The Story in the Rocks - Southwestern U.S.

The compression was from moving the left wall. The right wall is fixed.

Yes. In a normal geological situation, I would expect the major sense of motion to be the opposite, rocks on the left overriding the right. That is why I think there might be something in the initial state to have that particular symmetry.

However, if you look closely, the small, almost parasitic folds on the right side of the larger fold do have a left over right sense of motion. These form ridges on the surface of the geological material, effectively disrupting the unconformity surface.

Certainly, the deformation has to be concentrated on the side closest to the forces, so the location of the fold is not surprising. Forces cannot be transmitted very far in unconsolidated, soft (or wet) sediments.

Thanks for making me take a closer look at the resulting structure. (ETA: in fact, this may even help me with a structural problem that I've been dealing with for a couple of years now.)

Edited by edge, : No reason given.

However, if you look closely, the small, almost parasitic folds on the right side of the larger fold do have a left over right sense of motion.

To me, those small folds look like shear folding and/or drag folding related to shearing. You seem to have a model of incipient thrust (reverse) faulting.

The tension model shows normal shearing and a graben structure.

Moose

I understand that you are angry. That is my main take-away from your post. I can't do much about that.

You could try being fair. You could try realizing you have been playing sneaky games and cut it out, you could try realizing I've thought this through, you could try realizing that it's possible for someone to make a reasonable judgment of physical things without a degree in geology. You could try realizing you aren't god and you have no more right to my respect or deference than any nongeologist.

ABE Oh, and you could request the removal of your travesty of a POTM or suggest to Moose that he hide that post too since it's a stinkin straw man fraud motivated by anticreationist malice. /ABE

This is basically a scale model with its shortcomings,

The "shortcomings" are not just shortcomings, they disqualify the whole mess.

... but the point is still valid that the upper layers are uplifted and deformed. Do you see the lines cutting across the surface of the uppermost layer? Those are fault lines. See the fold that has been created? The axial plane of that fold will eventually rupture and form a major thrust fault that has to go somewhere and the only alternative is up.

I don't know for sure what you are talking about, since my eyes may not be good enough to see those lines you, but it sounds like the cracks in the strata I took into account with my many discussions of how I think the GC formed -- that tectonic pressure angled the lowermost strata beneath the Tapeats, (your loose sediments model couldn't possibly show this kind of effect -- the sediments have to be consolidated enough to hold together but flexible enough to deform without breaking) which I ascribe to the difference between the kinds of rock at the point where the force was beginning to dissipate. If all one kind of rock was involved I would expect there might not have been a detachment at all and a lot more destruction -- so the angling of the lower strata PUSHED UP the entire stack above it and in the case of the GC somehow that stack remained intact which doesn't seem to have happened anywhere else. The stack was complete and at least two miles deep from the Tapeats up, possibly much deeper than that.

SO HERE'S THE RELEVANT POINT: The strain of the uplift would have CRACKED THE UPPERMOST STRATA. Which is what I suppose you are calling FAULTS. You can see on the cross sections that the whole stack is uplifted right where the canyon cuts into it, slightly to the south of the uppermost height of the uplift. So I figure there were many very deep cracks in those uppermost strata at the top of the uplift, which began to break up and wash away in the receding Flood waters, washing away in all directions to the point of scouring off the limestone surface of the Kaibab Plateau, that limestone being another point of resistance in that area since it remained intact and didn't break up, the surface of the "Permian" period ending the Paleozoic, beyond which far to the north some of the stack from the Mesozoic through the Cenozoic remained intact while the tectonic disturbance cut away pieces of the strata to form the Grand Staircase

But back to the Gtand Canyon: the cracks that formed right over the center of the uplift broke up everything down to the Kaibab, and one of them became a crack or more likely series of cracks wide enough to become the canyon itself. It was then further widened by the chunks of strata breaking off and being washed into this largest crack or collection of cracks. It all washed down and out to the Gulf of California as the Flood receded, scouring out the canyon as it went.

