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Author Topic:   Depositional Models of Sea Transgressions/Regressions - Walther's Law
Faith
Member
Posts: 23953
Joined: 10-06-2001
Member Rating: 1.0


Message 526 of 533 (730658)
06-29-2014 3:20 PM
Reply to: Message 525 by Dr Adequate
06-29-2014 2:51 PM


In Message 480 Percy says the monuments have been exposed to erosion for tens of millions of years and that the sandstone erodes at a rate of around 15 cm per thousand years, and siltstone at a rate of about 5 cm per thousand years.

That's about 5000 feet in ten million years for the sandstone. Pretty much takes care of that, shouldn't be any left standing without even multiplying the "tens" of millions. And 1660 feet in ten million years for the siltstone. Kinda does it there too wouldn't you say? So which part do you disagree with, the tens of millions of years since they started eroding or the rate or what?

ABE: Of course the truth of the matter is that layers were deposited in the Flood to a depth of some three miles or more, then when the water receded it eroded away a lot of the upper strata all over the Southwest leaving all those interesting formations. After the water was gone the formations were subject to yearly erosion. That's how it really happened.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.

Edited by Faith, : add URL


This message is a reply to:
 Message 525 by Dr Adequate, posted 06-29-2014 2:51 PM Dr Adequate has not yet responded

Replies to this message:
 Message 527 by ringo, posted 06-29-2014 3:46 PM Faith has responded
 Message 531 by Percy, posted 06-29-2014 4:41 PM Faith has not yet responded

    
ringo
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Posts: 12815
From: frozen wasteland
Joined: 03-23-2005
Member Rating: 2.6


Message 527 of 533 (730661)
06-29-2014 3:46 PM
Reply to: Message 526 by Faith
06-29-2014 3:20 PM


Faith writes:

That's about 5000 feet in ten million years for the sandstone. Pretty much takes care of that, shouldn't be any left standing without even multiplying the "tens" of millions.


If it erodes 5 feet in ten thousand years and it's five feet in radius, we'd expect it to be gone in ten thousand years. We can extrapolate backwards to estimate how long it's been eroding. I don't know why you think you can tell that there "shouldn't" be any left. You don't know when it started eroding.
This message is a reply to:
 Message 526 by Faith, posted 06-29-2014 3:20 PM Faith has responded

Replies to this message:
 Message 528 by Faith, posted 06-29-2014 3:47 PM ringo has responded

  
Faith
Member
Posts: 23953
Joined: 10-06-2001
Member Rating: 1.0


Message 528 of 533 (730662)
06-29-2014 3:47 PM
Reply to: Message 527 by ringo
06-29-2014 3:46 PM


Percy said it began eroding tens of millions of years ago. I already said that.
This message is a reply to:
 Message 527 by ringo, posted 06-29-2014 3:46 PM ringo has responded

Replies to this message:
 Message 529 by ringo, posted 06-29-2014 3:51 PM Faith has not yet responded

    
ringo
Member
Posts: 12815
From: frozen wasteland
Joined: 03-23-2005
Member Rating: 2.6


Message 529 of 533 (730665)
06-29-2014 3:51 PM
Reply to: Message 528 by Faith
06-29-2014 3:47 PM


Faith writes:

Percy said it began eroding tens of millions of years ago.


And it will be gone in a few thousand years. How do you get that it "should" be gone already?
This message is a reply to:
 Message 528 by Faith, posted 06-29-2014 3:47 PM Faith has not yet responded

  
Percy
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Posts: 15485
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.7


(1)
Message 530 of 533 (730669)
06-29-2014 4:12 PM
Reply to: Message 487 by Faith
06-29-2014 9:16 AM


Faith writes:

Scree once positioned on the pile has no reason to keep disintegrating like that, it's just going to get covered over by more scree.

Scree is exposed to weathering, which means things like wind, rain, temperature variations and freeze/thaw cycles. Even buried scree is vulnerable, though to a lesser degree, to weathering. Particles flake off the scree, water erodes and carry some away, grinding against other pieces of scree creates flakes, and over time each piece becoming smaller and smaller. The tiers upon which the scree rests are also subject to erosion, and buried scree eventually loses its supporting platform and falls to the next tier, eventually reaching the valley floor. The tiny particles that flake off the scree become the soil of the valley floor.

Anyway, the more likely scenario is that in all that time the butte should have been eroded down to nothing but a pile of scree in itself. IMHO of course.

Yes, of course. In time the West Mitten Butte will erode down to nothing.

