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Author Topic:   Long build up of Sediments
roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 45 of 180 (294280)
03-11-2006 12:15 PM
Reply to: Message 37 by Faith
03-11-2006 9:41 AM


Yes, another problem for the flood scenario while you evade the problem for your scenario. Tell me how you expect fossilization to occur at the rates of sedimentation you postulate.
You appear to have a mistaken impression of what 'fossilization' actually looks like and what is required in marine or terrestrial settings.
In order for fossilization to occur in the terrestrial setting, life forms do generally need to be buried quickly or they will likely be eaten and the skeleton scattered. The best fossils we have of land-. dwelling organisms are usually ones that have fallen into a stream or lake bed and quickly buried, buried in the desert, died in a location with few predators or scavengers, got stuck in a mud hole or quick sand or tar pits, or even frozen and covered by snow.
In the marine setting, organisms don't require mineralizing fluids in order to be preserved. Anything on the bottom of the ocean is simply covered eventually and it helps that sea life has a lot of hard and bony parts. Shells are particularly easy to preserve, worms are not. So we see a lot of shells, teeth, bones, coral, sponge spicules, etc., but little shark or fish bodies, worms (except for evidence of burrowing), or other soft bodied organisms. Plants can be common, too.
We can find shell material that looks like it was buried yesterday that still has its pearly irridescence. Mineralizing fluids can replace shell material, but it is not required for preservation.

This message is a reply to:
 Message 37 by Faith, posted 03-11-2006 9:41 AM Faith has not replied

  
roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 51 of 180 (294355)
03-11-2006 7:07 PM
Reply to: Message 49 by Faith
03-11-2006 4:19 PM


Faith: (And what then made it change to another kind?) And eventually you have this extremely thick stack of individual sediments all formed under water and then the ocean level lowers and we have the Southwest USA from Arizona through Utah or what?
edge: Oh, lots of things. Climate change, mountain building, sea level changes...
Faith: And these processes are supposed to account for the observed ABRUPT changes from one sediment to another just along the line somewhere in those hundreds of millions of years? Give me a break.
Faith, I've explained sea level change and how it affects sedimentation several times already... although come to think of it, that may be the ones you refused to read.
Climate controls the amount of precipitation the continents get and microclimates control precip in the mountains, deserts, and the coasts. Water is the most efficient medium for erosion, transportation, and deposition of sediment. Without rain, erosion basically stops.
Mountain building is probably the biggest contributor/source of sediment. Remember we discussed that if there were only rolling hills on the pre-flood continent, erosion would stop as soon as the shallow basins were filled? This is why. Highlands erode, valleys store (the sediment). The Appalachians are eroding today at a modest rate, but raise them 5,000 feet and erosion rates would increase many times.
Sea level changes are also important because when sea levels drop, base level drops. Base level is the lowest point to which a stream can flow and this is also generally the point where sediment is deposited by a stream, because at base level, gradients and therefore stream flow rates decline. Drops in sea level cause incision of coastal rivers, which significantly increases the rate of headward erosion - which is a bit like the stream snaking it way back up into the high country.
Imagine a stream is draining a shaley environment and empties into the ocean. The sediment it carries right now is mainly mud, clay, silt, and is likely saline. Now say it manages to work it's way backward (headward erosion) and breaks it's way into a small valley capturing another stream. This other stream drains a high elevation granitic environment. Lots of quartz, cobbles, feldspars, magnetite, etc. Once the original stream captures this other mountain stream, the sediment load changes from mud and clay to quartz and feldspar. HUGE difference in sediment type. Downstream where the sediment load is deposited into the ocean, the strata changes from muds to sand. It might be gradual or it could be sudden. And if the sand is being deposited faster than the ocean can rework it, then the sand stays and possibly grows out into the ocean - a pro-grading delta.
These sorts of processes are happening today. We see it now and we can see it in the rock record. The most important ability a geologist has, and probably the hardest for non-geologists to replicate, is the ability to visualize these 3-dimensional environments in your head. That's why I often try to paint a picture with words because geology is a visual science.
And I haven't even discussed unconformities... there are many, many reasons why sediment can change abruptly.
The presentation of the strata is of neat straight layers -- yes not PERFECTLY neat and straight for the obsessionals out there who want to derail the point by mentioning the differences in thickness and the irregularities between the layers that are only visible very close up.
It's not obsessive, Faith, to point out that your idea of what strata looks like is wrong. And a trained geo can see the changes in texture, cement, etc. from the road going 75 miles an hour. They are insignificant to you because you lack experience about what those characteristics represent. The devil is in the details.
It seems to me that half the land area now in existence must once have been at the bottom of the sea considering how much of this layering makes up its mass and how much must be explained by underwater formation. Or what is geology's estimation of this? Climate change really explains it? How much can mountain building explain?
When sea levels rise, large portions of the continents are submerged. In the Cretaceous, sea levels were significantly higher than today and temperatures as well. marine rocks were deposited atop terrestrial rocks. When the sea levels finally dropped for the last time, terrestrial sedimentation resumed and these were deposited atop the marine sediments. This also happened in Australia.
Another thing, most continents are comprised of other smaller and older microcontinents, known also as cratons (or protocratons?). North America is an aggregate of six cratons: Slave, Superior, Rae, Nain, Wyoming, and Hearne. These appear to be aggregates of even smaller and ancient cratons, usually Archean in age.
Anyway, these all came together and broke apart many times throughout the history of the earth. And in between these cratons were often sea ways or large oceanic basins. As the cratons moved together and collided, oceanic crust was crushed between them, forming mountain ranges. In North America, each craton has a mountain range between it and often contains marine strata.
The majority of North American cratons are situated in Canada, with the exception of the Wyoming craton, and it doesn't take a rocket scientist to notice there is a whole lotta land west and south of Wyoming. All this extra land is younger and accreted. Using dating methods, if we dated rocks in central Wyoming, northern Colorado, etc. all the way down to new Mexico, the ages would get progressively younger.
I can't remember, but I think most of this new terrane was in the form of volcanic island arcs, similar to Japan and Indonesia. In between these island arcs and the continents was more oceanic crust, which also was crushed and pushed up into mountains when the arcs collided with the continent.
I'm sure the three examples above are not the only way to explain continental marine strata, but it's a good start.
This message has been edited by roxrkool, 03-11-2006 07:08 PM

