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Author Topic:   Evidence that the Great Unconformity did not Form Before the Strata above it
Faith 
Suspended Member (Idle past 1444 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 481 of 1939 (754340)
03-25-2015 11:54 PM
Reply to: Message 479 by edge
03-25-2015 11:51 PM


That Death Valley picture isn't evidence of much of anything, let alone cross bedding on the unconformity. It's undecipherable.

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 Message 479 by edge, posted 03-25-2015 11:51 PM edge has replied

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edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 482 of 1939 (754341)
03-25-2015 11:55 PM
Reply to: Message 480 by Faith
03-25-2015 11:53 PM


But they ARE exposed, as Percy just got me to clarify.
Yes, in the modern unconformity.
But hey, so much for civil discourse.
That ship has sailed.

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edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 483 of 1939 (754342)
03-25-2015 11:55 PM
Reply to: Message 481 by Faith
03-25-2015 11:54 PM


That Death Valley picture isn't evidence of much of anything, let alone cross bedding on the unconformity. It's undecipherable.
According to Faith.

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 Message 481 by Faith, posted 03-25-2015 11:54 PM Faith has not replied

  
edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 484 of 1939 (754345)
03-26-2015 12:24 AM


Don't know if this helps or not, but it makes some sense. Think it would work here? I have my doubts.
https://www.youtube.com/watch?v=Qe5pv4khM-Y
Is this why repeated attempts to extract an explanation, end up in oblivion?

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Tanypteryx
Member
Posts: 4344
From: Oregon, USA
Joined: 08-27-2006
Member Rating: 5.9


Message 485 of 1939 (754346)
03-26-2015 12:35 AM
Reply to: Message 484 by edge
03-26-2015 12:24 AM


Is this why repeated attempts to extract an explanation, end up in oblivion?
Short answer: yes....Long answer: yes
Sorry Dude.

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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Admin
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(1)
Message 486 of 1939 (754366)
03-26-2015 7:12 AM
Reply to: Message 472 by Faith
03-25-2015 10:22 PM


Faith writes:
I quoted amply for him to get the context.
This is what you said that Tanypteryx quoted:
Faith writes:
I thought that's what Percy wanted me to indicate: to explain the unevenness of the lower section as the result of erosion after the deposition of the above section. I'm sure you are still free to offer a different interpretation.
If I understand you correctly, you're referring to your belief that it is possible for erosion of a cliff face to affect the shape of an exposed boundary between two layers of solid rock. Participants like Tanypteryx and Edge have been saying that this makes no sense. If it actually does make sense then some clarification or explanation would be welcome.

--Percy
EvC Forum Director

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Admin
Director
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Joined: 06-14-2002
Member Rating: 2.2


Message 487 of 1939 (754367)
03-26-2015 7:53 AM
Reply to: Message 478 by edge
03-25-2015 11:49 PM


edge writes:
That's why there are so many stumps of the upright lower strata.
That was when they were exposed to weathering during Cambrian time.
I'm not sure you and Faith are referring to the same "stumps". I think your stumps might be where the vertical strata below the unconformity actually meet the unconformity. Faith may be referring to the parts of the gray rock near the center of this image that are not actually anywhere near the unconformity boundary, except near its top:
This gray rock is the same one Hutton drew from a different angle that appears in the "Bottom Layers" part of his diagram as a thick vertical stratum a little to left of center:
Here's an image that seems to come closer to replicating the angle from which the Hutton diagram was drawn:
After looking at so many images of Siccar Point it's apparent that the diagram is pretty good but only approximate. Some erosion of anywhere from 2 to 10 inches of rock would have taken place over a couple centuries, but the angle of that tall section of big gray strata could not have changed.
Edited by Admin, : Change author.

