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Author Topic:   Discussion of a specific Grand Canyon photograph
Minnemooseus
Member
Posts: 3945
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 10.0


Message 1 of 5 (787877)
07-18-2016 3:49 AM


This is a photo of the angular unconformity between the pre-Cambrian and the Paleozoic.
I don't know the actual compass directions in this photo, but for the sake of this discussion let's call away from us to be "north".
Now, this photo shows (to me) that perspectives can be deceiving. In the left ("west") 2/3s of the photo, the angular unconformity is obvious, below the thick vertically faced unit which appears to be horizontal or near horizontal.
But in the right ("east") 1/3rd of the photo, the units show no angular unconformity, and they all seem to be dipping to the lower-right ("southeast").
In reality, I think the thick vertically faced unit is still horizontal or near horizontal. The seeming dip to the lower right ("southeast") is a trick of perspective because you are looking down from above. And the lower pre-Cambrian units appear to have the same dip as the above unit because the strike of the lower units is parallel to the cliff face.
The lower pre-Cambrian units are actually dipping towards the upper-right ("northeast").
Moral of the story - Things aren't what they offhand appear to be.
Comments?
Moose
Edited by Minnemooseus, : Fill in the text of the message.

Replies to this message:
 Message 2 by Minnemooseus, posted 07-23-2016 1:11 AM Minnemooseus has not replied
 Message 4 by edge, posted 07-23-2016 5:47 PM Minnemooseus has not replied

  
Minnemooseus
Member
Posts: 3945
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 10.0


Message 2 of 5 (787878)
07-23-2016 1:11 AM
Reply to: Message 1 by Minnemooseus
07-18-2016 3:49 AM


Bump - Text has been added to message 1
Ready for promotion consideration.
Moose

This message is a reply to:
 Message 1 by Minnemooseus, posted 07-18-2016 3:49 AM Minnemooseus has not replied

  
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