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Author Topic:   Deposition and Erosion of Sediments
roxrkool
Member (Idle past 307 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 4 of 127 (191937)
03-16-2005 1:16 PM
Reply to: Message 1 by Faith
03-16-2005 12:25 PM


Sticking to the Grand Canyon at least for starters, because it is easy to visualize, it appears obvious to me that the individual strata are not eroded as roxrcool and others claim they are, as erosion over the millions of years designated for each of the layers would obliterate them, not leave them as neatly parallel/horizontal as they are. I'm sure some erosion can be demonstrated, but nothing like what should be expected from the millions of years assumed.

Faith, you are looking at PHOTOGRAPHS. People who have worked on the rocks themselves, looked and studied the contacts see the erosive events. You simply cannot make that sort of call without ever having looked at the rocks themselves.

Do some research on the Muav Limestone and the channels carved into the top of it. Those channels are filled with a fresh-water carbonate unit called the Temple Butte Limestone. Withing the Redwall Limestone formation, there is a low angle unconformity between the underlying Thunder Springs Mbr. and the overlying Mooney Falls Mbr. You cannot see these things in a photograph.

And no, when I say neatly I don't mean some kind of perfection. They LOOK parallel/horizontal to the naked eye.

Again, Faith, you are looking at photographs taken hundreds if not thousands of feet away from the rocks. While they ARE for the most part parallel and horizontal, they are also sub-parallel and sub-horizontal. THAT sort of detail you cannot see in a photograph.

This should be a pretty limited topic, sticking to the specifics of the creation of a single layer of the Geo Column for the most part as suggested by Admin, but including how a given layer started from sediment and built up from the bottom to become rock and stayed relatively flat and horizontal over millions of years, which I claim is impossible.

Large thickness of sediment can accumulate in basins by a process called basin subsidence. The weight of accumulating sediment causes the crust beneath the basin to deform and sink, thus providing ample accomodation space for continued basinal deposition. As long as the basin remains stable, it will continue to subside.

The deeper the limestone gets, the more it's subjected to increasing temperatures and pressures, both of which are responsible for lithification. Cement, in the form of either calcite or dolomite (for carbonate rocks), is also responsible for lithification, and it is sourced from the same rocks (usually).

As for how it remained horizontal, tectonics are usually responsible for tilting and/or deforming strata and if the basin was free of tectonic influences, little or no deviation from horizontal would occur.

However, the presence of a low angle unconformity between the underlying Thunder Springs Mbr. and the overlying Mooney Falls Mbr. suggests tectonic movement and erosion preceding deposition of the Mooney Falls Mbr., which disproves your assumption that all the layers are perfectly horizontal and neat.

(I stole and revised the above from my PNT topic.)


This message is a reply to:
 Message 1 by Faith, posted 03-16-2005 12:25 PM Faith has replied

Replies to this message:
 Message 11 by Faith, posted 03-16-2005 5:06 PM roxrkool has replied

  
roxrkool
Member (Idle past 307 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 20 of 127 (192000)
03-16-2005 7:16 PM
Reply to: Message 11 by Faith
03-16-2005 5:06 PM


"Erosive events" that occurred over millions of years would have obliterated any layer in its formative stage. This is elementary logic.

and

Such minuscule observations of the strata are not required for the obvious effects real erosion would have caused during a period of twenty million years or so. That geologists take such evidences as in any way representing the actions of erosive processes during the building-up period of sediment-to-rock of a single layer over such long ranges of time is evidence only that geologists are in thrall to the false evolutionistic theory, and not thinking about the reality at all.

Faith, first of all, I am having a really hard time following your arguments. They don't make any sense geologically.

It seems to me you are saying that as soon as sediment is deposited, it is subjected to erosion. If that's what you're suggesting, then that is not necessarily true - especially if we are referring to deep marine sedimentation.

The beach area and shallow marine environment, where the waves are washing back and forth, IS someplace where sediment is continually being moved around. If the water level never changes and the basin never subsides, and tectonics are not active, then this process would likely never result in net sediment accumulation. What is washed in, is washed out.

However, the deeper into the sea you go, the more stable the environment. Out there, depostional processes dominate over erosional processes, and there IS a NET accumulation of sediments (thanks for the word, Jar! :)). Sediment is building up and weighing down the basin. The basin subsides and sediment continues accumulating.

So NO, all erosion does not occur immediately preceding deposition, except in localized settings.

