Lab 3: Image interpretation and map construction (20 pts. - two parts)

Lab objectives:

This project will consist of two phases, completed over two weeks. First, you will answer specific questions about structural features or patterns visible at five localities using Google Earth (Part 1). This will require you to manipulate and capture some of the Google Earth images you find (ask if you are not familiar with how to do this). Submit your work through the Blackboard assignment function as a Word document. For the second week you will use a software program (either Inkscape or Illustrator) to create a geologic photo interpretation map for the Dougherty anticline in Oklahoma (link to part 2). This should also be submitted via the Blackboard assignment function.

The image to the right is an oblique air photo of portion of the central San Andreas fault. The fault scarp runs horizontally across the image in the lower third as a linear topographic feature with the far (east) side higher than the foreground. Also evident here is the mismatch in drainage patterns across the fault. The interpretation is that the main channel in the foreground left of center used to match the truncated pattern on the far side, and so the dextral movement of the fault is evident (far side moving to the right relative to the near side). The intent of the first part of the lab is to gain experience in interpreting imagery for the structural geology informatin it can contain. Image credit: Robert E Wallace of the USGS

Part 1

You will be instructed as to which 5 of the below possibilities to do. You can copy and paste the text from below into a Word document where you can insert your answers and images. The completed document can then be handed in through Canvas.

Zagros Mountains, Iran: Navigate to lat 28.0054 lon 54.9024, which should be in the Zagros mountains of Iran. The geologic feature is near Forg, but pretty much in the middle of nowhere. The focus of this exercise is the large grey body.

a) Zoom in and you will see that it is layered and the layering is tilted. What overall pattern does the tilted layering form (what type of structural geometry exists here).

b) How much topographic relief exists from the edge of the structure to the highest point near the middle. How would you describe the drainage pattern?

c) Navigate specifically to the area at lat 28.0565 lon 54.9108, and notice the numerous depressions in the area. These are sinkholes. What rock type other than limestone is soluble and could form sinkholes?

d) What type of structural feature is this? Some research may help.

Upheaval Dome, Utah: Use Google Earth to migrate to this location and answer these questions. Note the distinctive circular feature here - this is Upheaval dome.

a) Follow the drainage from the circular feature to the major river to the west. What is the approximate orientation of the strata near the juncture with this river?

b) Describe the dip pattern of the strata involved in the circular feature? Viewing different portions obliquely and keep tracking of the elevation as you trace a distinctive layer in Google Earth can help you figure this out.

c) Approximately how big across is the structure (use the measurement tool in Google)? This will be an approximation as exactly what is the outer bound of the structure is not shortly demarcated. Measure from the edge of where the strata are deformed across the center to the other edge where you can find the same strata.

d) Where are the oldest rocks likely exposed here?

e) Speculate on what might have been the cause of this localized structure surrounded by otherwise undeformed strata.

Badwater, California - Death Valley Navigate to Badwater, California, a popular locality within the active Death Valley Rift.

a) Navigate along the mountain front to the southeast of Badwater. You should see a number of well developed alluvial fans. Some of these are partially cut by recent fault scarps. These can be quite subtle, and can quickly degrade with time. Make sure you are not simply looking at a channel edge scarp. Use the Add Path tool in Google Earth to trace out an exemplary fault scarp (or two). Use the Save Image option of a screen shot to save the image (with scale, an option that can be turned on and off in Google Earth) and paste the image into your word document.

On the ground view of a recent fault scarp (red arrows) in Death Valley.

b) At a larger scale if the mountain front marks the approximate position of an active fault, how much can the orientation change in degrees at the scale of kms.

c) Starting from the Badwater alluvial fan, measure and list here the spacings between the 6 alluvial fans to the south (from apex to apex). What is average spacing?

d) Considering this is Death Valley, what might the very white area represent?

Bonus point: How might the the white area be related to border fault slip gradient?

