Long build up of Sediments

Just to let you know, her question was in response to a simplified example I had started with in trying to walk her step by step through the sediment issue. Unfortunately at each step she then wants to run toward a final conclusion. It's sort of like breaking a horse.I tried to address her quandry about where all the material could come from. So I started with a hypothetical of volcanic action pushing up to form a "pure" igneous mountain. I was trying to get her to see that with a constant influx of material from below, and erosion on top, the result could be lots and lots of sediment... the quantities she wonders about. Given those mechanisms and time accumulation to that amount has to be possible.Then I had to reign her in because she immediately want to have an explanation regarding the Grand Canyon using that pure hypthetical. I nixed answering that and tried to address the next issue, that a single source may provide various types of sediment, since she seems confused regarding how different sediments are generated. Starting simple, from the hypothetical, I was explaining that the igneous mountain is not going to produce only one kind of sediment, but because of the many different minerals will produce a variety of sediments that will get sorted during transport after erosion. This separation would start strata building of different seds, and over time lots of material.Her post now was an attempt to jump from that same simple hypothetical, trying to discuss process, to explain the entire geo column as we see it.Whooooooooaaaa Nelly!

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holmes
"What you need is sustained outrage...there's far too much unthinking respect given to authority." (M.Ivins)

NO! I am trying to show you how slow processes can work to build up the massive amounts of material within the geo column. I am starting with a very simple hypothetical and taking small steps toward a greater understanding.There is clearly more than just volcanic material in the geo column. Much of the material did originate from igneous (as compared to just volcanic) sources, but the strata are not all due to volcanic activity or generated from igneous material.Let's not jump to the end, when we are only at the beginning. The first point was to show you that there are sources of material, vast amounts, to account for the volume of material one sees, given time. The second point was to begin drawing out that a single source rock, may contain different minerals with different physical properties such that differential erosion and transportation will separate the various materials.Its sort of like chromatography, where materials (lets say ink), moved through another material (lets say paper) will "sort" during transport into components based on the different properties.Do you understand this so far? We have a source for vast amounts of material, and physical processes that will break down that original material (which is heterogenous), into its components and separate them spatially during transport?

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holmes
"What you need is sustained outrage...there's far too much unthinking respect given to authority." (M.Ivins)

I think the impression that Faith has got is that sediments can be deposited up to kilometres deep, but the reason why the strata seems only a few feet thick in many places is because these kilometre deep sediment deposits have been eroded away.

I am giving this thread a rest, but I have to say that your idea of what is needed, this walking me through some steps or other, is irrelevant. I don't have a problem with gigantic amounts of material, I have a SPECIFIC problem with the SPECIFIC sediments in the SPECIFIC layers of the geo column, especially if I am told they USED to be a lot thicker than they are now but got eroded down to present thickness from some rather astounding former thickness. These are SPECIFIC sediments, different kinds of limestones, shales, sandstones and so on.The question involves how these SPECIFIC sediments got there to such a depth over a broad swath of terrain and all so neatly (apparently) stacked one upon another.So far nobody has even come up with a present-day source of such a phenomenon that I can see, not to the scale of what is actually seen in, say, the area that stretches through Arizona and Utah. Sorry to keep focusing on that area but I simply have a pretty good visualization of it because of the GB thread a while back; lots of diagrams that show that the layers are consistent over that great territory. I understand that most of that was supposedly formed in a sea environment, while the idea is that other parts of the geo column may have been formed by mountainbuilding, and there was one other method given that I can not recall. And yes, I understand that although these represent specific time periods that the actual arrangement differs in different parts of the globe.But there is too much irritability on this topic so I'm just going to take my time with getting back to it.This message has been edited by Faith, 03-13-2006 09:35 AM

Yes, thank you, and that is the impression I got from edge himself, although he apparently was talking about a whole stack accumulating up to kilometers and being eroded down to a lot less, while I thought we were talking about a single layer, so there is still something there that needs explaining about the supposed accumulation of individual layers.

