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Author Topic:   Geology- working up from basic principles.
edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 114 of 156 (541936)
01-06-2010 10:24 PM
Reply to: Message 108 by stewartreeve
01-06-2010 7:11 AM


Re: Self-Sorting Slurry Flow
An example: Page not found – Sedimentology
(this person/group has done a fair bit of experimentation on this topic, and his/their stuff is worth reading...)
Oh no... You're not really going to reference a Berthault article, are you?
Honestly, i'm not a fan of just assuming Superposition, but believe that higher-energy mechanisms should also be included in the consideration (such as described above).
The problem here is that Berthault is conflating lithostratigraphy with chronostratigraphy. In other words, a time-horizon is not necessarily parallel to the lithological boundaries. Only at certain scales can we say this is the case.
However, at the scale Berthault worked, we are practically looking at individual grains. And I can pretty much assure you that each grain was deposited prior to the succeeding grains above it.
I also think he has kind of an odd wording for the principle of superposition.

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 Message 108 by stewartreeve, posted 01-06-2010 7:11 AM stewartreeve has not replied

  
edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 115 of 156 (541939)
01-06-2010 10:50 PM
Reply to: Message 111 by stewartreeve
01-06-2010 5:33 PM


Re: What is the creationist point, in bringing up Walther's Law?
Of course! But it does mean that, give the right conditions, that such features can be produced by moving slurry/sediment - that's my point. A general point-of-view comes into play, where we scientifically obliged to consider such mechanisms.
The main problem I see here is that, in most places where eolian deposits are interpreted, you don't have a slurry of sediments. You have a very well-sorted, nearly pure sand deposit. In the references, they show the current-deposited result of an unsorted 'slurry' common to alluvial deposits rathet than eolian deposits.
As for animal tracks: couldn't that simply imply that there was numerous events, one following another in a given local area, with sufficient time in between for tracks to be formed? I don't see why this is not a valid working hypothesis.
Rather wishful thnking here. Did you ever walk on a sandy creek bed? Were your tracks perserved? Or are you talking about the old wet-dry flood that oscillated back an forth between flooded and emergent conditions thousands of times during the flood?
Hence, it is not necessarily (ie. cannot be exclusively decucted logically from an "open" set of premises, as we deal with here, and in much of science about the past...) the case that it is wind-blown on the basis of this piece of evidence. I believe we have to be careful about what we call "data"/"evidence"/"fact" and what we call "interpretation"....i would call angles of repose, etching, tracks, size dsitribution, etc, etc, "data"/"evidence"/"fact", and anything more than these observables as "interpretation", where any interpretation is subject to further logical analysis/deconstruction (and that's how we like it, isn't it?!)
Scientist are pretty well aware of such facts. They also understand interpretations. The point is that they do not draw interpretations based on "this piece of evidence". They base interpretations on all of the evidence and not some whacky concept that "granites MUST be supernatural", as one of your reference states.
As for etching: I would have thought that one could also invoke slurry flow tooling as an etching mechanism (ie. "high-energy" particle-particle collisions)? That is, etching/frosting as a result of transport. I thought that was an observed phenomena....?
Ventifacts are readily recognizable in the field. They generally form on a grain that is stationary.
But again it makes me think: shouldn't we simply be asking "what can cause etching", and "how might tracks for preserved", and "can another mechanism (such as flowing slurry)" be invoked to form what we see?" and "Isn't it possible that an alternative mechanism might produce a logically-superior explanation?"
Do you seriously think that no one has considered such points? Do you have any background in geology?
As for "assuming a mechanism": logically speaking, data doesn't speak for itself - that's a fallacious notion. All people have the same data, and all have their starting points for logical interaction with it.
Not really. You see, YECs, for instance like to look at one little piece at a time and ignore certain inconvenient data. This is an indisputable fact.
If we invoke the same basic logical processes (in this case, the scientific method), a come up with a different result, then, logically speaking, it is only because we have different starting points, different starting assumptions.
What do you think the original assumptions were? Why do scientists accept some assumptions, and do you agree that some assumptions are reasonable while others are not?
But it's just a matter of WHAT premises one chooses to start from...and i'm just suggesting that, perhaps, an assumed mechanism involving flowing slurry/moving sediment is a valid and relevant consideration, given its experiementally-verified abilities to produce the same general forms and traits that are said to be wind-blown...
Isn't that a valid point of view?
Only if you ignore certain data and rationalize away certain principles.

