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Author Topic:   Evidence that the Great Unconformity did not Form Before the Strata above it
RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 1396 of 1939 (756568)
04-22-2015 10:08 PM
Reply to: Message 1381 by edge
04-22-2015 10:44 AM


I'm going to write something up on the 'fluid' topic later today. The thing is that sediments are, indeed, not fluids, ... but they can be fluidized.
Like quicksand.
Another term I remember from soils class is plasticity, where material is not loose sand or gravel, nor is it solidified rock. It behaves in a plastic manner, deforming under stress\pressure and not rebounding when stress\pressure is removed. It also would not flow down slope to level out due to cohesion and internal friction. Wet clay is an example.
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This message is a reply to:
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Faith 
Suspended Member (Idle past 1444 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 1397 of 1939 (756569)
04-22-2015 11:54 PM
Reply to: Message 1393 by PaulK
04-22-2015 6:26 PM


Showing that sediments may deposit on an incline does NOT show that they "drape." Too bad there isn't a photo of those areas of the Tapeats that McKee illustrated.

This message is a reply to:
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Faith 
Suspended Member (Idle past 1444 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 1398 of 1939 (756570)
04-22-2015 11:56 PM
Reply to: Message 1394 by edge
04-22-2015 8:09 PM


You've seen draped bedding and you won't post the pictures because I might interpret them differently than you do. Wow.

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


Message 1399 of 1939 (756571)
04-23-2015 12:42 AM
Reply to: Message 1396 by RAZD
04-22-2015 10:08 PM


draped sandstone continued
Another term I remember from soils class is plasticity, where material is not loose sand or gravel, nor is it solidified rock. It behaves in a plastic manner, deforming under stress\pressure and not rebounding when stress\pressure is removed. It also would not flow down slope to level out due to cohesion and internal friction. Wet clay is an example.
Which is the only condition I've been saying could produce "draped" layers over objects, whereas sediments in their original "fluid" form would not do this.
This picture edge posted way back there which I marked for Message 967 shows that condition of the layers on the left that have sagged into the depression in the gneiss on the left.
This is really not draping either, it's just a still-soft but clearly formed LAYER that sagged from its softness into that low spot. I think it's really the closest thing to draping that could occur, however.
Here I've circled the layer (or layers) I'm talking about:
I suppose it could be interpreted as the gneiss being pushed up into the layer on the right rather than its sagging into the low spot on the left, but in either case the layer I've circled is clearly a formed layer, not in any sense original loose sediment. It's formed but still soft/plastic at the time of its deformation, not exactly draping but in my opinion closer to it than you'd get with originally deposited sediment.
DRAPING implies clinging to another object as shown in the McKee drawings where the Tapeats sandstone drapes first over the rock and then over other layers of sandstone, ALL OF THEM HAVING THE RECOGNIZABLE FORM OF LAYERS. For this reason I interpret them as having already BEEN layers, already in that "plastic" condition, formed but not hardened, when the rock intruded from beneath, as I do not believe sediments in their original "fluid" condition would deposit in such a clearly LAYERED way that drapes over underlying objects. Showing that sediments may deposit on an incline does NOT account for what McKee has shown in the drawings. My own expectation is that they are more like the sagging layers in the photo above, and not quite as "draped" as the drawings indicate -- that is, I wouldn't expect that they cling closely to the underlying object, but sagged and stretched over it due to their plasticity. This is why it would be nice to have photos of that same area, since a drawing would leave out the necessary detail.
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.

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


Message 1400 of 1939 (756572)
04-23-2015 12:58 AM
Reply to: Message 1398 by Faith
04-22-2015 11:56 PM


You've seen draped bedding and you won't post the pictures because I might interpret them differently than you do. Wow.
So you ignored my new post. Why am I not surprised?

This message is a reply to:
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PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


Message 1401 of 1939 (756573)
04-23-2015 12:59 AM
Reply to: Message 1397 by Faith
04-22-2015 11:54 PM


If you can't think of any problem - and changing the subject pretty clearly indicates that you can't - then obviously you don't have a real objection.
However, I'm going to give you another chance.
If you accept that one layer can drape over an object, then why can't another layer drape over that ?

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 Message 1397 by Faith, posted 04-22-2015 11:54 PM Faith has replied

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


Message 1402 of 1939 (756574)
04-23-2015 1:01 AM
Reply to: Message 1401 by PaulK
04-23-2015 12:59 AM


You're missing the point. I'm saying that FRESHLY DEPOSITED SEDIMENTS IN THEIR "FLUID" CONDITION can't do that, but that FORMED LAYERS THAT ARE STILL PLASTIC could.