This message is a reply to:
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roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 81 of 180 (294490)
03-12-2006 11:59 AM
Reply to: Message 69 by Faith
03-12-2006 9:05 AM


Faith, geology is such a complex and dynamic science that it is impossible to offer explanation for such vague statements.
It would help immensely if you could offer an example of what you are referring to - a real-world example. Are you thinking about sediments in the Gulf of Mexico? Because I honestly do not know of any formation that is kilometers thick and consists of a discrete mineralogy or rock type.
The rocks deposited in the Cretaceous Seaway are possibly 10,000 feet thick (guesstimate) cumulatively, making it what... 3 kilometers or so thick. However, there are probably a good two hundred formations, members, units, etc. that make up the Seaway stratigraphy that are mostly based on rock types, such as shale, silty shale, calcareous shale, shaley limestone, limestone, calcarenite, siltstone, sandstone, chalk, marl, mudstone, etc., ad nauseum.

This message is a reply to:
 Message 69 by Faith, posted 03-12-2006 9:05 AM Faith has replied

Replies to this message:
 Message 86 by Faith, posted 03-12-2006 4:37 PM roxrkool has replied

  
roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 97 of 180 (294656)
03-12-2006 8:10 PM
Reply to: Message 86 by Faith
03-12-2006 4:37 PM


I think there may have been a miscommunication here. Strata several kilometers thick is not a problem, especially adjacent to a young and high mountain range.
Five kilometers of pure sandstone, or pure limestone, or pure shale, etc. is less likely, however. That's why I'm trying to clarify what exactly you think edge is stating, because reading back through the posts, I don't see him suggesting such a thing.
The strata in the Grand Canyon area are not pure though. Yes, they are a thick package, but you still see marine and terrestrial strata fluctuating between each other, gradational contacts, unconformities, angular unconformities.
In addition, are you also wondering about the lateral extent of formations? Marine formations can be quite extensive, but so can some terrestrial settings, such as deserts.