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Admin
Director
Posts: 12998
From: EvC Forum
Joined: 06-14-2002
Member Rating: 2.2


Message 488 of 1939 (754368)
03-26-2015 7:59 AM
Reply to: Message 479 by edge
03-25-2015 11:51 PM


edge writes:
Abrasion between upper and lower sections as already explained somewhere back there.
Except that there should be evidence of abrasion. Why is there evidence of cross-bedding?
I want to better understand this exchange. When I read Faith's post I wasn't sure what she meant, but I decided not to pursue it. In your view is Faith saying that there should be abrasion between two adjacent layers of rock buried within a stack of strata? Or is she saying that abrasion can happen only where the boundary between two layers is exposed in a cliff face? Or is she referring to abrasion long ago when the upper layer was being being deposited upon the lower layer?

--Percy
EvC Forum Director

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herebedragons
Member (Idle past 857 days)
Posts: 1517
From: Michigan
Joined: 11-22-2009


(1)
Message 489 of 1939 (754369)
03-26-2015 8:28 AM
Reply to: Message 476 by Faith
03-25-2015 10:47 PM


I only have a few minutes I can spend on this, but it seems like you are still having trouble visualizing what an unconformity is. The idea that the surface of an unconformity was exposed to weathering is an interpretation; THAT is what you want to argue... the interpretation of how an unconformity forms, but you seem to be arguing about what an unconformity IS, and that causes a LOT of confusion.
So, here I offer a definition that I think is a good description of what an unconformity IS without the added interpretations of how it forms or what it represents.
Unconformity: A boundary between two layers of strata where the upper layer does not sit conformably on the lower.
Which of course requires a second definition...
Conformable: A boundary between two layers that displays evidence of continuous deposition. Typically, one bed grades evenly into the other with no sharp or distinct break between the two.
In other words, an unconformity is a contact surface that does not display evidence of continuous deposition.
Regardless of HOW it formed, these definitions provide a description of it.
Here is another diagram of an unconformity
The first two drawings depict how it is thought to form, so just ignore them for now. So let's start at the last drawing and work backwards, because that's what we see in the field. Notice the black line represents the unconformity; it is the contact line that is exposed and represents the place where two layers meet where there is no evidence of continuous deposition - that is they meet unconformably.
Now, go to drawing 3 which has popped the upper layers off and look at the surface. That is the surface of the unconformity.
Drawings 1 and 2 work backwards even further and provide the idea of how these unconformities are thought to form. Those are the drawings you dispute, that you have an alternate explanation for. But we still seem to be arguing over drawing 3 and 4 which really aren't up for dispute. Those are observations, not interpretations (although the exact contour of the surface and the nature of the boundary might include some interpretation). But with respect to drawing 3 and 4, there are 2 options:
1. The contact shows evidence of continuous deposition or
2. The contact shows no evidence of continuous deposition.
If your answer is #1, then we need to discuss what the evidence is for continuous deposition.
If your answer is #2, then we all agree that it is an unconformity and we then need to move on to talking about HOW it formed - which is drawing 1 and 2.
The reason I think this all still needs some explanation is that you still seem to be indicating that erosion somehow affects the surface of the unconformity. So look again at drawing 3. Pick a point in the middle of that surface. Now put the upper layers back on. Now batter the exposed edges, the edges you can see in drawing 4, with erosion. Imagine cutting deep into the edges of that block - like maybe 1/8 of the way in. Now pop the upper layers off... has the point you selected changed or been affected? The answer should be "No." It has been protected deep within that block and is not exposed to erosion. It may change the perception of the line that represents the unconformity, but not the actual surface itself.
The horizontal gives less resistance to the weather than the vertical?
---------------------
---------------------
---------------------
---------------------
! ! ! !
! ! ! !
! ! ! !
! ! ! !
! ! ! !
! ! ! !
! ! ! !
Why would either of the above have more exposed surface? It is more likely to do with the resistance of the type of rock rather than orientation. However, this issue has nothing to do with the surface of the unconformity. This is where the confusion is coming from... we THINK you are saying that this differential erosion changes the SURFACE of the unconformity, but it doesn't. It only affects the exposed surface of the rock that is roughly perpendicular to the surface of the unconformity.
Again, I hope you don't take this as patronizing, I am trying to get across this concept so we can all be talking about the same thing - so communication can move forward.
HBD

Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for... I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca
"Nothing is easier than to persuade people who want to be persuaded and already believe." - another Petrarca gem.
Ignorance is a most formidable opponent rivaled only by arrogance; but when the two join forces, one is all but invincible.

