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Faith  Suspended Member (Idle past 1473 days) Posts: 35298 From: Nevada, USA Joined: |
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Author | Topic: Origin of the Flood Layers | ||||||||||||||||||||||||||||||||||||||||||||
edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined: |
edge left this unexplained so I thought I would give it a go since it is something I mentioned in the other thread.
I've been looking for a better picture of this phenomenon, but it's not usually what people focus on when looking at an unconformity. However, this photo may be a bit clearer.
Layer "A" is deposited. It is then exposed to the surface and subject to erosion. Erosion of layer "A" results in debris which is composed of material that originated in layer "A". Then layer "B" is deposited on top of layer "A". The debris which was a result of erosion of layer "A" and is composed of layer "A" material is then incorporated into layer "B". Material that is composed of layer "A" that has been incorporated into layer "B" is the "bullet-proof" evidence of what the sequence of events were. This is the Great Unconformity in the Red Rocks area of Colorado. It is actually a 'nonconformity' at this location since the underlying rocks to the lower right are granite and the overlying rocks are sand and gravel of the Fountain Formation that are derived directly from the older granite. Note that the rocks have been tilted to the left since deposition of the sedimentary rocks.
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined: |
I'll say that picture is about as weird as possible. The upper stuff looks like it was originally sort of frothy or something, with that front rolled edge, sort of like sticky candy before it hardens, and that when it rolled over the lower stuff the clasts stuck to it. It's not even apparent that the clasts are of the same material as the lower layer. If something isn't clear, and this isn't, you can't expect me just to accept whatever you say about it.
Well, they are not exactly the same material, however, I'm quite certain that the white quartz blocks are metamorphic quartz fragments from within the lower unit which is Vishnu Schist. It is not uncommon to have such pure white quartz veins in metamorphic rock. The upper unit is Tapeats Sandstone which is mostly derived directly from the Vishnu or the Zoroaster Granite. Anyway, I knew this would be a problem which is why I made my last post. As I said, few people look at the details of where the basal sediments come from in the Tapeats Sandstone. It is either very obvious to them or not of interest; however it is pertinent to this discussion. ETA: Perhaps some clarification should be made here. When a rock unit erodes at the surface, the produced sediment is always to some degree stripped away by erosion. That would be by mass-wasting, or streams or sheet runoff or debris flows etc. However, if that process is incomplete, there will very often be a zone immediately above weathered rock that includes fragments of that underlying rock. For instance, in the example I provided earlier, the granite is weathered to granite rock fragments, and grains of quartz, feldspars, and micas, etc. These may be carried far away or be hardly transported at all; but when lithified, they form a sedimentary rock that we call an arkose (usually a sandy or gravel deposit). In the case shown, the sediment was nor far removed from its source and forms a very nice, picturesque deposit known as the Fountain Formation immediately on top of the granite. While the Fountain Formation was deposited in the range of 300-400my ago, it's source was the much older granite. If you look up the subject "Red Rocks" you will find a beautiful setting outside of Denver, now used by humans for music concerts. This will be an interesting unconformity, perhaps in a few million years... Any questions, feel free to ask. This is actually a very interesting and sometimes non-intuitive subject. Edited by edge, : No reason given. Edited by edge, : No reason given.
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined: |
So, I figure the rocks above line (1) are the "sand and gravel derived from the older granite."
Actually, everything above '2' is the Fountain Formation. Line '2' (although not perfectly drawn) is the Great Unconformity. You can see the plaque at about the middle of the picture. The material between lines '1' and '2' are gravels, pretty massive but with some whispy light sands interbedded. Everything to the right of '2' is Precambrian granite. The horizontal lines have only to do with construction of the parking lot and debris coming off the outcrop.
Question is how the sand and gravel at the top came from the granite below with something completely different in between.
Actually, it's not completely different. It's a change of grain size, but of the same composition. The coarser material is only weakly bedded, but it is sedimentary. ETA: Here is my interpretation of the picture:
Edited by edge, : No reason given.
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined:
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In my scenario the Tapeats would have been laid down over the uppermost layer of the Supergroup before it tilted, and it would have been laid down over the schist and the granite as well. I don't think I've said anything to challenge that order of things.
