Lab 4_ Deformation and Geologic Maps_FA22
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© Michelle Stoklosa 2020 1 Laboratory Exercise 4: Deformation, structural diagrams and geologic maps
Introduction to Geology II: Earth’s Surface Processes
Name____________________
Score: _______/25
Note: In this exercise, you are asked to draw on a few diagrams. The best (and preferred) way for you to do this is to print out the page(s) you need to draw on (pages 2 & 3 for this lab), sketch directly on them, then take a photo (or a scan) of your drawings. The images can then be embedded directly into the Word file that you submit or uploaded separately with your completed assignment. If you cannot print, you might instead just sketch these diagrams in a separate piece of paper, take photos of your sketches, and upload those with (or embed into) your lab exercise. INTRODUCTION In this exercise, we will be learning about the different types of deformation using structural block diagrams and geologic maps. You might want to have your textbook handy to see some examples of these structures. Note that we will be using the terminology for block diagrams as shown below (and explained in the tutorial video in Canvas) Ludman & Marshak, 2015 Part A: Strike and Dip
Review the concept of strike and dip
in Chapter 9 of your textbook and watch the associated video on the lab tutorial page, then proceed with task A1.
© Michelle Stoklosa 2020 2 Task A1: Determining direction of strike and dip DRAW strike and dip symbols on the map view (the top) of the block diagram below, then address the following questions. (1 point) Ludman & Marshak, 2015
Questions: (Each question worth 1 point) 1. In which direction are the beds striking, North to South or East to West (pick just one of these two choices)? 2. In which direction are the beds dipping down towards, North, South, East or West? (pick just one of these 4 choices) Task A2: Complete the block diagram Now complete the block diagram below by DRAWING in the layers on the front and sides
. (1 point) Question: (1 point) 1. According to the strike and dip symbol on the block diagram above, towards which direction are the beds tilting downward, North, South, West, or East? (Assume North is to the back of the diagram, is with the diagram from Task A1.)
© Michelle Stoklosa 2020 3 Part B: Ductile Deformation & Block Diagrams Now we will look at some block diagrams and maps that illustrate ductile
deformation. Please review the major ductile deformation structures in Chapter 9 of your textbook (anticline, syncline, basin, and dome), then continue. Task B1: Anticlines and synclines on block diagrams Review the lab tutorial video about how to draw an anticline on a block diagram, then address the questions below: Questions (Each question worth 1 point) 1. Show a syncline
on the front of the blank block diagram below. Then complete the top and sides of the diagram.
Ludman & Marshak, 2015 2. Complete the diagram below using the strike and dip symbols to guide you (complete both the front and the right side). Is this diagram showing an anticline or syncline? ___________________ Ludman & Marshak, 2015
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© Michelle Stoklosa 2020 4 Task B3: Domes and Basins Domes and basins are broad downwarpings and upwarpings, respectively, of the lithosphere. Ludman & Marshak, 2015 Questions: (Each question worth 1 point) 1. For the diagrams above, does the left
one show a basin or dome? 2. For the structure to the right
, are the rocks exposed in the center the youngest or oldest rocks in the structure? Part C. Brittle Deformation and Block Diagrams
Review the different categories of faults in your textbook. Figure 9.8 (the figure showing different categories of faults) will be especially useful to have on hand for this part of the exercise. Task C1. Strike slip fault Use the block diagram of a strike-slip
fault below to answer the following questions. Ludman & Marshak, 2015
© Michelle Stoklosa 2020 5 Questions: (Each question worth 1 point) 1. Which type of stress causes strike-slip faults: tensional, compressional or shear? (choose just one) 2. At which type of plate boundary might this strike-slip fault be most common (divergent, convergent or transform)? (choose just one) 3. Is the fault above a right or left-lateral strike-slip fault? 4. Which direction are all of these beds dipping down towards? (Assume North is to the back of the diagram, as we have done before; use directions such as N, S, E or W). Task C2. Dip-slip faults Use the block diagram of a dip-slip fault
below to address the following questions (note that the fault is show in bold black, and offsets the layers; the red line is there to show you what vertical is):
Ludman & Marshak, 2015 Questions (Each question worth 1 point) 1. What is the strike direction for all of these beds, North-to-South or East-to-West? 2. Is the block on the right of the diagram the hanging wall or footwall? 3. Which type of dip-slip fault is this? 4. Which type of stress causes this fault, tensional, compressional, or shear? 5. At which plate boundary are these faults most common, divergent, convergent or transform?
© Michelle Stoklosa 2020 6 Part D. Geologic maps and deformation
For this section, you will be looking at a few geologic maps of real places and studying the deformation in each location. What is a geologic map, you ask? You were introduced to these in Week 2 with your field project checkpoint. These are maps that show the distribution of rocks at th
e Earth’s surface. T
hese maps should have a key that indicates such things as age, rock type, and geologic structures. A website defining what the symbols mean on a geologic map can be found on the lab tutorial page. Task D1: Geologic Map of Wyoming On the next page is a portion of a geologic map of Wyoming (called the Bull Creek Quadrangle), which you will use to address the questions following it. You will need to zoom in (maybe even 500%) to see all of the details on this map.
If you have any trouble seeing this map, let me know, and ask specific questions as to what you can’t see on the map
so that I can help you.
Note the symbols to the bottom right indicating different structures. After examining the map, address the questions below: Questions: (Each question worth 1 point) 1. According to the legend on the side, and what you know about the Geologic Time Scale, is the Phosphoria Formation older or younger than the Chugwater Formation? 2. There are quite a few strike and dip symbols on this map. Find one, draw it in the space below, and describe what that symbol indicates about the rock unit below it. 3. Find the anticline with the axis that runs right through the R in FOREST. If the anticline symbol was not there, describe how would you know it was an anticline by using the ages of the rocks in the key, and the geologic time scale? 4. Which type of fault is most abundant on this map? 5. What does the fault type you names in #4 indicate about the dominant type of stress that this area has experienced (tensional, compressional or shear)?
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© Michelle Stoklosa 2020 7 Portion of the Bull Creek Quadrangle Geologic Map Ludman & Marshak, 2015
© Michelle Stoklosa 2020 8 Task D2. Geologic Map of Michigan Below is a geologic map of a portion of the state of Michigan (minus the Upper Peninsula). Use it to answer the questions below it. Michigan Department of Natural Resources, 1999 Questions: (Each question worth 1 point) 1. Are the pink rocks exposed in the center of the map most likely to be the oldest or youngest rock on the map? 2. This geologic map pattern of concentric rings should be a familiar pattern for a type of ductile deformation. Which type of ductile deformation structure is being shown here (be specific, and use your answer to question 1 to help you decide)? Whew! That was a lot of work, wasn’t it? You’re finally done!
© Michelle Stoklosa 2020 9 References
All block diagrams from: Ludman, A. & Marshak, S. (2015). Laboratory Manual for Introductory Geology
, 3
rd
ed. New York and London: W.W. Norton & Company. Geologic map of Michigan from: Michigan Department of Natural Resources. (1999). 1987 Bedrock Geology Map of Michigan [online image]. Retrieved July 22 from http://www.michigan.gov/documents/deq/1987_Bedrock_Geology_Map_301466_
7.pdf
.
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