This message is a reply to:
 Message 476 by Faith, posted 03-25-2015 10:47 PM Faith has replied

Replies to this message:
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edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


(1)
Message 490 of 1939 (754381)
03-26-2015 10:17 AM
Reply to: Message 487 by Admin
03-26-2015 7:53 AM


I'm not sure you and Faith are referring to the same "stumps". I think your stumps might be where the vertical strata below the unconformity actually meet the unconformity. Faith may be referring to the parts of the gray rock near the center of this image that are not actually anywhere near the unconformity boundary, except near its top:
In this case probably not. This is just one of those things about unconformities that is not intuitive. Unconformities can intersect each other. On the Wiki page for unconformities there is something called a 'biconformity'. I can't find a very good diagram, but it looks like this.
Now just imagine that everything above the red line has not been deposited yet and you are standing on that red surface.
It would be directly analogous to Siccar Point. There are actually two unconformities:
-- the ancient unconformity outlined in black, and
-- what I call the modern unconformity in red.
In actual fact, the modern unconformity isn't really formed yet, because there is no overlying rock, but you can see the principle.
It appears that Faith is talking about both. Perhaps that is why she says that the unconformity is changing.
My point is that they are different unconformities. The original unconformity, as defined by the gently tilted rocks overlying the vertically tilted rocks does not change with time. It actually formed in the Devonian, as the Old Red Sandstone covered older, deformed Silurian rocks.
The modern unconformity is in the process of forming and can indeed change because it is undergoing active erosion.
The only change that the ancient unconformity can suffer at this time is is destruction by the modern erosion. It is not becoming deformed, nor is it changing shape by any other means. It is literally being obliterated.

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edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


(1)
Message 491 of 1939 (754383)
03-26-2015 10:36 AM
Reply to: Message 488 by Admin
03-26-2015 7:59 AM


I want to better understand this exchange. When I read Faith's post I wasn't sure what she meant, but I decided not to pursue it. In your view is Faith saying that there should be abrasion between two adjacent layers of rock buried within a stack of strata?
Yes. In order to fold the lower rocks, but not affect the upper rocks, you would need to have some kind of detachment between the two bodies. It is like pushing a brick along the concrete sidewalk. They cannot be attached to each other and there has to be some kind of friction in between. That friction should be evident as some kind of a feature in the rock.
Or is she saying that abrasion can happen only where the boundary between two layers is exposed in a cliff face?
I can't tell. I thought she was saying that some process actually deformed the unconformity surface in situ, kind of like salt dome formation; and that it happened within the last 200 years. However, she might just be confusing ancient with modern erosion.
Perhaps my previous post would help explain.
Or is she referring to abrasion long ago when the upper layer was being being deposited upon the lower layer?
If there was abrasion at the time of deposition, that doesn't sound like a sedimentary process. I suppose one could say that the upper unit slumped into place, but that would also cause some kind of evidence to that effect. For instance, cross-bedding would probably not remain intact.

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jar
Member (Idle past 394 days)
Posts: 34026
From: Texas!!
Joined: 04-20-2004


Message 492 of 1939 (754385)
03-26-2015 10:52 AM
Reply to: Message 491 by edge
03-26-2015 10:36 AM


trying to clarify or through a galss darkly
To make it really simple are we not asking Faith to explain how and where the rest of the Super Group rocks got removed from the Tapeats Sandstone/Vishnu Schist interface OR how the parts of the Super Group that still exist could get laid down if not before the Tapeats Sandstone was laid down?

Anyone so limited that they can only spell a word one way is severely handicapped!

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edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 493 of 1939 (754387)
03-26-2015 11:00 AM
Reply to: Message 492 by jar
03-26-2015 10:52 AM


Re: trying to clarify or through a galss darkly
To make it really simple are we not asking Faith to explain how and where the rest of the Super Group rocks got removed from the Tapeats Sandstone/Vishnu Schist interface OR how the parts of the Super Group that still exist could get laid down if not before the Tapeats Sandstone was laid down?
The rest is just details.