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edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 117 of 156 (541941)
01-06-2010 11:10 PM
Reply to: Message 116 by stewartreeve
01-06-2010 10:51 PM


A "Law" can't be a "law" if it has exceptions;
Nonsense. Under certain conditions, laws can break down. For instance, the SLoT. It does not necessarily apply to open systems.
... that's why the Principle of Superposition is only a Principle (which is great!) but perhaps no longer even deserves such a title, given that flowing slurries (a very common phenomena!) can produce the same basic features simultaneously.
Actually, it doesn't. See my earlier post.
A difficult pill to swallow, yes, but if a general principle is so easily shown to have exception by a relatively simple and common phenomena (in that vertically successive layers can be produced by a horizontal, simultaneous event), then surely the title of "Principle" should be brought into question, and reviews conducted? Crikeys...i think it's exciting...can't wait to do some flume work myself!
I hope you can do better than Juby, or whatever his name is. You know, we seldom let YECs do these things unsupervised. There's a reason for that.
Hopefully the clay-settling notion (of being slow) is also not a "Principle" (though i do hear that A LOT!), as isn't even the norm...i still scratch my head at why geos keep saying it's so....it's just not....
However, I notice that you never actualy told us the conditions under which flocculation occurs and how that is applied to large marine or fluvial systems, particularly under a current.

This message is a reply to:
 Message 116 by stewartreeve, posted 01-06-2010 10:51 PM stewartreeve has replied

Replies to this message:
 Message 122 by stewartreeve, posted 01-08-2010 9:06 AM edge has replied

  
edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 129 of 156 (542212)
01-08-2010 10:30 AM
Reply to: Message 122 by stewartreeve
01-08-2010 9:06 AM


OK - i need to clarify where you're coming from here, edge.
Are you saying that there are details that apparently differentiate water-formed simultaneous strata from wind-formed strata? On that i'd agree - there is boudn to be differentiating signatures...but it seems that you are suggesting that the water-formed simultaneous strata bear VERY LITTLE resemblence at all to what would be conventionally labelled wind-formed strata?
Let's just say that the differences are more obvious to the trained eye. For instance, some of your references do not seem to be very detailed in the composition of some of the cross-bedded deposits they depict.
Like i conceeded before - i'm not up on all the details, and how they might feature in differentiation...but also consider that any idiot (me, perhaps?) can see that there are some very significant, major similarities, and that i would think any idiot would be hesitant to dismiss them so casually...For example, the water-formed simultaneous mechanisms can produce:
i) parallel stratum
ii) cross-bedding
iii) inter-bedding
iv) angles of repose for cross-beds normally/conventionally interpreted as being categorically wind-derived
When so many major features have their boxes ticked "yes", how can one so easily dismiss it?
Who is dismissing it? You are creating a strawman here. I'm saying that my experience looking at eolian deposits of the Colorado Plateau show that there are some differences that are best explained by depositional environment.
Given such weight, isn't when compelled to consider, then, that, if we consider the hypothesis of high-energy water-dynamics as a theoretical starting point, it is reasonably possible that the finer details that are said to differentiate the strata as "necessarily wind-blown" might infact be conceivably (and even experimentally!) explained in another light?
Now it appears that YOU are the one ignoring evidence...
Could you conceed that my reasoning at least has some merit?
If you are saying that there are some similarities and there are some disimilarities, then yes, your statement has merit. However, it appears more to me that you are picking the evidence you want to address.
Of your 4 features listed above, I did not use one of them to discriminate between eolian and aquatic deposition.
What you seem to be saying is that if orangutans have two arms, two legs, and opposable thumbs they are probably the same as humans. So, does that make sense?

