Structural Geology (Geol 4013/6013)
Name_______________
Lab Exercise 5
Questions (29 pts), untilting (16 pts), unfolding (20 pts), Map (15). Cross section (20).
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Un-tiliting and unfolding (un-plunging and un-dipping) Attachments: Geological Map!
on stereonet. Geologic map and cross section
Study Chapter 5 and 6 of the Lab Manual by Donal M. Ragan:
“Structural Geology, an Introduction to Geometrical Techniques”.
PART I: CHAPTER 5. DO THE FOLLOWING FROM THE “5.10 EXERCISES” ON PAGE 107 OF THE LAB MANUAL:
CHAPTER 5, PROBLEM 2A, B AND C (PAGE 107). TOPIC: APPARENT AND TRUE DIPS USING STREONET
1. Given the attitude of a plane is N75W, 22N, what is its apparent dip along N50E?
a. 26
b. 11
c. 32
d. 18
e. 8
2. Given the apparent dip of a plane is 33, N47E, what is the true dip if the strike of the plane is N90E?
a. 24N
b. 43N
c. 33N
d. 12S
e. 12N
3. Given the true dip of a plane is 40N, what are the two possible trends for a 30o apparent dip?
a. N47W & N49E b. N26E & S42E
c. N90E & S34E d. S22E & S43W e. S56E & S7W
CHAPTER 5, PROBLEM 3 (PAGE 107). TOPIC: GIVEN TWO LINES, FIND THE PLANE CONTAINING THEM.
4. Given the attitude (plunge, trend) of line L1 is 30, 320 and line L2 is 20, 020, what is the attitude (strike, dip) of
the plane that contains L1 and L2?
a. 020, 24NW b. 030, 42SE c. 057, 30NW d. 320, 27NE e. 340, 46SW
5. What is the pitch of line L1 on the plane? (Note: pitch is a vector, e.g., 40N, which reads: ‘40 from north”, i.e.,
from the northern end of the strike line of the plane that contains the line’)
a. 44SW
b. 23NE
c. 12NE
d. 83SW
e. 70NE
6. What is the pitch of line L2 on the plane?
a. 14NE
b. 36SW
c. 64NE
d. 17NE
e. 41NE
7. What is the angle between L1 and L2, measured on the plane?
a. 32
b. 55
c. 17
d. 78
e. 90
CHAPTER 5, PROBLEM 4 (PAGE 108). TOPIC: FIND THE LINE OF INTERSECTION OF TWO PLANES
Note the typo in the book: “Two intersection planes” must be: “Two intersecting planes”!
8. Given the attitude of plane P1 is N5E, 15W and that of plane P2 is N15E, 10W, what is the orientation (trend,
plunge) of the line of intersection of P1 and P2?
a. N20E, 10
b. N15W, 5
c. S12E, 8
d. S18W, 23 e. N55E, 6
9. What is the acute angle between these two planes?
a. 16
b. 40
c. 46
d. 5
e. 33
Structural Geology (Geol 4013/6013)
Lab 5. Page 1
Part II – Chapter 6
CHAPTER 6, PROBLEM 1 (PAGE 128).
TOPIC: ROTATION OF PLANES ABOUT HORIZONTAL AND VERTICAL AXES
Given Plane P1 (horizontal) and the line L1 (trending N48E), lying on it. Plot the horizontal plane itself (i.e., as a great
circle or cyclographically), and then plot its pole with the  symbol. Plot the line with the  symbol. Rotate P1 by 50o
counterclockwise about a vertical axis. Notice that the orientation of the plane does not change! Why?
10. What is the new orientation (trend, plunge) of line L1 after the 50o ccw rotation?
Label it on the stereonet as L1’ using the ’ symbol
a. N2W, 0
b. S4E, 6
c. N4W, 6
d. b and c
e. none of the above
o
11. Rotate P1 and L1 60 clockwise about a N-trending horizontal axis. NOTE: First plot the horizontal line with the
 symbol, and then rotate the pole to the plane () about the horizontal line.
What is the new orientation (strike, dip) of P1 after the rotation? Show is with the ’’ symbol
a. 120, 34SW b. 069, 46SE c. 320, 22SW d. 000, 60W e. horizontal
12. What is the new orientation (trend, plunge) of L1 after the 60o cw rotation?
a. N12W, 4
b. N46W, 16 c. S28W, 40
d. S82E, 40
e. N18E, 00
/16 pts CHAPTER 6, DO PROBLEM 4 (PAGE 129):
TOPIC: UNTILTING (USE DIFFERENT COLORED PENCILS FOR DIFFERENT OPERATIONS!)
