Questions for Uniformitarianists

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Questions for Uniformitarianists

Post #1

Post by otseng »

Uniformitarianism is one of the most important unifying concepts in the geosciences. This concept developed in the late 1700s, suggests that catastrophic processes were not responsible for the landforms that existed on the Earth's surface. This idea was diametrically opposed to the ideas of that time period which were based on a biblical interpretation of the history of the Earth. Instead, the theory of uniformitarianism suggested that the landscape developed over long periods of time through a variety of slow geologic and geomorphic processes.

The term uniformitarianism was first used in 1832 by William Whewell, a University of Cambridge scholar, to present an alternative explanation for the origin of the Earth. The prevailing view at that time was that the Earth was created through supernatural means and had been affected by a series of catastrophic events such as the biblical Flood. This theory is called catastrophism.

Source: PhysicalGeography.net

Uniformitarianism is a geological doctrine. It states that current geologic processes, occurring at the same rates observed today, in the same manner, account for all of Earth's geological features. Thus, it assumes that geological processes are essentially unchanged today from those of the unobservable past, and that there have been no cataclysmic events in earth's history. As present processes are thought to explain all past events, the Uniformitarian slogan is, "the present is the key to the past."

Source: Uniformitarianism.net

Some questions for uniformitarianists:
Why are there distinct lines between the sedimentary layers?
Why are they parallel to each other?
How did the stratas get formed?
Where did all the material come from to form the stratas?
Where do we see evidence of stratas being formed now?
Why do the majority of faults split through multiple layers?
Why do sedimentary stratas generally start in the Cambrian layer? Why are there none before that?
Do sedimentary layers exist older than 500 MYA?
Why are there little to none sedimentary stratas on top of shields (exposed cratons)?
Why are there relatively little sediments on the ocean floors near the ridges?
Why are there gaps in time in the stratas?
If those layers got eroded away, how did it happen?

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Post #31

Post by Nyril »

If the metamorphic rock was once sedimentary, what exactly caused the transformation? How exactly does time and pressure cause sedimentary rock to become metamorphic rock? If one uses the general explanation of time, pressure (and heat) to form metamorphic rock, how does that cause sedimentary layers to become a rock with no evidence of any layers in the metamorphic rock?
Pretend you have an ice cube made by freezing a dozen different colors of water in sequence (freeze one layer, add liquid, freeze the next layer, etc...). Take that ice cube, and add heat to it. Pretty soon you won't have a nicely stratified ice cube anymore, you'll get liquid and then vapor.

Take that liquid or vapor and then add pressure, with enough you should be able to easily convert the liquid back into a solid, except you didn't get your layers back.

The same thing happens with rocks, except on a different scale. When you pack tons upon tons of sand together, pressure and heat will transform it into quartz. When you press other rocks and such, you get gneiss. Compress sandstone enough you get shale, compress and heat that to get marble.

There's nothing special about rocks that makes them behave in a means other then our special little ice cube there, we just get things other then ice when we're doing putting them back together.

As for the reason it doesn't turn back into sand when you pull the pressure off it, does your bread turn back into dough when it's cooled from the oven? Does your cake revert to an interesting mixture of eggs and flour? Can you perhaps take a clay jar you've put into a kilm and cool it to retrieve your mud?
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Post #32

Post by otseng »

Nyril wrote:
If the metamorphic rock was once sedimentary, what exactly caused the transformation? How exactly does time and pressure cause sedimentary rock to become metamorphic rock? If one uses the general explanation of time, pressure (and heat) to form metamorphic rock, how does that cause sedimentary layers to become a rock with no evidence of any layers in the metamorphic rock?


Pretend you have an ice cube made by freezing a dozen different colors of water in sequence (freeze one layer, add liquid, freeze the next layer, etc...). Take that ice cube, and add heat to it. Pretty soon you won't have a nicely stratified ice cube anymore, you'll get liquid and then vapor.

Take that liquid or vapor and then add pressure, with enough you should be able to easily convert the liquid back into a solid, except you didn't get your layers back.

The same thing happens with rocks, except on a different scale. When you pack tons upon tons of sand together, pressure and heat will transform it into quartz. When you press other rocks and such, you get gneiss. Compress sandstone enough you get shale, compress and heat that to get marble.

For metamorphic rocks, this does not apply. Creation of metamorphic rock is a "solid state" process.