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edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 130 of 156 (542216)
01-08-2010 10:44 AM
Reply to: Message 127 by stewartreeve
01-08-2010 10:24 AM


PaulK, i see your point, but i think the correction is quite trivial....perhaps i should re-phrase it as relating to the same relative or proportional point in the same layer?
Well to me, your complaint seems trivial. In every case a stratum is younger than the one beneath it, regardless of the scale. Your point is conflating the scales of observation.
Nonetheless, the point is that vertically-successive strata can be formed by a simultaneous, dynamic mechanism, by HORIZONTAL progression- and said strata, if analysed "blind", would conventionally be interpreted as forming one layer after another: the lowest first, then the next, then the next, and so on, according to the normal rendering of the Principle of Superposition; whilst the truth of the matter would be that the stratum were all formed at the same time: with the "youngest" part being at the horizontal "start", and not at the vertical "start" (bottom)...
Actually, no. In cross-bedded strata, we look at the cross-laminations as the chronological break.
This is a thought-experiment to help convey my point...
Your point is based on misunderstanding.
Also, if people want to appeal to a particle-by-particle deposition for the dynamic scenario as still validating the general Principle of Superposition, then i'd have to remind them (and myself!) that the principle is concerned with the inter-stratum chronology - true?
If I read your intentions correctly, yes.
Thus, this appeal would reduce the necessary validity of the PoSn to only having intra-stratum relevance, instead of the inter-stratum relevance it is intended to have.
Again, no, because the time-equivalent discontinuities are cross-bedded.

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edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 142 of 156 (542675)
01-11-2010 7:59 PM
Reply to: Message 139 by Percy
01-11-2010 1:26 PM


Re: On the timelyness of replies and focus on the topic
But, as I asked already (see where I concluded with, "Not millions, surely."), how much vertically compared to how much horizontally? For example, the vertical thickness of the layers in the Grand Canyon represent ten, twenty, sometimes more, millions of years. Only at most a few hundred feet thick, the horizontal extent of these layers is for miles and miles and miles.
Actually, over hundreds of miles, a formation can be considerably time transgressive. Your point is well-taken, however, that the time difference should be matched to the scale of observation, and the type of deposit.
If we look at a single bed, I think it is fair to say that some types of deposits, such as turbidites might be restricted in time. In other words it is essentially a time horizon. At the same time, we can kind of say that the Hell Creek Formation forms the top of the Cretaceous System in eastern Montana, but that may not be true in detail. However, it may be a useful marker for most discussions.
Petro mentions the ash deposits which are considered chronostratigraphic horizons, and I have seen them cutting fairly sharply across a coal bed in a matter of tens of meters. It's really kind of spooky, but when you think about the lifetime of a swamp, things seem to come together.
Obviously the horizontal transgressing is far, far faster than the vertical deposition rate, and so these layers, especially at the precision of millions of years, represent pretty clear time lines.
Okay, here you are defining your resolution. On a scale of millions of years you are probably correct most of the time. So, I cannot say you are wrong. But if you want detail, then it's necessary to find a time-strat unit to correlate from one location to another. Somtimes we use events such as ash falls to do this, but fossils can also be used. For instance, over a distance of less than 250 km, the Glossopleura (trilobite index fossil) Zone traverses from the top to the bottom of the Bright Angel Shale.
Edited by edge, : Add mention of deposit type.

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edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


(1)
Message 145 of 156 (542683)
01-11-2010 9:06 PM
Reply to: Message 144 by Iblis
01-11-2010 8:34 PM


Re: Sanity Check
I'm having trouble following this thread. It starts off real well, of course, easy to digest but doesn't tell me much I don't already know. Eventually though it veers off into a Rugby match about what may be mere technicalities and semantics or else could be very important, hard to say.
I think that, for the most part, the technical issues are not relevant in this discussion. That is what I was trying to explain away in my earlier post. I understand what Petro is saying, but I also see Percy's point. This is an issue that is really hard to understand without a full, class-room discussion using charts and tables.
As I understand it, a good example of the laws of superposition and its relative faunal succession was found in the coal mines of 18th and 19th century Britain. Lot and lots of unbroken layers, lots and lots of fossils, no exceptions to the rules. Is it not true that these layers represent a chronology covering millions of layers, millions of years, and millions of fossils?
For all practical purposes, on this board, yes. In any given location, the strata young upward and age downward. The problem comes in when one compares different locations, which is basically what the YECs are doing. Then it gets into the area of time correlation. It's not easy to visualize.
If I'm understanding what the people stirring this thread are saying, unbroken superposition is no guarantee of chronology, transgressions and slurries and other things create the appearance of unbroken layers but aren't really, the geological column is arranged randomly rather than chronologically, and its just some sort of awesome coincidence that we only find trilobites near the bottom and grass near the top.
No, this is not the case, though lateral changes make the picture pretty confusing. The problem starts when we try to explain it to YECs with their strawman arguments and no benefit of a course in stratigraphy. I remember going over this in my very first geology class. It took a while...
I don't believe this, I think it's fraudulent. Someone make me smarter than I am right now.
Well, you are correct. While there are complications due to structure, alteration, and lateral changes in the depositional environment, including unconformities, it really does make sense in the end. The geological record is not random or indecipherable.
I will try to find a reference on this but it will definitely be later or tomorrow, though this video may help:
https://www.youtube.com/watch?v=awkLZmQKpwc&feature=related