Read the problem. Hints:
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Plot the poles (symbol: , NOT their cyclograms!) to the two planes P1 (N30W, 40W) below an unconformity, and
P2 (N20E, 30E) above the unconformity.
Plot and label the poles of P1 and P2 as 1 and 2, respectively
Use a blue pencil, and rotate plane P2 (i.e., strata above the unconformity) to the horizontal.
This is done by first bringing the pole to the strata above the unconformity (2) to the E-W line, and then moving it
to the center.
While holding the tracing paper fixed, move 1 on a small circle (which it is sitting) to a new position ’1.
This is the pole to the strata before tilting of the overlying, unconformable strata.
Read the plane normal to ’1. This is done by bringing ’1 to the E-W line, and then drawing the plane (cyclogram)
normal to it (draw this with a red pencil).
Read the strike and dip of this plane.
13. Given the attitude of the strata below the unconformity (P1: N30W, 40W) and strata above the unconformity
(P2: N20E, 30E), what was the orientation of beds P1 before the tilting of P2?
a. N67E, 56NW
b. N18W, 32SW c. S50E, 56NE d. N13W, 63SW
e. N43W, 90
Structural Geology (Geol 4013/6013)
Lab 5. Page 2
Chapter 6, Do Problem 5 (Page 129). Topic: Unfolding
(NOTE: Use different colored pencils for different operations!)
Read the problem. Hints:
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Note that the fold axis is plunging. To undeform the structure, there should be two rotations that involve:
un-plunging the fold axis and de-dipping of the limb(s).
Using a black pencil, first plot the pole and the cyclogram of the bedding on the East limb (symbol: E).
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Plot the fold axis with the  symbol (it must fall on the bedding!)
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Plot the crest line (symbol: c) on the bedding (it also must fall on the bedding!).
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Un-plunge the fold by bringing the fold axis () to the E-W line. While holding the tracing paper down with one
hand and using a red pencil, move the axis to the Primitive, and determine the amount of angle needed to rotate it
to the Primitive. Draw the line (in red) that the axis moves to reach the Primitive (write the amount on the line),
and draw an arrow along the line to indicate the direction of rotation.
While the tracing paper is still in the same position, rotate the pole to the bedding (E) and the crestline of the
ripple marks (c) equal amount and in the same direction. This operation takes these two lines to their new
position (’E and ’c, respectively) after un-plunging.
De-dip the east limb (use a blue pencil for this operation): This is done by bringing the rotated pole to the east limb
(’E) to the E-W line, and then rotating it to the center of the stereonet (i.e., making the pole vertical). Mark the
direction and amount of rotation on the line.
While holding the tracing paper in position, rotate the unplunged crest line of the ripple marks, equal amount and
in the same direction. Mark the new position of the crestline as ’c .
If you have done everything correctly, both the bedding and the crest line should be horizontal by now.
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Please label everything on your stereogram using proper symbols (see above)!
14. Given that the attitude (plunge, trend) of the fold axis is 24, 040, and the attitude of the bedding on the east
limb is N5W, 32E, and the pitch of the crest line of the ripple marks on the east limb bedding plane is 70N,
what was the orientation of the bedding (whose pole is ’E) after unplunging of the fold axis?
a. S40W, 22SE
b. N35E, 34NW c. N40W, 18SW
d. S32E, 80NE e. N1E, 74W
15. What was the orientation (trend, plunge) of the crest line (’c), after unplunging of the fold axis?
a. N30E, 0
b. S46E, 8
c. N59E, 8
d. S20W, 11 e. S18W, 48
16. What was the original orientation of the crest line of the ripple mark (’’c), after de-dipping of the east limb?
a. N20E, 00
b. N56W, 00 c. N32W, 00
d. S20E, 00
e. N60E, 00
/ 20 pts Attach your stereogram for credit!
Structural Geology (Geol 4013/6013)
Lab 5. Page 3
CHAPTER 6, PROBLEM 6 (PAGE 129). TOPIC: UNFOLDING OF AN OVERTURNED FOLD
Topic: Unfolding
(Please use different colored pencils for different operations!)
