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Author Topic:   Young earth explanations for Angular Unconformities
Percy
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Posts: 15645
From: New Hampshire
Joined: 12-23-2000
Member Rating: 3.3


Message 181 of 202 (796799)
01-04-2017 4:58 PM
Reply to: Message 180 by edge
01-04-2017 4:31 PM


Re: a review
edge writes:

I think that part of the problem here is the difference between weathering and erosion.

I was wondering if that was the case - so what's the difference?

... then weathering removed some upper layer rock by mechanical erosion.

Not necessarily part of the story. In fact, I might say that the erosion that exposes the cliff face may be artificial, i.e. a road cut or something to that effect.

I don't think this could be the right image because I'm pretty sure Siccar Point is not artificial:

So again, I'm not sure which image you mean. Are we getting the Siccar Point and the "spheroidal weathering" cases confused?

The boulders are formed by spheroidal weathering of granite along fractures. The 'boulders' are not yet actual boulders.

Just to be clear, now we're talking about this image again:

I guess I don't know how to interpret those "boulders" if they weren't really boulders. I assumed they were granite boulders that were ground into spheroid shapes by the action of weather and by being scraped along fast-moving river bottoms. How did those shapes actually form? I did read this explanation from you:

The boulders are formed by spheroidal weathering of granite along fractures. The 'boulders' are not yet actual boulders. But they will be some ages hence. They are also not yet mechanically eroded, though they are chemically weathered.

But why would there be fractures along spheroid paths? And I guess the difference between "mechanically eroded" and "chemically weathered" is becoming important.

--Percy


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 Message 180 by edge, posted 01-04-2017 4:31 PM edge has responded

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


Message 182 of 202 (796803)
01-04-2017 6:34 PM
Reply to: Message 181 by Percy
01-04-2017 4:58 PM


Re: a review
I was wondering if that was the case - so what's the difference?

Weathering is a chemical attack on the rock. Erosion is the transport of that rock material. Solution of a limestone would also be erosion. In some cases weathering might be considered a part of erosion. In this case, I am trying to emphasize the difference because of Faith's statement about weathering at Siccar.

I don't think this could be the right image because I'm pretty sure Siccar Point is not artificial:

So again, I'm not sure which image you mean. Are we getting the Siccar Point and the "spheroidal weathering" cases confused?


That was in reference to the granite image.

I guess I don't know how to interpret those "boulders" if they weren't really boulders. I assumed they were granite boulders that were ground into spheroid shapes by the action of weather and by being scraped along fast-moving river bottoms. How did those shapes actually form? I did read this explanation from you:

By boulder, I'm referring to a size of rock fragment, as shown by this article:

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

As the cores of those spheroids fall out of their places they would become boulders.

But why would there be fractures along spheroid paths? And I guess the difference between "mechanically eroded" and "chemically weathered" is becoming important.

The fractures predate weathering. They allow access by water which slowly reacts with the rock.
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Faith
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Posts: 25249
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 183 of 202 (796814)
01-04-2017 9:48 PM
Reply to: Message 176 by edge
01-04-2017 2:34 PM


The decrepitude of both upper and lower blocks of strata
I mentioned the apparently equal weathering above and below the unconformity as evidence that the standard interpretation is false: i.e., that the lower section was laid down and then tilted, and that a long time later the upper section was deposited on top of it. Since millions of years are usually ascribed to such blocks of strata, there should be a difference in weathering apparent between the two blocks, but they show no such difference.

No. I said that the weathered rock was removed by mechanical erosion and that the lower rocks were covered shortly after erosion.

I don't get much out of your discussions with Percy about this or anything else. I still have no idea what you are saying here. It sounds like an irrelevant pedantic point. How does it change my observation that there is no difference in the appearance of the two blocks of strata -- doesn't matter if you want to call it erosion or weathering or whatnot, they look like they've been treated to exactly the same processes of deterioration from their original state to their current decrepit splintery state. I see no difference and so far nothing you have said has made sense of this.