A "solid-state" process is one which occurs in a material while it
remains a solid. For this reason, a rock-altering process can only be
classified as a metamorphic process if the rock remains in the solid
state.
Scott J. Badham - Department of Geology and Geophysics, University of Wyoming

The term metamorphic is derived from the Latin term meaning, "change of form". These rocks have been altered while in their solid state as a response to the environment. Extreme circumstances of pressure and temperature, or an introduction of certain chemicals, can cause the existing rocks minerals to recrystallize, and they may even become different minerals all together. It is important that you realize that the rock remains in its solid state.
RockDoctor

Therefore, it has yet to be explained why metamorphic rock does not contain layers if it originated from sedimentary rock.

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Post #33

Post by John S »

otseng wrote:My point is not that it has to cut through the Cambrian layer per se. That strata might not even exist in that locality. My point is that we should see an abundance of faults where at one strata on down, there is evidence of a fault. But at that point on up, there should be no evidence of a fault. If U15m is true, this should be abundant in the rock record.
This is what is seen in the rock record. I mentioned several different orogenies (mountain building events). I’ll use two of them, the Late Precambrian Grenville orogeny and the Early Paleozoic Antler orogeny as examples.

Grenville Orogeny

Someone at the University of Western Ontario maintains a website with a glut of information about the Grenville Orogeny. They scanned a geologic map of the Grenville in part of eastern North America that can be found here:

http://instruct.uwo.ca/earth-sci/300b-0 ... ap1800.jpg

All of the features on that map that have labels that end in “SZ” are shear zones (the key for the shear zones is at the bottom right of the image). You can see that none of these shear zones cut the overlying Paleozoic cover (the blue formation). This means that all of those shear zones became inactive before the Paleozoic cover was deposited, and so are pre-Paleozoic (Precambrian in other words) in age.

Antler Orogeny

I tried to find detailed geologic maps of rocks deformed during the Antler Orogeny that are available online, but I didn’t have much luck. I’ve found a generalized geologic map here:

http://www.nsm.buffalo.edu/courses/gly4 ... ntler2.pdf

Go to page 2 of the document. The left column is titled “Roberts Mountain (sic) Allochthon” There’s a linear feature on the map that’s labeled RMT, which stands for Roberts Mountains Thrust, one of the major faults that formed during the Antler Orogeny. You can get a rough idea about the age of that fault from this map. If you follow it north just about to the border of Nevada and Idaho you’ll see that the fault is truncated by a features labeled “Cenozoic cover.” Since the fault doesn’t offset this formation those rocks were deposited after the fault became inactive, and therefore the fault is pre-Cenozoic.

If you follow the fault to the south you’ll see that it’s truncated by a group of rocks labeled “Mesozoic plutons.” Since these rocks aren’t cut by the fault the Roberts Mountains thrust is pre-Mesozoic.

This isn’t shown on the map since it’s too generalized, but the fault cuts Early Paleozoic rocks, and so it’s older than that times. By looking at the age of the oldest formation that is not offset by the fault, as well as the age of sediments eroded from the fault when it was active, the Roberts Mountains thrust became inactive in Early Mississippian time.

Papers that discuss the timing of the Antler Orogeny:

There’s not much in the abstract of the first paper, but they have a section of their paper titled “General geology of the Antler orogen” that’s useful.

Burchfiel, B. C., and Royden, L. H. 1991. Antler Orogeny – A Mediterranean-type orogeny. Geology 19, 66-69.
Abstract: http://www.gsajournals.org/gsaonline/?r ... 2.3.CO%3B2


Johnson, J. G., and Pendergast, A., 1981. Timing and mode of emplacement of the Roberts Mountains allochthon, Antler Orogeny. Geological Society of America Bulletin 92, 648-658.
Abstract: http://www.gsajournals.org/gsaonline/?r ... 2.0.CO%3B2

otseng wrote: From the wikipedia, "The sedimentary rock cover of the continents of the Earth's crust is extensive, but the total contribution of sedimentary rocks is estimated to be only five percent of the total. As such, the sedimentary sequences we see represent only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks." From this, 95% of the rock total is not sedimentary rock. And practically all of it is a "thin veneer" on the surface. Sure, some sedimentary layers can be found below the Cambrian layer, but it is the exception. So, the question is, why only a "thin veneer"?
You’re making a couple of tenuous leaps here. The first is that you’re using the observation that sedimentary rocks make up a small part of the crust to infer that Precambrian sedimentary rocks are uncommon. That’s not justified in general, and it’s not justified from your link – I couldn’t find anything about Precambrian rocks at all on that page. Second I’ve shown you that Precambrian sedimentary rocks are really common –in North America alone I’ve given you information about many series of Precambrian sedimentary rock that are thousands of feet thick. You’ll find the same thing on other continents.

