ES1022B_lab5_structuralgeol_student_2023-1
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Dec 6, 2023
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ES1022A
Lab 5: Background Pages
1
EARTH SCIENCES 1022A
LAB 5: STRUCTURAL GEOLOGY
First, a few items to help you with this lab assignment.
Just for practice…you will be re-identifying 7 rock samples: I-9, S-2, S-7, S-7, S-9, S-11, M-1 and
M-2 for question 6.
Strike and
Dip -
together comprise the orientation (attitude) of strata (“
beds’).
Strike - compass direction of a horizontal line on a bedding plane.
Dip (aka “dip angle”): maximum acute angle between the bedding plane
and the horizontal.
Map Symbols
Types of Structures (note for relative ages of beds in diagrams: “Y” = younger, “O”=older)
Folds
Anticline
(“arch’)
Syncline
(“trough”)
Monocline
(“step”)
Asymmetrical fold
(asymmetrical
anticline in this case)
Plunging anticline
Plunging syncline
Dome
(“hump-shaped”)
Basin
(“bowl-shaped”)
20
axial plane - plane which divides the fold as symmetrically as possible
fold axis - line of intersection between the axial plane and any bed
fold limbs
Strike
and dip
Vertical
bedding
Horizontal
bedding
Plunging
syncline
Plunging
anticline
(Non-plunging)
anticline
(Non-plunging)
syncline
ES1022A
Lab 5: Background Pages
2
Faults
Normal dip-slip
Reverse dip slip
Thrust (low-angle
reverse)
Strike-slip (left lateral)
Unconformities
disconformity
Angular unconformity
Nonconformity
Note also that for all the maps in this lab, we will be assuming that the surface is flat and horizontal
(for the sake of simplicity). We will be adding topography in the next lab.
River Valley “V”s
Another thing you should make a note of this time is that on a map (provided that the land surface is
horizontal (flat)), the contacts between beds that are either horizontal or dipping will appear to form
a “v” where a stream valley cuts into the surface. If the beds are dipping, the narrow part of the “v”
will point in the down-dip direction (but be careful with this as a “v” will also appear if the beds are
horizontal but the top surface is sloping). The more prominent the “v” is, the more gentle the dip of
the underlying beds. Steeply dipping beds produce less prominent “v”s. And the beds are vertical,
“v”s will not appear in the bed contacts at all in a river valley.
Small “v” means
underlying beds
dip more steeply.
s
t
r
e
a
m
3
3
2
2
Map
1
A
B
Strata dip
to east.
Strata dip
to west.
North
More prominent “v”
means
underlying beds
dip more gently.
Oldest bed in middle means this
structure is an anticline.
On the left is an example of a simple map
depicting sedimentary beds/units exposed on
a flat ground surface with a river running
through it. The oldest bed is represented by
unit 1. Note the following:
1. The prominent “v”s in the river valley on
the right-hand side indicate that the
underlying beds dip gently toward the east.
2. The less prominent “v”s on the left,
indicate that the underlying beds dip more
steeply to the west.
3. The fact that the oldest bed occurs in the
middle of the structure indicates that the
structure is an anticline.
4. Differences in the width of beds on either
side of 1 are due to differences in dip angle
(narrower=steeper dip; wider=gentler dip)
ES1022A
Lab 5: Background Pages
3
Cross-Section Example
Continuing to use the previous map, we can construct a cross-section (side view) of the beds under
the surface. To make this as simple as possible, let’s imagine that we are looking at a side view of
the lower edge of the map (let’s call this transect A-B).
Drawing from the previous map, we can say that the underlying structure is an anticline, with beds
of the left fold limb dipping steeply westward and beds of the right fold limb dipping more gently to
the east.
You would draw this cross-section in the following steps:
B
s
t
r
e
a
m
3
3
3
3
2
2
2
2
Map
Cross-Section
1
1
A
A
B
Draw lines for bed
contacts down from
map to top surface
of cross-section
(note dashed
arrows)
Strata dip
to east.
Strata dip
to west.
North
Extending bed contacts
above cross-section
(dotted lines) help you
visualize this as an
asymmetrical
anticline.
On the surface,
the same bed
(e.g. bed 2) will look
narrower if
steeply
dipping, but
wider if gently dipping.
1. Mark the positions of bed contacts along
the top “surface” of your cross-section (A-B).
In this simple example, you can just extend
vertical lines from the map to the cross-
section.
2.
Draw in steeply dipping beds (dipping to
west) downward from cross-section
“surface” on left side.
3. Draw in gently dipping beds (dipping to
east) downward from “top surface” of cross-
section on right side.
4. Label the beds in the cross-section (in
this case 1-3)
5. Check to see if beds retain uniform
thickness by “restoring” the structure as it
existed before the cross-section “surface”
was eroded flat.
6. Note again that bed 2 looks wider on the
east side of the map than on the west
because it intersects the surface at a
shallower angle than the beds on the west
side.