Afar triangle faults: Navigate to lat ll.6060 long 42.5222, which should be in the Afar triangle area, just southeast of Lake Assal, near the road RN9. You should see lots of dark layered rocks cut by topographic scarps that are fault scarps.

a) What produced the dark layers?

b) Find the dip of a fault and mark it with Google Earth thumbtack. Then travel approximately 500 m along the fault and note the elevation just on either side of the fault scarp (below the talus deposits on the base). Insert a thumbtack labeled with the topographic difference on either side, which is a measure of the vertical offset (the throw) across the fault. Do this for another point about 500 m further along the fault. You should have the beginning of a map showing the throw gradient along the fault. Insert a copy of that image/map below.

c) Compute the throw gradients (offset change versus distance along the fault) for these two sections of the fault and report here.

d) Describe in a sentence or two the drainage pattern on top of the dark layers in between the fault blocks. What does the drainage pattern suggest about tilting of the fault block.

Sinai basement rocks - Navigate to 28° 42' 14.20" and 33° 50' 31.19" and at a window scale equivalent of several kilometers across. This is one of the more spectacular geologic patterns I have seen in Google Earth.

a) Note the array of thin dark lines running in different directions. What geologic feature do you think these represent? The rest of the questions below focus on these features.

b) Describe the preferred directions of these features that exist in this area?

c) Look for places you can tell what the relative age of two cross cutting examples of the feature are. Use the Save Image option to save the image (with scale) and paste it into your word document. In your example, which direction preceded the other?

d) Zooming in you can see that these features have some interesting tip and branching diagrams. Find an interesting example, and use the Save Image option to capture it and then paste it into your word document. Describe the geometry in a few sentences.

e) If you navigate to the North you find flat-lying, light colored sedimentary rocks. Are the features you have been looking at older or younger than these rocks (provide a reason for the age assignment)?

Pallet Creek, San Andreas fault, California: Navigate to 34° 27' 20.22' N and 117° 53' 0.41 W and you should see Pallett Creek Road right next to Pallett Creek.

a) Locate where you think the San Andreas fault (a distinctive linear topographic feature in this area) crosses the creek, and mark the path of the San Andreas fault with the Add Path tool. Now trace Pallett Creek across the San Andreas for 2 km or so. Use the Save Image option to capture the image and insert into your word document. The trace of Pallet Creek is consistent with what type of offset along the San Andreas fault?

b) Strike-slip faults can have an oblique component so that tectonically developed topography develops as the crustal blocks move. If there is one side of the San Andreas fault here that has an up component, which one is it?

c) About 2.8 miles SE of where the fault crosses Pallett Creekone one can find well exposed ridges of a white Miocene sandstone that are involved in a fold. Find the fold hinge area and use the Save Image option to capture a image of it and insert it into your word document. Is this an anticline or syncline, and what direction does it plunge?

d) Follow out the southwestern limb of the fold. What happens to it structurally, and provide the evidence/reasoning that led you to your conclusion?

North of Greybull, Bighorn Basin, Wyoming: Navigate to Greybull, Wyoming and then move about 4.7 mile at about azimuth 355. You should be on the crest of a large fold structure.

a) Navigate to an oblique view looking along the fold structure from a perspective that shows the form of the fold in cross section. Look for where a river cuts through the structure providing a natural cross section. Capture that image and insert into your word document. Describe the fold form in words as completely as possible, including visual estimates on the limb dip angles.

b) Focus on the brightly colored red rocks (Triassic redbeds) at each end of the fold structure. In terms of both shape and structural orientation describe how the two ends of the exposed fold pattern differ?

Bonus (2 pts. out of 10): The goal of this is to provide motivation to explore Google even further on your own. Find and report on a google locality that shows a well developed structural feature or pattern of interest and complete the following for it. There are many possibilities.

If you want to practice interpreting imager for geologic structures some more link to these air photo images:

(link to part 2)