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Author Topic:   Young earth explanations for Angular Unconformities
edge
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Posts: 3881
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 4.1


Message 136 of 202 (796674)
01-02-2017 9:53 PM
Reply to: Message 131 by Faith
01-02-2017 11:43 AM


Also I don't see why the shearing always has to create a perfectly flat surface. If there's enough resistance it could be pretty lumpy.

It doesn't have to be perfectly flat, but it has to be present and visible. It also should conform to the sense of direction of relative motion.

There is no such surface present at Siccar, nor any other of the places we have discussed.

That whole formation obviously tilted after it was laid down, same as at Siccar Point, since the upper section would have originally been horizontal. Whatever caused that tilting could have affected the surface of the lower section.

Should have. If your scenario were correct.

There is no such structure, there is no rock fabric that tells us that there was relative motion.

Edited by edge, : No reason given.


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edge
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Posts: 3881
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 4.1


Message 137 of 202 (796675)
01-02-2017 9:56 PM
Reply to: Message 134 by Percy
01-02-2017 4:37 PM


Re: Edge's photo of the GC
Is Edge referring to those granite boulders when he says, "weathering rinds"? What fractures is he referring to, the ones between layers, or the fracture in the layer to the right of the boulders? Anyway, because I didn't understand this paragraph, I wasn't sure how to interpret the next one either.

Weathering is beginning to form boulders which are visible in the image. This weathering takes time to happen, occurring along fractures in the granite.

Not all outcroppings of granite show this feature.


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edge
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Posts: 3881
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 4.1


Message 138 of 202 (796676)
01-02-2017 10:33 PM
Reply to: Message 132 by Percy
01-02-2017 2:47 PM


This is incorrect. As you can see in your own diagram, some of the layers are nearly upright, some are tilted, but at any rate the degree of tilt doesn't matter. What you're missing is that tilting or bending or buckling of underlying layers without affecting the layers above isn't possible because it requires cubic miles of material to simply disappear into thin air.

The missing material should be present in the section as an identifiable layer of what we call mylonite. It is essentially ground up rock that defines a plane or zone of shearing.

For the total strain evidenced by folding in the rocks (see Faith's diagram) this should be a substantial and identifiable layer in the section. Other features present should be slickensides and polished surfaces, such as the ones shown below.

No such thing is present at Siccar or any other place we have discussed. They are ubiquitous in any area that has been tectonized (which would include Faith's scenario for unconformities).

You are correct. The supposedly ground up material had to go somewhere and by appearances, there must have been a lot of it.

Edited by edge, : No reason given.

Edited by edge, : No reason given.


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Replies to this message:
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edge
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Posts: 3881
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 4.1


Message 139 of 202 (796677)
01-02-2017 10:39 PM
Reply to: Message 126 by Percy
01-02-2017 8:12 AM


Faith may not have followed your argument about the degree of mechanical action, and I may not either. You seem to be drawing a contrast between relatively fast erosion (high mechanical action) that leaves a clean and new looking surface, versus weathering which results from long exposure with small scale erosion (low mechanical action) that results in the aged appearance we're familiar with in some rocks such as at Siccar Point. If I have that right then I get it, but I'm not sure Faith does.

Yes, that is the point of my argument.

At Siccar, material was being constantly removed as it was weathered.

In other locations, the rock would be weathered deeply, in place, and not removed by mechanical erosion prior to deposition of the upper sequence above the unconformity.

I think we have seen the effects of weathering in many of the Grand Canyon images as well. One of the products of weathering would be paleosoils which we do see in the geological record, though not at Siccar or at the Grand Canyon.


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Faith
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Posts: 25251
From: Nevada, USA
Joined: 10-06-2001
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Message 140 of 202 (796678)
01-03-2017 1:50 AM
Reply to: Message 139 by edge
01-02-2017 10:39 PM


You keep claiming that this or that phenomenon WOULD HAVE been present if my theory is correct. But clearly the rock WAS folded, which can be seen on Lyell's drawing, and you say they don't show those phenomena. How can you explain that? Also how can you explain the folding at all without tectonic pressure? I asked that a post or two ago, did I miss your answser? AND assuming that the folding occurred before the strata above were laid down, how on earth could that happen at all, one, meaning I'd think it would be hard to explain how it could occur without a counterweight above it. and two, assuming somehow it did fold without anything above it, where did the material go that presumably disappeared by the time the strata came along? Is there evidence that it trickled down into the folds somehow? Doesn't seem to be the case, especially that much material that supposedly I have a problem accounting for. Seems to me you have at least as much of a problem explaining your senario as you think I have.

