so many can be retrieved in a single core sample.Coral reef deposits are bounded in depth,as well as latitude,and are always marine.

Question 4

How do detrital sedimentary rocks differ from chemical sedimentary rocks?

Question 5

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

Question 6

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

Question 7

What are some ways in which fossils are useful?

Question 8

What processes lead to soil degradation?

Question 9

How does loss of soil fertility exacerbate soil erosion?

Question 10

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

Question 11

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

Question 12

Briefly explain how hydrolysis results in the weathering of some minerals.

Question 13

Briefly explain the sequence in which a soil develops.

Question 14

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

Question 15

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

Question 16

Briefly explain how exfoliation domes form.

Question 17

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

Question 18

Briefly explain how coal forms.

Question 19

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

Question 20

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 21

Briefly explain how dolostone is formed.

Question 22

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

Question 23

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

Question 24

Why do small particles weather more rapidly than large particles?

Question 25

List some ways in which organisms contribute to mechanical weathering.

Question 26

Under what conditions do carbonates form?

Question 27

How does weathering differ from erosion?

Question 28

How does regolith differ from soil?

Question 29

Is banded iron formation a chemical or detrital sedimentary rock? Explain.

Question 30

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

Question 31

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

Question 32

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

Question 33

What is soil made of?

Question 34

What is an example of an evaporite sedimentary rock?

Question 35

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

Question 36

What makes up a chemical sediment?

Question 37

What are the two most common cements in sedimentary rocks?

Question 38

How does graded bedding form?

Question 39

In what climatic conditions is frost action most effective?

Question 40

How does mechanical weathering differ from chemical weathering?

Question 41

Three important chemical processes involved in chemical weathering are ____________________,____________________,and ____________________.

Question 42

The actions of ____________________ and ____________________ are responsible for most soil erosion.

Question 43

The most important factor controlling soil formation is ____________________.

Question 44

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

Question 45

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

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

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

Question 48

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

Question 49

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

Question 50

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

Question 51

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

Question 52

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

Question 53

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

Question 54

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

Question 55

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

Question 56

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

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

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

Question 59

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

Question 60

The economically valuable mineral resource produced by intense chemical weathering that is found only in laterite soils is called ____________________.

Question 61

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 62

Erosion is the:

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

Question 63

Frost wedging in the mountains produces talus.

Question 64

Chemical sedimentary rocks generally have an interlocking grain texture called:

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

Question 65

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 66

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 67

The properties used to describe detrital sediment are:

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

Question 68

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 69

Which coal contains the most carbon and is the hottest burning?

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

Question 70

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 71

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 deposit first coarse sediment then fine sediment.
D)cross-bedding is truncated.
E)turbidity currents deposit first fine sediment followed by coarse sediment.

Question 72

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

Question 73

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

Question 74

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

Question 75

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

Question 76

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 77

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 78

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 79

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 80

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.