Why would the Tapeats be laid down over the Vishnu sequence in your scenario? I thought you had all of the sediments deposited before anything else happened. In that case Supergroup rocks should always be between the Tapeats and the Vishnu. In fact we see Tapeats overlying all formations of the Supergroup in every cross-section visited, not just the uppermost.
Just as I've interpreted the quartzite boulder embedded in the Tapeats in earlier discussions, I would suggest that there is nothing in this photograph to suggest a long period of erosion before the deposition of the sandstone.
When you look at the source of the gravels at the base of the Tapeats, there is no other explanation for their distribution. Besides, it doesn't have to be a long period of erosion. A short period of erosion could conceivable remove a large part of the rock record. This is one of the things that people often do not understand about unconformities.
For one thing it doesn't even LOOK LIKE the surface of the Vishnu was eroded, it looks to me like a baked and dried-out wrinkled surface that hasn't been eroded, what one might expect of rock that had been subjected to the heat of magma, which became the granite associated with the schist.
Not really. These rocks have been heavily weathered and picture that I showed you attested to that fact.
I'm sure there is other evidence that isn't apparent on the photograph of course, but just by the look of it there is no evidence of erosion requiring me to agree with you.
The relationship of the basal gravel to the underlying rock is an established fact.
The thickly fluid sandstone -- (ABE: VISCOUS: that's the word that's been escaping me. /ABE) -- could have picked up fragments of quartz from the schist as it rolled over it if they were loosely embedded in it.
Where have you ever seen a 'viscous' sandstone? However, yes, some fluid (possibly even water???) has deposited sand on the large boulders that are directly weathered out of the Vishnu sequence.
Those clasts are obviously not of the same material as the schist, and edge says they are quartz, which is what they look like.
One of them looks like pure quartz the others appear to be granite pegmatite clasts composed of large quartz and feldspar crystals. This distinction, however, is unimportant as the the origin of the fragments. They clearly came from the older rocks. They are not exotic.
The photo seems to me to show the sandstone as having a thick forward edge to it that stopped at that point before hardening.
I think you are confusing the sandstones with volcanic rocks here.
I don't see any evidence that the Vishnu in front of it was ever eroded or that the sandstone had been eroded away from it after being deposited on it.
What do you mean 'in front of it'?
If the photo is not deceiving about this thick forward edge ...
What 'thick forward edge'? The unconformity is a gently dipping surface.
... it reminds me of that very strange formation in China I've posted on earlier, the striped rolling sandstone shapes that seem to have been squeezed out of a toothpaste tube or a pastry cone, originally a thick sort of paste.
So, you are saying that the Tapeats was extruded on to the surface of the earth?
I've wondered why we see that kind of sandstone only in that very strange formation in China, but your picture suggests it's really a typical way sandstone occurs, even in America. Here's the formation in China for reference:
It looks like normal bedding to me. Please explain.
Among other things, how does an unconformity result from such a sequence and timing of events?
Easy. It's called erosion.
What makes it an unconformity even if this order of things was the case? Again, of course I don't agree that your interpretation of the evidence is as ironclad as you think it is, but I still have this question even if you're right. What makes this an "unconformity?"
I have given you a definition and a link to an explanation of unconformities. Are you not reading our posts?
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined:
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Just to be as clear as possible, here's an updated version of that photo showing more precisely how I think the quartz most likely originally fit into the Vishnu:
But here is how they really look:
Do we really need to explain this to you? Edited by edge, : No reason given.
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined: |
Looking at this photo again, it looks to me like the sandstone had just plucked the quartz out of the Vishnu before it stopped moving forward over the Vishnu, then slightly receded in the process of hardening so that you can see it holding on to the quartz it had just lifted out of the Vishnu.
What do you mean by the sandstone 'stopped moving forward'? You are making no sense at all.