This is a perfect example of your problem. In order to understand explanations about specific sediments in specific layers, you need to first understand the general concepts which will be discussed.People already tried to explain the specifics (as I have in the past) and you don't understand what they are saying. So I tried from a general standpoint.You know a surefire way to never understand is to demand answers to specific questions which will require detailed answers, then complain they are too detailed and so irrelevant, then when someone tries to approach it from a simple perspective and build up claim it is not specific or detailed enough and so irrelevant. I don't think he meant what you took him to mean. If he did then I guess it would be of interest to see what is known (evidence) for erosion in the layers (and how anyone would know how thick the original layers were).That said, erosion can occur at a layers surface. Indeed erosion can wipe out several layers... JUST LOOK AT THE GRAND CANYON. The fact that you can see all those layers is because erosion has removed massive amounts of materials cutting down through layers to create valleys. Given enough time the cliffsides will be gone and so no valleys and no layers. It has to do with different environments and different materials combined with differential sorting during transport and changing shorelines (or river meanderings), over a long period of time. The nature of the specific sediment will help describe/identify the environment it came from.That's about as good a description you can get without getting technical (which you don't seem to want) or starting from scratch so that you can understand the technical aspects from a theoretical position.Is there a particular kind of sediment, or sediment layering you have a problem with?

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holmes
"What you need is sustained outrage...there's far too much unthinking respect given to authority." (M.Ivins)

You know, it seems to me it ought to be perfectly acceptable to pick and choose with whom I'd like to communicate on a thread that has many people posting to me. It is especially hard for me to communicate with you for some reason, so I hope you will understand if I don't respond to your points.

That's fine. Edge and Rox seem to be nearing an impasse with you on their own. I thought I'd try to help you understand it in a different way... less technical. My first post to you here was trying to cut through that problem by giving you material from other sources, including info from a biblical Xian. Okay. I'll still respond to points and if you want to take a look at the info then great. Especially if the others drop off maybe you can take a look. Heck if you want to I can completely remove any negative commentary and make it a purely instructional rather than debatable issue.My main interest will be attempting to explain in general terms answers to problems you say you are having, for the benefit of others that might have the same questions.

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holmes
"What you need is sustained outrage...there's far too much unthinking respect given to authority." (M.Ivins)

Yes, holmes. I noticed the same problem and commented on it a few posts back. The problem with geology as you know is that each area pretty much has it's own geological history. We can't extrapolate just any package of rocks to the Grand Canyon. The GC has it's own geologic history and everything must be viewed within the context.

Hi Faith,Please forgive my sharpness earlier. As I am sure you know sometimes participation on this board can get your blood boiling. I hope this explanation helps answer some of your questions and potentially pose some new ones. No it would not all be one kind of sediment. This is actually a very easy question to answer because you can go test this for yourself.The thing about erosion that is neat is that it sorts sediment and we know this because we can watch it happening today. If you go into the mountains and look at a shovel full of dirt you will see everything potentially from fist sized rocks to tiny grains of sand. On the opposite end of the spectrum you can go to a beach and look at a shovel full of dirt and see only very small rounded pebbles but mostly fine sand. In between you will run the gradient of different sizes and shapes. It will be the rare if not impossible circumstance that you are going to find a sharp and jagged granite boulder sitting on a beach where there are no mountains for miles.What sedimentary rock a bunch of sediment will create is all based on where it ends up and how much weathering the particles endured before it was buried. It wouldn't wash down in layers at all. What sedimentary rock is created is based on more than just the source. It is the source, the distance from the source, where it ended up, and how it got there. Not all beaches are sandy. Sometimes there are beaches, like in Hawaii, next to large volcanic cliffs. Here the beaches can have lots of larger rounded pebbles mixed in with sand and such. This is different from a beach, lets say in Florida, because the source is very close and the sediment didn't have to go far and thus was not weathered down to nothing. The America southwest is such a neat area because it has been preserved so well. It is unique because up until recently it had been a rather large inland sea. This gives the best case scenario for forming nice flat strata over a large area with fine grained sediment. Most other formations we see on land today are not like this because they didn't form under such unique circumstances. The reason the rock types change is because the environment changed. I know you don't accept this but it is a valid explanation because we can see this happening today all the time.I will use the Pacific islands as an example of this. The coral reefs around the islands are currently depositing limestone. On one island (forgot the name) there was mass deforestation and as a result much more large grained particles were not being held back anymore by the foliage. They made it to the rivers and the ocean killing off much of the reef. There was a shift then from limestone to sandstone and it will continue that way until the water is clear enough againt for the reef to return. This might take until the island itself is eroded to a nub in which case lots of sand will have built up before limestone could start again.This is a good example because it also shows how rock types can change so abruptly. The thing to remember though is that they don't always do so. There are plenty of places that are different from your poster child of the grand canyon where this is seen. Where they do occur abruptly there are numerous reasons why that can only be determined by the circumstances of the specific rocks.1. The easiest case is that the environment changed abruptly. The pacific island example and the example of a river changing course to capture new sediment are great examples of this. A tsunami might do it. Changes is biology might do it. Sometimes, all it takes is a few degrees temperature difference to kill off sea creatures. If earth's temperature rose or fell abruptly then you might stop seeing limestone and start seeing something else. Conversly it does not take long (geologically speaking) for life to colonise an area so that when conditions are suitable, there might be an abrupt change from some other fine grained ocean sediment into limestone.2. Sometimes there is a break in deposition. We have mentioned these before as unconformities. There are lot of these and they are easy to identify. When deposition stops this "buys" our scenario some time for a potentially more slow environment change to occur such as a change in sea level.3. Compression will make a more gradual transition seem abrupt until you look close. This is probably the case for some of the more abrupt appearing transitions in the GC that are not unconformities. You have to remember that originally these sediments were much thicker before they were buried and compressed with the weight of water and other sediments on top of them. Therefore what might have been a few feet of gradient as a transition was happening may only be represented by a few inches after it gets compressed.

