Quiz 10

Question 1

Absolute Geologic Age

Answer 1

precise dates of many types of geologic events

Question 2

Relative Geologic Age

Answer 2

the age of one event relative to another

Question 3

Principle of Original Horizontality

Answer 3

-sediments are deposited in horizontal or near-horizontal layers
-therefore, non horizontal layers have generally been folded or tilted from their original positions

Question 4

Principle of Superposition

Answer 4

-in any given succession of sedimentary rock layers lying in their original horizontal position the rocks at the bottom of the sequence are older than those lying above

Question 5

Principle of Original Lateral Continuity

Answer 5

-sediments are deposited in layers that continue laterally in all directions until they thin out as a result of nondeposition
-or until they reach the edge of the basin in which they are deposited
-therefore, if you find a layer that abruptly ends, something has cut this layer after it was deposited (faults, dikes, and erosion) can truncate otherwise laterally continuous layers

Question 6

Principle of Cross-Cutting Relations

Answer 6

any geologic feature is younger than any feature that it cuts

Question 7

Principle of Inclusions

Answer 7

an inclusion in a rock is older than the rock containing it

Question 8

Compressive stress

Answer 8

causes shortening and is an important type of stress at convergent tectonic plate boundaries

Question 9

Tensional stress

Answer 9

the principal stress at divergent boundaries, causes stretching

Question 10

Shear stress

Answer 10

causes one side of a body to slide past the other, and is the principal type of stress along transform-fault plate boundaries

Question 11

Elastic strain

Answer 11

temporary; if the stress is removed, the object snaps back to its original shape (think stretched rubber band)

Question 12

Plastic strain

Answer 12

permanent; if the stress is removed, the original size or shape is not restored (bending a piece of soft wire)

Question 13

Brittle deformation

Answer 13

a rock undergoing elastic strain which can suddenly break (a dry stick)

Question 14

Ductile

Answer 14

a rock that undergoes much plastic strain without rupturing (bent wire)

Question 15

Outcrop

Answer 15

visible exposures of bedrock or other geologic formations at the surface of the earth

Question 16

Contacts

Answer 16

surfaces separating adjacent bodies of rock of different types or ages

Question 17

Geologic maps

Answer 17

show the distribution of rock units at or very near the surface of the earth

Question 18

Geologic cross sections

Answer 18

vertical slices that show how the rocks would appear if they could be viewed on a cliff face

Question 19

Principle of Fossil Succession

Answer 19

fossil organisms succeed one another in time in a definite and recognizable order

Question 20

Principle of Fossil Assemblages

Answer 20

characteristic groups of fossil organisms also define unique geologic ages

Question 21

Unconformity

Answer 21

the erosion of a surface that represents a substantial gap in the geologic record

Question 22

Angular unconformity

Answer 22

-an erosion surface separating rocks whose layers are not parallel
-layers above and below meet at an angle
-underlying rocks were folded or tilted and eroded before the overlying layers were deposited

Question 23

Disconformity

Answer 23

-an erosion surface or a surface of nondeposition separating rocks whose layers are parallel
-an erosion surface is uneven and cuts layers of underlying rocks

Question 24

Nonconformity

Answer 24

-an erosion surface separating sedimentary rocks from older plutonic or massive metamorphic rocks

Question 25

Concordant

Answer 25

intrusive contacts parallel to layers in the intruded rock

Question 26

Discordant

Answer 26

intrusive contacts cut across layers in the intruded rock

Question 27

Anticlines

Answer 27

upward bends, or upfolds, with older rocks in the center

Question 28

Syncline

Answer 28

upward bends, or upfolds, with younger rocks in the center

Question 29

Upright fold

Answer 29

has a vertical or nearly vertical axial surface

Question 30

Inclined fold

Answer 30

has an axial surface that is not vertical or horizontal

Question 31

Overturned

Answer 31

beds on opposite limbs dip in the same direction

Question 32

Recumbent fold

Answer 32

has an approximately horizontal axial surface