In this exercise, you will apply the principles of relative age dating and your

Question

In this exercise, you will apply the principles of relative age dating and your knowledge of geologic structures (Chapter 15) to interpret geologic histories of various degrees of complexity. Rock units in the four structural cross sections that follow are labeled with letters that have no meaning with respect to relative age (i.e., A can be older or younger than B). In all diagrams, sedimentary and metamorphic rocks are labeled with uppercase letters, igneous rocks with lowercase letters. Not that the rocks and some contacts are labeled but the processes affecting those rocks are not. In the timeline on the right side of each cross section, arrange the materials in order from oldest (at the bottom- remember superposition) to youngest. Where an event has occurred (e.g., folding, tilting, erosion), draw an arrow to indicate the place in the sequence and label the event. In many cases, you will have no doubt about the sequence of events, but in some there may be more than one possibility. In the space provided after each diagram, briefly explain why you ordered your choices the way you did

Explanation / Answer

First, the sediments C,G,A,I,K,F were deposited horizontally followed by tilting due totectonic activity. It was followed by an event of erosion and non-deposition (unconformity). Since the beds underlying the unconformity strike an angle with the overlying beds, it is known as an angular unconformity. This event is then followed by the deposition of beds D, J, H, B.

Therefore, the sequence in which the beds were deposited are as follows(oldest at the bottom)

B

H

J

D

(Unconformity)

F

K

I

A

G

C

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