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Faith  Suspended Member (Idle past 1471 days) Posts: 35298 From: Nevada, USA Joined: |
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Author | Topic: Evidence that the Great Unconformity did not Form Before the Strata above it | |||||||||||||||||||||||||||||||||
RAZD Member (Idle past 1431 days) Posts: 20714 From: the other end of the sidewalk Joined: |
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. enjoy ... bad for building foundations (leaning tower of Pisa?)by our ability to understand Rebel☮American☆Zen☯Deist ... to learn ... to think ... to live ... to laugh ... to share. Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)
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Faith  Suspended Member (Idle past 1471 days) Posts: 35298 From: Nevada, USA Joined: |
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.
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Faith  Suspended Member (Idle past 1471 days) Posts: 35298 From: Nevada, USA Joined: |
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 1471 days) Posts: 35298 From: Nevada, USA Joined: |
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 1732 days) Posts: 4696 From: Colorado, USA Joined: |
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?
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PaulK Member Posts: 17827 Joined: Member Rating: 2.3 |
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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Faith  Suspended Member (Idle past 1471 days) Posts: 35298 From: Nevada, USA Joined: |
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 1471 days) Posts: 35298 From: Nevada, USA Joined: |
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: 17827 Joined: Member Rating: 2.3 |
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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Faith  Suspended Member (Idle past 1471 days) Posts: 35298 From: Nevada, USA Joined: |
NO. That is not "draping."
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Faith  Suspended Member (Idle past 1471 days) Posts: 35298 From: Nevada, USA Joined: |
These illustrate draping. Drag folds too.
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PaulK Member Posts: 17827 Joined: Member Rating: 2.3 |
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: 17827 Joined: Member Rating: 2.3
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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.
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Admin Director Posts: 13035 From: EvC Forum Joined: Member Rating: 2.0 |
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?
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Faith  Suspended Member (Idle past 1471 days) Posts: 35298 From: Nevada, USA Joined: |
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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