Given that the attitude of the fold axis is 50, 025, and the bedding on the overturned east limb is N45E, 74W (NOTE:
Error in the book: the attitude of the eastern limb is not N45E, 50W), and the trend of the sedimentary lineation on
the bedding is N90W.
Hint: Follow the procedure in problem 5. However, note that the bedding is actually overturned, i.e., it has gone beyond
90o during folding. This means that, after unplunging the fold, you must de-dip (un-dip) the bedding by the obtuse angle
(not the acute angle!). This means the pole is first moved to the primitive, and then from diametrically opposite side,
brought to the center (note the amount and direction).
Please use the following symbols in your plot:
Present day pole to the east limb: E
Pole to the east limb after the unplunging operation: ’E
Pole to the east limb after the de-dipping operation: ’’E
Present day sedimentary lineation: 
Sedimentary lineation after the unplunging operation: ’
Sedimentary lineation after the de-dipping operation: ’’
Show the unplunging with a red pencil
Show the de-dipping (un-dipping) with blue pencil
Please label everything on your stereogram!
Unplunge the fold (use a red colored pencil to do this operation.
17. What is the orientation of the bedding (whose pole is ’E) after unplunging?
a. N10E, 34NW b. N25E, 66NW
c. N24W, 90 d. N18W, 67SW
e. N18E, 26NW
18. What is the orientation (trend, plunge) of the lineation (’) after unplunging?
a. N82W, 00
b. N14E, 30
c. N2W, 46
d. N32W, 00
e. S58, 12
19. Un-dip (de-dip) the east limb (do this operation using a blue colored pencil).
What is the orientation of the original sedimentary lineation (’’) after un-dipping?
a. N23E, 00
b. N12W, 00
c. N77E, 00
d. S56E, 00
e. N60E, 00
Structural Geology (Geol 4013/6013)
Lab 5. Page 4
PART III: GEOLOGIC MAP AND CROSS SECTION
TOPIC: FOLDED AREA WITH UNCONFORMITY
Map 12 is a geological map of an area deformed by folding.
(The map and the topographic profile are attached!)
Draw the structural contours above and below the unconformity. The fold is under the unconformity, and you must
find the structural contours for the three limbs of the fold.
20. What is the orientation of the bedding above the unconformity?
a. N33E, 16NW b. N68W, 6NE
c. N12W, 18SW
d. N79E, 15SE e. N2E, 65NW
21. What is the attitude of unit B, in the western part of the map?
a. 000, 00
b. 000, 90
c. 000, 19W
090, 90
e. 000, 09E
22. What is the attitude of unit B, in the east side of the diamond shaped exposure of unit A?
a. 000, 00
b. 000, 90
c. 000, 19W
090, 90
e. 000, 19E
23. What is the orientation of the axis of the fold, on the western side of the map, where A is exposed?
a. 000, 00
b. 000, 90
c. 090, 00
d. vertical
e. 030, 00
24. What kind of fold is this?
a. syncline
b. monocline c. anticline
d. plunging syncline
e. non-plunging syncline
25. What is the vertical thickness of unit C?
a. 200 m
b. 100 m
c. 400 m
d. 50 m
e. 300 m
26. Draw the subcrop of unit D under unit X on the east side of the map. For this, you need to intersect the structural
contours for the two contacts of unit D, with equivalent structural contours of the unconformity, i.e., the
intersection line of the unconformity with the two contacts of unit D!
Approximately, how much do we have to drill at point X, in unit X, in the eastern part of the map, to reach unit D?
Note: elevation at X ≃ 930 m.
a. 100 m
b. 400 m
c. 70 m
d. 200 m
e. 250 m
27. What is the type of contact under the elliptical unit X, in the middle of the map?
a. Thrust fault b. unconformable
c. intrusive
d. conformable
e. normal fault
28. Why do we have the small elliptical exposure of unit X in the middle of the map?
a. It is folded with the other units
b. It is exposed under unit E
c. It has ‘survived’ after the rest of it is eroded d. it is a klippe
e. it is a window
29. What is the vertical thickness of unit X?
b. 200 m
b. 100 m
c. 400 m
d. 50 m
e. 300 m
/15 pts
Attach your map for credit!
Make sure to indicate the subcrop of unit D under the unconformable units.
/20 pts Draw a structural cross section along the PQ line (the profile is provided).
Attach your cross section PQ!
Structural Geology (Geol 4013/6013)
Lab 5. Page 5