Re: overhangs or separations, you don't get sloppy contacts at deposition
Faith writes:
Hold your horses, I'm coming to that eventually.
Nope, you got to it and blew straight through it with this:
Layers don't deposit with overhangs, that's evidence of displacement after deposition just as separation would be.
Turns out layers don't deposit with slots in them right where highways need to go either ... so they blast the layers into submission creating your precious overhangs, etc.
Well, there are the drag folds themselves for evidence....
Ah, good.
You are using the presence of drag folds as evidence that they are drag folds.
Context, context. You asked for evidence of shearing after saying that drag folds would indicate shearing, so I answered that the drag folds themselves would be the evidence of shearing you asked for.
I would suppose so {that the gravel came from the Archaean hill}, and since they appear to be a bit of a distance from the hill and embedded in the sandstone it seems very likely they were sheared off that hill during the intrusion.
Then you can provide evidence for shearing, right?
Drag folds, drag folds, my dear Watson. In fact if you look closely at that illustration you'll see that the gravel appears to be embedded along the lines of contact between layers of the Tapeats where they form the drag folds. Sort of like they were caught there. Interesting anyway.
You know what's odd about that? The fact that there is no lava spill indicated at the "unconformity," i.e. the surface of the hill, such as occurred at the top of the Grand Staircase over the Claron, and in other parts of the Grand Canyon. Here it is illustrated as abruptly cut off.
Well, if that were the case, the it would show that the dike is younger than the unconformity, right?
But of course I would assume it is younger than the surface of the Archaean hill whether it spilled over or not.
I'd guess it was all part of the same tectonic event that created the GU everywhere, and that there WAS shearing involved in the push of the underlying rock up into the Tapeats, which displaced the upper part of the dike. In this case I suppose it should be found somewhere in the Tapeats. Just a guess but it IS odd how it's just cut off like that.
And, of course, you can do that?
Do what?
I don't discount anything on such a diagram and I wondered what those lines indicate. So they indicate VERTICAL STRATA? Into which water has seeped, deforming the layers on the sides? How about water from the already-deposited but formed and still soft and damp sandstone it intruded up into perchance?
So, you think it happened during sometime while the Tapeats still consisted of soft sediments?
A guess, a guess, consistent with my basic theory that the lower rocks intruded into the upper while the upper were still soft.
I'd suggest perhaps it means an assymetrical entry of the intruding rock myself, causing asymmetrical drag.
And, of course you have some kind of evidence for the kinematics of that intrusion? Can you tell us which direction the older rocks were moving?
Slightly tilted to the left of straight up would be my guess. Just a guess. Evidence would of course be the direction of the drag folds themselves but you would know the direction indicated in this case where I can only guess.
Seems like you've made a decent case for your view. I still like mine of course and continue to view the draping sandstone as my best evidence, but I also like that embedded gravel for evidence too.
What is 'embedded gravel'?
Gravel that came off the Archaean hill and is now in the Tapeats sandstone, as can be seen on the illustration, which I will reproduce here:
And perhaps you can show us your evidence that it was emplaced by shearing?
Drag folds, as per your own information cited above. The same drag folds of the sandstone layers along the contact lines at which the gravel seems to be emplaced.
Re: overhangs or separations, you don't get sloppy contacts at deposition
Turns out layers don't deposit with slots in them right where highways need to go either ... so they blast the layers into submission creating your precious overhangs, etc.
I notice you don't offer any evidence for your contention, apparently just another of your rude remarks to no purpose. The evidence looks to me to show what I've said and since you've offered none for your interpretation I think we can ignore it.
The idea that a layer would be displaced into overhangs or separated from others, either one, by a blast, is absurd. That layer was SOFT when it was deformed, the rock was cut when lithified. A blast would have shattered the layer, not formed overhangs. Sheesh.
And my "precious" overhangs are JonF's who was contradicting me. It does help to read in context.
It may not be in the case described in your quote, it may be the result of sedimentary processes themselves as is claimed. The important point for me at the moment is just that drape occurs to FORMED BUT SOFT ROCKS, not newly deposited sediments.
That is what we would call soft sediment deformation.
OK. Well, that's pretty much all I've been talking about.
So, basically, no matter how it happened, you have a sedimentary environment with sands being deposited on an irregular surface.
That's a non sequitur. My claim is that the sands were deposited before the irregular surface occurred, intruded etc. When the intrusion occurred, which I'm postulating was the result of tectonic activity, the Tapeats sandstone was already bclearly formed into layers, as shown in the drawings, but soft enough to deform and drape over the intruding rock.
I don't care if it happened on a sloping surface, in cross beds, or as soft sediment deformation - it is sedimentary. Not tectonic.
You seem to think you've given evidence for this but I have no idea what the evidence is that you think you've given. Or even, again, what the point is of insisting on the label as you do.
Actually I've consistently had in mind FORMED LAYERS THAT ARE SOFT ENOUGH TO DEFORM AROUND OBJECTS, neither sediments nor rocks.
Makes no difference: they are soft sediments. They are not rocks until lithified. They are, however, strata.
You should be happy, then, that I call them strata and not rocks until they lithified.
