Register | Sign In


Understanding through Discussion


EvC Forum active members: 65 (9162 total)
4 online now:
Newest Member: popoi
Post Volume: Total: 915,808 Year: 3,065/9,624 Month: 910/1,588 Week: 93/223 Day: 4/17 Hour: 1/1


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Origin of the Flood Layers
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 354 of 409 (753510)
03-20-2015 11:25 AM
Reply to: Message 351 by Admin
03-20-2015 11:16 AM


Re: Moderator Clarification
It does help a bit, but not enough. It just feels like something's missing. How is it that in the distant past there was a cliff of Vishnu Schist towering above a riverbed of Vishnu Schist?
Why does it have to 'tower' over itself? I've seen plenty of streams with one formation from base to the top of the bank.
I can only guess at the answer, but I assume it's one that must be very obvious to you.
Well, I've seen a lot and probably take a lot for granted, but when questions are posed in an intelligible way by someone truly interested in an answer, I don't mind spending some time.
My guess is that the river eroded down through the Vishnu Schist, creating the cliff faces from which pieces of quartz broke off.
See my previous post for a diagram that might explain. But actually, I don't think it needs to be a cliff. In fact the unconformity was the surface in question.
But once I come up with that guess I question it, because if that was the case then where is that ancient cliff face now?
Well, there could be anything a short distance into the rocks; but, as mentioned, any kind of surface, even a flat one, would suffice.
Edited by edge, : No reason given.

This message is a reply to:
 Message 351 by Admin, posted 03-20-2015 11:16 AM Admin has replied

Replies to this message:
 Message 366 by Admin, posted 03-20-2015 2:51 PM edge has replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 355 of 409 (753511)
03-20-2015 11:37 AM
Reply to: Message 346 by JonF
03-20-2015 11:04 AM


High dynamic range composite:
This is an excellent picture. Not sure what you did to create the highlights, but it clarifies some things I suspected.

This message is a reply to:
 Message 346 by JonF, posted 03-20-2015 11:04 AM JonF has replied

Replies to this message:
 Message 357 by JonF, posted 03-20-2015 12:16 PM edge has not replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 361 of 409 (753548)
03-20-2015 1:52 PM
Reply to: Message 359 by Faith
03-20-2015 12:46 PM


Look, I'd be happy enough if it was as shallow as you say because finding out the tiny scale of the image changed most of my view of it.
HOWEVER, as I analyze even your lightened version I still think that's a depression the clasts came out of. That IS the physical edge of a depression, not just the edge of the shadow that was originally there.
The lightened area is red on your image, and the edge, which I've marked in blue on my own copy of the image, is the color of the schist. The remaining shadow that is still visible under the clasts indicates that they are suspended over the depression.
So, if you are correct, we should be able to find similar occurrences within the Vishnu Schist. The occurrences should have a fragmented appearance with schist on both sides.
You may want to do this search, but I'm going to abstain for the time being (likely a very long time).
In the meantime, could you explain why we do not have these veins or dikes in the Tapeats?
The clasts still appear to be suspended above the depression.
Interesting observation. Why do you think that is that case? What does that material between the clast and the schist seem to be?
The lightened area where the shadow was is the schist at the bottom of the depression, it is not continuous with the surface.
Why do you suppose it looks different? Is there anything else you can say about that material?

This message is a reply to:
 Message 359 by Faith, posted 03-20-2015 12:46 PM Faith has replied

Replies to this message:
 Message 362 by JonF, posted 03-20-2015 2:02 PM edge has replied
 Message 369 by Faith, posted 03-20-2015 7:42 PM edge has replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 363 of 409 (753551)
03-20-2015 2:04 PM
Reply to: Message 360 by JonF
03-20-2015 1:52 PM


It's the edge of the shadow that was originally there. It's the boundary between the un-lightened and lightened version.
Actually, I think it's a different material, also. The question is, what is it? It has something to do with the process of creating an unconformity.
Oh, the clasts are definitely slightly above the Vishnu surface. That's why your idea of encroaching sandstone picking them up off the Vishnu is so silly.
I don't have a problem with the clasts being transported, just not from those 'depressions', and probably not by the same flow regime that deposited the sandstone. And I don't think they were transported very far. The clasts are what I would call sub-angular, meaning that they have been transported a short distance, but more than simply plucked up and resettled in the same place.
You are also seeing something that is interesting to me. You are pointing out a fabric in the softer, shadowed material. How did that form and from what material? Does it look like sand?

