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Author Topic:   Growing the Geologic Column
Percy
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Posts: 20334
From: New Hampshire
Joined: 12-23-2000
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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.


Replies to this message:
 Message 4 by RAZD, posted 07-19-2014 11:45 AM Percy has acknowledged this reply
 Message 6 by Faith, posted 07-19-2014 11:16 PM Percy has responded

  
Percy
Member
Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


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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Percy
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Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


(2)
Message 45 of 740 (733789)
07-21-2014 9:31 AM
Reply to: Message 22 by Faith
07-20-2014 10:31 PM


Re: observed net erosion ¨ deposition must occur somewhere
Hi Faith,

I think you missed a couple of important posts. One is my Message 15, which includes four examples of locations where sediments are being deposited today atop geologic columns composed of only the types of layers your definition allows. The other is Capt Stormfield's Message 18, which draws a very helpful analogy of geology with history.

Edge has already described why it isn't true that a geologic layer is "all sandstone or all limestone etc.," that most geologic layers are a messy combination of different minerals, the assigned name deriving from the dominant mineral, so I'll just address this:

Faith writes:

And, looking up the Niobara formation I find that it too is characterized by identifiable sediments:
...
Chalk
Limestone
Shale

I'm focusing once more on your use of the modifier "identifiable". A layer doesn't have to be identified to be part of the geologic column. If we map out a column of layers using seismic techniques we could end up knowing where layers begin and end, but not their composition, which would remain unidentified. But our inability to identify the composition of the layers doesn't mean they're not part of the geologic column.

In order to use a definition of the geologic column that geologists use, you're going to have to remove the "identifiable" modifier from your own personal definition.

I'm moving on now to another part of your flawed definition, that layers must be sedimentary in order to be considered part of the geologic column. I know that most definitions of strata say that they are sedimentary, but this is an obvious oversimplification. Igneous rock from a volcanic eruption is obviously part of the geologic column, and only by the loosest of definitions could it be considered sedimentary. In any discussion of the strata of a geologic region that includes volcanic deposits, the volcanic layers are considered strata. Type the phrase "volcanic strata" (including the quotes) into Google and you'll get thousands of results.

I think most people would agree with you that intrusions should not be considered part of the geologic column, but it makes no difference to this discussion. When sediments are being deposited atop a geologic column, whether at Lake Mead or in the Gulf of Mexico or in Chesapeake Bay or in the Sahara or anywhere else, it makes no difference whether that geologic column includes intrusions. Whether intrusions are present or not, sediments are still being deposited atop a geologic column.

Even the sea floor has a geologic column, albeit generally much briefer than geologic columns on continents. The oldest sea floor in the world is only around 200 million years ago, because most sea floor is eventually subducted into the mantle. But beneath the sea floor in any part of any ocean is a geological column of rock extending down to the molten mantle. Our ability to explore these layers is much diminished because they lie beneath a depth of water, sometimes a great depth of water. Above the original sea floor that forms at mid-oceanic ridges will be sedimentary layers, primarily of mid-ocean ooze far from shore, but of limestone, shale and sandstone closer to coastlines. Below the original sea floor the layers, especially in mid-ocean, are very unlikely to be sedimentary, but there will be layers of different kinds of rock nonetheless that, to the extent we can study them, would be divided into types and time periods as best as we could manage, just like any other geologic column.

--Percy

Edited by Percy, : "igneous layers" => "intrusions" in next to last paragraph.


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Percy
Member
Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


Message 47 of 740 (733794)
07-21-2014 11:12 AM
Reply to: Message 32 by Faith
07-21-2014 3:19 AM


Re: Defining the Geo Column again
Faith writes:

I want to quote this one part though because it answers the idea that the Geologic Column is made up of all the rocks beneath the surface which some have been claiming here:

Misconception No. 3. The strata systems of the geologic column are worldwide in their occurrence with each strata system being present below any point on the earth's surface.

The notion that the earth's crust has on "onion skin" structure with successive layers containing all strata systems distributed on a global scale is not according to the facts...

I noticed that the reaction of some was that Steve Austin was lying in some way, but my own feeling is that this could easily be a common misconception, and not just among YEC's.

