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Faith  Suspended Member (Idle past 1444 days) Posts: 35298 From: Nevada, USA Joined: |
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Author | Topic: Evidence that the Great Unconformity did not Form Before the Strata above it | |||||||||||||||||||||||||||||||||
JonF Member (Idle past 168 days) Posts: 6174 Joined: |
It just underscores your incredible ignorance of relevant processes. Large temperature changes, or addition or removal of material can change volume. Extreme pressure (which is applied "hydrostatically" or from all directions simultaneously can reduce volume in some cases. Stretching... not so much.
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Faith  Suspended Member (Idle past 1444 days) Posts: 35298 From: Nevada, USA Joined: |
Well, rock, including sandstone, does stretch:
http://en.wikipedia.org/wiki/Lineation_(geology) But if that isn't the cause of the greater volume between contacts, then it must be that the narrower part to the right was formed by compaction. I'm OK with either explanation. Edited by Admin, : Fix link.
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ThinAirDesigns Member (Idle past 2373 days) Posts: 564 Joined: |
Faith, stretching does NOT increase volume. Play with any pliable plastic substance to prove this to yourself.
JB
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Faith  Suspended Member (Idle past 1444 days) Posts: 35298 From: Nevada, USA Joined: |
I agree. You are right.
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Minnemooseus Member Posts: 3941 From: Duluth, Minnesota, U.S. (West end of Lake Superior) Joined: Member Rating: 10.0
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And as Moose stated earlier, the layers have the appearance of dipping downward away from the rock face, so the tilt isn't exclusively left-to-right. There are two variations of the "dip" concept, true dip and apparent dip. If a geologist is talking about "dip", s/he is referring to true dip. Now, dip is the slope (and, to be complete, also the slope direction) of a planar geologic feature. We have been talking about bedding, but a metamorphic foliation is another type of planar feature. To be able to determine the true dip of a feature requires some variety of 3 dimensional exposure. If all you have is a 2 dimensional exposure (which our road-cut photo essentially is), all you can see is an apparent dip. An apparent dip is probably less than the true dip. Indeed, it is possible to have a horizontal apparent dip, and at the same time, a vertical true dip. I have seen bedding exposed on a flat horizontal surface. Without somehow having a third dimension, it is impossible to determine the amount of dip. In the photo, the true dip appears to be fairly shallow and leftward into the rock face. But it is hard to tell from just a photo. But, the bedding lines you see on the rock face only show an apparent dip, which is less than the true dip. In the geological business, a dip has two components, orientation and slope. It is commonly mapped and stated as "strike and dip". The "strike" is the compass bearing of a horizontal line on the bedding face. The "dip" is the slope at a right angle to the strike. A dip could also be stated at a slope measurement and the slope direction. On a geologic map, the dip symbol is a squat "T", probably with a number. The top line of the "T" shows the strike direction and the bottom line of the "T" shows the dip direction. A number will indicate the degrees of slope of the dip. There are also special symbols for horizontal bedding, vertical bedding, and overturned bedding. Foliation dip symbols are different. Bottom line - There is only one true dip at a given location. Any other dips seen are only apparent dips. And on a more vulgar note, there is a special technique for determining the dip direction of near horizontal bedding. It's called the "piss on it" method. Pouring your liquid of choice on the bedding surface, the direction the liquid runs is the dip direction. Moose BTW, did you know that Firefox recognizes "exfoliation" as a correct spelling, but "foliation" as an incorrect spelling.
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Admin Director Posts: 12998 From: EvC Forum Joined: Member Rating: 2.3 |
Faith writes: I think there is still some narrowing of the lower layers over the gneiss as seen from the frontal view:
But the frontal view does make it clear that the sagged layers are on a much less steep slope than appears from the other angle. I don't know that everyone would draw the lines in the same places that you have. But I think everyone can agree that the layers tilt consistently upward to the right, and that the lower set of layers are a little thicker to the left of the outcrop. We can't tell from the image why that portion of layers is thicker. Some of the individual layers might be thicker. Or some of the layers might stop at the outcrop. There's no way to tell. But we can still examine your rationale for the sagging you say happened. You attribute the greater thickness to sagging, that the layers became thicker as they sagged, but as THD pointed out this would have required the rock to increase in volume. You then claimed the rock must have stretched, but THD then pointed out that stretching does not increase volume. The angle of tilt does not change from left to right, and rock cannot increase its thickness. What are you seeing in the image that leads you to believe the left side sagged? One question you might ask yourself is if you had seen the Google Street View image without having first seen that other image, would you still have thought those layers sagged?