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Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)

I have a great example for what you are looking for Faith! All we have to do is look at another inland sea. The one I am thinking about the best is the Black Sea in Asia. This is a neat example because not only does it show the same kinds of things you can see in the GC but because it contains a great example of a drastic change in deposition types.The Black Sea used to be an inland freshwater sea depositing sediments that were eroded from its shoreline and the rivers that fed it. There was a natural dam between it and the Mediterranean Sea that broke which drastically changed it into a saltwater sea. Now it was getting source material mostly from the Mediterranean so there was an abrupt change in the deposition.You should be able to find plenty of source information about the Black Sea because of this unique circumstance of how it became a saltwater sea and because it happened relativly recently.

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Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)

to parallel the GC, the sediments must be relatively pure, not mixtures, that is, must be either limestone or shale or sandstone. All you say is that first the shore of the sea was eroded and deposited, then the Mediterranean broke through and left a different deposit on top of the first. Two layers, and nothing about the sediments themselves.So, were the very deep strata of the Arizona-Utah area once an inland sea and are its edges traceable?This message has been edited by Faith, 03-13-2006 12:02 PM

I saw that Holmes addressed this, and I thought this picture of the geologic layers between Cedar Breaks and the Grand Canyon is just the one for his answer: You have to look at this at full size to read the fine print. On the left hand side at Cedar Breaks are a number of layers that are not present at the Grand Canyon, which is on the far right. If the diagram is to scale then approximately a mile and half of sedimentary layers lay above the Grand Canyon at one point in time, but have since eroded away.--PercyThis message has been edited by Percy, 03-13-2006 12:19 PM

Heheheh... thanks percy, that was exactly the type of image I was going to look for tonight!

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holmes
"What you need is sustained outrage...there's far too much unthinking respect given to authority." (M.Ivins)

Well of course they are. What you have at first are lake deposits. If my memory serves me right I believe there are even evaporite deposits around the rim. SO you have many layers of lake environment deposits. Then you have a sudden change to deep marine deposits such as fine grained silt. These are not very deep yet because it hasn't been a saltwater sea for very long and that was sort of the point. You wanted a modern day example of this happening. Well certainly I didn't say there were just 2 layers. Obviously the sea had its own geologic history before the dam broke and there are many layers that are different for their own reason one big one being the coming and going of the ice age that preceeded the dam breaking. I was just trying to keep it simple. Right now there are different sediments being deposited in different areas of the Black see due to depth and proximity to the shoreline just like there are in the America SW. Yes they sure are and we can even trace how the shoreline grew and shrank over time. Where I am standing right now is on the transitional boundary where sometimes it was under the ocean while others it was the beachhead. While it was a sea it had existed long enough for sea levels to rise and fall many times and we can find the shoreline at various places "times" in the geologic column.BTW. Did you like my post prior to this one that you responded. I know it was long but I am trying very hard to get you good information. Every once in awhile it feels like we get this bouts of cooperation.

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Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)