Edited by Faith, : No reason given.


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PaulK
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Member Rating: 3.0


(3)
Message 141 of 202 (796679)
01-03-2017 2:07 AM
Reply to: Message 140 by Faith
01-03-2017 1:50 AM


The point - which seems rather obvious to me - is that the tectonic events only affected the strata below the unconformity. Also that the surfaces at the unconformity do not show the effects that should have been generated under your scenario.

There is no need for a counterweight as simple experimentation should show you.

Material removed from the surface by erosion is typically carried away - only a relatively small proportion would remain. The problem for your scenario is that the erosion occurs deep underground where that cannot happen.

All this should be obvious.


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Percy
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Posts: 15645
From: New Hampshire
Joined: 12-23-2000
Member Rating: 3.3


(1)
Message 142 of 202 (796690)
01-03-2017 9:04 AM
Reply to: Message 135 by Faith
01-02-2017 7:40 PM


The degree of tilt doesn't matter. It's the same problem no matter what the degree of tilt. The missing material has to go somewhere. In the view of standard geology the missing material was once at the surface and was removed by the forces of erosion and carried away toward the lowest elevation (most often the ocean where most sedimentary layers originate) by wind, rain, streams and rivers. Erosion tends to level a landscape, and then when deposition begins again sediments are deposited in mostly flat layers upon the older eroded surface. The boundary between the older layers and the new layers is an unconformity.

Your scenario is impossible, and I can explain why. Here are the sedimentary layers as they originally appeared. I've labeled them A through H:

And here are the layers after E through H rotated 90 degrees to become vertical:

I've labeled as X and Y the regions next to layers E through H. What fills regions X and Y now? Your answer is that material scraped and eroded and broken off from layers D through H should fill region X and Y.

But the reality is that X and Y are not filled with material from layers D through H. At the Grand Canyon (where the tilt is much less than 90 degrees) X and Y are filled with Vishnu basement rocks. At Siccar Point X and Y are filled with other sedimentary layers. And as Edge has pointed out, there is also no evidence of shear at the boundary.

Once tilted vertical, layers E through H have a limited extent, bounded by layers A through D at the top and by other rock at the bottom. In your scenario the miles of extent of layers have become truncated into a very short distance. Where did all the missing material go?

--Percy

Edited by Percy, : Grammar.


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Percy
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Posts: 15645
From: New Hampshire
Joined: 12-23-2000
Member Rating: 3.3


(2)
Message 143 of 202 (796691)
01-03-2017 9:17 AM
Reply to: Message 140 by Faith
01-03-2017 1:50 AM


Faith writes:

You keep claiming that this or that phenomenon WOULD HAVE been present if my theory is correct. But clearly the rock WAS folded, which can be seen on Lyell's drawing, and you say they don't show those phenomena.

This isn't the point that's being made. No one thinks the layers weren't folded by geologic forces. The point is that when the layers were folded the current overlying layers were not present. There were other layers atop the folded layers that were folded along with them and then were later eroded away.

AND assuming that the folding occurred before the strata above were laid down, how on earth could that happen at all, one, meaning I'd think it would be hard to explain how it could occur without a counterweight above it.

Why do you think tectonic forces generated from within the Earth require some sort of counterweight?

and two, assuming somehow it did fold without anything above it, where did the material go that presumably disappeared by the time the strata came along?

It was eroded and carried away to the lowest geologic point (often the ocean) by wind, rain, streams and rivers. It's the same process we see happening all around the world today. The present is the key to the past.

It's amazing that after all your time here you still don't know the basics of geology. To disagree with them is one thing, but to not even know them despite years of discussion is unfathomable.

--Percy


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Replies to this message:
 Message 144 by Faith, posted 01-03-2017 10:41 AM Percy has responded
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Faith
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Posts: 25251
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 144 of 202 (796695)
01-03-2017 10:41 AM
Reply to: Message 143 by Percy
01-03-2017 9:17 AM


You keep claiming that this or that phenomenon WOULD HAVE been present if my theory is correct. But clearly the rock WAS folded, which can be seen on Lyell's drawing, and you say they don't show those phenomena.

This isn't the point that's being made. No one thinks the layers weren't folded by geologic forces.

Then why bother talking about supposed evidence for folding that in fact is not present although you know folding occurred? And what is a "geologic force" pray tell? Why not say "tectonic" or is there some other kind of "geologic force" that explains this.

The point is that when the layers were folded the current overlying layers were not present. There were other layers atop the folded layers that were folded along with them and then were later eroded away.