But no one here in this thread has this misconception, nor has anyone expressed anything remotely like this, so I'm concerned that the fact that you felt the need to say this indicates some misunderstanding on your part, but I'm not sure what. We all know that a geologic column exists at every point around the world, different everywhere, and incomplete nearly everywhere so far as representing the entire geologic timescale. No one here thinks that all of the geologic time scale is represented in every geologic column, nor even very much of it.

AbE: After reading your message one more time I now understand why you cited this misconception. You thought it was a response to the assertion that a geologic column represents all the rocks beneath some location. It's not. It's a response to the misconception that all of geologic time is represented in the geologic column everywhere around the Earth. Two different concepts.

The Geologic Column is a specific recognizable formation of sedimentary strata that is found as partial stacks here and there, some more complete than others but none fully complete.

Concerning your use of the word "recognizable," and earlier of the word "identifiable," realize that most of the world's strata lie deeply buried and inaccessible, so I think what you really mean to say is that were we able to examine them that we would be able to tell where layers begin and end and what their composition is. But if we were to stand on a spot about which geologists were completely ignorant of what lay beneath, we'd still be standing atop a geologic column. An uninvestigated one, but a geologic column nonetheless.

So anywhere around the globe sediments are being deposited, they're being deposited atop the geologic column at that location. It doesn't matter whether that geologic column has intrusions or volcanic layers or regions of solidified mantle, and it doesn't matter whether its layers are slanted or deformed or faulted or intruded, it's still a geologic column, and the sediments being deposited atop it now would be part of a Holocene (the current epoch) layer.

--Percy

Edited by Percy, : AbE.


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 Message 32 by Faith, posted 07-21-2014 3:19 AM Faith has not yet responded

  
Percy
Member
Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


Message 65 of 740 (733837)
07-22-2014 8:49 AM
Reply to: Message 60 by Faith
07-22-2014 5:00 AM


Faith writes:

That's because it ISN'T the Geologic Column as I have understood it and tried to define it here.

I think you may have missed a few helpful messages.

I've posted a couple messages that describe how sediments are accumulating right now atop layers that you accept are geologic columns: Message 15, Message 45

And Capt Stormfield has very helpfully analogized geology with history in Message 18, describing how coherent stories for both history and geology emerge from a jumble of of widely dispersed data.

--Percy


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 Message 60 by Faith, posted 07-22-2014 5:00 AM Faith has not yet responded

  
Percy
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Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


(3)
Message 71 of 740 (733862)
07-22-2014 11:10 AM
Reply to: Message 69 by Faith
07-22-2014 10:56 AM


Faith writes:

THE Geologic Column is what I've been focused on,...

"THE Geologic Column" is an abstraction and isn't the focus of this thread.

This thread makes the point that a geologic column exists beneath every point on the globe, and that everywhere sedimentary deposits are accumulating the geologic column is growing at that location. For those who will only accept geologic columns made up of sedimentary layers, Message 15 and Message 45 describe examples of sedimentary deposits accumulating atop such geologic columns.

--Percy


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 Message 69 by Faith, posted 07-22-2014 10:56 AM Faith has responded

Replies to this message:
 Message 72 by Faith, posted 07-22-2014 11:24 AM Percy has responded

  
Percy
Member
Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


Message 75 of 740 (733872)
07-22-2014 12:37 PM
Reply to: Message 72 by Faith
07-22-2014 11:24 AM


Faith writes:

Well, my interest has been in THE Geologic Column, so apparently there is no point in my remaining on this thread.

This thread's intended purpose was to provide the information, evidence and arguments supporting the view that sedimentary deposits are adding to geologic columns all around the world.

--Percy


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 Message 72 by Faith, posted 07-22-2014 11:24 AM Faith has responded

Replies to this message:
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Percy
Member
Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


(1)
Message 86 of 740 (733903)
07-22-2014 8:20 PM
Reply to: Message 84 by Faith
07-22-2014 7:54 PM


Re: Mt. Pinatubo is Proof Positive
Hi Faith,

"The Geologic Column" is an abstraction.

The information, arguments and evidence for sediments adding to geologic columns around the globe that accord with your views of what constitutes a geologic column can be found in Message 15 and Message 45.

