I mean that - as anyone with eyes can see - at the edge of the Canyon the Supergroup tilts up (towards the Canyon) while the layers above it dip. It's really, really obvious. How could you possible miss it ? Even if I hadn't mentioned it.
I had described the upper strata as mounding OVER the Supergroup. "Dipping" is not a term I'd use for it. The point of the mounding is that it demonstrates the pushing up of the upper strata from beneath, since the strata would not follow the contour of the mound if they were laid down afterward. There is really no other reasonable explanation.
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I had described the upper strata as mounding OVER the Supergroup. "Dipping" is not a term I'd use for it.
Instead of quibbling about terminology why don't you just deal with the fact that, at the Canyon edge, the tilt of the Supergroup and the tilt of the "mounding" are opposed. The Supergroup goes up as you approach the Canyon, the "mounding" goes down.
Now since the original tilt is what I was talking about all along, so long as you restrict yourself to the "mounding" you aren't addressing my point at all, let alone disproving it.
I had described the upper strata as mounding OVER the Supergroup. "Dipping" is not a term I'd use for it. The point of the mounding is that it demonstrates the pushing up of the upper strata from beneath, since the strata would not follow the contour of the mound if they were laid down afterward. There is really no other reasonable explanation.
Actually, there are a couple of other possibilities, however, it's kind of irrelevant particularly since that contact is probably based on a very limited amount of data.
The most likely explanation is that the surface is actually more irregular than depicted and since the surface is an erosional unconformity, the best explanation is that this is just a regional slope toward a sea to the west.
I wouldn't read to much into the 'hump'. On the other hand the boundaries of the GC Supergroup are kind of important in the history of the canyon area.
So how do you explain the quartzite boulder fifteen feet in diameter that was clearly broken off the Shinumo quartzite but is found embedded in the Tapeats sandstone a quarter of a mile from the Shinumo?
So how do you explain the quartzite boulder fifteen feet in diameter that was clearly broken off the Shinumo quartzite but is found embedded in the Tapeats sandstone a quarter of a mile from the Shinumo?
I don't have a problem with that at all. Along many seashores there are boulders with no obvious attachment to their sources. Here are some in New Zealand.
The point here is that we are dealing with an erosional surface and an encroaching sea.
ETA: I am reposting some pictures of erratic boulders on beaches. The boulders above, it turns out are concretionary and do not make the point that I wanted. Most erratics like the Shinumo boulder are considered to be glacial in origin.
Here is a glacial erratic in British Columbia:
It is obviously of exotic character in both size and composition to the surrounding sand and must have been transported.
Then there are exotic boulders like these that don't have a definite explanation.
They are just boulders isolated in a beach sand.
And then, of course, there are the drop stones that we talked about last year:
I hope you don't mind if I tell you that I laughed out loud at your picture of boulders on a beach in answer to my question. The cleverness involved is quite amusing.
Let me ask: Would you expect to find the source of any of those rocks in a sedimentary layer buried under that beach?
Do blocks of strata normally underlie beaches?
How would you account for the separation of the rock from its source?
Do you expect that beach someday to be like the Tapeats layer in the GC?
So, the GC was formed by intermittent risings of water over the land depositing this or that, some six of them altogether? So I suppose the land had to sink to the necessary level for each new shallow sea to cover it without being deep enough to associate it with Noah's Flood? So it keeps sinking for each new sea transgression until it gets all the layers laid down, and then what? Then we get the pushing up of the Colorado plateau because of course those miles of layers aren't going to stay below sea level?
I hope you don't mind if I tell you that I laughed out loud at your picture of boulders on a beach in answer to my question. The cleverness involved is quite amusing.
I thought that might happen. However, we know that boulders can move down very gently slopes and there are a number of mechanisms, including some glacial effects.
Let me ask: Would you expect to find the source of any of those rocks in a sedimentary layer buried under that beach?
Possibly, but the fact that the rocks are rounded suggests that they have been transported.
ETA: I have to correct this. These particular rocks are rounded because they are concretions. Most such erratic rocks are not so well-rounded, but are enough to say that they are obviously transported.
Do blocks of strata normally underlie beaches?
If you go deep enough, yes.
How would you account for the separation of the rock from its source?
Gravity acting on a slope.
Do you expect that beach someday to be like the Tapeats layer in the GC?
If it doesn't get eroded away before then.
So, the GC was formed by intermittent risings of water over the land depositing this or that, some six of them altogether? So I suppose the land had to sink to the necessary level for each new shallow sea to cover it without being deep enough to associate it with Noah's Flood?
Actually, the Grand Canyon was formed by erosion.
So it keeps sinking for each new sea transgression until it gets all the layers laid down, and then what? Then we get the pushing up of the Colorado plateau because of course those miles of layers aren't going to stay below sea level?
The origin of the Colorado Plateau is getting more technical as we study it. This post was about isolated boulders in a sandstone.
Let me ask: Would you expect to find the source of any of those rocks in a sedimentary layer buried under that beach?
Here on the prairies we have rocks coming up out of the earth all the time, lifted by the freeze/thaw cycle. They were originally eroded smooth and brought here by glaciers and then lots and lots of sediment was deposited on top of them. How could a single flood event accomplish all of that?
I find it hard to consider the quartzite boulder as having occurred by the same processes that produced the boulders you have illustrated. It is embedded IN the Tapeats sandstone a small space above the Great Unconformity a quarter mile from the Shinumo layer, in such a way as to suggest it was broken off that layer and carried that distance by the forces I keep describing.
Here's the video I saw it in. I don't know how to set it at the right spot to find it, but it's at 1:06:31. (It seem to be at that location somehow, so if you just click on the arrow it should be there): / /
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