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HAND-IN PAGES
Student Name:______________________ Student Number: _____________________
Page
1
of
5
Lab Section (indicate yours)
Earth Sciences 1022A
Lab 5: Structural Geology
Hand-In Sheets
Question 1 (12 marks total)
This question is designed to help you visualize geologic structures in three dimensions. Complete
the block diagrams above by filling in the small circles with the correct bed number (for “after
faulting” and “after erosion” in example 1 and “after erosion” for examples 2 and 3), Note: 1 = oldest
bed. (2 marks each for each example (0.5 marks/circle filled), 12 marks total). You can add
additional labels if you like, but only the circled numbers will be marked.
3
3
3
3
4
4
4
4
5
5
5
5
HAND-IN PAGES
Student Name:______________________ Student Number: _____________________
Page
2
of
5
Question 2 (6 marks total)
1
2
2
3
4
5
1
Draw symbols for the following on this geologic map (Note:
1 = oldest bed):
- fold axis, showing fold type (syncline/anticline) (1 mark)
- plunge direction (1 mark)
-strike and dip symbols in the boxes indicated (4 marks)
Question 3 (12 marks total)
4
3
2
2
1
3
4
5
Name of structure:
____________________
(1 mark)
Completed block diagram (2 marks)
6
2
3
4
4
5
3
5
6
5
5
Name of structure:
_________________
(1 mark)
Completed block diagram (2 marks)
2
3
3
4
4
5
5
Name of structure:
_________________
(1 mark)
Completed block diagram (2 marks)
3
3
2
4
5
6
Name of structure:
_________________
(1 mark)
Completed block diagram (2 marks)
Complete the block diagrams above (for folds, indicate if plunging or non-plunging in structure
name). Label bed numbers in your cross-section. Note: smallest number = oldest bed. (2 marks
each, 8 marks total). Also, you are not given specific dip angles, so it is the general pattern of beds
that you will be marked on.
HAND-IN PAGES
Student Name:______________________ Student Number: _____________________
Page
3
of
5
Question 4 (5 marks total)
Sketch cross-section D-D'. (1 = oldest bed). Complete
the cross-section for this map, labelling bed numbers
in your cross-section (4 marks) showing approximate
dip angles (within 5 degrees or so).
The contact between units 2 or 3 and unit A
is called
a(n) : ___________________ (1 mark)
Question 5 (6 marks total)
Complete the above cross-sections, labelling bed numbers in your cross-sections (1= oldest bed).
(2 marks each, 6 marks total).
4
3
3
2
5
6
4
B
B
B
B
B
B
s
t
r
e
a
m
s
tre
a
m
2
2
3
3
3
4
4
2
2
2
1
1
1
5
A
A
A
A
A
A
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HAND-IN PAGES
Student Name:______________________ Student Number: _____________________
Page
4
of
5
Question 6 (21 marks total)
Answer the following questions / do the following for the large block diagram above (21 marks total):
1. Complete the legend for the rock types represented in the diagram based on the rock samples
provided (try to identify them first without looking up the numbers…just for practice). (7 marks)
2. There is a large fold represented in the block diagram. Circle the terms (in italics) that best apply
to the fold in this diagram.
a)
non-plunging / plungin
g (circle for 1 mark)
b)
symmetrical / asymmetrical
(circle for 1 mark)
c)
syncline / anticline
(circle for 1 mark)
Hornfels
HAND-IN PAGES
Student Name:______________________ Student Number: _____________________
Page
5
of
5
3. Which of the following best describes the dip of beds on the left limb of the fold (circle correct
answer)?
a) dip angle: 30
0
, 45
0
, 65
0
, 85
0
(circle best approximation)(1 mark)
b) dip direction: North, East, South, West (circle correct answer)(1 mark)
4. Which of the following best describes the dip of beds on the right limb of the fold (circle correct
answer)?
a) dip angle: 35
0
, 60
0
, 70
0
, 85
0
(circle best approximation)(1 mark)
b) dip direction: North, East, South, West (circle correct answer)(1 mark)
5. Correctly draw a strike/dip symbol with the dip angle indicated, in each of the dotted-line boxes on
the “surface” view of the block diagram (2 marks).
6. In the long, vertical box with dashed lines (on the “surface” view of the block diagram, draw the
correct symbol for the fold represented in the diagram (see background pages), with plunge
direction indicated if applicable (1 mark).
7. A fault is also represented in this diagram. There are two parallel lines on either side of the fault
near the bottom of the diagram. Draw arrowheads on these lines to show the relative direction of
movement (1 mark).
8. This fault is a reverse dip slip fault / normal dip-slip fault / strike slip fault (circle correct answer (1
mark)).
9. The strike of the fault (orientation as viewed at surface) is:
northeast-southwest, northwest-southeast, north-south, east-west (circle correct answer (1 mark))
10. Based on the strike direction, the fault must dip in which general direction?:
a) toward the east, b) toward the northeast, c) toward the northwest, d) toward the north (circle
correct answer (1 mark))
Total Possible Marks for Lab:
62