This message is a reply to:
 Message 176 by edge, posted 01-04-2017 2:34 PM edge has responded

Replies to this message:
 Message 184 by edge, posted 01-04-2017 10:05 PM Faith has responded

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


Message 184 of 202 (796817)
01-04-2017 10:05 PM
Reply to: Message 183 by Faith
01-04-2017 9:48 PM


Re: The decrepitude of both upper and lower blocks of strata
I don't get much out of your discussions with Percy about this or anything else. I still have no idea what you are saying here. It sounds like an irrelevant pedantic point. How does it change my observation that there is no difference in the appearance of the two blocks of strata -- doesn't matter if you want to call it erosion or weathering or whatnot, they look like they've been treated to exactly the same processes of deterioration from their original state to their current decrepit splintery state. I see no difference and so far nothing you have said has made sense of this.

As I said. The sandstone was deposited on eroded rocks that were being removed as they were being weathered. Hence, there was very little weathering of the older rocks before the sandstone was deposited.

This means that there should be little difference in the total amount of weathering, which was your observation.


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 Message 183 by Faith, posted 01-04-2017 9:48 PM Faith has responded

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Faith
Member
Posts: 25249
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 185 of 202 (796818)
01-04-2017 10:18 PM
Reply to: Message 184 by edge
01-04-2017 10:05 PM


Re: The decrepitude of both upper and lower blocks of strata
As I said. The sandstone was deposited on eroded rocks that were being removed as they were being weathered. Hence, there was very little weathering of the older rocks before the sandstone was deposited.

I must have read that a dozen times by now and it makes no sense to me. I don't know what the problem is but it isn't getting through. I'm afraid even to venture to try to interpret it for fear it will only create more confusion.


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PaulK
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Posts: 12759
Joined: 01-10-2003
Member Rating: 3.0


(3)
Message 186 of 202 (796822)
01-05-2017 12:04 AM
Reply to: Message 185 by Faith
01-04-2017 10:18 PM


Re: The decrepitude of both upper and lower blocks of strata
Again it seem obvious. With regard to the rock below the unconformity, erosion removed the weathered material from the surface, thus the material that remained shows relatively little weathering.

Although I have to add that it seems to me that you prefer to judge weathering by looking at cross-sections rather than the surfaces. Since weathering is related to exposure to the elements that is a rather odd thing to do - without knowing when and how the cross-section became exposed you can't even know what weathering to expect.


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 Message 185 by Faith, posted 01-04-2017 10:18 PM Faith has responded

Replies to this message:
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Faith
Member
Posts: 25249
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 187 of 202 (796823)
01-05-2017 12:15 AM
Reply to: Message 186 by PaulK
01-05-2017 12:04 AM


Re: The decrepitude of both upper and lower blocks of strata
I'm not looking at any cross sections, I'm looking at the usual view of Siccar Point.

Both segments of the unconformity look like they've been subjected to a very great degree of weathering or whatever has left them so desiccated and splintery looking.

Erosion removed the weathered material....How do you know that? Why does it end up looking exactly like the rock above the unconformity, where presumably erosion did not remove the westhered material?

Edited by Faith, : No reason given.


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Replies to this message:
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 Message 191 by edge, posted 01-05-2017 10:57 AM Faith has responded

    
PaulK
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Posts: 12759
Joined: 01-10-2003
Member Rating: 3.0


Message 188 of 202 (796824)
01-05-2017 12:22 AM
Reply to: Message 187 by Faith
01-05-2017 12:15 AM


Re: The decrepitude of both upper and lower blocks of strata
quote:

I'm not looking at any cross sections, I'm looking at the usual view of Siccar Point.

Both segments of the unconformity look like they've been subjected to a very great degree of weathering or whatever has left them so desiccated and splintery looking.