Wowsy wow. Now there's an entirely new theory I've never heard before. Never ever has such an idea entered into these discussions of the formation of angular unconformities. And if this is the point, again I ask why bring up evidence of folding when there is no such evidence present in the current examples? Eh? This discussion has gone from confused to bizarre.

There were layers present when it folded? And they got folded with them and then were so completely eroded away there isn't a trace of them to be found? Unfortunately you've removed all the words I might reasonably use to describe this sort of ridiculousness.

AND assuming that the folding occurred before the strata above were laid down, how on earth could that happen at all, one, meaning I'd think it would be hard to explain how it could occur without a counterweight above it.

Why do you think tectonic forces generated from within the Earth require some sort of counterweight?

Golly gosharoony, I was making the intelligent rational point that folding isn't too likely to occur without some resistance above it. More than a layer or two I'd venture. And I note that you don't have an explanation. Perhaps you should leave such questions to edge.

and two, assuming somehow it did fold without anything above it, where did the material go that presumably disappeared by the time the strata came along?

It was eroded and carried away to the lowest geologic point (often the ocean) by wind, rain, streams and rivers. It's the same process we see happening all around the world today. The present is the key to the past.

The thing is, we've got these folded slabs of rock that cover who knows how much geography when first formed, and somehow their tops were cut off, presumably by erosion before strata were laid over them. Thing is, they would form a surface riddled by cracks, not a surface conducive to, say, water runoff, and yet the cracks wouldn't be large enough to hold much eroded material. Seems to me it would pile up. Ya know, on ordinary physical principles, given the actual surface that would have been formed by folded sheets of wannabe rock.

It's amazing that after all your time here you still don't know the basics of geology. To disagree with them is one thing, but to not even know them despite years of discussion is unfathomable.

What we have here is wild empty name-calling. This discussion at this point has absolutely nothing to do with the basics of geology. This idea you've been describing has never before entered into the discussion of angular unconformities. I strongly recommend that you stay out of it to avoid contributing further to the utter nonsense. Edge is capable of confusing things enough without your help.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.


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Replies to this message:
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Faith
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Posts: 25251
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 145 of 202 (796697)
01-03-2017 10:50 AM


...

Edited by Faith, : No reason given.


    
edge
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Posts: 3881
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 4.1


Message 146 of 202 (796700)
01-03-2017 11:24 AM
Reply to: Message 142 by Percy
01-03-2017 9:04 AM


Once tilted vertical, layers E through H have a limited extent, bounded by layers A through D at the top and by other rock at the bottom. In your scenario the miles of extent of layers have become truncated into a very short distance. Where did all the missing material go?

One argument would be that the space is taken up by folding of the underlying sequence. It could, theoretically, be doubled, tripled or even more in thickness by folding.

In reality, however, this would be effectively impossible unless the lower block had absolutely no strength and could flow wherever forced. But then that would mean that all bedding would be fluidized and the section would be unrecognizable as a sedimentary rock.

What you are talking about is what we used to call a 'room' problem. In deforming the rock, you either create space that has to be filled with something, or you force so much material into a small space that it is forced to escape. In either case, you have caused certain deformation features that would be easily recognizable.

Folding produces crests and troughs. The crests basically move upward and the troughs downward to accommodate shortening in a lateral direction. This would necessarily involve the upper layers. They would have to be moved and/or broken.


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edge
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Posts: 3881
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 4.1


Message 147 of 202 (796702)
01-03-2017 11:34 AM
Reply to: Message 143 by Percy
01-03-2017 9:17 AM


Why do you think tectonic forces generated from within the Earth require some sort of counterweight?

I think that Faith is trying to describe a confining pressure. Confining pressures are mostly due to overburden weight in earth processes.

My question for Faith on this would be, "which rock section would have more confining pressure, the upper block or the lower?"

So which one should deform first, everything else being equal?

Here is an example:

Note that the upper layers are folded, whereas the lower layers resisted folding. That is because the upper layers only had to lift themselves and the air above them. The lower layers tend to be confined.

Lower layers also tend to be stronger since they have been lithified for a longer time. However, in an overthrust situation, older rocks will override younger.

Notice also that the detachment surface cuts across beds in the lower section along a smooth surface.

ETA: By the way, this is a true detachment fault where the upper block has slipped across the lower for an uncertain distance.

Edited by edge, : No reason given.

Edited by edge, : No reason given.

Edited by edge, : No reason given.