There would not be merely minuscule evidences of "erosive events" you'd have to examine the rocks to discover over such a period of ages, there would simply be not much of a layer left at all. As I've repeatedly said, what actual real erosion obviously does in the Grand Canyon area, is create the Grand Canyon itself.

Again, your statements don't make much sense. What do you mean by layer? The entire unit (e.g., Muav, Redwall) or the individual layers (i.e., beds) that make up the units?

Because if you attempted to erode 5,000 feet of limeSTONE, millions of years would likely only erode a portion of that, leaving some behind. If instead you are eroding 2 feet over millions of years, then yeah, that stuff would likely be completely eroded.

Take a look at the following images and note all the unconformities:

There are at least 14 unconformities that have been identified. Those represent gaps in the rock record - that means MISSING rock. The amount of time represented is in the millions of years, perhaps some of that time is accounted for by non-depostion, but for the most part, it represents eroded rock. What you see in the GC is what was left behind AFTER erosion. It's the rock that survived due to changes in climate, eustasy, tectonics, etc.

So Faith, the erosive evidence is hardly "miniscule." The channels carved into the top of the Muav Limestone are large and often deep. You can't see them in pictures of the GC unless the pictures are taken close enough. Unfortunately, I didn't find any online. And the other unconformities, except for the Great Unconformity don't pop out in the photos. Just because YOU can't see them, does not mean they aren't there.

Additionally, these channels tell you that at one time, the Muav Limestone was exposed to the surface. If the Muav was carved by channels, then logically, the Muav must have been thicker than what is currently seen at the GC. And perhaps there were all sorts of other rock layers on top of that. But erosion worked it all down to its current thickness and all those other rocks are gone from the GC.

Not only that, but freshwater limestone, the Temple Butte Limestone now fills those channels. Originally, how thick was that? Were there other layers on top of that, too? But erosion worked all those rocks down, too.

So at that one contact, there are AT LEAST TWO erosive events and who knows how much was eroded. I suspect that more research would find the answer or simply looking through the literature as there are likely Muav- and Temple Butte-equivalent limestones in other parts of the region.

If you require posters to take geology field trips and speak geologese here, it should be posted up front at this site so that we can stay away and you won't have to deal with mere logical thinkers without a degree in Geology. Or just don't post to us.

I don't require anything of you. It was a suggestion that, instead of relying on photographs to do your geology, perhaps you should actually see the rocks for yourself before making judgements and calling into question the work of thousands of professional scientists.

No one likes an armchair geologist - no matter how 'logical' they think they are.

What is your point? Which theory are you giving for the formation of a single layer of the Grand Canyon? Only it's lowest layers were tilted so why mention that at all?

PLEASE explain what you mean by "a single layer." Is that a lithologic unit or a single bed IN the rock? Because your question again makes no sense.

This message is a reply to:
 Message 11 by Faith, posted 03-16-2005 5:06 PM Faith has not replied

  
roxrkool
Member (Idle past 307 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 70 of 127 (193159)
03-21-2005 9:41 PM
Reply to: Message 67 by Admin
03-21-2005 2:37 PM


Re: Great Debate Thread Reopened
Sorry, Percy, I wasn't sure where to post a reply to this.

For my part, I'm sorry to say I'm not particulary interested in discussing geology with Faith at the moment. While Faith is obviously an intelligent person, she's under the mistaken impression that she already knows enough about geology to make valid arguments. She doesn't. I can't even figure out what she's arguing for or against in 99% of her posts.

I'm willing to concede my geologic arguments are wrong - I certainly don't know everything about geology - but before I concede such a point, I require much more than, "it's impossible because the thought of such a thing happening is mind boggling."

It's a complete waste of time, not to mention exceedingly frustrating, to discuss the validity of scientific observations with someone who places no value on such observations at all. Having dealt with my fair share of armchair geologists in real life, I simply don't have the desire nor the patience to deal with another one on-line.

In addition, I'm trying to finish my thesis by next Monday and I need to devote my time to that at the moment. I'm not even supposed to be here right now since I made myself swear off messageboards until I was finished. :) Ummm... it's been a bit tough...


This message is a reply to:
 Message 67 by Admin, posted 03-21-2005 2:37 PM Admin has not replied

Replies to this message:
 Message 72 by edge, posted 03-21-2005 11:33 PM roxrkool has not replied

  
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