This message is a reply to:
 Message 360 by JonF, posted 03-20-2015 1:52 PM JonF has replied

Replies to this message:
 Message 365 by JonF, posted 03-20-2015 2:37 PM edge has not replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 364 of 409 (753553)
03-20-2015 2:09 PM
Reply to: Message 362 by JonF
03-20-2015 2:02 PM


Well it sho' looks like that to me.
Well, according to Faith that seals it. It 'looks like' is pretty solid evidence.
Looks like air from here.
I don't know if even Faith would think it was always air, but if the Vishnu at this location has always been exposed to the surface (never buried), you never know...

This message is a reply to:
 Message 362 by JonF, posted 03-20-2015 2:02 PM JonF has not replied

Replies to this message:
 Message 367 by Admin, posted 03-20-2015 2:57 PM edge has not replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 368 of 409 (753568)
03-20-2015 3:18 PM
Reply to: Message 366 by Admin
03-20-2015 2:51 PM


Re: Moderator Clarification
So in my reply I tried to be consistent with that pictured scenario of a cliff face over a riverbed. I understand it doesn't have to be a cliff face, just a difference in height.
Sure, all scenarios of topographic relief are valid, and they do happen.
But it's the difference in height combined with the transport that is a part of the scenario that I think many people will miss when you say that the material atop the Vishnu Schist is from the Vishnu Schist. I think many will assume you mean it came from that exact spot of the Vishnu Schist, or perhaps just be confused.
That is why I included that image of different types of placer gold deposits. There are differing degrees of transport.
And, there is little doubt in my mind that some of the material just above the unconformity is actually part of the schist itself.
Also, the material coming off that cliff face can be from other layers above the Vishnu Schist. We can only see Vishnu Schist in that photo, but somewhere above out of view are other layers. It's another part of the potential confusion that when it is said about that clast photo that when clasts from the lower layer are found embedded in the layer above that it is evidence of an unconformity, many will conclude that you mean the clasts always have to be from that lower layer. They don't. They could be from some layer above that layer, and even possibly below that layer depending upon how "interesting" the geological history has been.
Exactly. All Jon and I are saying is that if it is incorporated into the sand, its source is older than the sand; and since the sand is a product of erosion, then erosion must be occurring somewhere, probably at a higher elevation.

This message is a reply to:
 Message 366 by Admin, posted 03-20-2015 2:51 PM Admin has seen this message but not replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 370 of 409 (753582)
03-20-2015 7:51 PM
Reply to: Message 369 by Faith
03-20-2015 7:42 PM


Not much point in my sticking around either. When an argument is about an observation it helps to have others see the same thing along with you and I'm always just one against many.
Some kind of common observation is one of the main requirements of science. If you consistently see something different, could there be something wrong with your sensors? Or maybe your processing is out of calibration?
Takes heat and pressure I would expect, plus the fact that schist is made up of many rocks and minerals including those that form quartz or pegmatite veins.
Well, the geological level of the Tapeats isn't much different from the GC metamorphic suite: and the composition of the pegmatites is mostly quartz, so I'm not sure why the Tapeats would be exempt from forming such veins and dikes.
Do you think there could be an age difference?

This message is a reply to:
 Message 369 by Faith, posted 03-20-2015 7:42 PM Faith has replied

Replies to this message:
 Message 371 by Faith, posted 03-20-2015 8:00 PM edge has replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 372 of 409 (753584)
03-20-2015 8:04 PM
Reply to: Message 371 by Faith
03-20-2015 8:00 PM


Heat and pressure does it for me.
Does what for you?
And no, I'm seeing the clasts and the depression correctly, you aren't.
You don't even know what I think about the depressions. I've been careful about that...