This message is a reply to:
 Message 86 by Faith, posted 03-12-2006 4:37 PM Faith has replied

Replies to this message:
 Message 98 by Faith, posted 03-12-2006 8:31 PM roxrkool has replied
 Message 103 by edge, posted 03-12-2006 10:59 PM roxrkool has not replied

  
roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 99 of 180 (294681)
03-12-2006 8:57 PM
Reply to: Message 90 by Faith
03-12-2006 5:27 PM


Re: Many mountains are much more of a mess, than just being a pile of horizontal stra
Faith writes:
With a whole mountain chain I suppose you could get sediment kilometers thick, but I still have my questions. Would you get just one kind of sediment topped by another kind of sediment -- like those seen in the Southwest, say, etc?
I've been told that mountainbuilding is one of the ways we get the sediments that form the strata. I don't see how you get one and only one kind of sediment out of a mountain for starters, or how you get many different kinds stacked on top of each other.
It depends entirely on what the mountains are composed of, what is being exposed, and the rate of uplift. Mountains can be composed of ancient marine rocks, terrestrial sediment, and cored by igneous and/or metamorphic rocks. In addition, rocks are all affected differently by weathering and erosion.
So if some mountain is composed entirely of granite, then the stuff (grains, cobbles, boulders, etc.) coming off of it is going to be composed of quartz, feldspar, biotite, magnetite, etc.
But if the mountain is basalt on top, marine rocks underneath, and metamorphic rocks inside, then you can have a variable combination of sediment coming off the mountain range. The stuff up top will weather and erode first, followed by the stuff underneath. If they are different, they will result in different sediment.
The resulting seds can be picked up, sorted, and transported by fluvial systems. Transport causes cobbles and boulders and even individual minerals to break down and become round.
Of course it's much more complex than the above. That's why it's very difficult to answer general questions about geology. The answer to the questions depends on the geology.

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 Message 90 by Faith, posted 03-12-2006 5:27 PM Faith has not replied

  
roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 100 of 180 (294692)
03-12-2006 9:10 PM
Reply to: Message 98 by Faith
03-12-2006 8:31 PM


Yeah, I think there is a miscommunication in there.
Right now I am in the process of logging core that contains many layers of bentonite, which is altered volcanic ash. Using radiometric dating, I can choose two bentonite layers above and below a 10 foot package of shale, and date the bentonites.
If the difference in the dates is 1 million years, then we can get an average depositional rate for that 10' of shale. However, it's not that easy, we much make several assumptions, such as how much compaction has occurred, so it's not perfect. But what is useful about these averaged rates is that it tells us how average depositional rates have changed over time and then attempt to see if the rocks and/or fossils point to such a conclusion. If they do, then we can wonder about climatic conditions or other things. If not, then we have to wonder why, maybe unconformities. We keep looking, though, for explanations.

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 Message 98 by Faith, posted 03-12-2006 8:31 PM Faith has not replied

  
roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 101 of 180 (294696)
03-12-2006 9:13 PM
Reply to: Message 96 by Faith
03-12-2006 7:29 PM


Re: Many mountains are much more of a mess, than just being a pile of horizontal stra
I don't understand your first question. Could you elaborate?
There are places around the world where you can drill 2000 feet and hit nothing but volcanic and intrusive rock, so in those areas, yes, the geologic record/column is composed entirely of igneous rock and completely barren of other sediment.

This message is a reply to:
 Message 96 by Faith, posted 03-12-2006 7:29 PM Faith has not replied

Replies to this message:
 Message 106 by Silent H, posted 03-13-2006 4:24 AM roxrkool has replied

  
roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 114 of 180 (294878)
03-13-2006 11:05 AM
Reply to: Message 106 by Silent H
03-13-2006 4:24 AM


Re: Many mountains are much more of a mess, than just being a pile of horizontal stra
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.

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roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 138 of 180 (295144)
03-14-2006 9:19 AM
Reply to: Message 126 by Faith
03-13-2006 11:43 PM