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Admin Director Posts: 12998 From: EvC Forum Joined: Member Rating: 2.3 |
Minnemooseus writes: I don't follow the relevance of that detail, but that portion of the red line is flat out wrong. It should be pretty much straight across. Yeah, I noted that possibility back in Message 1481, Edge seemed to agree, and I reminded Faith of this in Message 1565.
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ThinAirDesigns Member (Idle past 2373 days) Posts: 564 Joined: |
Faith writes: But if that isn't the cause of the greater volume between contacts, then it must be that the narrower part to the right was formed by compaction. I'm OK with either explanation. Since you're "Ok with either explanation", you're openly saying that you're still Ok with an explanation that has no substance behind it -- that rocks can puff up their size at will. Just don't expect anything heaped on that idea other than ridicule. Think of how unstable buildings would be if rocks suddenly could just become bigger now and then. Concrete would fall apart. Foundations would blow open. Buildings would suddenly tilt and fall over. Bridges would fall. Construction as we know it would never have started and stone would be one of the most unstable and useless building materials of all time. But as we know ... stone is the most stable and predictable of all construction materials precisely *because* we can count on it to not suddenly change it's volume whenever Faith decides it's convenient. JB
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ThinAirDesigns Member (Idle past 2373 days) Posts: 564 Joined: |
Faith writes: ... it must be that the narrower part to the right was formed by compaction. I'm OK with either explanation. Ok, let's explore the "compaction" explanation. Here is your originally marked up photo that I've been working from:
Just to review, you're premise is that the rock represented by the "sagged and tilted" orange lines that you drew there were once in the same plane as the rock represented by the yellow lines. I've modified my zoom image to include a few extra circles (pink) so I can better understand your position.
With your "compaction" explanation, are you saying that rather than the orange lines having sagged down from the yellow level (which would require the magical expanding rock bs), you are saying that your short yellow lines were pushed UP from the orange level to where they are now, and the material within the pink circles was compacted that extra distance? Just checking. JB
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Faith  Suspended Member (Idle past 1444 days) Posts: 35298 From: Nevada, USA Joined: |
I didn't say the sagged layers became thicker as they sagged although I can see how someone could have read it that way. I was talking about the layers ABOVE the sagged area, where the contacts are so tight and yet tilt slightly from the horizontal lines to the right -- those aren't horizontal, we can see now from the street view, but there is nevertheless a slight tilt down from those in the contacts on the left just above the sagged area.
I was asked how the space between the contacts could be larger,or that's how I heard it, and I just tossed off the thought that since the rocks were still soft they must have stretched in that area. He then kept insisting it would involve volume so I said OK then the volume must have expanded that small amount, not really thinking. Eventually I took that back. But it was never about anything other than the couple of layers above the sagged area, to explain how there could be such tight contacts there if the layers are wider than those to the right. The answer I'd give now to explain the difference is that the layers to the right must have thinned. No, I probably wouldn't have said the left side sags if I had only the street view to go by. I might still have argued for original horizontality though. But since it looks like a sag on the other view and can still be identified somewhat on the street view, I'll still try to make the case. Edited by Faith, : No reason given.
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Faith  Suspended Member (Idle past 1444 days) Posts: 35298 From: Nevada, USA Joined: |
Yeah, I noted that possibility back in Message 1481, Edge seemed to agree, and I reminded Faith of this in Message 1565. The odd thing is I never even noticed that jog until you "reminded" me of it. Then I said there couldn't be any jog there at all. Who drew that line originally? I missed it at the time.