The usual view IS a cross-section. That is how you can see the strata. If you were looking down on to the surface you obviously wouldn't see the rock underneath.

quote:

Erosion removed the weathered material....How do you know that?

You seem to forget that I am explaining what Edge is saying. However it is a quite normal occurrence - it's where a lot of sediment comes from.


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


(1)
Message 189 of 202 (796834)
01-05-2017 8:19 AM
Reply to: Message 187 by Faith
01-05-2017 12:15 AM


Re: The decrepitude of both upper and lower blocks of strata
Hi Faith,

Before replying I'd like to make some general requests to everyone:

  • When you're talking about a specific place, mention the place at least once. For instance, do not begin, "Below the unconformity...", but rather, "Below the Siccar Point unconformity..."

  • Every time you refer to an image, include the image. Images are cheap, each one is only cached once. To get an image's URL just right click on it on a Windows machine, or control click on a Mac. You'll be presented a menu that includes the item "Copy Image Address". You can now paste the image address into the [img] dBCode.

  • Quote the text you're replying to.

I'm not looking at any cross sections, I'm looking at the usual view of Siccar Point.

The cross section is the mostly vertical portion showing the relationships between all the strata:

Both segments of the unconformity look like they've been subjected to a very great degree of weathering or whatever has left them so desiccated and splintery looking.

The appearance of weathering is not a measure of how long something has been weathered. Likely none of the surfaces present when Hutton viewed Siccar Point are present today because they've been eroded away. Contrast a recent image with Hutton's drawing - they're different:

So you can't reason about the relative age of layers based upon degree of weathering, because that depends upon degree of exposure to the elements (in this case, wave/wind/rain exposure is most important) and the material composing the individual strata.

Erosion removed the weathered material....How do you know that?

It couldn't be any other way. Very small weathered material has been carried away by wind and water. Larger material is still there at the base of the cliff face where it accumulates as minor scree or talus but is eventually weathered itself into smaller particles and is carried away, or perhaps becomes part of the ground.

Why does it end up looking exactly like the rock above the unconformity, where presumably erosion did not remove the weathered material?

Of course erosion removed the weathered material. The weathered material from the strata above the unconformity has to fall away from gravity and be washed down and/or blown away. This is a very exposed place just on the water.

--Percy


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jar
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Posts: 29007
From: Texas!!
Joined: 04-20-2004
Member Rating: 2.6


Message 190 of 202 (796837)
01-05-2017 8:40 AM
Reply to: Message 189 by Percy
01-05-2017 8:19 AM


Re: The decrepitude of both upper and lower blocks of strata
Percy writes:

Faith writes:

Erosion removed the weathered material....How do you know that?

It couldn't be any other way. Very small weathered material has been carried away by wind and water. Larger material is still there at the base of the cliff face where it accumulates as minor scree or talus but is eventually weathered itself into smaller particles and is carried away, or perhaps becomes part of the ground.

Have you considered other ways the material might have been removed like geologists taking samples away or tourists taking mementos away or pixie dust?


My Sister's Website: Rose Hill Studios My Website: My Website

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


Message 191 of 202 (796844)
01-05-2017 10:57 AM
Reply to: Message 187 by Faith
01-05-2017 12:15 AM


Re: The decrepitude of both upper and lower blocks of strata
Both segments of the unconformity look like they've been subjected to a very great degree of weathering or whatever has left them so desiccated and splintery looking.

If I stood out there for years in the weather along the North Sea, I'd look pretty desicated and splintery too.

Erosion removed the weathered material....How do you know that?

Well, for one, we see this happening all over the world including in the images of Siccar Point.

Beyond that, we can see rounded boulders of the lower sequence (below the unconformity) as a basal conglomerate just above the unconformity. So, we know that the lower rocks were eroded.

In fact, I think (IMO ... I've not actually been there) there are small channels of conglomerate in the sandstone that contain fragments of the lower rocks.

Why does it end up looking exactly like the rock above the unconformity, ...