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 Message 144 by Iblis, posted 01-11-2010 8:34 PM Iblis has not replied

  
edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 146 of 156 (542687)
01-11-2010 10:15 PM
Reply to: Message 143 by Percy
01-11-2010 8:23 PM


Re: To Edge and Petrophysics1
I think if you guys go back to my posts you won't be able to find where I object to anything about transgressions and so forth. I understand it, I agree with it. You can stop trying to convince me.
I don't remember inferring any such thing.
I had a different and somewhat minor point. Petrophysics1 said that layers are not time lines except in special circumstances. But on a scale of millions of years the vast majority of layers are timelines.
I didn't disagree.
quote:
The Grand Canyon is one giant gallery of such time lines, and the Grand Canyon is not a special circumstance. In fact, it is probably where most laypeople get their best impressions of the geologic column and the succession of geological eras.
At this scale of observation that is true. The top of the Redwall is essentially a time-stratigraphic horizon.
I made the point because I was afraid that some might conclude that Petrophysics meant that layers that laypeople are actually likely to see are not actually much like timelines with dates that we have confidence in, that, for example, the Coconino sandstone layer of the Grand Canyon is not really from around 260 million years ago, but actually varies in age a great deal as you go from one end of the canyon to the other. I very much doubt that the age of such layers varies by more than a couple percent across hundreds of miles.
I still don't see where we disagree. Personally, I think that Petro was a bit over the top in his point. This is an arcane bit of geology, not pertinent to the overall discussion here and obviously confusing to the laymen. I was only attempting to eplain the issue.

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edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 148 of 156 (542817)
01-13-2010 12:03 AM
Reply to: Message 144 by Iblis
01-11-2010 8:34 PM


Re: Sanity Check
I don't believe this, I think it's fraudulent. Someone make me smarter than I am right now.
Well, I don't know if this is working or not, but I have found a diagram that I like, to explain chronostratigraphy. Try this link and go to Figure 4.
SEPM Sequence Stratigraphy: Seismic Interpretation
You will notice several discontinuities between the different formations (colors) in northeast Alaska.
First, there are flat lines. Notice that they would be parallel to the time divisions as shown on the right side of the diagram. These are time-constained lines at the scale we are observing them.
Second, there are slanting or jagged lines. These boundaries are time-transgressive. An example is the the Savaganirktok-Canning boundary. Note that each of these formation is of a different age at different locations. This has been determined by biostratigraphy.
The third type of line is wavy. These are unconformities and represent longer times of non-deposition and often, erosion. If there is a rapid transgression, the unconformity is horizontal; if slower it is sloped such as the one at the base of the Pebble Shale unit.
So what does this mean? It means the the discontinuities in bedding might be stratigraphic or chronologic. It depends on the scale of observation and the type of sedimentary environment.
The conclusion I draw is that, for most purposes, the discontinuity between units is contemporaneous throughout its observed extent, say, 'as far as you can see'. Now, if one wanted to be extremely picky, one could say that in a transgressive sequence a given formation boundary would have to be older in the seaward direction. This would be Petro's point. However, that isn't realisitic in that we cannot measure the actual difference in age from one side of the Grand Canyon to the other, so it's kind of impractical for our purposes. Now in the Gulf of Mexico, it might be extremely important to reach a certain, definite time-stratigraphic unit, but here we are worried only about the major divisions of time and their stratigraphic counterparts.
This is the pitfall of YEC reasoning. To them, the difference of a few seconds in deposition of cross-laminations is a big deal. That is how we actually got into this discussion. They have reduced that scale of observation down to the laminations and sedimentary grains. But again, if we are forced to be picky, every grain must be deposited on another previously-deposited grain of sand, so superposition holds.
By the way, my understanding of the Law of Superposition refers mainly to beds, and 'bed' has a very distinct meaning in geology. Perhaps I'm wrong on this, but it really isn't that significant a point.
I am not a professor, so this may not be clear or sufficient to explain things to the lay person. At least it should show that a lot of thinking has gone into the study of chronostratigraphy and lithostratigraphy and how they intersect. I stress this point because so often I get the impression that YECs believe these things have never really been thought about.

