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Friday Field Foto #80: Thrust fault contact in Nevada

April 10, 2009

This week’s Friday Field Foto is a close-up view of the Keystone Thrust in southern Nevada.

The key criterion for correctly recognizing a thrust fault is to demonstrate that there are older rocks on top of younger rocks (assuming the whole thing isn’t upside down). In many cases, this isn’t necessarily straight-forward.

What’s great about the Keystone Thrust, at least in this location, is that dark gray Cambrian (540-490 Ma) limestones are on top of bright pinkish and buff-colored sandstones of the Jurassic (200-145 Ma) Aztec Formation. The contact is very easy to see!

(© 2009 clasticdetritus.com)

Keystone Thrust contact, near Valley of Fire, southern Nevada (© 2009 clasticdetritus.com)

Happy Friday!

see this older Friday Field Foto for a different view of this same outcrop

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2 Comments leave one →
  1. April 10, 2009 7:13 am

    That’s a neat thrust photo – it makes it look like the contact is irregular rather than smooth, or maybe that’s just the way the limestone erodes. I don’t think I’ve ever seen this thrust before…

  2. maureenlynn permalink
    April 10, 2009 10:55 am

    “The keystone thrust… is that some sort of maneuver?” –My sister

    Awesome photos. Yay geology!

    http://maureenlynn.wordpress.com

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