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Author Topic:   The Story in the Rocks - Southwestern U.S.
Tanypteryx
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Posts: 1592
From: Oregon, USA
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(3)
Message 1 of 121 (775856)
01-05-2016 8:55 PM


I want to post some photos of geological formations from the Southwest that I have taken on trips the last few years. I would like to discuss what is known about how the rocks formed and when, and what processes acted on them between then and now, and what processes exposed them so we can see them today.

The formations in this photo are in north central Arizona along a stretch of Hwy 89, south of Navajo Bridge over the Colorado River and north of Cameron.

I think this valley may have had a number of layers volcanic ash-like material deposited that has been eroded leaving these short buttes that are composed of soft non-lithified material that almost looks like it is melting in the occasional summer rains.

(ABE: Looking in my Roadside Geology of Arizona I see this is the Chinle formation and it is volcanic ash.)

We have similar looking formations in Oregon around the John Day Fossil Beds.

We have had discussions and debate about interpreting photos in several other threads about the flood where we went down a bunch of rabbit holes arguing about minutia of lines, or shadows, that didn't help the discussion progress. I would rather not repeat that. I don't want to spend a bunch of time talking about things that are not supported by the evidence found in the rocks. I want to find out what the evidence tells us.

Geology forum please.

Edited by Tanypteryx, : Added 2 more image

Edited by Adminnemooseus, : Tiny code fix.


What if Eleanor Roosevelt had wings? -- Monty Python

One important characteristic of a theory is that is has survived repeated attempts to falsify it. Contrary to your understanding, all available evidence confirms it. --Subbie

If evolution is shown to be false, it will be at the hands of things that are true, not made up. --percy


Replies to this message:
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AdminAsgara
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Message 2 of 121 (775858)
01-05-2016 9:31 PM


Thread Copied from Proposed New Topics Forum
Thread copied here from the The Story in the Rocks - Southwestern U.S. thread in the Proposed New Topics forum.
    
edge
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Posts: 4002
From: Colorado, USA
Joined: 01-09-2002
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(1)
Message 3 of 121 (775928)
01-06-2016 6:09 PM
Reply to: Message 1 by Tanypteryx
01-05-2016 8:55 PM


The formations in this photo are in north central Arizona along a stretch of Hwy 89, south of Navajo Bridge over the Colorado River and north of Cameron.

I think this valley may have had a number of layers volcanic ash-like material deposited that has been eroded leaving these short buttes that are composed of soft non-lithified material that almost looks like it is melting in the occasional summer rains.

(ABE: Looking in my Roadside Geology of Arizona I see this is the Chinle formation and it is volcanic ash.)

We have similar looking formations in Oregon around the John Day Fossil Beds.


These formations are indeed volcanic ash, now altered to smectite clays, such as the commonly known bentonite. It make devilish roads and trails, undrivable with the least amount of rain. Sticks to everything.

Here is a photo from the Bisti Badlands in NW New Mexico.

Sometimes flowing water will funnel into pipes that eventually flow out at lower elevations. This is has been called "pseudo-karst."

The first time I ran into that term was regarding some of those more bizarre badlands in China with bright colors and almost a layered, cotton-candy type of appearance. When the article called it karst, I freaked out until I realized that they meant pseudo-karst. In lots of these places, you can find bunch of petrified wood.


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Tanypteryx
Member
Posts: 1592
From: Oregon, USA
Joined: 08-27-2006
Member Rating: 4.9


Message 4 of 121 (775930)
01-06-2016 7:18 PM
Reply to: Message 3 by edge
01-06-2016 6:09 PM


These formations are indeed volcanic ash, now altered to smectite clays, such as the commonly known bentonite. It makes devilish roads and trails, undrivable with the least amount of rain. Sticks to everything.

I see this in quite a few places in eastern Oregon. Dirt roads that look like they should stay firm even in rain get super-soft and sticky.

with bright colors and almost a layered, cotton-candy type of appearance.

When I was a kid I thought these distinctively shaped mounds were material that had been somehow extruded from below. Later, when I saw buttes with flat tops I realized that they were really the last remnants of a soft layer that was almost melting away. The colors are sometimes very striking.

It seems to me that the way these formations erode shows what the strata of the Southwest would all look like if it was deposited by a flood only a few thousand years ago.

Is this material, bentonite, good for radiometric dating?

Are there components of the material that are water soluble?

Is there a way to tell if these deposits occurred in water or on dry land?


What if Eleanor Roosevelt had wings? -- Monty Python

One important characteristic of a theory is that is has survived repeated attempts to falsify it. Contrary to your understanding, all available evidence confirms it. --Subbie

If evolution is shown to be false, it will be at the hands of things that are true, not made up. --percy


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 Message 3 by edge, posted 01-06-2016 6:09 PM edge has responded

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edge
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Posts: 4002
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 2.7


(2)
Message 5 of 121 (776033)
01-07-2016 7:39 PM
Reply to: Message 4 by Tanypteryx
01-06-2016 7:18 PM


It seems to me that the way these formations erode shows what the strata of the Southwest would all look like if it was deposited by a flood only a few thousand years ago.

