EvC Forum: The Story in the Rocks

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Topic: The Story in the Rocks - Southwestern U.S.

Minnemooseus

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From: Duluth, Minnesota, U.S. (West end of Lake Superior)

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Message 75 of 121 (781831)
04-07-2016 11:52 PM

Reply to: Message 68 by edge
04-07-2016 9:44 PM

Re: compound/complex forces

Replaying message 58:

Here is an image of deformed sediments in a compression.

And here is one in tension.

In both cases, you can see that the uppermost layers are deformed, even more so than the lower layers. Some vertical deformation is required to take up strain.

In this case, there's something about the setup that looks like it caused the right side to override the left.

The compression was from moving the left wall. The right wall is fixed.

Moose

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	Message 68 by edge, posted 04-07-2016 9:44 PM		edge has replied

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	Message 76 by edge, posted 04-08-2016 12:10 AM		Minnemooseus has replied

Minnemooseus

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Posts: 3976

From: Duluth, Minnesota, U.S. (West end of Lake Superior)

Joined: 11-11-2001

Member Rating: 6.1

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Message 77 of 121 (781834)
04-08-2016 12:43 AM

Reply to: Message 76 by edge
04-08-2016 12:10 AM

Reverse and normal faulting etc.

However, if you look closely, the small, almost parasitic folds on the right side of the larger fold do have a left over right sense of motion.

To me, those small folds look like shear folding and/or drag folding related to shearing. You seem to have a model of incipient thrust (reverse) faulting.

The tension model shows normal shearing and a graben structure.

Moose

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	Message 76 by edge, posted 04-08-2016 12:10 AM		edge has not replied

Minnemooseus

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Posts: 3976

From: Duluth, Minnesota, U.S. (West end of Lake Superior)

Joined: 11-11-2001

Member Rating: 6.1

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Message 120 of 121 (786815)
06-27-2016 5:59 PM

Reply to: Message 119 by Tanypteryx
06-26-2016 2:25 PM

Re: Unconformities?

Just because you see tilted rocks and (apparently) flat lying rocks in the same view doesn't automatically mean angular unconformity. You might, for example, be seeing a tilted limb of an anticline in the foreground and the flat lying crest of the same anticline in the distance. I think you need to see more detail to make a judgement.

Also, topography/perspectives can create illusions. You can look at a rock face and the bedding may appear to be flat, when it is indeed dipping steeply. This is the difference between apparent dip and true dip.

I've been through that area of Wyoming, albeit 20+ years ago. I think you MIGHT have an example of a monocline there.

Moose

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	Message 119 by Tanypteryx, posted 06-26-2016 2:25 PM		Tanypteryx has seen this message but not replied

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