You've lost me here. I thought you agreed that the rocks above and below were very different. That's how it looks to me. One is a red sandstone (above) and the other is a greenish-gray graywacke (below). I can describe other differences if you want.

... where presumably erosion did not remove the westhered material?

Well, it is being removed now, so I'm not sure what you mean.

If mean the previous period of erosion, sure. The upper rocks (the sand) were deposited after erosion of the lower layer.


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 Message 187 by Faith, posted 01-05-2017 12:15 AM Faith has responded

Replies to this message:
 Message 192 by Faith, posted 01-05-2017 1:44 PM edge has responded

  
Faith
Member
Posts: 25249
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 192 of 202 (796852)
01-05-2017 1:44 PM
Reply to: Message 191 by edge
01-05-2017 10:57 AM


Re: The decrepitude of both upper and lower blocks of strata
Why does it end up looking exactly like the rock above the unconformity, ...

You've lost me here. I thought you agreed that the rocks above and below were very different. That's how it looks to me. One is a red sandstone (above) and the other is a greenish-gray graywacke (below). I can describe other differences if you want.

I've been saying from the point I entered this thread that the upper and lower segments of the Siccar unconformity look about equally weathered. The appearance of weathering (or erosion or whatever is the cause of the obvious breakdown of the rocks into their splintery form) is the only comparison I've commented on. The point has been from the beginning that I see no evidence of the usual interpretation of angular unconformities, that there is a difference of millions of years between the tilted lower portion and the upper horizontal portion of such formations. If that were the case, I argued, the lower section should be utterly reduced to a small pile of splintery rock at a location like Siccar Point with the constant battering of the elements. MILLIONS of years. I don't think such a huge time span can be encompassed by anybody's mental set, it's beyond comprehension. But sedimentary rock should disintegrate under the conditions at Siccar Point in far far less time.

The upper segment is identified as Devonian, the lower as Silurian, the usual difference in age between these time periods being in the millions. This is all I've been referring to from the beginning. I thought you answered earlier in terms that reduced the difference in age. Now you are answering in terms of the appearance of age. On the appearance of age I argue that the differences couldn't possibly reflect millions of years.

That's all.

... where presumably erosion did not remove the westhered material?

Well, it is being removed now, so I'm not sure what you mean.

How long does it take? How long has the upper section been there? Even that section should have been reduced to rubble by now according to the usual time spans proposed by standard geology. That any of the formation is still standing at all is testimony to a much shorter span of time than that.

The topic is still pretty confused it seems to me.

Edited by Faith, : No reason given.


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 Message 191 by edge, posted 01-05-2017 10:57 AM edge has responded

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PaulK
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Posts: 12759
Joined: 01-10-2003
Member Rating: 3.0


(2)
Message 193 of 202 (796855)
01-05-2017 2:17 PM
Reply to: Message 192 by Faith
01-05-2017 1:44 PM


Re: The decrepitude of both upper and lower blocks of strata
quote:

I've been saying from the point I entered this thread that the upper and lower segments of the Siccar unconformity look about equally weathered. The appearance of weathering (or erosion or whatever is the cause of the obvious breakdown of the rocks into their splintery form) is the only comparison I've commented on

Aside from the subjectivity (and failing to check that the rocks are equally hard) it does seem very clear that you are looking at an exposed cross-section rather than the surface.

quote:

The point has been from the beginning that I see no evidence of the usual interpretation of angular unconformities, that there is a difference of millions of years between the tilted lower portion and the upper horizontal portion of such formations.

You are the only one who fails to see it. The evidence that there has been major erosion between the folding and the deposition of the strata above the unconformity is quite clear.

quote:

If that were the case, I argued, the lower section should be utterly reduced to a small pile of splintery rock at a location like Siccar Point with the constant battering of the elements. MILLIONS of years.

