The Great Unconformity Frenchman Mountain Southern Nevada

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What is an Unconformity?
What is the great Unconformity of Frenchman mtn?
What creates them?
Where did the name come from?

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  • http://geoscience.unlv.edu/pub/rowland/Virtual/geology.html#whatis
  • http://geoscience.unlv.edu/pub/rowland/Virtual/hike.html
  • http://geoscience.unlv.edu/pub/rowland/Virtual/hike.html
  • http://www.idahosummits.com/frenchman/images/lake%20mead.jpg
  • The Great Unconformity Frenchman Mountain Southern Nevada

    1. 1. The Great Unconformity Frenchman Mountain Southern Nevada
    2. 2. http://www.geotimes.org/nov05/Travels1105.html http://www.terraprints.com/catalog/nevada_satellite_map.jpg Or, how I learned Why we need Nevada!
    3. 3. • What is an Unconformity? • What is the great Unconformity of Frenchman mtn? • What creates them? • Where did the name come from?
    4. 4. • An unconformity is a buried erosion surface. It is a surface of rock that was exposed on the Earth's surface and was then covered by younger layers. • Unconformities are important because they represent missing intervals of the geologic record, like pages missing from a history book. The Great Unconformity of Frenchman Mountain represents about 1.2 billion years, which is more than one fourth of the age of the Earth. http://geoscience.unlv.edu/pub/rowland/Virtual/geology.html#whatis
    5. 5. • The concept of an unconformity arises from two of the oldest principles of geology, first stated in 1669 by Nicholas Steno: • Layers of sedimentary rock (strata) are originally laid down flat, parallel to the Earth's surface. That's the law of original horizontality. • Younger strata always overlie older strata, except where the rocks have been overturned. That's the law of superposition. http://geology.about.com/od/geoprocesses/a/unconformities.htm
    6. 6. Frenchman Mountain http://www.idahosummits.com/frenchman/images/frenchman%20mountain.jpg
    7. 7. LAS VEGAS “BOWL” EAST- Frenchman Mountain Range; WEST - Spring Mountain Range; NORTH - Sheep Mountain Range; SOUTH - McCullough Mountain Range http://nevada-history.org/facts.html
    8. 8. http://geoscience.unlv.edu/pub/rowland/Virtual/hike.html
    9. 9. Forming the Great Unconformity http://geoscience.unlv.edu/pub/rowland/Virtual/geology.html#name
    10. 10. FROM THE GRAND CANYON TO THE LAS VEGAS BOWL…HOW A MOUNTAIN MOVES. 6-10 Million years ago western North America begins moving west due to interaction between the North American and Pacific lithospheric plates, which today slide past one another along the San Andreas fault in California. Movement of blocks becomes tilted as secondary faults encounter a nearly horizontal master fault causing the blocks to tilt eastward while moving westward. Continuous sliding on the master fault causes Frenchman Mountain to move about 50 miles from original position. http://geoscience.unlv.edu/pub/rowland/Virtual/geology.html
    11. 11. Precambrian granite (about 1.7 billion years old) and beginning with the white rocks exposed along the slope of the low hill, are the Cambrian Tapeats Sandstone (about 500 million years old).
    12. 12. • Above the Great Unconformity we see the sedimentary Tapeats Sandstone with recycled large, light gray, angular, quartz pebbles. These rocks have a dark coating called desert varnish or rock varnish which is a thin manganese- and iron- rich coating that develops on exposed rock surfaces and is most common in desert regions. Bacteria, using chemicals from dust particles,[produces this varnish over thousands of years http://geoscience.unlv.edu/pub/rowland/Virtual/hike.html
    13. 13. FRENCHMAN MOUNTAIN WAS PARTLY CREATED BY MOVEMENT ALONG THE FRONT RANGE FAULT SHOWN BELOW http://www.wheaton.edu/ACG/trip/jpgs/35b.jpg
    14. 14. http://img.geocaching.com/cache/log/423d19f3-5359-49b0-97ea-25560519bb36.jpg Granite intrusion in the schist.
    15. 15. http://img.geocaching.com/cache/log/577d4037-28e0-4cc6-8aaa-9433f8aaf221.jpg Precambrian granite and schist / Tapeats sandstone
    16. 16. Some old guy and The Great Unconformity
    17. 17. CROSS SECTION OF FRENCHMAN MOUNTAIN.
    18. 18. Vishnu granites and the overlying Tapeats Sandstone http://www.wheaton.edu/ACG/trip/stop2a.html
    19. 19. •Clarence Dutton in his 1882 book Tertiary History of the Grand Cañon District. •People assume that the Great Unconformity was so named due to the large interval of time it represents in the Earth’s history. •The truth is Dutton had no idea of the age of the rocks on either side of the Unconformity. •Basically, he knew the importance of this find and that something was missing but had no idea of the extent of time that had passed between the Cambrian age Tapeats sandstone and the granite and schist that lie beneath it. WHERE DID THE NAME “GREAT UNCONFORMITY” COME FROM? http://geoscience.unlv.edu/pub/rowland/Virtual/geology.html#name
    20. 20. Great Unconformity Geologic Interpretive Site andTrail http://geoscience.unlv.edu/pub/rowland/Virtual/virtualfm.html
    21. 21. http://www.flickr.com/photos/kitkattt9/2061774736/
    22. 22. http://www.flickr.com/photos/kitkattt9/2061775502/
    23. 23. West face
    24. 24. Igneous laccolith, Lava Butte south of Frenchman Mtn, Alluvial fans and Lake Mead. http://www.idahosummits.com/frenchman/images/lake%20mead.jpg
    25. 25. Eastern Face of Frenchman Mtn. with Las Vegas in the foreground.
    26. 26. Peak of Frenchman mtn.

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