Today, you will be learning the basic principles of geological mapping. In this activity you will learn to identify layers of rock, group them into mappable layers, and identify dip direction using satellite imagery in Google Earth Pro. The take-home assignment you will complete aims to link together all the topics covered in this lab to introduce you to geological mapping using satellite imagery.
Before you get started, download Google Earth Pro (free) for desktop. Web or Mobile versions are also available but they do not have all the features you will be required to use in this activity.
Download the 1101 Lab 9.kmz file provided by your instructor. In Google Earth Pro, click File, Open and navigate to wherever you saved the downloaded .kmz file.
In the left panel you should see a list of places in this kmz file, double click on “Raplee Anticline”. We will begin by examining the Google Earth satellite imagery only, so uncheck the box next to “Mexican Hat Topographic Map”.
1. Examine the area around Raplee Anticline from an altitude of ~5 km. Write down any observations you have about this area.
2. Notice the different colours. What might these different colours represent?
3. Why are we examining this area to study bedrock geology? Why not look around Calgary? Why not look around Vancouver, BC?
Turn on the “Mexican Hat Topographic Map” layer by checking the box next to it in the Places sidebar. Make sure the map is 100% opaque (not transparent at all).
- To adjust the transparency, right click on the name of the layer in the Places sidebar, and select Properties.
- A dialogue box should appear. Click and drag the bar to adjust the transparency of the topographic map overlay.
Now that you are examining a topographic map draped over the 3D landscape in Google Earth, let’s review some concepts about topographic maps from Lab 8.
4. What units are used to show elevation on this topographic map?
5. What is the contour interval on this topographic map?
6. What do topographic contour lines do when they cross a stream? If you’re not sure, examine one of the streams to the northwest of the Raplee Anticline, but still on the east side of the San Juan River.
Adjust the transparency of the topographic map such that it is almost transparent but the topographic contour lines are still visible.
7. Examine the immediate area around the Raplee Anticline in plan view (remember, you can press r on your keyboard to return to plan view). What do you notice about the contour lines relative to the contacts? Hint: the contacts are the planes between layers of rocks of different colours.
8. Rotate the view to examine the area in 3D. Circle the correct answer: do these layers in the immediate area around Raplee Anticline appear to be horizontal, vertical, or dipping?
9. If you were to walk 500 m from Raplee Anticline, heading due west, would you be walking over progressively younger or older rocks? What principle of stratigraphy did you use to determine this?
10. Examine the strata directly to the west of Raplee Anticline but still on the east side of the San Juan River. Again, compare the strata that you can recognize by the variations in colour to the contour lines. Do these strata appear to be horizontal as well? Why or why not?
11. Rotate the view until you are looking directly east toward Raplee Anticline. Look closely at the jagged-looking layers of red and grey rocks. Notice how if you try to trace a single layer of rock it makes a jagged line? That is because these layers are dipping. Rotate your view to see this in 3D and confirm these layers are indeed tilted, or using proper terminology, they are dipping.
- Take another look at one of the streams you examined earlier, just to the NW of Raplee Anticline.
- Zoom in, press r to return to plan view, and pick a distinctive stratum (a single layer of rock) to trace.
- Trace your chosen stratum across this stream. Notice how it makes a “V” shape and the point of the “V” points in the direction of dip.
12. What is the dip direction of these dipping strata? Remember, think of dip direction as the direction water would flow if poured onto the layer of rock.
So far, you have seen that dry, arid climates make excellent areas for virtual field work because there is little vegetation to obscure your view of the geology! You have observed that different rock units may be distinguished even in satellite imagery based on colour differences. You have seen how horizontal strata have contacts that are parallel to topographic contour lines, and how dipping strata have contacts that deflect across contour lines. You have also practiced using the Rule of V’s to determine dip direction.
Let’s explore a couple more arid regions of the world with spectacular geology: Karkh, Pakistan and Dekhuyeh, Iran.
13. Use the Rule of V’s to determine the dip direction of the light beige coloured layers of rock near Karkh, Pakistan.
14. Use the Rule of V’s to determine the dip direction of the light beige coloured layers of rock near Dekhuyeh, Iran.
Finally, let’s explore one more field area to relate the geology you can see in Google Earth to a geological map. Navigate to “Sheep Canyon Area” and examine this area from an altitude of ~9 km. Notice how you can see the different layers clearly because this area has very little overburden and vegetation to hide the bedrock geology. Turn on the “Sheep Canyon Geological Map” layer. Toggle the layer on and off, or adjust the transparency.
15. How are the rocks of different colours that you could see in the satellite imagery depicted on the geological map?
In Lab 8 you created a fluvial surficial geology map – a map of sediment deposited by a river. That is one type of map used in geology, to show deposits of loose sediment on the Earth’s surface. Another type of geological map shows the bedrock, meaning the layers of hard, fully-lithified rocks that are exposed at the Earth’s surface. All the layers of rock you have been studying today are examples of bedrock.
Rocks are typically mapped in packages that are often formally named formations or groups. Notice how each formation on the Sheep Canyon geological map has a map code associated with it to link each formation to the legend.
16. Can you see anywhere on this map or in the Google Earth satellite imagery where you could use the Rule of V’s to determine dip direction? For which unit could you do this? State the complete formation name, the map code, and the dip direction.
Now that you have a sense of how to visualize layers of rocks in three-dimensions, and what the different colours on a geological map represent, we are going to focus in on how to read geological maps. Close Google Earth Pro, and open the digital PDF copy Sheep Canyon Geological Map to answer the following questions.
17. What is the full title of this map?
18. Who is the author of this map?
19. What is the scale of this map?
20. What is the distance in kilometers measured along Highway 14-16-20 from the intersection with Highway 310 to the intersection with the pipeline?
21. What information is provided for each mapped unit in the legend of a geological map?
22. In what order are the formations listed in the legend?
23. What is the map code, name, age, and lithology of the oldest unit on this map?
24. In what general area of the map would you find this unit exposed at the surface?
25. What is the map code, name, age, and lithology of the youngest formation on this map?
26. In what general area of the map would you find this formation exposed at the surface?
27. What are the full names of the two formations deposited during the Pennsylvanian? Which of the two is oldest?
28. If you were going to start a drywall manufacturing business, which formation(s) would you be most interested in exploring?
- 1101 Lab 9.kmz file by Siobhan McGoldrick. Derivative of Kmz file of placemarks for other structural mapping examples by Barbara Tewksbury, Locations in Google Earth for teaching geologic mapping and map interpretation, used under CC-BY-NC-SA 3.0.
- Mexican Hat Topographic Map © USGS. Public domain.
- Sheep Canyon Geological Map by Robert E. Ladd © Wyoming State Geological Survey. All rights reserved. Used with permission.
a general rule for determining dip direction of dipping planar contacts deflected or bent as they cross a valley or stream
direction of maximum dip, the direction water poured onto a dipping plane would flow
A body of rock identified by lithic characteristics and stratigraphic position; it is prevailingly but not necessarily tabular and is mappable at the Earth’s surface or traceable in the subsurface.
The lithostratigraphic unit next higher in rank to formation; a stratigraphically-continuous series of related formations.