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Percy
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Posts: 15645
From: New Hampshire
Joined: 12-23-2000
Member Rating: 3.3


(3)
Message 148 of 202 (796704)
01-03-2017 12:15 PM
Reply to: Message 144 by Faith
01-03-2017 10:41 AM


Faith writes:

This isn't the point that's being made. No one thinks the layers weren't folded by geologic forces.

Then why bother talking about supposed evidence for folding that in fact is not present although you know folding occurred?

I'm not sure why there's any confusion about this, so I'll just repeat the point, but first here's the image again:

Of course folding is present. No one said folding isn't present.

The point is that when the layers were folded the current overlying layers were not present. There were other layers atop the folded layers that were folded along with them and then were later eroded away.

Wowsy wow. Now there's an entirely new theory I've never heard before. Never ever has such an idea entered into these discussions of the formation of angular unconformities.

It's amazing that you don't already understand this. It's very basic geology. Before new layers were deposited atop it, what did you imagine was being eroded away to form the top surface of the angular unconformity?

Here's a modified copy of the Siccar Point diagram showing in red where the layers that were eroded away might have been:

All the red layers that I added were eroded away, the sediments carried away to lower elevations like the ocean by wind, rain, streams and rivers. Then the layers visible today atop the angular unconformity were deposited.

Golly gosharoony, I was making the intelligent rational point that folding isn't too likely to occur without some resistance above it. More than a layer or two I'd venture. And I note that you don't have an explanation. Perhaps you should leave such questions to edge.

Ah, okay. I don't think "counterweight" was the word you were looking for. All it takes is one area being uplifted or subsided more than another to bend or fold layers. That could mean different amounts of force in different areas, or it could mean different amounts of overlying layers, or a combination.

The thing is, we've got these folded slabs of rock that cover who knows how much geography when first formed, and somehow their tops were cut off, presumably by erosion before strata were laid over them. Thing is, they would form a surface riddled by cracks,...

It *does* "form a surface riddled by cracks," but not in the way you're thinking. Erosion and weathering, especially things like rising/falling temperatures and freezing/thawing water, cause minute cracking and flaking of rock, gradually wearing it away particle by particle.

...not a surface conducive to, say, water runoff, and yet the cracks wouldn't be large enough to hold much eroded material. Seems to me it would pile up. Ya know, on ordinary physical principles, given the actual surface that would have been formed by folded sheets of wannabe rock.

The eroded material is carried away to the lowest elevations, often the ocean, but on its journey it will encounter many local low elevations, and there the eroded material will remain until it piles high enough to continue toward even lower elevations. Any landscape eventually erodes away, and the eroded material it contains eventually reaches a low elevation.

This discussion at this point has absolutely nothing to do with the basics of geology. This idea you've been describing has never before entered into the discussion of angular unconformities. I strongly recommend that you stay out of it to avoid contributing further to the utter nonsense. Edge is capable of confusing things enough without your help.

I think we should appreciate all the help we can get from Edge. Hopefully he can confirm what I've told you about angular unconformities, that basic geology believes they form when the higher portions of the tilted layers are eroded away.

--Percy


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edge
Member
Posts: 3881
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 4.1


(1)
Message 149 of 202 (796706)
01-03-2017 12:34 PM
Reply to: Message 148 by Percy
01-03-2017 12:15 PM


I think we should appreciate all the help we can get from Edge. Hopefully he can confirm what I've told you about angular unconformities, that basic geology believes they form when the higher portions of the tilted layers are eroded away.

I don't think it's too much of a stretch to say that the layers you reconstituted in the modified diagram were continuous and were present prior to erosion.

The full thickness would be unknown to us without looking at regional geology to see what other formations might have been on top of the lower sequence of rocks. It could be quite substantial.

This seems to be another case where YECs deny the effects of erosion which always puzzled me since we actually live on an unconformity...


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Faith
Member
Posts: 25251
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 150 of 202 (796711)
01-03-2017 2:13 PM
Reply to: Message 147 by edge
01-03-2017 11:34 AM


I don't see how most of what you and Percy are talking about is relevant to the points I've been trying to make. I suppose I could speculate about the picture you posted, though I think I'd need more information such as where it is located, and the supposed age or time period of the folded rocks, but since I don't see its relevance to the discussion I don't see putting in the effort. The angular unconformities appear to have been formed as I've described. They are a different thing. And this idea that there were strata above them that eroded away before more strata were deposited, is, as I said, a brand-new idea never before applied in the discussion of these things. Which introduces some of the flavor of a flim-flam even though its purposes isn't at all clear.

Upshot: I don't see any point in continuing this discussion. You and Percy might as well go on with your irrelevant musings.


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