Again, the strain of the uplift caused by the upending and pushing up of the lowermost strata caused by the lateral tectonic force, caused the cracking of the uppermost layers two to three miles up, that broke up and washed away, a lot of it into the cracks that became the GC. Have I dealt with your faulting sufficiently? If not, go soak your head.

So, where are those faults cutting the cutting the Great Unconformity?

There is a fault line shown cutting down the canyon itself. There are also fault lines where the lowermost strata of the Supergroup beneath the canyon are broken and uptilted. If that's not sufficient for you go soak your head.

The underlying rocks are weakly to severely folded, so the strain must be very high. You cannot avoid the displacement.

Is the pushing up of the Paleozoic strata in the GC enough or not? Is the cutting of the canyon because of strain to the uppermost layers enough or not? The GC is very interesting for the very fact that the upper (Paleozoic) strata remain intact to an enormous depth. That doesn't exist anywhere else, right? At other locations the same tectonic force seems to have had somewhat different effects, but nevertheless you can see its effect in the formation of the entire GC-GS area.

If this isn't sufficient for you, go soak your head.

Even if we accept your detachment theory, the strain is not uniform and there should be some implications for the overlying rocks.

The uplift, the breaking up of the uppermost layers possibly to a depth of as much as two miles, at least a mile, above the Permian or Kaibab, which cracked sufficiently to create the Grand Canyon itself, scour the Kaibab, cut all the stairs of the Grand Staircase with its canyons etc etc etc. Is that enough implications for the overlying rocks or not. If not, go....

In a dynamic analysis, you would need to explain how you apply the compressive forces to just a lower block. It is not clear how this is possible. What exactly is the vise-like plate that you envision? Please describe the source of the forces.

It's from looking at the various angular unconformities that I realized that the force had to come against the lower strata, and then I realized that tectonic pressure on the continental plates would be strongest the lower you go, and its energy would most likely dissipate by the time it reached a certain level in the stack, at which point it could affect a weak point, say the contact between two different kinds of rock, which does appear to be the case in angular unconformities -- two kinds of sandstone in the case of Siccar Point, Tapeats sandstone over I'm not sure what at one location but over schist and granite in others, which I believe would make for a point of least resistance -- at which point the lower stack would buckle under that contact, (or even compress into schist and granite since this is all accompanied by a volcano beneath the center of the uplift sending up fingers of magma into the rocks which would add heat to the compressive force) and the buckling would raise the stack above it. Sliding between the upper and lower rocks would also happen.

And I haven't even started on the necessary shear that must accompany your scenario.

Yeah, well, it's the shear that accounts for those very straight tight horizontal contact lines I showed in the pictures linked somewhere above, (see HERE) and where it all went is that most of it got forced out and washed down the canyon, which I think explains the situation in the pictures the Great Dragonfly god posted.

You can spare me the kneejerk debunkery, I couldn't care less. I'll be refining this same idea for some time to come I'm sure, and your debunkery is irrelevant.
'

ABE: If my description doesn't relate to faults, that's not important, I was guessing about what you were expecting to see. Apparently I was wrong about that but it doesn't matter.

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Faith, you seem stressed out. I suggest that you take a deep breath and focus on what your mission is here at EvC. It is not to carry on petty feuds and personal attacks. Let me try and straighten this topic out. We have too many topics wandering off of initial focus and into the petty feud territory. Forum Guidelines

Please stay on topic for a thread. Open a new thread for new topics.

Points should be supported with evidence and reasoned argumentation.

The sincerely held beliefs of other members deserve your respect. Please keep discussion civil. Argue the position, not the person.

