I could do a dry angle-of-repose experiment now, getting back to Coragyps' challenge, but the others I really can't set up properly and want to wait until family get here toward the end of June. They can also get some of the material I need that would be hard for me to get.
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That's a great find, very similar to the other road cut situation, and the arguments are the same ones we've been pursuing. I didn't even know my own argument already existed.
So they dismiss the idea of a fault on the unconformity line. That pretty much leaves trying to find out if layers like those and the ones in the other road cut really will form by deposition on the slope.
Just wondering: Would you say the layered rocks in the picture are highly compacted?
I'm aware of the variations in thickness across huge distances. Nevertheless the impression of the strata over pretty huge distances, such as seen for instance from a distance in the Grand Canyon, is of a remarkable evenness of thickness.
Not in the case of the Tapeats which we see pinching out over short distances as shown by McKee.
Visible variations of thickness within a few hundred or even perhaps thousands of feet would suggest something other than normal deposition patterns to me.
And yet, they happen. Suggestions to you are not evidence.
ABE: I'll grant that there is more drape effect in the experiment than I would have expected, ...
Considering that you expected there would be no drape effect, yes, there is 'somewhat more'.
... but unlike the McKee drawings it's so evenly distributed it just comes off as thinly coating the slopes on the way down to pooling in the depressions, rather than forming draped layers as in the drawings.
I'm not sure that your eyesight isn't deceiving you. When I look at McKee's drawings, I see layers thinning to the point where they completely pinch out in some cases.
I know this seems picky but that's how it hits me. Maybe you need to get something more asymmetric to make your case. /ABE
Something hitting you is not evidence, although we have tried that. Again, I'm not sure what you are looking at, but I see assymetric deposition of layers in the demonstration akin to the ones in McKee's diagrams.
As for the draped sandstone I'm not sure how it should be set up. I DON'T see the same draped effect in the video experiment; I DON'T see sediment pooling in the depressions on the drawings, just draped layers.
Again, I'm thinking you are looking at a different video. Some of the layers on the basement high are quite thin compared to the depressions.
"Drape upon drape" means to me something more like layers of equal thickness that start thin at the top but drape down into the depressions with equal thickness like actual layers except they're draped, if that conveys anything. That's what I see in the McKee drawings. Maybe steeper "monadnocks" are needed for the experiment.
I'm not sure what you mean by being of equal thickness if they 'start thin at the top...'.
And what do you mean by draping 'into the depressions with equal thickness'? Equal to what?
In other words it's got to prove your argument or it's not worth it?
I think he is referring to your tendency to dismiss evidence and conclusions without explanations other than 'it kinda, sorta looks that way'.
You've lost me every time you've said this about compaction and "forced folding." Sometimes I'll look up your terms but sometimes they are so unrelated to what's on my mind at the moment I just let them go. Anyway, if you want me to understand what you are saying here you need to translate.
With consistent sedimentation rates across the slope, what are you imagining could prevent layers being deposited evenly?
I'd rather not get into an argument about this now, I'd rather see what happens in an experiment if you don't mind.
In that case please put your views about the impossibility of non-horizontal deposition on the back burner until such time as you can provide rationale and/or evidence. Just so it doesn't catch you by surprise later on let me say that this means you can't argue for your view that there's a change in the angle of tilt in the layers of the road cut that could only have been caused by sagging of the layers to the left.
In responding to your post I'm going to make a moderator ruling.
In other words it's got to prove your argument or it's not worth it?
I think what HBD is saying is that you're dismissing evidence and arguments out of hand while providing specious counter arguments ("it looks like...", "it just comes off as..."), and that if you're going to continue in this way then there's little point in putting effort into providing even more evidence and arguments to you.
I'll grant that there is more drape effect in the experiment than I would have expected, but unlike the McKee drawings it's so evenly distributed it just comes off as thinly coating the slopes on the way down to pooling in the depressions, rather than forming draped layers as in the drawings. I know this seems picky but that's how it hits me. Maybe you need to get something more asymmetric to make your case.
