Laboratory Manual for Introductory Geology 4e

EXERCISE 10.8
Name:
Course:
Interpreting Unconformities on a Block Diagram (continued)
Section:
Date:
(c) In Block 3, in which direction are the post-unconformity strata dipping?
(d) In Block 4, a gray area at the north edge of the block appears on the map surface. What geologic observation(s) could
prove that the contact between the gray area and the sedimentary beds is an unconformity and not an intrusive
contact?
EXERCISE 10.9
Interpreting Intrusions on a Block Diagram
Name:
Course:
Section:
Date:
(a) Blocks 1 and 2 (on the next page) show sedimentary beds and intrusions. Match the type of intrusion to the
appropriate letter on the block.
Pluton Block 1: Block 2:
Dike Block 1: Block 2:
Sill Block 1: Block 2:
(b) The principle of cross-cutting relationships states that if one rock cuts across another, it must be the younger
rock (see Chapter 12 for more on cross-cutting relationships). Using common sense to interpret cross-cutting
relationships, list the sequence of intrusions for each block. If you can’t determine an answer from the information
shown, indicate so.
Block 1:
Block 2:
Oldest Middle Youngest
(c) Analyses indicate the unlabeled intrusion in the front cross-section face of Block 2 is part of the same body as
Intrusion A exposed on the top surface. Explain why you can’t see the connection between the map-view exposure
and the subsurface cross section on this block.
(continued)
254 CHAPTER 10 INTERPRETING GEOLOGIC STRUCTURES