Tanypteryx writes: I want to post some photos of geological formations from the Southwest that I have taken on trips the last few years. I would like to discuss what is known about how the rocks formed and when, and what processes acted on them between then and now, and what processes exposed them so we can see them today. The formations in this photo are in north central Arizona along a stretch of Hwy 89, south of Navajo Bridge over the Colorado River and north of Cameron. I think this valley may have had a number of layers volcanic ash-like material deposited that has been eroded leaving these short buttes that are composed of soft non-lithified material that almost looks like it is melting in the occasional summer rains. (ABE: Looking in my Roadside Geology of Arizona I see this is the Chinle formation and it is volcanic ash.) We have similar looking formations in Oregon around the John Day Fossil Beds. We have had discussions and debate about interpreting photos in several other threads about the flood where we went down a bunch of rabbit holes arguing about minutia of lines, or shadows, that didn't help the discussion progress. I would rather not repeat that. I don't want to spend a bunch of time talking about things that are not supported by the evidence found in the rocks. I want to find out what the evidence tells us.

I don't know for sure what you are talking about, since my eyes may not be good enough to see those lines you, but it sounds like the cracks in the strata I took into account with my many discussions of how I think the GC formed -- that tectonic pressure angled the lowermost strata beneath the Tapeats,

I'm not sure what you mean by 'angled'.

Please describe to us the process by which you deform the lower block while leaving the upper on essentially undeformed. Describe the forces, where they came from and how they were applied.

I don't think I'm the only one who is skeptical of your scenario.

... (your loose sediments model couldn't possibly show this kind of effect --

I'm not sure why not. You are simply saying this as far as I can see. The demonstration shows how layered materials accommodate compressive stresses. Every layer in the model was deformed.

... the sediments have to be consolidated enough to hold together but flexible enough to deform without breaking) ...

But below, you say that the rocks fractured.

And I would say that the sediment did hold together since the layers remain distinct, and yet they seem to have been flexible enough to fold.

... which I ascribe to the difference between the kinds of rock at the point where the force was beginning to dissipate.

What force? How did it dissipate? In general, we would 'dissipate' stress by deformation.

If all one kind of rock was involved I would expect there might not have been a detachment at all and a lot more destruction -- ...

There are multiple rock types below the unconformity. Between the intrusive rocks, the schist and the GC Supergroup, there is a lot of diversity. And truly, every bedding plane is an opportunity for detachment.

So why don't we see it?

... so the angling of the lower strata PUSHED UP the entire stack above it and in the case of the GC somehow that stack remained intact which doesn't seem to have happened anywhere else.

Seems to me that would be clue that it didn't happen at the GC...

Are you saying that the lower block (for lack of a better description) was pushed downward under the upper block?

SO HERE'S THE RELEVANT POINT: The strain of the uplift would have CRACKED THE UPPERMOST STRATA.

So, the rock was hard enough to crack. I thought you said it was soft.

You are saying that it was uplifted probably thousands of feet while the underlying rocks were strained to the point of tight folding and yet there is no real sense of deformation of the Paleozoic rocks.

And there is no detachment between the two blocks. That's pretty amazing. Particularly since we know that the surface was not smooth and planar.

Which is what I suppose you are calling FAULTS.

Not really. Faults would disrupt the bedding planes and the unconformity. And with the degree of strain we see in the pre-unconformity rocks, there should have been swarms of abundant thrust faults, which we do not see by the way. If you are talking about fractures, then they are fractures along which there is no relative motion.

So I figure there were many very deep cracks in those uppermost strata at the top of the uplift, which began to break up and wash away in the receding Flood waters, washing away in all directions to the point of scouring off the limestone surface of the Kaibab Plateau, ...

Problem is that you've got meandering channels which formed near sea level, so the erosion did not occur after uplift of the plateau.

that limestone being another point of resistance in that area since it remained intact and didn't break up, the surface of the "Permian" period ending the Paleozoic, beyond which far to the north some of the stack from the Mesozoic through the Cenozoic remained intact while the tectonic disturbance cut away pieces of the strata to form the Grand Staircase

However, there are cracks throughout the Paleozoic section. If cracking controlled the erosion, why do we see incised meanders? Why did the erosion stop at the Kaibab?