Well, possibly. They were certainly never lithified.

quote:
Is this material, bentonite, good for radiometric dating?

Yes, being potassic, they would be amenable to K-Ar methods. However, this article says that there are analytical errors. I haven't read it but it turns out that U-Pb and Ar-Ar on associated zircons and sanidine crystals give more reliable dates.

http://www.gov.mb.ca/iem/geo/field/roa13pdfs/GS-12.pdf

In oil exploration, bentonite helps form definitive marker beds in the stratigraphy because of the large amount of potassium that they contain. It is easily recognized by gamma ray detectors.

quote:
Are there components of the material that are water soluble?

Bentonite, being a smectitic clay can adsorb and release a large amount of cations which can change with the amount of water and whatever solutes it might contain. This may be part of the problem with dating bentonite directly.

quote:
Is there a way to tell if these deposits occurred in water or on dry land?

Good question. I think that the preservation of such large deposits would require some kind of transport into a basin since volcanic ash is so erodable. A big clue is the presence of other layered clastic sediments such as the sandstones that form the tops of the mesas that you see in some of the photos. There has certainly been plenty of water present in the ash layers as that is a component to the alteration of glass to clay. If the deposits were subaerial, they might be associated with some welded tuffs which would be much more resistant to weathering and erosion.
This message is a reply to:
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Tanypteryx
Member
Posts: 1592
From: Oregon, USA
Joined: 08-27-2006
Member Rating: 4.9


Message 6 of 121 (776035)
01-07-2016 8:41 PM
Reply to: Message 5 by edge
01-07-2016 7:39 PM


Thanks for the answers.

I wrenched my back on Tuesday and I am not able to drive over to my lab where my desktop computer that I use for images and almost all of my internet stuff is, so I may not get much posting done for a few days.

It is amazing that I was moving fine and then just twisted wrong and suddenly every movement is excruciating. Oh well, maybe I casn catch up on some reading.


What if Eleanor Roosevelt had wings? -- Monty Python

One important characteristic of a theory is that is has survived repeated attempts to falsify it. Contrary to your understanding, all available evidence confirms it. --Subbie

If evolution is shown to be false, it will be at the hands of things that are true, not made up. --percy


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 Message 5 by edge, posted 01-07-2016 7:39 PM edge has not yet responded

    
Tanypteryx
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Posts: 1592
From: Oregon, USA
Joined: 08-27-2006
Member Rating: 4.9


Message 7 of 121 (777299)
01-28-2016 6:23 PM


The Kayenta Formation & Dinosaur Tracks
A few miles west of the Chinle formation volcanic ash mounds I saw bipedal dinosaur tracks in the once soft mud of these 200 million-year-old Mesozoic rocks.

There are a number of Navajo guides who will accompany you around the area and "highlight" the tracks with a squirt water bottle. There were also some exposed bones that were probably misidentified. Their 2 favorites were Tyrannosaurus and Triceratops for the tracks as well.

I think they told me these were eggs but I have some doubts.

The Jurassic Kayenta formation is younger than the Triassic Chinle formation.


What if Eleanor Roosevelt had wings? -- Monty Python

One important characteristic of a theory is that is has survived repeated attempts to falsify it. Contrary to your understanding, all available evidence confirms it. --Subbie

If evolution is shown to be false, it will be at the hands of things that are true, not made up. --percy


Replies to this message:
 Message 8 by Dr Adequate, posted 01-28-2016 10:51 PM Tanypteryx has responded

    
Dr Adequate
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Message 8 of 121 (777309)
01-28-2016 10:51 PM
Reply to: Message 7 by Tanypteryx
01-28-2016 6:23 PM


Re: The Kayenta Formation & Dinosaur Tracks
I think they told me these were eggs but I have some doubts.

They're some sort of nodule, I'm fairly sure.


This message is a reply to:
 Message 7 by Tanypteryx, posted 01-28-2016 6:23 PM Tanypteryx has responded

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Tanypteryx
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Posts: 1592
From: Oregon, USA
Joined: 08-27-2006
Member Rating: 4.9


Message 9 of 121 (777311)
01-28-2016 11:13 PM
Reply to: Message 8 by Dr Adequate
01-28-2016 10:51 PM


Re: The Kayenta Formation & Dinosaur Tracks
I think they told me these were eggs but I have some doubts.

They're some sort of nodule, I'm fairly sure.

That way what I thought also.

There was a time many years ago when I took chips from rocks that I found and analyzed them on an X-ray powder diffraction system at work. I could ID compounds and figure out what minerals were present. It was good practice trying to ID what I had.