The second leap has to do with what a thin veneer of sedimentary rock on the crust means. The average thickness of continental crust is ~ 40 km. Five percent of that thickness is 2 km, or almost 6,600 ft. From a crustal point of view that’s pretty thin, but from a human point of view that’s pretty thick. When you look at the planet as a whole, which has a radius of almost 6,400 km, the entire crust (all tens of thousands of feet of it) is just a very thin veneer.

The 2 km/6,600 ft thickness I calculated above doesn’t have much meaning – sedimentary rocks aren’t spread evenly across the surface of the earth; there are places where they’re much thicker than that, and there are places where there aren’t any at all. The deepest sedimentary basin in North America, the Anadarko Basin, is ~ 12 km deep. At the depth the temperature will be ~300 degrees C (assuming a geothermal gradient of 25 deg C/km) and the pressure will be ~320 Mega Pascals (almost 3200 atmospheres) (assuming a bulk density of 2700 kg/m^3). That sort of pressure and temperature is already enough to lightly metamorphose the rocks, and the deeper you go the hotter the temperature and the greater the pressure, and so the greater the degree of metamorphism. You can’t have a sedimentary sequence as thick as the entire crust because the pressure and temperature deep in the crust will cause metamorphism.
otseng wrote: If the metamorphic rock was once sedimentary, what exactly caused the transformation? How exactly does time and pressure cause sedimentary rock to become metamorphic rock? If one uses the general explanation of time, pressure (and heat) to form metamorphic rock, how does that cause sedimentary layers to become a rock with no evidence of any layers in the metamorphic rock?
Take a look at the figure labeled “Metamorphic Facies” at this website:
http://www.tulane.edu/~sanelson/eens211 ... facies.htm

The temperatures and pressures involved in metamorphism are extreme. The temperature and pressure in the deep sedimentary basin that I mentioned above are in a facies at the very low end of the scale (the upper left corner of the graph).

From your reply to Nyril I get the impression that you think that because metamorphism is a solid state processes (any rock that melts moves into the igneous realm) that the original features of the sedimentary rock (bedding) should be preserved. This isn’t the case – metamorphism isn’t a static processes, the heat and pressure induce changes in both the composition of the rock (new minerals grow as old minerals disappear) and that changes the fabric of the rock. One of the websites you linked to discusses this.

From the first site you linked to, including the sentence you quoted and the following two sentences:
A "solid-state" process is one which occurs in a material while it remains a solid. For this reason, a rock-altering process can only be classified as a metamorphic process if the rock remains in the solid state. Having seen gneisses, it may be difficult for you to believe that mineral grains could migrate and/or recrystallize to form the compositional banding that is characteristic of gneisses without the rock having become a liquid. However, experiment and observation have shown us that rock material can become very mobile, even in the solid-state, when exerted to such extreme conditions.
http://www.newton.dep.anl.gov/askasci/env99/env271.htm

So the short answer to “What happens to sedimentary bedding during metamorphism” is that it is destroyed by the recrystallization that accompanies metamorphism. In some low grade metamorphic rocks you can see both bedding and the rock fabric called foliation that forms in response to metamorphism. This picture is a great example of that:

http://home.moravian.edu/users/phys/mej ... otated.jpg

Bedding is dipping to the left of the photograph, and the metamorphic foliation is traced in red. As metamorphism increases more and more of the rock is recrystallized and the metamorphism foliation becomes more pronounced as the bedding is obliterated. The slate that was shown in the image above will become a schist (http://www.gc.maricopa.edu/earthsci/ima ... schist.htm ) which will become a gneiss (http://www.gc.maricopa.edu/earthsci/ima ... gneiss.htm ). Solid state doesn’t mean static.

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Post #34

Post by John S »

Nyril wrote:The same thing happens with rocks, except on a different scale. When you pack tons upon tons of sand together, pressure and heat will transform it into quartz. When you press other rocks and such, you get gneiss. Compress sandstone enough you get shale, compress and heat that to get marble.
Hi Nyril,

I think you've got the gist of metamorphism, but you're wrong in some of the particulars. Sand is largely composed of quartz to begin with (most of the picturesque beach sands are almost entirely quartz). You'll never form a shale from a sandstone, shale is another type of sedimentary rock (composed largely of clay). You won't form a marble from either a sand or a shale. Marble is composed largely of calcite (CaC03), and forms when carbonates like limestone or dolostone are metamorphosed.