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Faith 
Suspended Member (Idle past 1444 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 494 of 1939 (754390)
03-26-2015 11:28 AM
Reply to: Message 491 by edge
03-26-2015 10:36 AM


Abrasion at unconformity
I'm glad Percy is monitoring this thread but communication is nevertheless still difficult.
I just want to try to explain how I think abrasion could have occurred between upper and lower sections of an angular unconformity.
edge writes:
In order to fold the lower rocks, but not affect the upper rocks, you would need to have some kind of detachment between the two bodies. It is like pushing a brick along the concrete sidewalk. They cannot be attached to each other and there has to be some kind of friction in between. That friction should be evident as some kind of a feature in the rock.
I've speculated that the "detachment" needed is the fact that, at least in the Great Unconformity of the Grand Canyon and the one at Siccar Point, the upper (horizontal) and lower (folded or tilted) sections are different kinds of rock. At the G.U. it's Tapeats sandstone above either schist or a block of strata of different kinds of rock, and at Siccar point it's red sandstone above grey sandstone / "greywacke." I speculate that there is enough textural difference between the two sections for there to be some potential for disengagement between them under lateral tectonic pressure on the lower section. That plus a point in the stack where the weight of the stack above gives resistance equal to the tectonic force from below. A combination of these two factors would pinpoint the contact between two layers that would have the most "slippage," allowing the lower to buckle and slide under the upper. [ABE: KEEP IN MIND that I'm assuming that there was a very deep stack of strata above the current horizontal section, at Siccar Point just as there is in the GC, as well as the whole formation's extending horizontally across the whole land area. /ABE]
Admin writes:
Or is she saying that abrasion can happen only where the boundary between two layers is exposed in a cliff face?
edge writes:
I can't tell. I thought she was saying that some process actually deformed the unconformity surface in situ, kind of like salt dome formation; and that it happened within the last 200 years. However, she might just be confusing ancient with modern erosion.
My answer is No to Percy, exposure is not required. And to edge: No, in my scenario I believe it happened under the tectonic force that occurred as the Flood water was receding -- about 4300 years ago. ( In my scenario erosion would have occurred at the time of the movement between the layers, but in these recent discussions of Siccar Point I'm talking about "modern" erosion that has occurred since its formation, through the intense weather on the coast of Scotland.
Or is she referring to abrasion long ago when the upper layer was being being deposited upon the lower layer?
If there was abrasion at the time of deposition, that doesn't sound like a sedimentary process. I suppose one could say that the upper unit slumped into place, but that would also cause some kind of evidence to that effect. For instance, cross-bedding would probably not remain intact.
I think I've answered this in my explanation above.
Here are some of my Blog posts on Siccar Point. I do explain the idea of how the two sections of an angular unconformity could already have existed when the lower was tectonically folded. These are old posts and I haven't updated them but I'd change a few things since recent discussions here. Nothing, however, that affects the idea of how the lower section could have been moved while the upper remained intact.
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.

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jar
Member (Idle past 394 days)
Posts: 34026
From: Texas!!
Joined: 04-20-2004


Message 495 of 1939 (754391)
03-26-2015 11:37 AM
Reply to: Message 494 by Faith
03-26-2015 11:28 AM


Re: Abrasion at unconformity
Yet you have offered no evidence there has ever been a Biblical flood or why a flood would cause tectonic activity or why weathering on the coast of Scotland would be greater than at the Grand Canyon or how your imagined slippage could happen without leaving evidence or how the rest of the Super Group rocks got removed from the Tapeats Sandstone/Vishnu Schist interface OR how the parts of the Super Group that still exist could get laid down if not before the Tapeats Sandstone was laid down or any explanation that is not totally refuted by all the evidence.

Anyone so limited that they can only spell a word one way is severely handicapped!

This message is a reply to:
 Message 494 by Faith, posted 03-26-2015 11:28 AM Faith has replied

Replies to this message:
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