But back to the Gtand Canyon: the cracks that formed right over the center of the uplift broke up everything down to the Kaibab, and one of them became a crack or more likely series of cracks wide enough to become the canyon itself.

Not really.

Fracture controlled drainages would look very different from the incised meanders that we see in the Grand Canyon.

It was then further widened by the chunks of strata breaking off and being washed into this largest crack or collection of cracks. It all washed down and out to the Gulf of California as the Flood receded, scouring out the canyon as it went.

This is mainstream stuff.

Again, the strain of the uplift caused by the upending and pushing up of the lowermost strata caused by the lateral tectonic force, caused the cracking of the uppermost layers two to three miles up, that broke up and washed away, a lot of it into the cracks that became the GC. Have I dealt with your faulting sufficiently? If not, go soak your head.

No. As you can see from the experiment, as folding intensifies (more strongly deformed) the faulting becomes more complicated, more abundant and is attended by folding/disruption of the unconformity.

So, where are those faults cutting the cutting the Great Unconformity?

I'm SO sorry you can't understand what I'm talking about. I could explain some of it but with you there's no point.

As I kept saying, go soak your head.

Edited by Faith, : No reason given.

Faith writes: ...three's nevertheless no doubt it was originally horizontal.

It is already a settled issue that there is no requirement for original horizontality. Sedimentation upon a slope will form a slope. See Evidence that the Great Unconformity did not Form Before the Strata above it, specifically Message 1841.

Please, no replies to this message.

Starting after this post I will be handing out suspensions for Forum Guidelines violations. I'll be posting the same note to Report Discussion Problems Here 4.0.

Going back to the opening post, I thought I'd show a picture from the bentonite (volcanic ash) beds in New Mexico at the Bisti Wilderness.

These beds are the same material as shown in the OP, but in this case you can see where, because of cracks and fossils and other impurities, water has carved out pipes from the top of ridges down into the arroyos. We call it pseudokarst since it is karst-like but not due to dissolution of limestone.

You can see some smaller black gravels laying about the surface that were probably erupted along with the ash.

Can you tell us a little more about those beds. It certainly looks quite different than the Hawaii lava beds and what would that tell us about the origin, age, environment at the time they were laid down and environment since they were laid down?

I'm not very familiar with these particular beds since I was just a tourist at the time, but they probably originated as ash flows or ash falls. That means that they were composeed of fine glass fragments mostly without crystals or rock fragments. The glass reacted with water to form various types of clay. In this case they formed bentonite, a loose term for a class of expansive clays. Devilish stuff to walk or drive on when wet.

The Hawaiian volcanic rocks were not as explosively erupted so ithere was not as much ash formed. They are also much younger.

Many places where I see these types of deposits they seem to be relatively deep (tens of meters). It must have been overwhelming for any animals living there to be buried in sudden ashfalls.

The John Day Fossil Beds in Oregon have some very colorful deposits that yield thousands of fossil mammals that were buried about 40 million years ago.

No, Tany, not meant as an insult...

... just the understatement ... it tickles ... deep!

It must have been overwhelming for any animals living there to be buried in sudden ashfalls.

doh, ya think?

sorry!

... just the understatement ... it tickles ... deep! It must have been overwhelming for any animals living there to be buried in sudden ashfalls. doh, ya think?

Yeah, I know. My excuse is I was distracted, trying to remember where my John Day shots are and also, because I am working on a set of shots for a discussion of Hurricane Fault.

Plus, I am in the planning stages of a road trip through the SW and then continuing on to Tennessee to hook up with my best travel pal to look for an undescribed very large dragonfly that we have only seen twice. This trip will bee mid-May to mid-June.

Then we have another road trip to a DSA meeting in Utah in July.

Anyway, I think we have some more ashfall layers mixed into the exposed strata layers along the Hurricane Fault.

Besides, the ashfall deposits may not have been a single continuous event. There is layering within the deposits.

wings writes: Besides, the ashfall deposits may not have been a single continuous event. There is layering within the deposits.

How can you know that is the case?