A rule of thumb is quartzite forms when sandstone is metamorphosed; slate (or schist or gneiss if pressure and temperature are great enough) form when shale is metamorphosed; marble forms when carbonates are metamorphosed.

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Post #35

Post by Jose »

otseng wrote:Therefore, it has yet to be explained why metamorphic rock does not contain layers if it originated from sedimentary rock.
As John has pointed out, there is often enough heat to "blur" the outlines, if you will. If you melt the rock entirely, then re-freeze it, you'll lose the striations. But this isn't true of all metamorphic rock, or all Precambrian metamorphic rock. Take a peek at my photograph of the Vishnu Schist in the Grand Canyon thread. The Vishnu Schist, taken as the classic example of pre-flood rock in Flood Geology models,is striated. It contains layers, albeit rotated almost 90 degrees by earth movements. It is metamorphosed sedimentary rock, neither amorphous granite (which is amorphous even in its youngest form), nor gneiss (metamorphosed granite), but sedimentary rock.

Indeed, not all metamorphosed rock is ancient or amorphous. Make a study of marble (metamorphosed limestone) as you see it in public buildings, banks, and tile/carpet stores. A lot of it contains fossils. If the flood formed the fossils, then something else came along later and metamorphosed the limestone and its fossils into marble. Normal geology explains this as the result high pressure and temperature as the sediments are buried, and forced deeper and deeper.

Why aren't these deposits still buried deeply? To quote John McPhee, "the top of Mt. Everest is marine limestone." If you shove India under Asia, a few centimeters a year, you lift up the southern edge of Asia. Eventually, this forms the Himalayas, even if the rock of which they are made was originally below sea level.
otseng wrote: If the metamorphic rock was once sedimentary, what exactly caused the transformation? How exactly does time and pressure cause sedimentary rock to become metamorphic rock? If one uses the general explanation of time, pressure (and heat) to form metamorphic rock, how does that cause sedimentary layers to become a rock with no evidence of any layers in the metamorphic rock?
John has addressed this better than I can, but I will offer a delightul example of metamorphism. It's a bit out of the way, but Mt. Ellen in southern Utah shows some very nice things. (You'll need 4WD with compound low, if only because the road down is steep enough that without the compound low, you burn up your brakes.)

Mt. Ellen, like all of the peaks in the Henry Mountains, is an un-erupted volcano--a "granitic intrusion" that pushed up into the overlying sedimentary rock, but never broke the surface. Subsequent weathering has revealed a variety of geological features, from the granitic core to the sedimentary layers that the core pushed into. At some distance from the mountain, the strata are primarily horizontal. As you start to climb the mountain, you see the strata are at a slight angle. As you go higher, the strata are at a steeper angle. As you near the peak, and come closer to the granitic core, you find that the shale metamorphoses to slate, and the limestone to marble.

Not only is this a great example of the ability of slow, steady pressure to bend the strata (they don't fold and pop like YEC has said it is "obvious" they would do). It is also a wonderful example of heat metamorphosing rock. You can walk along it, and there it is.

There are also a couple of good volcanic necks outside of Grants, NM, that have been sliced by erosion of canyons, to produce cross-sections that you can see as you drive along on Interstate 40. There's the vertical basaltic neck itself, and to the right and left, visible gradations of the rock through which the basalt flowed upward. Near the neck, it is metamorphosed from the heat. Far from the neck, it is un-metamorphosed.
John S wrote: I think it’s a mistake to use local surface exposures (even very impressive ones like the Grand Canyon) to make generalizations about the entire rock record.
This is probably one of the most profound statements in this thread. Thanks, John. It gets at some of the questions I posed in The Flood as Science, in which we ask just what the flood model predicts. While it may be possible to develop an idea based on one locale (say, the Grand Canyon), that idea is not supported by examination of other locales. Yet, the one-locale explanation is quite common in this debate.

My guess is that there is a difference in what different people consider "scientific" to be. To many, an explanation is "scientific" if it explains the specific phenomenon in question. That's enough to meet the criterion of "science." This is consistent with the Grand Canyon flood geology story, the polonium halo story, etc. What is missing is what other people include in "scientific" explanations: consistency with other observations from other places, and the ruling out of other alternative explanations.

One of the things that hasn't been discussed broadly is eolian deposits. I'd chosen the Chinle sandstone, which one can (or could) hike through when visiting White House Ruins. The Navajo is also good. With you link to modern eolian deposits at White Sands, showing how natural processes we can study today create this kind of sediment, I can't think of a way to wiggle out of the conclusion that these types of sandstone are, indeed, petrified dunes.

And--the petrified dunes are both overlain and underlain by shales and limestones! This seems like pretty clear evidence that there had to be at least three time periods that must be accounted for by any flood model: the first batch of sedimentation in the flood, then a waterless period in which great dunes could form, and then another period of underwater sedimentation.

This is very much like the finding of forest above forest above forest in coal mines. If the ancient forest was killed by the flood, which forest was it, and what killed and covered the others? There must have been many floods, not just one--and probably local ones, at that, because that's what happens on earth extremely commonly.

Having said all of this, I will recall a bit of otseng's original post at the beginning of the thread, and comment on "uniformitarianism." This term does not mean that everything happens at a specific, linear rate, fully uniformly. It means that what happened long ago was pretty much what happens now. The term was invented to be a contrast to a giant catastrophe like a world-wide flood. At the time the term was invented, geologists knew about erosion, and sediment formation, etc, so it was easy to imagine that these were reasonably uniform processes. It doesn't take much brainpower to add to the idea of "normal processes," and include volcanic eruptions that bury everything nearby in ash (a catastrophe, all right, and certainly not "uniform," but still a "normal process"). It is easy to add local floods, mudslides, collapse of cliffs, wind-blown sand, or even meteor impacts. There's a lot of stuff that happens that is not uniform over the whole world, or uniform in time. "Uniformitarianism" doesn't really make sense any more (and has, therefore, largely been abandoned, in the same way as "gradualism" in reference to evolution).
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Post #36

Post by otseng »

John S wrote:I mentioned several different orogenies (mountain building events).
I will defer on detailed comments on orogenies until I start a thread on plate tectonics.
otseng wrote:Sure, some sedimentary layers can be found below the Cambrian layer, but it is the exception. So, the question is, why only a "thin veneer"?
You’re making a couple of tenuous leaps here. The first is that you’re using the observation that sedimentary rocks make up a small part of the crust to infer that Precambrian sedimentary rocks are uncommon.
Again, I grant that Precambrian sedimentary layers exist. I am not disputing that. But, I am asking, why don't we see a lot of it? Certainly erosion must've happened millions of years ago.

The oldest known rocks is estimated at 4100 MYA. The Cambrian is estimated at 488 MYA. Should we not see lots of evidence of erosion (sedimentary rocks) between this timeframe? Why should there be a distinction before or after the Cambrian layer on how much sedimentary layers should exist? What is so special about the Cambrian layer? And if they turned into metamorphic rock, why shouldn't there at least be evidence of layering? (I know you addressed this prior, but I'll touch on this below)

Also, there are many references to the fact that Precambrian rocks are composed primarily of non-sedimentary rocks:

"The rocks of this region (Precambrian), and of the Early Precambrian as a whole, are generally granite , schist , or gneiss."
http://www.encyclopedia.com/html/P/Precambr.asp

"The Precambrian Shield forms the core of Canada and is composed of old, massive crystalline rocks"
http://www.lights.com/waterways/geology/article.htm

"The PreCambrian basement rocks consist mainly of quartzite, schist, gneiss and granite which are overlain by about 500 ft of Cambro-Ordovician sediments."
http://www.geoscience.co.uk/geofrc/geobasenamerica.html

"Although over 4000 exploratory wells have penetrated the Precambrian in Western Canada, the bulk of the geological information on the basement has been derived from the 400 wells cored.
...
High grade metamorphic and/or deep-seated igneous rocks are dominant in all areas."
http://www.ags.gov.ab.ca/publications/A ... 05_F.shtml
From your reply to Nyril I get the impression that you think that because metamorphism is a solid state processes (any rock that melts moves into the igneous realm) that the original features of the sedimentary rock (bedding) should be preserved. This isn’t the case – metamorphism isn’t a static processes, the heat and pressure induce changes in both the composition of the rock (new minerals grow as old minerals disappear) and that changes the fabric of the rock.
However, chemical composition does not change during metamorphism (except where there is water present). If sedimentary stratas are different chemically from one layer to the next, then the metamorphisized rock should retain the original chemical composition. This should be evident in the metamorphic rock record if it originated from sedimentary rock. One would guess that this should produce visible layering in metamorphic rock, even if crystalline structures were different.

I certainly do not understand this statement, "However, experiment and observation have shown us that rock material can become very mobile, even in the solid-state, when exerted to such extreme conditions." What exactly does it mean that some solid is "very mobile"? And even if it was "very mobile", its mobility would not alter its chemical composition.

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Post #37

Post by otseng »

Jose wrote:As John has pointed out, there is often enough heat to "blur" the outlines, if you will.
Then what we should see are blurred outlines.
To quote John McPhee, "the top of Mt. Everest is marine limestone." If you shove India under Asia, a few centimeters a year, you lift up the southern edge of Asia. Eventually, this forms the Himalayas, even if the rock of which they are made was originally below sea level.
I'm so tempted to start that thread on plate tectonics, but I feel too stretched thin already.
Having said all of this, I will recall a bit of otseng's original post at the beginning of the thread, and comment on "uniformitarianism." This term does not mean that everything happens at a specific, linear rate, fully uniformly. It means that what happened long ago was pretty much what happens now. The term was invented to be a contrast to a giant catastrophe like a world-wide flood.
And this is how I am using Uniformatarianism, as a contrast to the global flood. If there is a better term to use for the discussions here, I am willing to use that term instead.

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Post #38

Post by John S »

otseng wrote: I will defer on detailed comments on orogenies until I start a thread on plate tectonics.
Sounds good to me. I can certainly appreciate you feeling stretched too thin, and I definitely prefer taking enough time to discuss a topic thouroughly instead of just blasting through.
otseng wrote: Again, I grant that Precambrian sedimentary layers exist. I am not disputing that. But, I am asking, why don't we see a lot of it? Certainly erosion must've happened millions of years ago.

The oldest known rocks is estimated at 4100 MYA. The Cambrian is estimated at 488 MYA. Should we not see lots of evidence of erosion (sedimentary rocks) between this timeframe? Why should there be a distinction before or after the Cambrian layer on how much sedimentary layers should exist? What is so special about the Cambrian layer? And if they turned into metamorphic rock, why shouldn't there at least be evidence of layering? (I know you addressed this prior, but I'll touch on this below)
I'm going to start off being with a little nit pick - the beginning of the Cambrian was ~ 540 Ma. If you want an up to date geologic time scale you can find one from the Geological Society of America here: http://www.geosociety.org/science/timescale/timescl.htm

Now moving on to more substantial topics. There isn't a pronounced change in the nature of sedimentary rock at the Precambrian/Cambrian boundary, that boundary doesn't mark anything special in terms of sedimentation. I'm not sure what else I can provide in terms of data - I've already talked about sequences of sedimentary rock tens of thousands of feet thick in the Precambrian. Clearly though, I haven't adequately answered your question or you wouldn't have to repeat it. Let me try this:

You want the Precambrian/Cambrian boundary to coincide with the beginning of the Flood. That can't be the case because nothing special happens in terms of the nature of sedimentation across that boundary: In terms of layering, etc. the thick sequences of Precambrian sedimentary rock I've described look just like post-Cambrian rock (the fossils are different, sure, but that's not what we're talking about). If you're arguing that the layering that's observed in post-Cambrian (can I just call it Phanerozoic?) rock is diagnositc of the Flood, I really don't see how you can support that claim - there's the same sort of layering in rocks that were deposited before that time, and there's the same sort of layering in really young rocks (which I'm assuming you'd classify as post-Flood). Given that, I don't see how you can conclude that sedimentary layering has anything at all to do with the Flood. At best, I think you could try to push the boundary of the Flood back into the Precambrian (assuming that the onset of the Flood marks the first appearance of layered sedimentary rock in the geologic record). But then you'd still have to explain post-Flood sedimentary rocks.