I've marked the edges of the depressions in the Vishnu which fit the shapes of the quartz stuck in the sandstone. In other words, no erosion had to occur to expose that quartz, that's just the way it was embedded in the Vishnu in the first place:
So, all of these fragmental pegmatites just happened to form in the schist right at the surface where your sandstone lava flow(?) just picked them up and put them back down. This is just bizarre. As a footnote, I knew way back in post 210 that this discussion was going to go to the dogs.... Edited by edge, : No reason given. Edited by edge, : No reason given.
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined: |
However, I never can see the need of those hundreds of millions of years and can't see it here either.
A photograph is not going to give you that information. It is the additional information that we have regarding these rocks that tell us of the age difference. But that's not the point of this discussion. The point is that erosion is happening in the geological record before the end of sedimentary deposition in the Grand Canyon area.
The source of the Fountain formation's being the granite isn't problematic, though it's not clear to me how it got there, ...
That is because it was eroded in place and you refuse to accept that interpretation.
and I don't know why the contact between the two is considered to be an unconformity.
As I said earlier, you have been told this. Your refusal to accept an erosional event early in the geological history of the GC area has led you to a state of confusion.
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined: |
This schematic depicts how weathering occurs.
In any case they represent the same thing - a period of erosion prior to continued sedimentation. I chose this image because it shows what would happen to a quartz vein during weathering and eventual transport. If removal were near complete, we would expect to just see a few clasts resting on the bedrock surface. And guess what we actually see in HBD's picture of the Great Unconformity.
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined:
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OK, but because the Supergroup always has Tapeats overlying it, doesn't mean that Tapeats can't also overlie schist somewhere else.
That's not the point. The point is that you said 'the upppermost'. You were wrong. Again.
OK but how short?
Not material. I'm just showing that you don't really know much about unconformities.
Yes, the clasts that HBD showed you and the beds that I showed you are gravels.
So, yes, you missed something. Again.
Do you mean the one I've been discussing, where the Tapeats is shown partly covering it, with the quartz clasts stuck in it?
Yes, and practically every other one you've seen. Some of them have paleosoils.
What basal gravel? It isn't showing in this photograph, right? The only thing we see is the hunks of quartz (or pegmatite) which look like they were just plucked out of the Vishnu.
So, you are saying that they are transported by moving water? Do you understand that is erosion?
Never, of course, but this sandstone looks like it had to have once been describable that way, before hardening, just as those strange formations in China suggest the same previous condition. Or do you have another explanation for those Chinese sandstone shapes?
As many times as you have been demonstrabl wrong, you expect anyone to believe this? Yes, they are sedimentary rocks of different colors. Probably also photographed through a filter.
"Deposited sand on?" Are we looking at the same picture? I see an expanse of what you identified as Tapeats sandstone with these quartz or pegmatite boulders stuck in its front edge ("front" meaning where the Vishnu schist begins to be exposed in the foreground, and where it looks (to me) like there are holes in the Vishnu that very nicely fit the size and shape of the boulders.) I don't any sand "deposited" on the boulders, I see boulders stuck in the sandstone. (By "boulders" I'm assuming you mean the quartz clasts. There is no way to tell the scale in that picture but if they are "boulders" perhaps they are as large as that quartzite boulder I've mentioned before, which is about fifteen feet in height. Do you know the scale of the objects in the photo?)
Whatever the scale, the large clasts would not be transported along with the finer sands. And no, Faith, there is no 'front' in this photo. It is like a cross section. So, you are wrong again...
Are you still looking at the same picture I am? I'm talking about the one HBD discussed, where the Tapeats is shown with the quartz (or pegmatite) clasts (boulders?) stuck in it. Nobody has identified any volcanic rocks in this picture and I don't see any, just the Tapeats sandstone overlying the schist, which is exposed in the foreground of the picture.
You are the one referring to the sandstone as a 'viscous flow'. I have no idea what you are talking about and I'm pretty sure you don't either.
In the foreground of the picture.
That would be 'below', not 'in front of'.
I've outlined the top and bottom of what I see as the "thick forward edge" of the sandstone, which I think is pretty clearly defined by the shadow that shows it's vertical or near-vertical, although the surface of the sandstone in the background is horizontal. This "forward edge" is where the clasts / boulders are stuck. The size of the boulders should indicate how high this forward edge is, but I don't see any way in the photo itself to determine the scale.