This message is a reply to:
 Message 371 by Faith, posted 03-20-2015 8:00 PM Faith has replied

Replies to this message:
 Message 374 by Faith, posted 03-20-2015 9:47 PM edge has replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 379 of 409 (753598)
03-20-2015 10:38 PM
Reply to: Message 374 by Faith
03-20-2015 9:47 PM


One of the many difficulties of trying to have a discussion with you is that you NEVER read in context. Heat and pressure does it for me without the factor of great age, about which you had just asked me. Does that clarify or do I need to copy out every quote, even the most recent? I guess I could do that but since this is only one of many difficulties I don't expect it to be worth the time anyway.
Have you been a complainer all of your life? All I wanted some clarification.
OK, but didn't you just respond to JonF by suggesting that the material in the depression / shadow is not schist?
I'm pretty sure that it's not just air. Whatever it is, it appears to have a laminated fabric not related to the original schist. However, I think it was derived from the schist. What do you think it is?
And please make something else clear: You called the clasts "boulders" at one time, ...
I probably misspoke. I had been looking at some images on line where there were some fairly large boulders in a sandstone above an unconformity. My error, however, such things do exist.
... and referred to that little ridge in the Tapeats as a "bedding plane."
Yes, there is a bedding plane in the image.
Did you see Percy's post since then that showed the area of this photo to cover about twenty square inches?
Actually, I pointed this our well before Percy did. I mentioned that the larger image with the geologist was from the exact location of the original picture that you posted.

This message is a reply to:
 Message 374 by Faith, posted 03-20-2015 9:47 PM Faith has replied

Replies to this message:
 Message 381 by Faith, posted 03-20-2015 10:55 PM edge has replied
 Message 399 by JonF, posted 03-21-2015 8:57 AM edge has not replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 382 of 409 (753602)
03-20-2015 10:55 PM
Reply to: Message 378 by Faith
03-20-2015 10:11 PM


Re: how do you make heat and pressure?
The Vishnu does not have to have existed AS SCHIST before the magma intrusions, just as rock rubble the magma plus weight from above then metamorphosed into schist.
Well, it doesn't have to, I suppose, but it probably did. First of all, the development of a schist (with a platy foliation) is dynamothermal, meaning that there was deformation along with heating. If the intrusion caused the schist development, then there should be some geometric relationship of the intrusion to the orientation of the foliation. That does not appear to be the case.
As to the burial origin of the foliation, if that is due to the Paleozoic section being deposited, then the foliation should be closer to vertical (ETA: this should read 'horizontal'). In fact, IIRC, there are some folds in the schist, which would suggest some kind of lateral compression.
Edited by edge, : No reason given.

This message is a reply to:
 Message 378 by Faith, posted 03-20-2015 10:11 PM Faith has replied

Replies to this message:
 Message 385 by Faith, posted 03-20-2015 11:01 PM edge has not replied
 Message 392 by Faith, posted 03-20-2015 11:55 PM edge has replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 386 of 409 (753606)
03-20-2015 11:04 PM
Reply to: Message 381 by Faith
03-20-2015 10:55 PM


I think it is schist. The lightening of the image made the whole area of that dark shadow reddish and not a whole lot easier to read than the original. No idea where you get the "laminated" idea.
I am concerned only with the foliation in that material and it is completely different from the underlying schist. I'm pretty sure that it is schist weathered to some kind of clay or soil and then compacted, or it is transported clay minerals derived from the schist that are now deformed around the base of the clasts. It is also visible where there are no clasts.
The true color is actually dark red, being indistinguishable from a dark shadow. I'll try to work on an annotated image, but there's a lot of basketball on this evening and I'm hungry.
Yes, in fact there is a boulder of quartzite about fifteen feet in diameter embedded in the Tapeats elsewhere in the canyon, above the unconformity, that clearly broke off the Shinumo quartzite of the Supergroup, and that's what the term suggested to me when you said it.
Yes, more evidence of erosion during the Great Unconformity time.
That "bedding plane" is about half an inch deep and follows the curved border area between the Tapeats and the Vishnu. You really call that a bedding plane?
Yes, there is probably some draping, but as you know images can be deceiving.
I misread you then. I thought you were merely saying that picture was taken in the vicinity of the other.
I believe I said 'exactly'. Maybe not...