Soft enough to deform, hard enough to maintain their shape as layers. The underlying rocks, however, are all apparently lithified, metamorphosed etc. and, I'm arguing, probably tectonically pushed upward.
But without evidence, yes.
Drag folds, plus evidence from other locations, such as the road cut where it's clear the layers on the left were soft enough to sag into the low place on the left AT THE TIME of the disturbance that deformed the gneiss and some of the sandstone above it.
And in many places provided an extraordinarily level platform for the purpose.l.. ...OR the GU formed after the Tapeats was already there.
For which you have not found any evidence, yet.
Road cut order of events is clear evidence that the metamorphosed rock was deformed ALONG WITH the layers above it.
1. I don't understand your remark about its being a sedimentary environment if they were deposited on a slope.
If sediments are being deposited, then it is a sedimentary environment.
But I'm still not getting your point. I'm not talking about sediments being deposited, only about formed layers that are still soft enough to deform.
But there is no evidence for intrusion.
Draped sediments, drag folds, timing of events at other locations of the GU.
2. If faults are a necessity and you don't see any faults I guess I'm stuck with just the impression of the draped sediments as my evidence for the intrusion of the underlying rocks into the Tapeats, and you reject that, so perhaps the argument is at an end for now.
To get the amount of relief shown in the McKee diagrams, a fault should be obvious.
That makes sense but perhaps the faults are buried out of sight.
{This is a side issue but I found myself wondering about that high relief, especially in the picture I posted which I think is at the same location as two of McKee's illustrations (I can find it again and reproduce it here), where the Archaean rock soars quite high above the position of the photographer, with the Tapeats above it. That is at Mile 262 of the Colorado River according to McKee's own legend, and I found that the elevation of the river at that point is about 500 feet.. Just thinking how that's a lot of basement rock exposed to such a height. Again,just a side issue, just a pondering, no interpretation at the moment but perhaps someone else will have a thought about it.}
3. bI don't know what you mean by asking why layers above the formed layers weren't formed. I assume they all were formed into layers, which is clearly illustrated in the drawings, don't know how I gave a different impression.
But in this case the deformation does not extend into the overlying rocks. Even in your 'deformed area' the bedding passes through with almost no offset.
This is a road cut. Any separation of layers and broken rocks are a result of cutting and/or blasting the rock to make the road cut and of any subsequent weathering due to wind, rain, snow and freeze/thaw cycles.
Nope. The actual evidence I've been discussing does not support that idea. The separation or overhang as JonF says it really is, without offering evidence or reasoning, occurred to SOFT rock that sagged due to its softness, and any blasting or cutting would have been done in lithified rock and shattered it, not separated it.
The larger circled area shows a bush and discolored rock with a more irregular surface, but that's a function of making the road cut. There's nothing to indicate a tectonic disturbance,
Oh yes there is. The irregular surface shows the same disturbance that roughed up the gneiss and caused the layers to sag on the left WHILE THEY WERE OBVIOUSLY SOFT. That area marks the spot where the left side began its sag. NOTHING to do with the road cut that I can see, and since you merely assert it and give no reasoning to support it, your interpretation is worthless.,
...and the smaller circled area shows where the layer itself was broken.
The smaller circled area shows rock that was broken when the road cut was created or maybe by later weathering, and a shadow. Again, nothing to indicate a tectonic disturbance.
Funny it's right where the layer sagged due to softness then. Again you are merely asserting and failing to answer the clear evidence I've given for a disturbance that occurred to the sandstone when it was still soft.
So there's no evidence that tectonic activity changed the tilt of the layers, so the original question remains. What leads you to believe the layers must originally have been horizontal?
It's you who lack the evidence for your interpretation. Mine is quite clear.
The separation or overhang as JonF says it really is, without offering evidence or reasoning,
I thought it was so obvious that none was necessary. But since it's you... you wrote:
showing that the layers are separated from each other, not laid neatly one on top of the other as you see in fresh deposition
Separation is defined as:
quote:1. an act or instance of separating or the state of being separated. 2. a place, line, or point of parting. 3. a gap, hole, rent, or the like. 4. something that separates or divides.
"Separation" would mean gaps or something inserted between the layers (and the latter would be a layer in itself). I.e. layers floating in the air above each other. The layers are laid on top of each other, touching with no gaps. At the edge of the cut some layers were affected differently than others and formed overhangs. Neat or not, they are laid on top of each other, not separated.
Let's see your evidence and reasoning that they are "separated". I need a good laugh.
In this case I've marked some indicators of the deformation of the rocks. The arrows point to the contacts between the layers, showing that the layers are separated from each other, not laid neatly one on top of the other as you see in fresh deposition; and I circled places where the rocks broke at the edge, or "hinge" if you will, of the area to the left that sags away from the central area. The larger circled area shows the general disturbance that occurred in the stack at that point, and the smaller circled area shows where the layer itself was broken. These are clear indicators that the layer was already formed when the disturbance occurred that caused the left side to sag. Formed enough to break but soft enough to sag.
If the layers had been deposited into that low place after the disturbance had occurred there would be no gaps between them or breaks in the sandstone at all. So there's some evidence that doesn't rely on the horizontality argument.
