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Orderville Geology Question

Discussion in 'General Discussion' started by Yellow Dart, Sep 5, 2019.

?

Ever licked a rock, just for kicks?

  1. Yes

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  2. No

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  3. Leave my lickings outta this

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  1. Yellow Dart

    Yellow Dart It's only hubris if I fail.

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    On a recent hump up and out Orderville after dropping Englestad, noticed many large limestone boulders.

    My friend MurrPurr, who has a geology degree herself, and I were wondering how they got there, what with the vast majority of the limestone around Zion peaking out around 3500' (the rough elevation of the Virgin River Valley as it flows from Rockville west and down off the Hurricane Bench).

    For reference, we were around 5500' in Orderville when we noticed them.

    Also noted a great deal of rounded and smoothed quartzes of varied color, some red agate too; common in Zion, but mainly found in the conglomerate layer around 4400', some 1000' down in elevation from Orderville. Not as curious as the limestone, but still interesting.

    Do we have much for geologists or other rock nerds here in the CC that could shed some light on the limestone boulders?

    I wagered glaciers in the Pleistocene, but MurrPurr did not concur.
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  2. ratagonia

    ratagonia

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    The Carmel Formation overlies the Navajo Sandstone, as does the Temple Cap. Both of these have Limestone members which are quite hard and persist while the softer rock erodes away from below them.

    https://en.wikipedia.org/wiki/Carmel_Formation

    Tom
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  3. Yellow Dart

    Yellow Dart It's only hubris if I fail.

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    Ahh, I always assumed those were sandstone. It explains the brilliant red and pink in the boulders we saw, the color of which I haven't seen in limestone here before. Thanks for the quick turn-around.
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  4. ratagonia

    ratagonia

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    Also, altitude is not a good indicator, but it helps. Where you are in the stack is what is important, and the stack does not lie flat. But you knew that.

    Tom
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  5. Scott Patterson

    Scott Patterson

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    That's true of the Carmel, but does the Temple Cap really have limestone layers? I haven't seen any in the Temple Cap, but maybe it does in places? Maybe the very top?

    The Carmel has a lot of limestone and it has some nice fossils with huge clam shells. There's a lot of them if you look around the base of R1 in Birch Hollow.
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  6. ratagonia

    ratagonia

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    Yes and no. Temple Cap has limestone, but not much. https://www.nps.gov/zion/learn/nature/temple-cap.htm
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  7. Bootboy

    Bootboy Atwood Gear

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    It may also be possible that said limestone boulders may be from strata above the Carmel and Temple Cap. Though layers containing rock of sufficient resilience to persist in the slots as presently formed do not typically lie in the stratigraphic sequence west of the Kaiparowits plateau, or are volcanic in nature.

    As to the occurence of limestone in the Carmel and Temple Cap - a regularly observed phenomenon in many layers of the Colorado Plateau are "lenses". These are localized deposits of carbonate (or other) minerals that formed when there were temporary changes in the conditions that formed the surrounding layer, e.g., a shifting river bed flowing through sand dunes or the advance and retreat of shallow tropical seas (depositional conditions for limestone). After these temporary changes, the previous depositional conditions resume, like wind blowing sand dunes over now dry alluvium.
    Last edited: Sep 6, 2019
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  8. Yellow Dart

    Yellow Dart It's only hubris if I fail.

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    While this relatively recent thread on geology is fresh, am looking for thoughts on these guys I found on a recent rip through Lodge. In all my outings in Zion, or southwest Utah in general, never have I see green sandstone before.

    Any ideas on what made it this color? There was another chunk I found in the canyon, that I broke open to make sure it was green throughout, which it was. One on left is size of my hand.
    IMG_20191004_1705358.
  9. Scott Patterson

    Scott Patterson

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    Proably copper, but possibly chlorite. Volcanic ash or some organics an make sandstone green too, but usually that stuff is super crumbly and finer grained than what you see in the picture.

    Green mudstone and shale is very common in Utah, but tends to be finer grained.

    The green rocks above look like the copper bearing sandstones near Moab (especially Lisbon).
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  10. Bootboy

    Bootboy Atwood Gear

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    Also, it could be iron in a reduced state (iron atom gained an electron from the elements its reacted with), as opposed to oxidized.

    In the context of the geochemistry of the Colorado Plateau, iron that undergoes reduction reactions often yields green hues, while oxidation reactions yield red.

    [​IMG]
    Last edited: Oct 5, 2019
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  11. Yellow Dart

    Yellow Dart It's only hubris if I fail.

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    On a recent expedition with the feral Murr Purr on the east side of Zion, going up a particularly undisclosed canyon, we started finding more and more, larger and larger chunks of green sandstone, eventually coming to one the size of a VW Bug.


    From that boulder, looked up the sheer walls around us in search of the green stone in-situ. It was not to be seen.


    Continuing up-canyon, we found no more deposits, surmising that somewhere between where we were standing and 40 vertical feet below, at the VW-sized boulder, is where the green layer had to be. Alas, it was all the standard color of Navajo: grey with yellow and tan bits here and there.


    Where was the green? Murr Purr had an suspicion.


    Her being the geologist that she is, and my being the helpful monkey that I am, we sourced large pieces of stalwart steely (well, iron'y technically) desert varnish, an set to striking the grey walls here and there, down the vertical run, until we were back at the green boulder.


    There it was, hiding right in front of us, only a fraction of an inch beneath the grey surface: a 20 vertical foot band of green sandstone, in-situ.


    Why was the wall grey? Why was the grey only skin-deep?


    Turns out, @Bootboy was correct.


    The green sandstone is known as glauconite (glock-uh-night), and gets its color from the reduction of iron molecules.


    Oxidation (burning) removes electrons giving iron a positive charge, which is what we call rusting and turns it red. Reduction adds electrons giving iron a negative charge, which turns it green.


    Dr. Murr Purr's deduction: the green glauconite lens (band, layer, etc.) in-situ, in the high sun (UV) and air (oxygen) environment, had oxidized the topmost layer of glauconite - returning it to its neutral color: the same grey as the rest of the Navajo, with some bits oxidizing further to occasional swirls of yellow.


    Basically, the green burned away to grey, disguising it as regular sandstone. But hit it with a rock and fresh deep-green glauconite is exposed, only a sixteenth of an inch beneath the oxidized top layer.


    Back at my desk a while later, did deep dive on glauconite layers in Zion, and could find only one reference:
    "Some Features of the Navajo Formation in Zion National Park, Utah - Grater R.K. - 1948"
    American Journal of Science, Volume 246, Number 5, pages 311-318


    Bought a digital copy for $10. I tried to attach it, but apparently 4.3Mb is too large for the CC server to handle; uploaded it to my mediafire, link below. Interesting stuff, especially consider it was published 20 years before the Plate Tectonics Revolution.


    The last page, while unrelated to glauconite, was particularly interesting, regarding water tables and coloring of the basal elevations of Navajo.


    It astounds me how much I have learned since moving here in early 2015, just from living in this beautifully diverse place. Makes me wonder how much more I will know by 2025.


    https://www.mediafire.com/file/irp4..._Am_Jour_Sci_v246_no5_p311-318_-1948.pdf/file
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