What if Eleanor Roosevelt had wings? -- Monty Python

One important characteristic of a theory is that is has survived repeated attempts to falsify it. Contrary to your understanding, all available evidence confirms it. --Subbie

If evolution is shown to be false, it will be at the hands of things that are true, not made up. --percy


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 Message 8 by Dr Adequate, posted 01-28-2016 10:51 PM Dr Adequate has not yet responded

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edge
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Posts: 4002
From: Colorado, USA
Joined: 01-09-2002
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(1)
Message 10 of 121 (777425)
01-30-2016 7:26 PM
Reply to: Message 9 by Tanypteryx
01-28-2016 11:13 PM


Re: The Kayenta Formation & Dinosaur Tracks
That way what I thought also.

Well, here are a couple of things that I found in a younger sandstone a year ago in NM.

This is petrified cannonball. Well, it could be...

Actually, it's a sandstone concretion formed by overgrowths of a center of cementation. They litter the ground in some places. A weak carbonate(?) cement grew outward from a 'seed' in concentric layers, most likely.

Here is a barite nodule from the same formation:


The growth pattern here is different in being radial rather than concentric. I'm not sure how the enclosing sediments were excluded from the nodule itself. It may have formed in mudstone.

This is an agglomeration of concretions from the same sandstone:


Again, it consists of cemented sandstone. Actually, the form is hollow and may have formed around a clay ball in sandstone.

I guess my point is that we find a lot of weird 'forms' in younger sandstone that has not been overly lithified and/or metamorphosed and you can compare them to common objects. I think that the objects you are seeing are things that formed early in the lithification process. It would be necessary to look at them in person and possibly break some rocks to really see what's going on.

I know that sometimes wet sands can actually liquefy and flow into the surrounding mudstones and claystones. Now, that's confusing...


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edge
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Posts: 4002
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 2.7


(2)
Message 11 of 121 (777477)
02-01-2016 7:53 PM


Just for fun:

Dinosaur (according to some) at the top of the Jurassic Entrada Formation, Colorado National Monument.


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Pressie
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From: Pretoria, SA
Joined: 06-18-2010
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(3)
Message 12 of 121 (777482)
02-02-2016 7:33 AM
Reply to: Message 11 by edge
02-01-2016 7:53 PM


My wife says that she's never seen a better looking dinosaur before (but she's an inorganic chemist; what would she know?)

Edited by Pressie, : No reason given.

Edited by Pressie, : No reason given.


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Tanypteryx
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Posts: 1592
From: Oregon, USA
Joined: 08-27-2006
Member Rating: 4.9


(1)
Message 13 of 121 (779293)
03-02-2016 7:15 PM
Reply to: Message 11 by edge
02-01-2016 7:53 PM


A couple miles to the north of the dinosaur footprints there are exposed, eroding, remains of the Navajo Sandstone that show nice cross-bedding patterns of ancient sand dunes.

I do not understand the process involved with the lithification of sand dunes that preserves the cross-bedding pattern.

And here is a different type exposure just a mile south of those boulders.

The Navajo Sandstone is the same layer that is exposed to erosion many miles to the west in Snow Canyon, just north od St. George, Utah.

According to Geology of the American Southwest, by W. Scott Baldridge, the Navajo Sandstone is Jurrasic, deposited 144-206 million years ago and overlays the older Kayenta Formation.

quote:
Together with the with the laterally equivalent Nugget and Aztec Sandstones, these formations comprise one of the largest ancient sand dune deposits preserved on Earth, stretching over an area of more than 150,000 km^2.

.


What if Eleanor Roosevelt had wings? -- Monty Python

One important characteristic of a theory is that is has survived repeated attempts to falsify it. Contrary to your understanding, all available evidence confirms it. --Subbie

If evolution is shown to be false, it will be at the hands of things that are true, not made up. --percy


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 Message 11 by edge, posted 02-01-2016 7:53 PM edge has responded

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edge
Member
Posts: 4002
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 2.7


(2)
Message 14 of 121 (779324)
03-03-2016 11:33 AM
Reply to: Message 13 by Tanypteryx
03-02-2016 7:15 PM


I do not understand the process involved with the lithification of sand dunes that preserves the cross-bedding pattern.

Sand dunes are manifest in the geologic record as large-scale cross-beds such as the ones in your pictures.

Lithification of Jurassic sandstone on the Colorado Plateau is pretty basic. It consists simply of weak cementation, mostly by calcium carbonate. In dry climates they can be preserved as positive topographic features. Even slight differences in the degree of cementation and/or fracturing can result in some of the spires and buttes that are common on the CP.


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Dr Adequate
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Message 15 of 121 (779331)
03-03-2016 12:30 PM
Reply to: Message 14 by edge
03-03-2016 11:33 AM


I read something interesting recently in a very old geology book (by Gideon Mantell, the guy who discovered Iguanadon, so yeah, that old). He said that sandstone could be produced by compaction alone, and adduced the fact that cannonballs shot at sandbags produced sandstone where they impacted. I've not seen this repeated anywhere else, I'd be interested to know if there is any sandstone anywhere that was lithified just by compaction.
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