Faith, dear, I really think you need a new computer monitor. You circled a bush as evidence of "disturbance." You have arrows pointing to small overhangs/recesses that you see as gaps between layers. In a previous image, you circled a camera as evidence of disturbance. Your monitor must be in really bad shape, you just can't rely on these details you are seeing.
HBD
Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for... I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca
"Nothing is easier than to persuade people who want to be persuaded and already believe." - another Petrarca gem.
Ignorance is a most formidable opponent rivaled only by arrogance; but when the two join forces, one is all but invincible.
I was just trying to be a facilitator when I asked you to clarify why you believed you saw evidence of tectonic disturbance in that road cut. You replied by stating that the shape of the broken rocks of the road cut were evidence of tectonic disturbance. I'll continue to try to facilitate on simple issues, but before getting into this issue further I just want to be sure you're aware that you've taken a position that will seem to most people to be wrong, irrational and perverse, similar to your position on the appearance of the exposed layers at Siccar Point that were just a result of weathering but that you thought told you something more.
So just to be safe I want to caution everyone to remain civil and focused on the topic.
Faith writes:
This is a road cut. Any separation of layers and broken rocks are a result of cutting and/or blasting the rock to make the road cut and of any subsequent weathering due to wind, rain, snow and freeze/thaw cycles.
Nope. The actual evidence I've been discussing does not support that idea. The separation or overhang as JonF says it really is, without offering evidence or reasoning, occurred to SOFT rock that sagged due to its softness, and any blasting or cutting would have been done in lithified rock and shattered it, not separated it.
When you say the layers were separated, do you mean that while still buried and before the road cut was made that the layers were no longer immediately adjacent to each other, that there was a space between them? Or do you mean they were no longer bound to each other?
Here is the image again:
Do you see the evenly spaced vertical channels? These are the drill holes into which explosive charges like dynamite were placed. Here's a video of blasting for road cuts:
The rock was blasted away, then the loose rock was picked up and carted away by heavy equipment that must have repeatedly banged into the rock face, then weathering set in on the exposed rock. The shape of the surface of the rock left behind cannot tell you anything about tectonic forces.
Discolorations that spans multiple rock layers are usually due to chemicals leaching out of the rocks and/or soil above when it rains and staining the rock surface as it runs down (Edge's comments on the discoloration in the larger circled area would be helpful).
Re: overhangs or separations, you don't get sloppy contacts at deposition
Faith writes:
I notice you don't offer any evidence for your contention, apparently just another of your rude remarks to no purpose.
The evidence for the blasting results is in the picture. You can see the drill holes in typical road cut blasting distribution. Live anywhere with hard rock near the surface and you can see examples mile after mile.
That is at Mile 262 of the Colorado River according to McKee's own legend, and I found that the elevation of the river at that point is about 500 feet.. Just thinking how that's a lot of basement rock exposed to such a height. Again,just a side issue, just a pondering, no interpretation at the moment but perhaps someone else will have a thought about it.
Not really sure what your reference is about, but it starts with river mileage at the southern international border. River mileage usually starts at Lee's Ferry, which is where McKee's mileage would have come from. So, the location of mile 262 would be at a different location.
Here is a really great 3D Grand Canyon Tour for your enjoyment. There are views for each 8 mile section of river. A lot of really good descriptions for each section.
HBD
Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for... I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca
"Nothing is easier than to persuade people who want to be persuaded and already believe." - another Petrarca gem.
Ignorance is a most formidable opponent rivaled only by arrogance; but when the two join forces, one is all but invincible.
Faith, dear, I really think you need a new computer monitor. You circled a bush as evidence of "disturbance." You have arrows pointing to small overhangs/recesses that you see as gaps between layers. In a previous image, you circled a camera as evidence of disturbance. Your monitor must be in really bad shape, you just can't rely on these details you are seeing.
You may be onto something here. Combine the fact that she sees things that aren't actually there, uses words that don't mean what she thinks they mean supported by logic that doesn't follow and you have quite a recipe for misunderstanding.
I've never imagined that someone would take the uneven, blasted to smithereens face of a road cut and attempt to attribute tectonic activity to the blow to bits exposure. Strange things are afoot at the Circle K
I've never imagined that someone would take the uneven, blasted to smithereens face of a road cut and attempt to attribute tectonic activity to the blow to bits exposure. Strange things are afoot at the Circle K
I did initially see that area above the bush as looking like it had been disturbed, possibly by some uplift of the center section. It could just be an artifact of the road cut, it is really difficult to tell from the photograph. So I wouldn't stake my reputation as a "geologist" on it
HBD
Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for... I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca
"Nothing is easier than to persuade people who want to be persuaded and already believe." - another Petrarca gem.
Ignorance is a most formidable opponent rivaled only by arrogance; but when the two join forces, one is all but invincible.
My incredulity with regard to her response centers around her assertion that there is some meaning to the small overhangs on the blasting face.
Without evidence of a fault, the fact that the layers aren't perfectly horizontal is merely more evidence for the known fact that sediment doesn't deposit perfectly horizontal.
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