HBD provided this image:
It has asymmetry reflecting flow. Contrary to your claims of even distribution (paraphrasing, just thin coats with pooling in the depressions), the bottommost layer (it's yellow) does become slightly thinner as it rises up the slope, and on the far side it disappears altogether for a while. The next layer up (it's brown) looks precisely like some layers in the McKee diagram.
And the next layer above that (a lighter brown) almost completely pinches out on the far side of the mound.
Ideally both sides in a discussion would bow to the evidence and move on, but as that isn't happening here I'm therefore ruling that unless you can present a rationale for your position that has far more substance and far better correspondence to the evidence than "it just comes off as thinly coating the slopes on the way down to pooling in the depressions" that the geological position that the boundary between the Tapeats and Archean is an erosion unconformity, not an intrusion, has succeeded and that discussion should move on.
The first few layers did somewhat drape so that was interesting, but they also filled in the low places. After it was all covered up to a level point then they deposited horizontally, no tilting there. Although you want me to see the result as like the McKee drawing the only similarity I see is the initial draping. There is no filling of the low places in the drawing, or in any of the other drawings either; and there is nothing in the experiment like the drape-upon-drape in the drawing. That drape-upon-drape effect is more apparent in one of the other drawings as I recall but I couldn't find that illustration.
This doesn't appear to have any correspondence to the video at all. It's like you're looking at something completely different than everyone else, or as if you are unable to see obvious similarities in images. In his reply Edge commented similarly.
If you want to pursue the point then you're welcome to argue it again, but some points need significant modification if they're to make sense to anyone. To point out just one example, you say "There is no filling of the low places in the [McKee] drawing," yet everyone else sees the layers thickening the deeper they are in the basins. If you're looking for identicalness between the sedimentation experiment and the McKee drawings then you're not going to find it and should by no means expect it. The experiment was to illustrate general principles of sedimentation, not to replicate what happened in specific regions of the Tapeats boundary with the Great Unconformity. To continue arguing your point you need to make observations that don't cause people to wonder if you're looking at the same images they are, and you need to provide a reasonable rationale for why the sedimentation experiment and the McKee Tapeats diagrams aren't uncannily similar.
Just out of curiosity, I was looking at some inclined bedding references and ran across this article on the Lawrence Formation in Kansas. Here is one of the explanatory diagrams.
The caption says:
quote:"Figure 12--Three patterns of channel fill: A) horizontal layers, common in subaerial channels; B) layers conforming approximately to the channel shape, common in subaqueous channels; C) asymmetric fill by inclined layers, common in tidal regimes (from Reineck and Singh, l975, p. 63; based on McKee, l957)."
Note that the horizontal, flat channel fill sedimentary strata are 'common in subaerial channels'.
So, even though the layers occur as Faith would like them to be, it still implies an unconformity occurring somewhere above sea level.
I rather like the inference of 'tidal regimes' for the assymetric fill because it suggests a shoreline along the Tapeats sea as it rose across the Great Unconformity land surface.
For those interested, here is a schematic strat column for the study area. Note that the age of these rocks is Pennsylvanian, which would be at a time between the Redwall Limestone and the Hermit Shale in the Grand Canyon. That would be at the time when Faith says there was no erosion or tectonism going on in the Grand Canyon and, ostensibly, no where else in the world.
(Ooops, I forgot, we have to ignore what's going on outside of the Grand Canyon).
This is one of the common ways that some detail is added to the normal stratigraphic column by showing erosional channels cut into lower formations. As you can see, it is quite complex.
Earlier in the thread someone asked if drag folds could form without faulting. The answer is 'not really', because 'drag' implies friction between two bodies.
However, it is possible that folding may precede faulting and consequent drag folding.
Here is a diagram depicting the stages in development of a 'monocline' (a fold with only one limb).
In this case the fold 'drapes' over the basement fault but shows drag after the fault has developed. One can see that if faulting continued in this diagram, the fault would propagate upward through the remaining sedimentary rock layers.
Note that this 'draping' is different from soft sediment drapes, but the driving force is still gravity. There is no compression such as what we see in normal fold development.
Here is an image of an actual monocline in the northern part of the Uncompahgre Uplift in Colorado.
Often times the hinge zones of these folds are highly fractured (and consequently more eroded) suggesting they were hard rocks when deformed or the strain rates were rapid. Here is an example: