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Author Topic:   Growing the Geologic Column
Percy
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(3)
Message 1 of 740 (733604)
07-19-2014 9:04 AM


This thread continues the discussion taking place at the end of the Continuation of Flood Discussion thread about how sediments add to the geologic column.

The real geologic column, the actual physical one beneath any point on Earth as opposed to the conceptual and generalized one used for teaching the principles of geology, consists of all rock from the surface down to the molten mantle. This rock is organized into layers of different composition called strata.

Some will argue that because strata is defined as sedimentary layers that some types of rock formations, like igneous intrusions or salt domes, are not strata and are therefore not part of the geologic column. This is a valid point, but the specifics of the rock layers making up the geologic column are not relevant to this thread's topic, so agreement on this point should be unnecessary. In this thread when I say geologic column I shall mean every bit of rock vertically beneath some point on the Earth's surface.

Sufficiently low lying regions are areas of net deposition of sediments. In all low lying regions of the world as sediments are deposited the geologic column grows. Since most low lying regions are submerged we cannot directly observe this process in our daily lives, but there are some exceptions.

The Sahara Desert is one such exception. A recent news item reports that the fictional Star Wars city of Mos Espa, constructed for Star Wars Episode 1 in the Tunisian desert in 1997, is slowly being reclaimed by the desert. Within a century it will be completely covered by sand, which in this case is a windblown sediment. It is a terrestrial location where we can easily discern the year-by-year growth of the geologic column as it covers the buildings.

Lake Mead is another example of growing the geologic column, but in a part of the world very familiar to these discussions: the Grand Canyon region. As soon as it began forming in 1936 it began accumulating sediments. But the Hoover Dam won't last forever. When it's gone so will be Lake Mead, and these sediments will erode away, shrinking the geologic column at that location.

But if the region should subside beneath the waves while Lake Mead still lives then sediments will continue to accumulate, perhaps deeply enough for lithification to occur. turning the sediments to rock.

--Percy

Edited by Percy, : Grammer.


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AdminNosy
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Message 2 of 740 (733606)
07-19-2014 10:18 AM


Thread Copied from Proposed New Topics Forum
Thread copied here from the Growing the Geologic Column thread in the Proposed New Topics forum.
  
JonF
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Message 3 of 740 (733608)
07-19-2014 11:41 AM


Not all definitions of stratum require sedimentary rock. E.g. Google "define stratum" and you get 'a layer or a series of layers of rock in the ground. "a stratum of flint"'
  
RAZD
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Message 4 of 740 (733610)
07-19-2014 11:45 AM
Reply to: Message 1 by Percy
07-19-2014 9:04 AM


observed net erosion → deposition must occur somewhere
Sufficiently low lying regions are areas of net deposition of sediments. In all low lying regions of the world as sediments are deposited the geologic column grows. Since most low lying regions are submerged we cannot directly observe this process in our daily lives, but there are some exceptions.

Another way to look at this is that there are many areas where we can readily observe net erosion, lots and lots of erosion, particularly in the Grand Canyon area, Bryce Canyon area, etc.

That eroded material has to go somewhere, it doesn't evaporate, but it can be very fine particles.

Where every those particles come to rest and are buried by other particles, they then become deposition zones. adding to the local column.

The surface of the earth is in flux, changing. Where we live there is constantly very fine dust being deposited on our vehicles, where it is readily observed, and it is logical to assume that this occurs on all surfaces locally in a similar degree, that rain will wash most off high or sloped surfaces down to low flat surfaces (yards and lawns), and gradually this would accumulate ... so gradually that it is not noticed in normal day to day timescales.


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Faith
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From: Nevada, USA
Joined: 10-06-2001
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Message 5 of 740 (733665)
07-19-2014 11:01 PM
Reply to: Message 4 by RAZD
07-19-2014 11:45 AM


Re: observed net erosion deposition must occur somewhere
Just wondering how often you find the dust that settles on your car is entirely sand or entirely fine clay particles or entirely carbonate, or foram ooze. Do I need to explain? The sedimentary strata of the Geologic Column are made up of such different sediments, not mixtures.
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Faith
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From: Nevada, USA
Joined: 10-06-2001
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Message 6 of 740 (733666)
07-19-2014 11:16 PM
Reply to: Message 1 by Percy
07-19-2014 9:04 AM


You seem to want to divorce the Geo Column from the Geo Time Scale but the funny thing is when you google the column it comes up either in connection with the time scale or in some cases as identical with it. And in that connection it MUST be identified by its sedimentary layers because those are the ones that mark the time periods of the Geo Time Scale. Igneous intrusions are of course more recent because they ARE intrusions and therefore out of order on the time scale. Also the sedimentary layers are the ones that contain the fossils that are the major evidence for Evolution. You don't find fossils in the igneous intrusions.

And of course whatever sediments are being deposited today are "Holocene" on the Geologic Time Scale. Just wondering how often you find that these new sediments are depositing on top of identifiable layers that are recognized to have preceded the Holocene as they can be shown to have done for instance in known strata formations such as the Grand Staircase. Do you know what lies under them in any case at all? Shouldn't there be at least some identifiable time periods represented there, if not Pleistocene then maybe Permian? SOMETHING identifiably of the Time Scale? I mean the Geologic Column, in order to BE a column at all, must in some places actually appear as a column, wouldn't you think? One datable layer on top of one or two other datable layers? So if you are claiming that it is continuing to build wherever sediment deposits, it just seems logical that you could show that what it is building ON is recognizably earlier strata recognizably identifiable as time periods. Preferably of course the whole recent block of "time" such as Pleistocene, Pliocene, all that. Of course you can always say it eroded away, that takes care of it, but then you really have no evidence that the column is continuing to be built at all.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.


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NoNukes
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(1)
Message 7 of 740 (733668)
07-19-2014 11:52 PM
Reply to: Message 6 by Faith
07-19-2014 11:16 PM


You seem to want to divorce the Geo Column from the Geo Time Scale but the funny thing is when you google the column it comes up either in connection with the time scale or in some cases as identical with it

This is not worth the trouble as long as things are kept straight. We need some way to talk about all of the layers.

Igneous intrusions are of course more recent because they ARE intrusions and therefore out of order on the time scale.

Intrusions are out of order, yes. But let's not forget that we've pointed out igneous layers that are not intrusions. An example would be that lava layer on Ascension Island. I and others pointed out other igneous layers that exist.

f you are claiming that it is continuing to build wherever sediment deposits, it just seems logical that you could show that what it is building ON is recognizably earlier strata recognizably identifiable as time periods.

I hope you'll add detail to this, because it does not seem to make any sense. If sediment is depositing today on top of a sediment and any other layers that were there yesterday, that would seem to meet the requirement. We don't need to date them to know that.


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If there is no struggle, there is no progress. Those who profess to favor freedom, and deprecate agitation, are men who want crops without plowing up the ground, they want rain without thunder and lightning. Frederick Douglass


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Faith
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From: Nevada, USA
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Message 8 of 740 (733669)
07-20-2014 12:25 AM
Reply to: Message 7 by NoNukes
07-19-2014 11:52 PM


Intrusions are out of order, yes. But let's not forget that we've pointed out igneous layers that are not intrusions. An example would be that lava layer on Ascension Island. I and others pointed out other igneous layers that exist.

There are no sedimentary layers on Ascension Island because it is a volcanic island, therefore no Geologic Column at least as it is customarily associated with the Geologic Time Scale. That may not be an intrusion there, but then it is a layer among other volcanic layers, and not part of the Geologic Column. It seems to have been completely ignored that my original point was that lava is not part of the Geologic Column. The picture presented looked identical in form to pictures I found of coal seams. Then it turns out that it's on Ascension Island which is volcanic. But nobody bothered to note that therefore it was not part of the Geologic Column.

The "other igneous layers" that were pointed out turned out to be intrusions -- sills -- when I researched them.

I hope you'll add detail to this, because it does not seem to make any sense. If sediment is depositing today on top of a sediment and any other layers that were there yesterday, that would seem to meet the requirement. We don't need to date them to know that.

Yes, any deposition is going to be more recent than whatever it is deposited upon, but the point is that the Geologic Column IS associated with the Geologic Time Scale and the strata that are identified with that are quite identifiable as separate sediments, often to a great depth, and the core sample presented by CS on the other thread was very far from anything like those strata.

The problem, in other words, is that the Geologic Column really is a distinct identifiable stack of sedimentary layers, historically identifiable, and not just a pile of stuff, like the dust RAZD thinks could become another layer of said Column, or like the core samples CS presented.

Seems to me you should have to show that you are building on those particular identifiable strata that have been historically identified as rungs in the Time Scale ladder, and not just some motley lumpy deposition of shallow layers that isn't anything at all like the Column or the Time Scale.


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NoNukes
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From: Central NC USA
Joined: 08-13-2010
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Message 9 of 740 (733671)
07-20-2014 12:54 AM
Reply to: Message 8 by Faith
07-20-2014 12:25 AM


It seems to have been completely ignored that my original point was that lava is not part of the Geologic Column.

That is a valid point. But it was not ignored. As I recall, you expressed the opinion that lava could not even form layers. That's the reason you received responses showing pictures of lava layers.

In any event, the issue with lava being or not being relevant was discussed in Percy's Op and he indicated that he has reason to discuss all of the rocks under our feet. Lava layers may be relevant to the discussion without being a sedimentary layer.

Yes, any deposition is going to be more recent than whatever it is deposited upon, but the point is that the Geologic Column IS associated with the Geologic Time Scale and the strata that are identified with that are quite identifiable as separate sediments

The Holocene layer is still under construction. What you are asking for is not necessarily going to exist in very many places on earth. Perhaps you should explain why that is problematic for you.


Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)

I have never met a man so ignorant that I couldn't learn something from him. Galileo Galilei

If there is no struggle, there is no progress. Those who profess to favor freedom, and deprecate agitation, are men who want crops without plowing up the ground, they want rain without thunder and lightning. Frederick Douglass


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Minnemooseus
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Message 10 of 740 (733672)
07-20-2014 1:39 AM
Reply to: Message 6 by Faith
07-19-2014 11:16 PM


You seem to want to divorce the Geo Column from the Geo Time Scale but the funny thing is when you google the column it comes up either in connection with the time scale or in some cases as identical with it.

I think to a geologist, the geologic column is the geologic time scale, especially if the context is that we are referring to THE geologic column. I don't have a lot of real world experience, and what I did have was quite a few years ago, but I don't recall geologists referring an area's rocks as being "the geologic column". The rocks themselves are "the rocks", "the geology", or "the stratigraphy". A column is a graphic representation on paper.

But even if you wish the "geologic column" to mean the rocks, there is no single "THE geologic column".

And no, an areas geology is not inherently tied to the geologic time scale. A geologist could look at an area of rocks, map them out, do cross sections, etc., totally independent of the time scale. As a student, I've mapped a number of areas where I never did know the ages.

Moose

Added by edit:

I don't like the forums glossary definition of "geologic column":

quote:
Geologic column - A diagram representing divisions of geologic time and the rock units formed during each major period.

That makes it sound like each time period has characteristic rock types. They don't.

Edited by Minnemooseus, : Added by edit.


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edge
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Posts: 3900
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 4.1


Message 11 of 740 (733673)
07-20-2014 4:01 AM
Reply to: Message 5 by Faith
07-19-2014 11:01 PM


Re: observed net erosion deposition must occur somewhere
Just wondering how often you find the dust that settles on your car is entirely sand or entirely fine clay particles or entirely carbonate, or foram ooze. Do I need to explain? The sedimentary strata of the Geologic Column are made up of such different sediments, not mixtures.

I beg to differ. In fact, most sediments, particularly water-lain sediments are mixtures of various types of sediments. I could show you thousands of feet of drill logs that show this. Of course you could say that the Niobrara Formation is not part of the geological column of NE Colorado, but you would be wrong again.

How can you possibly justify some of the outrageous assertions that litter your posts?


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edge
Member
Posts: 3900
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 4.1


Message 12 of 740 (733674)
07-20-2014 4:13 AM
Reply to: Message 6 by Faith
07-19-2014 11:16 PM


You seem to want to divorce the Geo Column from the Geo Time Scale but the funny thing is when you google the column it comes up either in connection with the time scale or in some cases as identical with it.

As I have explained at least twice, the geologic time scale is a framework in which we classify rocks of all ages. They cannot be 'divorced'.

And in that connection it MUST be identified by its sedimentary layers because those are the ones that mark the time periods of the Geo Time Scale.

No, certain strata helped to define the time scale. It is not dependent upon any particular stratigraphic sequence.

Igneous intrusions are of course more recent because they ARE intrusions and therefore out of order on the time scale. Also the sedimentary layers are the ones that contain the fossils that are the major evidence for Evolution. You don't find fossils in the igneous intrusions.

But they all occur within the geologic time scale. The geological column is basically a record of life and events. Just because an ignimbrite does not have fossils (though some do) does not mean that it is not part of the record.

And of course whatever sediments are being deposited today are "Holocene" on the Geologic Time Scale. Just wondering how often you find that these new sediments are depositing on top of identifiable layers that are recognized to have preceded the Holocene as they can be shown to have done for instance in known strata formations such as the Grand Staircase.

Are you saying that the Grand Staircase is an example? I'm pretty certain that the Holocene is continuous from the Pleistocene in the Mississippi River Delta, all the way down to the Triassic at least.

Do you know what lies under them in any case at all?

Certainly. I just told you.

Shouldn't there be at least some identifiable time periods represented there, if not Pleistocene then maybe Permian? SOMETHING identifiably of the Time Scale?

I'm not sure what your problem is. Of course we know in a lot of places.

I mean the Geologic Column, in order to BE a column at all, must in some places actually appear as a column, wouldn't you think?

Partial columns are fine. We know that there are erosional discontinuities in the geological record.

One datable layer on top of one or two other datable layers?

Why are you saying that these don't exist?

So if you are claiming that it is continuing to build wherever sediment deposits, it just seems logical that you could show that what it is building ON is recognizably earlier strata recognizably identifiable as time periods.

And I just gave you an example. Please explain your problem?

Preferably of course the whole recent block of "time" such as Pleistocene, Pliocene, all that. Of course you can always say it eroded away, that takes care of it, but then you really have no evidence that the column is continuing to be built at all.

Hunh? Why not? Where are you getting all this?
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edge
Member
Posts: 3900
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 4.1


(1)
Message 13 of 740 (733675)
07-20-2014 4:18 AM
Reply to: Message 8 by Faith
07-20-2014 12:25 AM


There are no sedimentary layers on Ascension Island because it is a volcanic island, therefore no Geologic Column at least as it is customarily associated with the Geologic Time Scale.

Completely wrong. Anyone who has studied rocks knows that the boundary between sedimentary and igneous is pretty vague considering that pyroclastic rocks have sedimentary features, and you also have the problem of reworked volcanic rocks.

That may not be an intrusion there, but then it is a layer among other volcanic layers, and not part of the Geologic Column.

It is for Ascension Island...

It seems to have been completely ignored that my original point was that lava is not part of the Geologic Column.

Which is a wrong point...

The picture presented looked identical in form to pictures I found of coal seams. Then it turns out that it's on Ascension Island which is volcanic. But nobody bothered to note that therefore it was not part of the Geologic Column.

Repeating a loony statement is not going to make it true.

Yes, any deposition is going to be more recent than whatever it is deposited upon, but the point is that the Geologic Column IS associated with the Geologic Time Scale and the strata that are identified with that are quite identifiable as separate sediments, often to a great depth, and the core sample presented by CS on the other thread was very far from anything like those strata.

Why do they have to be the same?

The problem, in other words, is that the Geologic Column really is a distinct identifiable stack of sedimentary layers, historically identifiable, and not just a pile of stuff, like the dust RAZD thinks could become another layer of said Column, or like the core samples CS presented.

It is identifiable in each location on earth.

Seems to me you should have to show that you are building on those particular identifiable strata that have been historically identified as rungs in the Time Scale ladder, ...

The rocks are not the ladder.

Do you have problems telling maps apart from actual roads?

... and not just some motley lumpy deposition of shallow layers that isn't anything at all like the Column or the Time Scale.

What rule says they must be. Please document your assertions. As it is, you are just making stuff up.

Edited by edge, : No reason given.


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edge
Member
Posts: 3900
From: Colorado, USA
Joined: 01-09-2002
Member Rating: 4.1


Message 14 of 740 (733676)
07-20-2014 4:30 AM
Reply to: Message 10 by Minnemooseus
07-20-2014 1:39 AM


I think to a geologist, the geologic column is the geologic time scale, especially if the context is that we are referring to THE geologic column.

As I have tried to analogize before, the time scale is like a calendar that records the deposition of rocks. Some days, not much happens, while on other days there's a lot of events being recorded. The reason the time scale exists in its form is because we see profound changes in the the deposits and the life represented in them.

I don't have a lot of real world experience, and what I did have was quite a few years ago, but I don't recall geologists referring an area's rocks as being "the geologic column". The rocks themselves are "the rocks", "the geology", or "the stratigraphy". A column is a graphic representation on paper.

A good point. A column is a graphic representation and what we loosely call the 'geological column' is really a generalization. Each location actually has its own stratigraphy which we could, more properly call, a stratigraphic sequence.

And no, an areas geology is not inherently tied to the geologic time scale. A geologist could look at an area of rocks, map them out, do cross sections, etc., totally independent of the time scale. As a student, I've mapped a number of areas where I never did know the ages.

Yes, you can do geology without a time scale (other than the relative scale).
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Percy
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From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.4


Message 15 of 740 (733680)
07-20-2014 9:48 AM
Reply to: Message 6 by Faith
07-19-2014 11:16 PM


Faith writes:

You seem to want to divorce the Geo Column from the Geo Time Scale but the funny thing is when you google the column it comes up either in connection with the time scale or in some cases as identical with it.

I don't think anyone's trying to divorce them from one another. It's just that no one understands why you think the timescale is relevant to new sedimentary deposits. When new sediments deposit upon old they add to the geologic column at that location. The ages of the layers below are not a factor.

A geologic column exists at every location around the globe. Every rock beneath your feet down to the mantle, including igneous and volcanic rock, is part of the geologic column. There is no place on Earth where there is no geologic column. You have to understand this before the discussion can make any progress. I think what you're trying to do is define your problem away by claiming that anywhere new sedimentary deposits are forming, there's no geologic column there.

But even by your erroneous constraints on what qualifies as a geologic column I have provided examples of sedimentary deposits forming atop them. New sedimentary layers are forming atop what you consider valid geologic columns in many regions.

Here's the geologic column for the Lake Mead region, which is underlain by many of the same layers as the Grand Canyon. Notice that it includes Quarternary deposits (the Quarternary is the most recent geologic period):

And here's a generalized geologic column for the northern Gulf of Mexico, where sediments are accumulating at a prodigious rate. Walther's Law applies at the coastal margins of the Gulf of Mexico where sandstone, mudstone/siltstone and further out limestone and mid-ocean ooze are accumulating:

And here are geologic columns for three regions of the Sahara Desert:

And here's a geologic cross section showing layers underlying the Chesapeake Bay and a coastal portion of the Atlantic Ocean. Runoff from land is depositing sedimentary layers atop the existing layers of the geologic column. The central feature in the diagram is a buried crater that formed around 35 million years ago:

In these four regions, Lake Mead, the Gulf of Mexico the Sahara Desert, and the Chesapeake Bay, new sedimentary layers are being deposited atop old layers of the geologic column. And, though of course we know you don't accept this, new sedimentary layers are adding to the geologic column in low lying regions around the world, especially the sea floor.

We understand that you believe the sea floor has no geologic column. Certainly it does not often contain sedimentary layers that in any way resemble the Grand Canyon, but the sequence of rock types extending from the sea floor surface down to the mantle is a geologic column nonetheless, and the sediments being deposited upon it are adding to the geologic column.

In geology as in much science, the present is the key to past. Geology believes that the same forces and processes we observe today have been at work on our planet since its beginning. That's why we believe that existing sedimentary layers from long ago formed in the same way we observe sedimentary layers forming today, namely slow deposition over at least thousands of years.

--Percy


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