--Percy


This message is a reply to:
 Message 84 by Faith, posted 07-22-2014 7:54 PM Faith has responded

Replies to this message:
 Message 87 by Faith, posted 07-22-2014 8:25 PM Percy has responded

  
Percy
Member
Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


Message 106 of 740 (733927)
07-22-2014 9:25 PM
Reply to: Message 87 by Faith
07-22-2014 8:25 PM


Re: Mt. Pinatubo is Proof Positive
Hi Faith,

Faith writes:

I know it's an abstraction...

This thread isn't about the abstraction you're calling The Geologic Column. That abstraction is a generalization of reality based upon an aggregation of data, but it has no real existence, and so there can't be anywhere in the world that sedimentary deposits are forming above The Geologic Column.

This thread's purpose is to present the information, arguments and evidence supporting the view that sedimentary deposits are forming today above geologic columns at many places around the globe.

...and as long as you keep repeating that as if I hadn't said it myself many times I am not going to read the links you've posted.

I haven't posted any links (and if I had I would have used them for reference only, just as the Forum Guidelines require). If you look at Message 15 and Message 45 you'll find that they contain information (including images of geologic columns for specific locations) , arguments and evidence that address the topic of this thread.

--Percy


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 Message 87 by Faith, posted 07-22-2014 8:25 PM Faith has not yet responded

  
Percy
Member
Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


(4)
Message 128 of 740 (734079)
07-25-2014 8:18 AM
Reply to: Message 123 by Faith
07-25-2014 4:12 AM


Re: a partial review
Hi Faith,

This thread was proposed for the purpose of presenting the information, arguments and evidence showing false your claim that the geologic column was no longer growing anywhere in the world. That's been accomplished and I think this thread's purpose has been accomplished.

But you've made other incorrect statements, some of them matters of simple fact or even just of straightforward definition, that could serve as the basis for new threads:

Faith writes:

...I've many times defined my view of it as specific to the particular strata that define the Geo Time Scale, that are very thick and very extensive and so on.

There's nothing that requires strata to be "thick and very extensive". Strata can be thin and local to a small region.

And really, they should probably be defined as only those that contain fossils, since they are definitive of the Time Scale.

Fossils are just part of the evidence for dating strata. The much more definitive data is radiometric dating. The idea that non-fossil bearing strata should be excluded from the geologic column doesn't deserve serious consideration.

Igneous rocks are not part of this.

Igneous rock layers that aren't intrusions are part of the geologic column, where you might have a sedimentary layer, then a basaltic layer from a volcano, then another sedimentary layer. The basaltic layer is as much a part of the geologic column at that location as are the sedimentary layers and fits right into the geologic timescale.

They may be part of some poster's idea of the geo column but they aren't part of mine.

I recommend you use the same standard definitions of geology that everyone else is using. Answers.com has a simple and clear definition of geologic column: The vertical sequence of strata of various ages found in an area or region. There's nothing in this definition about fossils or rock type or thickness or extent.

So if you want to ignore my idea of it, fine,...

I don't think your idea of the geologic column has been at all ignored. In fact, I think people have, as a group, been quite voluble and specific about what's wrong with your idea of the geologic column.

Then there were people who kept misrepresenting me as not knowing the Geo Column is an abstraction,...

I think you've misunderstood the criticism, which is this: In a thread seeking to present evidence of sedimentary deposits accumulating today atop real geologic columns it makes no sense to focus on an abstract geologic column. Sedimentary deposits do not accumulate atop abstractions, except conceptually. I could draw you my conception of sedimentary deposits accumulating atop The Geologic Column, but it would prove nothing.

But those places are awfully limited when you compare the great extent of some of the layers that extend across states and continents.

First, the Gulf of Mexico and the continental shelf of the eastern United States (I showed just the Chesapeake Bay area, which is representative) are not "awfully limited." They're enormous, here's a Google Maps image. All the light blue regions are continental shelf which have geologic layers beneath them very similar to those beneath the continents and which conform to your restricted definition of the geologic column, and they're all receiving sedimentary deposits:

Such continental shelves exist off most continental coasts, just check Google Maps (in satellite mode) if you don't believe this. And if instead of your limited definition of geologic column we apply the one from standard geology then across 3/4 of the globe sedimentary deposits are accumulating atop geologic columns, because 3/4 of the globe lies beneath lakes, seas and oceans.

