Use the geologic crow sections below. Place letters in the lines along the right

Question

Use the geologic crow sections below. Place letters in the lines along the right tide of the crocs section to indicate the relative ages of the rock units and other features (unconformities, fault) from oldest (first) to youngest (last). In the 1^st figure below, all rock units area sedimentary except for units A and E, which are intrusive igneous rocks. H represents a fault. The black squiggly lines represent unconformities, and the dark stippled pattern adjacent to intrusive igneous rocks represents a zone of contact metamorphism, created before the magma cooled The second figure below is a geologic cross section of the Grand Canyon. All rock are sedimentary except, unit F and J. which are intrusive igneous rocks. Unit K is a metamorphic rock. And letters R and S represent unconformities. Be sure to label the type of unconformity below (Read about the different types of unconformity in Section 9.3) What type of unconformity in R? _ What type of unconformity is most of S?_

Explanation / Answer

In Diagram 1:

N- Youngest

P

E

L

G

D
C

A

J

M

D

O

N

R

K

S- Oldest

In Diagram 2:

S- Youngest

F

J

K

M

E

L

D

C

B

R

A
I

K

M

G- Oldest

What type of unconformity is R? – Angular unconformity (An angular unconformity is an unconformity where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers.)

What type of unconformity is S? - Buttress unconformity (A buttress unconformity occurs when younger bedding is deposited against older strata thus influencing its bedding structure.)

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