The top of the butte represents former valley floor. The current valley floor was once a thousand feet higher than it is now. But when the region was uplifted it became an area of net erosion. Riverbeds crisscrossed the valley and gradually eroded it down, creating canyons that gradually widened and joined, leaving a valley of buttes behind. Almost all the material that once filled the current valley is now gone, only a few buttes remaining.

But of course we don't know the actual amount there do we? And if you look closely at the scree area it appears that it isn't all scree but that the scree has collected on top of a tier of layers that were already there which would of course take up quite a bit of the total volume of that talus or skirt. Unless those tiers were built to hold the scree? Hard to tell from the picture.

Yes, clearly the layers form tiers upon which the scree rests.

Seems to me we need to know just exactly how much scree there is in that pile.

If you wanted to know whether the current amount of scree represents the accumulations of a hundred thousand years or a million years or ten million years, then yes, we need to know precisely how much scree is present, precisely how fast it erodes off the sides of the butte, and precisely how fast it weathers away. But if you just want to know if that much scree could accumulate in a mere 4300 years then the answer is no, there's far too much scree to have accumulated in so brief a period of time. The entire valley floor is scree and the particles weathered from scree.

I don't recall estimating the speed of the water running off around the monuments.

That's true, you didn't provide an estimate, but I did provide a lower bound for you. Niagara Falls used to erode back about 5 feet per year before the diversion of water for electric power generation. The floor of Monument Valley used to be at least a thousand feet higher than it is today, and it is miles across. How do you imagine your flood eroded away an entire valley a thousand feet deep and at least 50,000 feet across in just a year when Niagara Falls can only manage 5 feet?

Somewhere back in those discussions about all that it was proved by some official link or other that drying does indeed form rock in some cases,...

Yes, someone did happen to mention that there actually are some types of rock that can form by drying, but they aren't the types of rock that make up most sedimentary layers, which are limestone, siltstone, sandstone and shale in this region and in most regions throughout the world. These types of layers form by deep burial, compaction, and cementation.

I've read ahead in this thread, and so I won't reply to your Message 488 because it looks like you figured out that the White Cliffs of Dover are eroding off their face, not off their top (at least not significantly). The English Channel widens every year.

--Percy


This message is a reply to:
 Message 487 by Faith, posted 06-29-2014 9:16 AM Faith has not yet responded

    
Percy
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Posts: 15485
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.7


(1)
Message 531 of 533 (730670)
06-29-2014 4:41 PM
Reply to: Message 526 by Faith
06-29-2014 3:20 PM


Faith writes:

In Message 480 Percy says the monuments have been exposed to erosion for tens of millions of years and that the sandstone erodes at a rate of around 15 cm per thousand years, and siltstone at a rate of about 5 cm per thousand years.

Ringo already addressed this, but it doesn't hurt to say it another way. The region didn't begin eroding until it was uplifted some tens of millions of years ago. At the time the surface that would eventually become Monument Valley was a thousand feet higher, and what would eventually become the buttes were just buried sedimentary layers miles and miles in extent. Rivers crisscrossed the valley cutting it into canyons whose sides eroded away, eventually joining and continuing to erode and finally leaving behind only the buttes we see today.

That's about 5000 feet in ten million years for the sandstone.

That's not a bad estimate. Another way of looking at it is that these buttes were once as wide as all of Monument Valley. It did take millions and millions of years to erode them away to their current breadth of only thousands of feet. There must have been many more buttes millions of years ago, but they've eroded away to dust.

--Percy

Edited by Percy, : Improve phrasing.


This message is a reply to:
 Message 526 by Faith, posted 06-29-2014 3:20 PM Faith has not yet responded

    
Adminnemooseus
Director
Posts: 3740
Joined: 09-26-2002


Message 532 of 533 (730674)
06-29-2014 5:48 PM


Terminal off-topic, summary mode now
Faith launched this thing off-topic at message 448, and I'm pretty sure there's been no contact with the topic theme since.

Summary mode - One last message per member, hopefully something about depositional models.

Adminnemooseus


Or something like that.

    
Faith
Member
Posts: 23953
Joined: 10-06-2001
Member Rating: 1.0


Message 533 of 533 (730682)
06-29-2014 6:37 PM


There is nothing to summarize. The thread was already off topic before I posted Message 448. If it was going to be interrupted for being off topic that should have been done pages ago because it picked up momentum and to stop it now is cruel. So many threads have been left to go severely off topic over the last many months why even bother at all?

Edited by Faith, : No reason given.


    
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