Lab: How to Interpret Geologic Maps , geology homework help

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Lab 9: How to Interpret Geologic Maps
Background on Geologic Maps: A geologic map depicts the aerial distribution
of various rock types of different ages. Rocks are broken out into mappable units
or formations. A formation is a rock type that is distinct enough to separate from
the other rocks in the area, and thick enough to show accurately on the map.
Each formation is represented by a unique symbol and color on the geologic
map. The symbol indicates the rock’s age and formation name. The geologic
pattern and symbol for each formation are usually overprinted on a topographic
map. Other symbols are located on the map to indicate the orientation of
geologic structures such as folds, faults and inclined beds.
1. General Questions on Geologic Maps and Strike and Dip
a) Draw a diagram of a normal fault. Label the hanging wall, footwall, and
scarp.
b) Draw strike-dip symbols for a symmetrical syncline that trends E-W and
has a dip of 300.
c) A bed has a strike of N 500 E and is inclined toward the southwest.
What is the actual compass direction of dip?
d) A bed has a direction of dip of N 450 E. what is the strike?
e) Why is it necessary to measure the dip angle perpendicular to the strike
of an inclined bed?
f) Can a reverse fault cause older beds to overlie younger beds? What
about a normal fault?
g) Describe the effects of faulting on inclined beds.
h) What is the difference between a plunging and non-plunging fold?
i) When measuring strike, what feature of a fold is used to orient the
strike? for a fault?
2. Internet Activities
a) Go to the following site to practice strike and dip readings or to use their
template:
http://lpc1.clpccd.cc.ca.us/lpc/hanna/examspractice/geo10lab/strikeanddip/
strikeanddipB.htm
b) Go to the following site and complete Activities 1 and 3:
http://college.cengage.com/geology/resources/protected/physicallab/thelab
/geologicmaps/index.htm
c) Go to the following site to view a You-tibe lecture on this topic:

3. Background on Interpreting Folds
Block Diagram Exercises – Folds
A. Block Diagrams I
B. Block Diagrams II
C. Draw Map View of the Structure
Plunging Anticline with NE axial trend
Asymmetrical Syncline with limbs dipping to the north and south
D. Map Interpretation
Study the example below of the field geologic map (Map 1) and the derivative
interpretive geologic map (Map 2). Notice how contacts between the limestone and
shale were inferred. Likewise, the contact was drawn between the shale and the
sandstone, and between the sandstone and the schist. Notice how a line was drawn
between the large area of conglomerate to the south, and the rest of the lithologies to
the north.
Questions:
1. Notice how the limestone outcrops in the northwest portion of Map 2 dip towards
each other. What type of fold structure does this imply in this area?
2. Notice how the conglomerate formation dominates the south portion of the map. The
contact of the conglomerate cuts across the bedding of the schist-sandstone-shalelimestone sequence. Is the conglomerate older or younger than the schist-sandstoneshale-limestone sequence?
3. Make an interpretive geologic map (Map 4) from the field geologic map (Map 3).
4. Draw the approximate trace of a fault, with a heavy dash line, based on the presence
of breccia.
5. Which direction do the rocks in the northwest portion of the map dip?
6. Is the granite older or younger than the fault?
4. Background on Interpreting Faults:
Block Diagrams – Faults
For each of the following diagrams, identify the type of fault.
A.
B.
C.
Note: The block diagram C is a bit tricky. There are two possible interpretations, but the
river eliminates one of them. Why?
D.
E.
F.

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