Name:
Class day and time:
Web Extras for Chapter 14: Structural Geology
8.
Web extras: Inferring structures from geologic maps. Many state geological surveys post geologic and
other maps on the Web. Go to www.ohiodnr.com/geosurvey/, link to Geology of Ohio, then Bedrock Geology,
and then click on Page-sized Bedrock Geologic Map of Ohio. Because of the scale of the map and the low
relief of Ohio, this map is comparable to the top surface of a block diagram. As indicated by the explanation,
the rocks are grouped into the geologic time periods in which they were deposited. If you’ve forgotten the
relative ages of geologic periods, consult Figure 13.7 or www.geosociety.org/science/timescale/timescl.pdf.
a.
Where are the youngest units on the state map (not the cross-section) and what is their geologic age?
Where are the oldest units on the state map (not the cross-section) and what is their geologic age?
What is the age of the oldest unit in the cross-section?
b.
Which way do the rock units in the eastern half of the state dip and how do you know? How would you tell
if there was no cross-section?
Which way do the rock units in the northwestern most part of the state dip and how do you know?
c.
9.
What is the large structural feature centered in the western half of the state and how do you know? How
would you tell if there was no cross-section?
Geologic structures from space. Google Maps (or similar websites) offer an excellent way to see actual
geologic structures. Name the geologic structure that appears in the center of each of the locations that follow.
Each link below takes you to a satellite image. To see a shaded relief map, click on the box labeled Map and
then underneath this box click Terrain. Clicking on Satellite gets you back to the original image. You may
want to zoom in or out or move around the image to figure out what structure you are looking at.
a.
Lander, WY: http://maps.google.com/maps?q=laramie,+wy&hl=en&ll=42.842996,108.822327&spn=0.246444,0.467606&sll=38.89474,-104.881625&sspn=0.0327,0.058451&t=h&z=12
Look at the sedimentary layers west of Boulder Flats, Milford, and Lander. Which way are they dipping?
Sheep Mountain, just north of Greybull, WY:
http://maps.google.com/maps?q=Greybull,+WY&hl=en&ll=44.574084,108.076115&spn=0.120325,0.195179&sll=44.040219,-108.992615&sspn=1.94279,3.122864&t=h&z=13
What is the geologic structure?
Would you expect the oldest beds to be in the center or along the edges of this structure?
Web Extras for the Laboratory Manual for Physical Geology by Jones and Jones (McGraw-Hill).
Was this structure formed by extension, compression, or shear?
b.
Spring Mountain Ranch State Park, near Las Vegas, NV:
http://maps.google.com/maps?q=Las+Vegas,+NV&hl=en&ll=36.095441,115.51815&spn=0.136489,0.195179&sll=37.0625,-95.677068&sspn=66.915969,99.931641&t=h&z=13
The contact between the dark and light rocks that runs roughly north-south is a fault. The rocks to the west
of this contact are dipping down to the west. The fault puts the brown rocks (the Cambrian Bonanza King
Formation) on top of the light rocks (the Jurassic Aztec Sandstone). What type of shallowly dipping fault
puts older rocks on top of younger rocks?
Was this fault (known as the Keystone Fault) produced by extension, compression, or shear?
c.
Wallace Creek, CA: http://maps.google.com/maps?q=San+Luis+Obispo,+CA&hl=en&ll=35.270079,119.827366&spn=0.034477,0.048795&sll=37.0625,-95.677068&sspn=66.915969,99.931641&t=k&z=15
Wallace Creek is in the middle of the image. If you turn ‘Labels’ off under the Satellite menu, it is easier
to focus on the creek drainages. As you can see, many of the creek drainages are offset to the northwest
where they cross a major fault that is making a roughly linear trace from southeast to northwest. What type
of fault is this (be as specific as possible)?
Does this fault indicate active extension, compression, or shear?
d.
Lake Albert and Summer Lake, OR: http://maps.google.com/maps?q=oregon&hl=en&ll=42.786331,120.105286&spn=0.99172,1.561432&sll=36.133161,-115.42614&sspn=0.272848,0.390358&t=h&z=10
This area has been cut by a lot of faults that cause the footwall to drop relative to the hanging wall. The
result is a lot of cliffs (click on Map, Terrain to see the shaded relief map of this scene). Big examples
include the high escarpment east of US 395 and the cliffs along the east side of the lakes in the basin with
the ‘State Holding’ marker. To the west, Summer Lake has a smaller scarp along its west side, plus a series
of small scarps can be seeing north and east of the lake. What type of fault makes the cliffs and scarps that
characterize south-central Oregon?
Do these faults indicate that south-central Oregon is being subjected to extension, compression, or shear?
You can see photos of this beautiful area here:
http://geology.about.com/od/geophoto_tours/ig/oregonoutback/.
e.
Near Cahuisa, Chile: http://maps.google.com/maps?q=chile&hl=en&ll=-20.807472,69.082031&spn=0.311624,0.365639&sll=37.0625,-95.677068&sspn=66.66237,54.140625&t=h&z=12
Roughly horizontal beds are seen resting on top of nearly vertical beds. What type of unconformity is this?
Web Extras for the Laboratory Manual for Physical Geology by Jones and Jones (McGraw-Hill).