I think some of the problem may lie in not realizing just how long a span of time the Precambrian represents - the Precambrian extends from 4.6 billion to 540 million years ago, which is ~4,100 million years, compared with post-Cambrian (Phanerozoic) time, which is 540 million years. In other words, Phanerozoic time represents ~11% of Earth's history. Even if you don't accept radiometric dating (yet another topic), you've got to recognize that Precambrian rocks record a geologic history that's just as significant and varied as post-Precambrian rocks. Trying to lump them into a single rock type won't work.
otseng wrote: Also, there are many references to the fact that Precambrian rocks are composed primarily of non-sedimentary rocks:
The presence (or even dominace) of metamorphic rock in the Precambrian doesn't help your case. The older a rock, the greater the chance that something (i.e., metamorphism) happened to it, so it shouldn't be unexpected that the oldest rocks on Earth are metamorphic (although as Jose pointed out, not all metamorphic rocks are Precambrian). So sure, as you go further back in Earth's history to ratio of metamorphic to non-metamorphic rock increases. Sure early Precambrian times (like Archean) have proportionally more metamorphic rock than late Precambrian rocks, but that doesn't help your case. You're arguing that layered sedimentary rocks are unique to rocks depostited post-Cambrian, and that's not the case. Again, if layered sedimentary rocks occur before, during, and after what you'd call the Flood then why would you infer that layering has anything at all to do with the Flood?

The links you provided also refer to schists and gneisses, most of which have a chemical signature (i.e., aluminous phases) indicating that they originated from sedimentary rocks like shales. So that doesn't help your case - in old Precambrian rocks metamorphic rocks may be more common than sedimentary, but a lot of those metamorphic rocks still preserve a record of their sedimentary origin (see below).
However, chemical composition does not change during metamorphism (except where there is water present). If sedimentary stratas are different chemically from one layer to the next, then the metamorphisized rock should retain the original chemical composition. This should be evident in the metamorphic rock record if it originated from sedimentary rock. One would guess that this should produce visible layering in metamorphic rock, even if crystalline structures were different.

I certainly do not understand this statement, "However, experiment and observation have shown us that rock material can become very mobile, even in the solid-state, when exerted to such extreme conditions." What exactly does it mean that some solid is "very mobile"? And even if it was "very mobile", its mobility would not alter its chemical composition.
A couple of issues here - the process of metamorphism does produce "layering" - this was illustrated by the photo that I linked to showing both bedding and metamorphic foliation. That layering doesn't have anything to do with sedimentary bedding. So, I guess the next question is how does this foliation form? Here's the answer:

Let's assume that chemical composition does remain constant during metamorphism (which is neither likely nor relevant). Let's start with a shale and metamorphose it into a slate. A shale is composed dominatly of clay minerals (illite, smectite, kaolinite, etc.), with a bit of quartz and feldspars. When you start to metamorphose that shale (subject it to increased heat and pressure in other words), those phases aren't stable (they're stable at low temperatures like those that occur in rocks in sedimentary basins), and they're going to transform into new phases that are stable at higher temperature and pressure, like micas. In other words the elements that are arranged into clays in the shale are rearranged into micas in the slate. The micas don't grow parallel to bedding, their growth is controlled by the stresses that exist during metamorphism (they grow so that they're oriented perpendicular to the maximum principal stress, which in this case is equivalent to the maximum compressive stress). You can see this in the picture I linked to - the metamorphism-related micas, which control the foliation (traced in red) in that picture, aren't oriented at all like bedding. So as that shale is subjected to greater degrees of metamorphism more and more of the clay minerals are transformed into micas, and the original bedding becomes less and less visible as the metamorphic foliation grows and become more and more pronounced. By the time you metamorphose a rock enough to move from a slate to a schist there's not much of the original sedimentary character of the rock left - almost all of the original minerals have been recrystallized by the metamorphism. By the time you get to a gneiss, none of the original sedimentary bedding is preserved - the only thing that's preserved is the chemical composition, which indicates that the rock was once sedimentary (this isn't true of all gneisses, but the details of metamorphism are beyond the scope of this discussion). If the rock is furter metamorphosed into a gneiss, the pressure adn temperature are so great that micas aren't stable, so the elements in micas rearrange themselves into new stable phases. Gneisses have a very strong metamorphic foliation - that's what the light and dark color bands that are characteristic of gneiss are. The elements don't necessarily leave the system, but they do rearrange themselves into minerals that are stable at the pressures and temperatures they're subjected to.

Metamorphism is also associated with deformation (folding, faulting, etc.), and that further obscures any sedimentary features that may survive metamorphism. To metamorphose a rock it needs to be brought down to the deep crust (~ 10 to 100 km), and then to be exposed at the surface those rocks have to be exhumed from that depth. During that travel those rocks are deformed, which is another characteristic of metamorphic rocks.
Last edited by John S on Thu Mar 24, 2005 9:33 am, edited 1 time in total.