This message is a reply to:
 Message 144 by Iblis, posted 01-11-2010 8:34 PM Iblis has replied

Replies to this message:
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edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 151 of 156 (542934)
01-13-2010 10:55 PM
Reply to: Message 150 by RAZD
01-13-2010 6:58 PM


Re: Sanity Check
So if I understand correctly ....
As the sea level rises (or land subsides) specific areas can transition from land to swamp to shore to shallow marine to deep marine - these geological "habitats" move horizontally with the shoreline.
Same in reverse when sea level falls (or land rises), and once again the geological "habitats" move horizontally but in the other direction.
In each case the geological "habitats" can leave sediment deposits characteristic of their "habitat."
So you get a "swamp" layer that is from different timelines as the shoreline moves in and out, and it cuts diagonally through the timelines of the deposits at different elevations in different areas, but we still see sediment deposited on top of what was there.
In general, the change of depositional environment will happen relatively rapidly if the paleoslope is gentle. In such a case, the lithostrat unit approaches identity with the chronostratigraphy.
And I'll stop there in case I'm way off base.
For the purposes of this discussion you are on target.

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edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 154 of 156 (543051)
01-14-2010 10:10 PM
Reply to: Message 153 by RAZD
01-14-2010 9:33 PM


Re: The Core Issue with the Law of Superposition
But this is getting off the topic - the law of superposition. I think it has been fairly well demonstrated that no matter the horizontal pattern, that the vertical pattern still demonstrates the validity of the law of superposition.
You asked our YEC friend to show you somewhere in the real world where that experimental flume deposition occured. Have a look at the Gilbert deltas in Maine. Foreset/crossbeds from 10-25 degrees deposited in water. Check the photos out.
Maine.gov - Error - Page Not Found
quote:
quote:
--------------------------------------------------------------------------------
Sediments that were carried all the way to the front of the delta cascaded down into deeper waters, forming the sloping foreset beds on the delta front. The foresets are inclined in the general direction of sediment transport and delta growth, and are typically composed of sand or mixed sand and gravel (Figures 7 and 8).
Figure 8. Close-up of foreset beds in marine delta south of Erskine Academy, South China, Maine.
This is exactly where our YEC friends become confused. They think that comparing the time of deposition of the lower part of the lamination on the right with the upper part of a lamination on the left refutes superposition. As if no geologist ever noticed this before...
Anyway, each lamination is essentially a time-strat unit, a compositionally uniform deposit occurring essentially instantaneously. And, as it turns out, the real comparison is one lamination with another - superposition holds.
At the same time, each 'bed' which contains laminar elements overlies another 'bed', also with laminar elements, and is younger. Supersposition holds again.
And I would (previously) have assumed that the layers were tilted after formation instead of formed at these angles with the sediment running (pouring?) downslope as the delta formed.
Correct (now), this is a primary depositional feature. Very common in current-laid sediments.
So those layers could be older to the left and younger to the right, even though the right end is lower than the left end?
Correct. However, keep in mind, that in this type of deposit the laminations are usually deposited quickly enough that age difference in the geologic record cannot really be resolved. Coarser-grained deposits such as these can be laid down very quickly.
So the law of superposition holds for any vertical core through those deposits, but the timeline\age will be different for the same depositional environments ("geologic habitats") for a core 5 or 10 feet to the right.
Yes, even though the actual ages might be very slightly different. They are the same bed.
By the way, your 'core' example is a very good way to describe this to the lay person.

This message is a reply to:
 Message 153 by RAZD, posted 01-14-2010 9:33 PM RAZD has seen this message but not replied

  
edge
Member (Idle past 1706 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 155 of 156 (543052)
01-14-2010 10:15 PM
Reply to: Message 153 by RAZD
01-14-2010 9:33 PM


By the Way...
Regarding the picture you included in your post. When I first looked at it, I thought to myself, "not eolian", before I read the caption. Do you think our YEC friends could tell us why?

This message is a reply to:
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