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


Message 1403 of 1939 (756575)
04-23-2015 1:12 AM
Reply to: Message 1395 by edge
04-22-2015 8:19 PM


So this is the post you claim I "ignored?"
So I'll comment on it now:
Differential compaction causes drape over reefs and sand bodies and this can form traps. A sandstone or carbonate layer above the bar or reef can be bent in such a way as to have closure, that is, the ability to contain and trap hydrocarbons. The bending is caused by the fact that the reef or sand body does not compress to the same degree as the shales to either side of it. Therefore a topographic high can be propagated upward through the section for quite some distance.
"These traps look like folds in a cross section or on the dipmeter patterns. They were not formed by tectonic activity, but rather by the sedimentary process itself. Dips underneath the reef or bar will be regional, in contrast to the anticline. Drape is important in identifying sedimentary structures from dipmeter data, and is often overlooked as a trapping mechanism in the beds lying above the target formation.
"Drape is illustrated schematically for both the reef and the sand bar case. Channel fill can also cause drape, again due to differential compaction of surrounding shale. Bedding inside the channel may be complex, but is usually regional under the channel. However, the mass of a reef or channel sand may compact the rock under the body, causing apparent sag below the base of the zone."
( Crain's Petrophysical Handbook | Login Page)
The examples of sag or drape that are described in the quote are consistent with what I've been saying about this occurring with soft but formed layers but not with sediments depositing in the "fluid" or "loose" condition.
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.

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PaulK
Member
Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


Message 1404 of 1939 (756576)
04-23-2015 1:27 AM
Reply to: Message 1402 by Faith
04-23-2015 1:01 AM


Again, you're not giving any answer to the question.
If a single layer can drape over an object why can't another layer drape over the top of that ?
Even if the layers were deposited in a "fluid state" (which is your invention) that would apply equally to the first layer, and it would also apply to other situations where layers were deposited one on top of the other.
I'm not missing the point - you aren't making one.

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 Message 1406 by Faith, posted 04-23-2015 1:38 AM PaulK has replied

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


Message 1405 of 1939 (756577)
04-23-2015 1:33 AM
Reply to: Message 1404 by PaulK
04-23-2015 1:27 AM


NO. That is not "draping."

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


Message 1406 of 1939 (756578)
04-23-2015 1:38 AM
Reply to: Message 1404 by PaulK
04-23-2015 1:27 AM


These illustrate draping. Drag folds too.

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PaulK
Member
Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


Message 1407 of 1939 (756579)
04-23-2015 1:43 AM
Reply to: Message 1405 by Faith
04-23-2015 1:33 AM


What isn't "draping" ? WHY isn't it "draping" ?
If you can't give a sensible answer then just admit it. Sometimes "tell, don't show" is the right approach.

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PaulK
Member
Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


(1)
Message 1408 of 1939 (756580)
04-23-2015 1:56 AM
Reply to: Message 1406 by Faith
04-23-2015 1:38 AM


Looking at the diagram on the left:
In the earlier layers of the Tapeats formation, the sediment piled up a little on the sides of the archaean outcrop. When they got sufficiently close to the top, a layer draped over the outcrop and later layers draped over that. Really, no relevant differences there.

This message is a reply to:
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Admin
Director
Posts: 12995
From: EvC Forum
Joined: 06-14-2002
Member Rating: 2.3


Message 1409 of 1939 (756581)
04-23-2015 6:54 AM
Reply to: Message 1399 by Faith
04-23-2015 12:42 AM


Re: draped sandstone continued
Hi Faith,
I am, as always, reading forward sequentially and responding as I go as needed. In this case I'm seeking clarification. Since I haven't yet read the messages after this one I have no way of knowing if the issues I'm going to raise have already been clarified, but if they have then please just ignore this message.
Another term I remember from soils class is plasticity, where material is not loose sand or gravel, nor is it solidified rock. It behaves in a plastic manner, deforming under stress\pressure and not rebounding when stress\pressure is removed. It also would not flow down slope to level out due to cohesion and internal friction. Wet clay is an example.
Which is the only condition I've been saying could produce "draped" layers over objects, whereas sediments in their original "fluid" form would not do this.
I don't recall you ever saying that compression of layers around a hard object like a rock would cause draped sedimentary layers. I thought your position was that a dropstone falling and embedding itself into sedimentary layers would immediately produce this appearance:
Uh, did you alter the above image? It now has a couple lines through the top three layers, I assume to indicate that the dropstone disrupted them while passing through. I don't recall seeing them before. Perhaps I simply missed them, but now I have to comment that no such disruption appears in the layers above dropstones, indicating that they did not pass through those layers but instead had sedimentary layers deposited above them after they fell:
About this image:
Since you now concede that sedimentary layers can deposit evenly on a slope, what is it you see in this image that leads you to conclude it was originally horizontal and only tilted later?

--Percy
EvC Forum Director

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


Message 1410 of 1939 (756582)
04-23-2015 7:10 AM


McKee diagram in photo?
From Google Images a photo (below) that I think pictures the area of two of the diagrams by McKee, (b) and (e), which I found by searching on the location references at the bottom of the page. But it's one of those touristy pictures that is more interested in the sunset than the formation so you only get a hint of the Tapeats layers.
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.

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