There is no 'forward edge'. This photo is like a cross-section.
Yes that's what it looks like to me in this picture of this location.
Well, I'm sure you would know. It's sort of like that viscous sand flow in Never Never Land.
Not easy to reconcile with the Flood scenario I guess, but that's what it looks like.
Well, if it looks so, then it must be.
A thick viscous sandstone moving forward (toward the foreground) over the schist, then stopping its forward movement right over some clasts embedded in the schist, that then stick in it and get pulled up out of their position in the schist when the sandstone hardens and retracts.
Sure, it happens everywhere.
Are you talking about the Chinese formation or the photo now? The Chinese formation does sort of look like "bedding," puffy folds of striped cloth bedding. I can't imagine how it looks "normal" to you. Where else on earth is anything like this formation seen?
Parallel beds of different colors? What's the problem? It's kind of funny how this article on the Danxia rocks don't mention sedimentary flows or toothpaste-like structures....Danxia landform - Wikipedia Well, in the case of this picture the erosion looks like it may have been created by the Tapeats sandstone flowing over it and dislodging whatever can be dislodged.
Evidence that this happened? Perhaps an example of a sand flow?
Right, the erosion at the surface before being covered by the sandstone. Which again I don't find convincing.
Although you can't really say why and have no alternative explanation that exists in this reality. ETA: By the way, how do sand flows retain their cross-bedding structures? Edited by edge, : No reason given.
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined: |
However, I'd guess that wall of rock was probably not subjected to a mass of viscous sandstone rolling over it as is shown in the other picture. Otherwise the sandstone would very likely have picked up chunks of the stuff here too.
So, you admit that there was erosion going on at the Great Unconformity.
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined: |
Okay, so I shot off my mouth claiming that the Danxia pictures that Faith referred to were enhance by filters, without actually checking first.
Let's see what I found out with a little research: Here is one of many photos that I found.
Now how is this so unusual? Or this one:
Does it look like the one that Faith provided? Does it look that unusual? Would you like to see some of my photos from New Mexico? Well, probably I just spelled the location wrong in my search...
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined: |
As for your correction of "in front of" as "below," yes the Vishnu is literally beneath the sandstone but it's also in front of it as I read the photo.
Heh, heh ... Then I suggest we have to reinterpret all of the cross-sections you have ever presented to us... Edited by edge, : No reason given.
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined: |
Perhaps you could look up the definition of an "unconformity" and then cease to struggle with what one is.
Thin Air, meet Faith...
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined: |
So are they enhanced in some way?
Yes, the colors are enhanced. The true colors are shown in the photographs that I located on line.
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edge Member (Idle past 1735 days) Posts: 4696 From: Colorado, USA Joined:
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That's what it looks like. It looks like a thickly fluid sand{stone} flowed across the Vishnu schist and then ran out of material, came to its end, no more wet fluid pre-sandstone.
So, you are saying that the Tapeats Sandstone just ended right at this point? That's fortuitous.
Like icing on a cake that runs out before you've covered the cake (and that's a good analogy too since if you aren't very careful the icing will pick up chunks of cake and soon be a complete mess), It looks far more like this than it looks like it was eroded back from the schist, IMHO. If you look at the photos I've marked you should at least see what I'm seeing. And I ask you again to please mark a photo yourself so I can see what you are seeing in it.
It's not obvious to me, nor probably anyone else. And I'm not sure what I can annotate to make it clearer. There is a bedding plane cutting diagonally across the upper third of the photo. I fail to see how this would be preserved in a viscous flow model.
What would be wrong with just having sand deposited on top of some pebbles sitting on the Vishnu? Do you realize that if this was the end of the Tapeats, then the next layer being deposited on the Vishnu as shown would indicate another unconformity?
I've marked the edges of the depressions in the Vishnu which fit the shapes of the quartz stuck in the sandstone. In other words, no erosion had to occur to expose that quartz, that's just the way it was embedded in the Vishnu in the first place:
That is not what the evidence shows. You have seen a picture of how the quartz/pegmatites actually occur in their original setting. The do not look like clasts laying on a surface composed of Vishnu Schist.
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