This message is a reply to:
 Message 381 by Faith, posted 03-20-2015 10:55 PM Faith has not replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 389 of 409 (753609)
03-20-2015 11:19 PM
Reply to: Message 388 by Faith
03-20-2015 11:10 PM


Re: how do you make heat and pressure?
Even geologist edge didn't say it was completely out of the question that the magma could have caused the schist, though he gave some technical reasons why he doesn't think that is what happened.
You read me wrong, Faith. What I'm saying is that there is no evidence to support your statement.
Now, I could imagine some exception to the case such as local effects or maybe an intrusion that we presently know nothing about; but these are completely unsupported. When I combine that with the schistosity formation, your point goes out the window. And when I combine all that with your misplaced confidence, it actually becomes a ridiculous notion.

This message is a reply to:
 Message 388 by Faith, posted 03-20-2015 11:10 PM Faith has replied

Replies to this message:
 Message 390 by Faith, posted 03-20-2015 11:26 PM edge has replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 391 of 409 (753612)
03-20-2015 11:55 PM
Reply to: Message 390 by Faith
03-20-2015 11:26 PM


Re: how do you make heat and pressure?
OK, fine, I will hold my theory alone then that magma intruding into rock rubble could transform it into schist, especially with the added pressure of the enormous weight of three miles of strata above it. However it happened, though, the mere presence of granite in the schist shows the presence of enough heat from magma in the general vicinity to fry the stuff.
I'm sure you would know.

This message is a reply to:
 Message 390 by Faith, posted 03-20-2015 11:26 PM Faith has replied

Replies to this message:
 Message 393 by Faith, posted 03-20-2015 11:56 PM edge has not replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 394 of 409 (753616)
03-21-2015 12:08 AM
Reply to: Message 383 by Faith
03-20-2015 10:58 PM


Re: how do you make heat and pressure?
No it wouldn't. The magma intrusion baked whatever it was into schist.
Actually, just baking the rocks would not create a schistosity (foliation) in the metamorphic rocks. And there is no indication of dynamic (deforming, such as folding) related to intrusives visible in the GC.

This message is a reply to:
 Message 383 by Faith, posted 03-20-2015 10:58 PM Faith has not replied

  
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 395 of 409 (753617)
03-21-2015 12:14 AM
Reply to: Message 392 by Faith
03-20-2015 11:55 PM


Re: how do you make heat and pressure?
Tectonic pressure is usually lateral isn't it?
No. For instance, we don't see compressional folding in the Paleozoic rocks.
That's what I attribute the whole scenario to, the Kaibab uplift, the tilted Supergroup, the formation of Vishnu and granite, the erosion between unconformity and Tapeats caused by sliding of the Supergroup etc.
Then you would be wrong on several accounts.
In my scenario all the strata above is present three miles deep and then the upper two miles above the Permian broke up due to the uplift also. Heat from below, pressure from above and from the side both.
There's not enough horizontal stresses to fold the Paleozoic rocks, but the metamorphic sequence is severely deformed.
That means that you are wrong before you get out of the starting gate.

This message is a reply to:
 Message 392 by Faith, posted 03-20-2015 11:55 PM Faith has replied

Replies to this message:
 Message 396 by Faith, posted 03-21-2015 12:25 AM edge has replied

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2023 by EvC Forum, All Rights Reserved

™ Version 4.2
Innovative software from Qwixotic © 2024