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Admin Director Posts: 12998 From: EvC Forum Joined: Member Rating: 2.3 |
Hi Faith,
Earlier today I wrote that not everyone might place the lines on the image in the same way as you did. This is how you originally placed the lines on the image in your Message 1648:
And you've just proven that even you will draw the lines differently each time, because here's how you just drew them with a much more pronounced leveling off toward the right, presumably because that's the point you wanted to make this time:
So I'm going to repeat the caution yet again, more emphatically this time: You are overinterpreting a very low resolution image. Even high resolution images must be approached with caution. Perspective, lack of 3D, illumination angle, shadows, etc., all get in the way of accurate interpretation. Nothing beats being there. If there are any particular views you would like of the layers in the area around the outcrop, either close-up or distant, then you might want to pass SnapDragon some additional ideas.
Original horizontality is a principle more than something that should need to be proved,... There is nothing in science that doesn't need to be proved, i.e., supported with evidence and demonstrated likely true through replication that is able to persuade the relevant scientific community. That's why Steno's principle of horizontality turned out to be only partly correct.
But not to lose the point of the distinction: if the layers deposited horizontally and then deformed, that suggests that the deformation was caused by the deformation of the gneiss over which they now lie and to which they appear to be conformed in basic shape. This would be evidence... What would be evidence? You've proposed a scenario for what might have happened, not presented evidence. If you think the layers experienced deformation then you must describe what you are seeing that indicates deformation.
If, however, they were deposited on top of the already-deformed gneiss,... What are you looking at in the gneiss that indicates it experienced deformation?
...conforming to its contours as seen, that would support the idea of pre-existing gneiss already eroded... Is this gneiss "already deformed" or is it "already eroded". You've just said both. I think everyone could agree about "already eroded" because that's what we already know about the boundary between the Precambrian gneiss and the Potsdam sandstone. I'd like to bring up something that was under discussion a while back, your doubt that erosion can result in flat horizontal surfaces. I just serendipitously came across this GIF of a meandering river changing its course:
Meandering is what happens to rivers that travel across relatively level landscapes. The changing meanders that you see in the above image level out the area. Over more years the river will change its course even more dramatically, with changing meanders that flit about (in geologic time), flattening and leveling the landscape. Flat plains are generally just way stations for sediments that are being carried from higher elevations to lakes or seas.
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Faith  Suspended Member (Idle past 1444 days) Posts: 35298 From: Nevada, USA Joined: |
I spoke too soon, that's all. Please see my explanation to Percy in 1675.
Edited by Faith, : No reason given.
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Faith  Suspended Member (Idle past 1444 days) Posts: 35298 From: Nevada, USA Joined: |
With your "compaction" explanation, are you saying that rather than the orange lines having sagged down from the yellow level (which would require the magical expanding rock bs), you are saying that your short yellow lines were pushed UP from the orange level to where they are now, and the material within the pink circles was compacted that extra distance? Something like that, yes. There has to be an explanation for the difference in width, either expansion or compaction, and compaction appears to be the best explanation. But I never said the straight tight contacts indicated by the orange lines "sagged," that word I only applied to the layers below. I used the term "slight tilt" for those above. Edited by Faith, : No reason given.
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Faith  Suspended Member (Idle past 1444 days) Posts: 35298 From: Nevada, USA Joined: |
When I drew the line to indicate the sag I was looking at a much bigger closeup picture where the curve is more apparent. I don't know why only one layer seemed to show up whereas at the greater distance I identified two.
yes of course it makes a difference to see a different perspective. if snapdragon gets some good shots maybe it will make enough of a difference to give up the whole argument. I used "eroded" for the gneiss as the statement of the conventionalview that I'm arguing against. "Deformed" refers to its being higher in one place than the other but that concerns the idea that it was pushed up into the sandstone, which I still have to give better evidence for according to you although I think I've given good evidence already. HOW flat is the surface eroded by meanders? They leave raised areas at the edges of their sharp turns, don't they? Edited by Faith, : No reason given.
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