John S
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Post #39

Post by John S »

Jose wrote:
John S wrote: I think it’s a mistake to use local surface exposures (even very impressive ones like the Grand Canyon) to make generalizations about the entire rock record.
This is probably one of the most profound statements in this thread. Thanks, John. It gets at some of the questions I posed in The Flood as Science, in which we ask just what the flood model predicts. While it may be possible to develop an idea based on one locale (say, the Grand Canyon), that idea is not supported by examination of other locales. Yet, the one-locale explanation is quite common in this debate.
Thanks very much for the compliment Jose, I'm glad my posts are proving useful. I hope it generates renewed intered in "The Flood as Science" thread, I'd certainly welcome the chance to participate in a discussion there. Thanks again for all the effort you've put into your posts to this board, I really enjoy reading your posts.

Thanks as well for your examples of metamorphism in the Henry Mountains. I think it's important to realize that metamorphism isn't limited to Precambrian rocks, just as it's important to realize the sedimentary rocks aren't limited to post-Cambrian rocks. Both of those help to illustrate the difficulty (impossibility?) for the Flood geologist of identifying just which rocks are pre-Flood, which are Flood-related, and which are post-Flood.
Last edited by John S on Thu Mar 24, 2005 9:35 am, edited 1 time in total.

John S
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Post #40

Post by John S »

I wish I had more time to devote to this post, but I’ll be out of town until the beginning of April, and I’ve got to get my affairs in order before I leave.

I’ve tried to make the point that the nature of sedimentary bedding that’s seen in Paleozoic and Mesozoic rock’s isn’t different than the bedding that’s seen in Precambrian rocks (which would be classified as pre-Flood) and young rocks (which would be classified as post-Flood).

One of the best places to look at young areas of sediment accumulation is the oceans. The oldest sediments in the ocean are Jurassic, while the youngest are modern (in other words, sedimentation in the oceans is still occurring). One of the largest sources of data about the sediments in the ocean is the Integrated Ocean Drilling Program (IODP) and its predecessors the Ocean Drilling Program (ODP) and the Deep Sea Drilling Project (DSDP). IODP maintains several ships that are dedicated to ocean research, and a lot of that research involves imaging the ocean floor and the sediments in the subsea and obtaining samples of those sediments by drilling holes into the ocean floor. They have three core repositories; one in Germany, one in the eastern US, and one in Texas. At these repositories they have huge refrigerators that are full of core. The repository in Texas (http://owen.nhm.ac.uk/odp/curation/gcr/gcrwebpage.html), which houses samples from the Pacific and Indian Oceans, has a really impressive amount of core – 60 miles from many different drilling projects.

The IODP has some descriptions of its current projects on its webpage (http://www.iodp.org/publications/pre_report.html). The projects there describe two expeditions; one to the North Atlantic Ocean, and one to the Juan de Fuca plate in the Pacific Ocean off the coast of western North America.

The Juan de Fuca project has some very good seismic images of the areas they drilled through (both the sediments and the underlying basalts). (http://iodp.tamu.edu/publications/PR/301PR/301PR.PDF )

Figure F2 shows the bathymetry of the ocean floor where the samples were collected, as well as the subsurface contact between the sediments and the underlying basalt. From Figure F2A you can see that the oldest crust is 5 Ma, which means that the sediments are younger than that. These are very young sediments, which would be classified as post-Flood by Flood geologists. Since these sediments are well-layered, something like Noah’s Flood isn’t needed to produce sedimentary layering.

Figure F4 has some beautiful seismic images through the areas that were drilled. The layering in the sedimentary rocks is very visible.


You’ve asked before about rate of sedimentation, and sequence stratigraphy is a great example of the differing rates of deposition that are recorded in the rock record. There are superimposed scales of variation in the rock record, and those scales correspond to events with different durations (a larger scale event corresponds with a longer period of time). You can get an idea about some of the timescales represented in sedimentary deposits by looking through the other drilling report on the IODP site “Expedition 303 Preliminary Report, North Atlantic Climate”

http://iodp.tamu.edu/publications/PR/303PR/303PR.html

In that report you’ll see that one of the questions the researchers are trying to answer is describing the millennial-scale variability that recorded in the rock record. This is a good illustration that geologists don’t just assume that the rock record is the result of processes that operate at a slow and steady rate for millions of years.

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