Re: That Grand Canyon diagram
Faith writes:
It appears that all over the southwest the strata built up layer by layer and then after the entire stack was in place magma pushed up from below which opened the cracks that became the canyons,
No. Magma, if you are referring to the Zoroaster Granite, did not intrude the Vishnu Schist after the entire package of rocks at the Grand Canyon was deposited and in place.
The evidence is very clear that the granite does not ever intrude any sediments overlying the Vishnu. The granite intruded after the Vishnu protosediments were metamorphosed, but before the Grand Canyon Supergroup was deposited atop it. After the Supergroup was depostited, faulting occurred which preserved portions of the Supergroup prior to Cambrian deposition. Incision by the Colorado River was one of the last processes in the Grand Canyon.
and draining waters washed across the stack and eroded huge quantities of it away, leaving the Grand Staircase, leaving the Grand Canyon, and all the other odd formations of the southwest, the various pillars and so on that are everywhere. In other words massive erosion happened to the whole area at once after the whole stack was laid down.
I'd say this is a seriously premature conclusion seeing as the last time we discussed the nature of the pre-flood world, you claimed there were only rolling hills. You conceded this was problematic for sourcing the massive amounts of sediment required to populate the entire geologic column- several thousand feet thick.

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roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 151 of 180 (295193)
03-14-2006 11:00 AM
Reply to: Message 143 by Silent H
03-14-2006 10:03 AM


Re: That Grand Canyon diagram
Stylolites are dissolution surfaces that form sometime between sedimentation and post-lithification. The formation of stylolites is still highly debated as far as I know, but can be considered a form of 'internal erosion,' I think.

This message is a reply to:
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roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 153 of 180 (295203)
03-14-2006 11:32 AM
Reply to: Message 141 by Faith
03-14-2006 9:55 AM


Re: That Grand Canyon diagram
NONE of the layers look like they "blend gradually" and certainly not gradually enough to justify the millions of years allotted to the process.
This is a silly thing for you to say, Faith. Unless you have read the pertinent geologic literature that specifically discusses the contacts between each formation in the Grand Canyon, you cannot make these sorts of statements.
According to Berthault (a creationist), the Tapeats Sandstone and the Bright Angel Shale (of the Cambrian Tonto Group) have a gradational contact.
In addition, the name, Bright Angel SHALE, is a bit of a misnomer as according to this paper (page 642) this formation is "primarily interstratified, subfeldspathic to quartzose sandstone beds and green papery to fissile mudshale." And on page 643 of the same paper is a strat column of the Bright Angel Shale that shows only about 50% of the unit actually IS shale. Again, the devil is in the details.
If you read other similar type of detailed geologic papers concerning Grand Canyon units, you will see these two units are not the exceptions.
I will again remind you that you are looking at a generalized cross-section of the Grand Canyon strata. It doesn't matter how pretty the picture is or how well it's drawn, it is still just a diagram. The only things depicted on it are large scale items such at the formations, formational contacts (NOT indicating sharp or gradational contacts), structure (faults), and intrusions. That's it.
This message has been edited by roxrkool, 03-14-2006 11:42 AM

This message is a reply to:
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roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 172 of 180 (296591)
03-19-2006 12:14 PM
Reply to: Message 169 by lfen
03-19-2006 2:40 AM


I've mentioned this before, but the degree of fossilization required for 'preservation' is different between terrestrial and marine settings - and I'm assuming the foot sedimentation/year was in the marine setting.
In terrestrial settings, special circumstances greatly improve the chances of preservation for a land organism. However, in the marine setting, there is a constant rain of sediment onto the ocean floor, many of the marine organisms have hard shelly parts that do not decompose or disintegrate except under certain conditions. Of course it doesn't hurt for marine fossils to become replaced by sulfide or another mineral, but that is not as necessary for marine fossils as it is for terrestrial fossils.
In some rocks, bivalves can look as fresh as those you find on the beaches today, so for Faith to use the argument that such slow rates of sedimentation will not preserve marine fossils is meaningless.
In addition, I'm not sure if Faith has any idea of how fossils appear in marine rocks. How many fossils does she thing we find? Some rocks are highly fossiliferous, but many others are basically fossil-poor, but go to a beach and you can find places where empty shells accumulate because of waves. There are some formations that always seem to contain a lot of fossils over large aerial extent, while others are virtually fossil-free.
Another thing Faith does not understand is that the rocks are a highly compacted representation of the original sediments. I can't remember what the average percentage of compaction is for marine rocks, but I would guess somewhere upwards of 75%. So if the original sediments were 100 feet thick with fossils scattered throughout, compaction would result in a 25 foot thick assemblage. This process will break up the fossils, flatten them, and concentrated them - making them appear very close together when originally they were not.
This message has been edited by roxrkool, 03-19-2006 12:17 PM

This message is a reply to:
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