Given the fact that quite large amounts of rock were lost between the folding and deposition starting - and that you would need to know that the conditions causing the erosion were so harsh that we should expect more - that really doesn't seem to be much of an objection. Without good estimates of how much has been lost and how much should have been lost you are just guessing.

quote:

The upper segment is identified as Devonian, the lower as Silurian, the usual difference in age between these time periods being in the millions.

The age of the fold would seem far more relevant than the time the greenwacke was deposited. Exposure time is what matters, not age.

quote:

How long does it take? How long has the upper section been there? Even that section should have been reduced to rubble by now according to the usual time spans proposed by standard geology.

As I point out above, that is no more than a wild guess. (However I will note that an inability to account for observed erosion in the Biblical timescale was one of the earliest clues to the fact that the Earth was much older than the Bible suggested)

quote:

The topic is still pretty confused it seems to me.

The confusion is mostly yours.


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


Message 194 of 202 (796857)
01-05-2017 2:28 PM
Reply to: Message 192 by Faith
01-05-2017 1:44 PM


Re: The decrepitude of both upper and lower blocks of strata
I've been saying from the point I entered this thread that the upper and lower segments of the Siccar unconformity look about equally weathered. The appearance of weathering (or erosion or whatever is the cause of the obvious breakdown of the rocks into their splintery form) is the only comparison I've commented on. The point has been from the beginning that I see no evidence of the usual interpretation of angular unconformities, that there is a difference of millions of years between the tilted lower portion and the upper horizontal portion of such formations.

I'm not sure how to explain it any more simply.

As the rocks are weathered, the weathered parts are carried away by mechanical erosion. This exposes more fresh rock to weathering. That way, the rock always looks fresher than one might expect. The exposed surface is being constantly renewed.

If that were the case, I argued, the lower section should be utterly reduced to a small pile of splintery rock at a location like Siccar Point with the constant battering of the elements. MILLIONS of years. I don't think such a huge time span can be encompassed by anybody's mental set, it's beyond comprehension. But sedimentary rock should disintegrate under the conditions at Siccar Point in far far less time.

And they do. The question is, how long has that particular part of the rock been exposed to weathering.

Why do you think that geologists carry hammers? It's to break through the part of a rock that is weathered to see the original rock characteristics.

The upper segment is identified as Devonian, the lower as Silurian, the usual difference in age between these time periods being in the millions. This is all I've been referring to from the beginning. I thought you answered earlier in terms that reduced the difference in age. Now you are answering in terms of the appearance of age. On the appearance of age I argue that the differences couldn't possibly reflect millions of years.

They don't.

You understand that the Silurian rocks were being weathered in the Devonian, right up until they were being covered by the sand.

We can't even tell when the weathering started. That's one of the tricky things about unconformities. They seem like a fairly simple concept, but when you really get into it, there's a lot of complications and implications.

How long does it take? How long has the upper section been there?

The upper section started forming in the Devonian. The lower section was eroded sometime after it was deformed. All we really know is that erosion ended in the Devonian.

Even that section should have been reduced to rubble by now according to the usual time spans proposed by standard geology. That any of the formation is still standing at all is testimony to a much shorter span of time than that.

Not really. Erosion is a process, it starts when the rock is exposed to the elements and it ends when deposition begins anew.

The topic is still pretty confused it seems to me.

Well, frankly, it is confusing to most people. But most people will try to understand the processes acting over time.
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 Message 192 by Faith, posted 01-05-2017 1:44 PM Faith has responded

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


Message 195 of 202 (796858)
01-05-2017 2:32 PM
Reply to: Message 193 by PaulK
01-05-2017 2:17 PM


Re: The decrepitude of both upper and lower blocks of strata
The age of the fold would seem far more relevant than the time the greenwacke was deposited. Exposure time is what matters, not age.

This is very true (except that it is a graywacke). Just because the lower rocks are Silurian in age does not mean that they were eroded in the Silurian.

In geology terms, the erosional surface cuts the folded rocks, therefor it is younger than the folding.


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