And we won't know for a few million years I guess whether what is building on them has anything at all in common with that Column in the end.

What kind of rock do you imagine forms when a layer of sand becomes buried beneath a mile of other sediments? Sandstone, maybe?

Sediments that haven't yet turned to rock are called unconsolidated. Unconsolidated sedimentary layers forming today have the same composition as lithified layers that have been deeply buried.

I'd still argue that the true Geo Column was all laid down...But it's not something I can prove.

It's not even something you can offer a shred of evidence for, nor even a coherent perspective.

--Percy


This message is a reply to:
 Message 123 by Faith, posted 07-25-2014 4:12 AM Faith has responded

Replies to this message:
 Message 136 by Faith, posted 07-25-2014 9:35 PM Percy has responded

  
Percy
Member
Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


Message 171 of 740 (734153)
07-26-2014 9:08 AM
Reply to: Message 136 by Faith
07-25-2014 9:35 PM


Why can't geologic columns grow today?
Faith writes:

I guess I can't get across why the geo column can't be growing on the continental shelves etc,...

If you provide the facts and arguments for why the geologic column cannot be growing on the continental shelves then, assuming the facts are correct and the arguments contain no flaws, you'll convince everyone here. But until you can do that, because the continental shelves consist of sedimentary layers upon which more sediments are being deposited, it's impossible to avoid the conclusion that the sediments are adding to the geologic column.

...or why the definitive strata are thick and cover a huge area.

For the sake of argument let us assume the Flood really happened and deposited the sedimentary layers we observe today. What prevented the flood from depositing any small (in horizontal extent), thin layers? I'm trying to understand your objection to them.

This is what I've been equating with the Geo Column, but I'm more interested in getting across this picture of the strata building up and then stopping.

The picture you're trying to paint is contradicted by the sedimentary layers we see forming atop other sedimentary layers of the geologic column all around the world. You will not have much success convincing people that something they can see happening isn't really happening.

You go on to discuss some other things outside the scope of this thread, so I won't comment.

--Percy


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 Message 136 by Faith, posted 07-25-2014 9:35 PM Faith has responded

Replies to this message:
 Message 179 by Faith, posted 07-26-2014 3:01 PM Percy has responded

  
Percy
Member
Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


Message 172 of 740 (734154)
07-26-2014 9:59 AM
Reply to: Message 143 by Faith
07-25-2014 11:28 PM


Re: dating by magma sills and dikes
Faith writes:

I just don't see how there could be actual lava layers among the sedimentary layers.

Large volcanic eruptions will deposit a layer of lava and tuff (rock that was originally volcanic ash) across the local landscape atop the sedimentary layers that are already there. The lava eventually cools into igneous rock, and the unconsolidated volcanic ash becomes rock if deeply buried. If the region is an area of net deposition then sedimentary deposits will accumulate atop the igneous rock that was once lava and the tuff that was once volcanic ash.

Sequences like this are represented in many places in the geologic record, and Hooah pointed out a number of them. Here's a diagram of the geologic column in Yellowstone Park. In the column on the left, which is actually an expanded detail of the top portion of the column on the right, lava flow layers are interspersed with shale layers:

Those lava layers are the same ones that Hooah presented in this image from Yellowstone. The lava layer (in this case of rhyolite) is central in the image, and a shale sedimentary layer lies above it:

--Percy


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 Message 143 by Faith, posted 07-25-2014 11:28 PM Faith has responded

Replies to this message:
 Message 180 by Faith, posted 07-26-2014 3:30 PM Percy has responded

  
Percy
Member
Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


Message 176 of 740 (734173)
07-26-2014 1:46 PM
Reply to: Message 174 by herebedragons
07-26-2014 1:25 PM


herebedragons writes:

Not sure why you would say that the sill is not a layer. There it is, a rock pancake - right between two other layers. How is it not a layer? Sure it's not a sequential layer or a sedimentary layer, but why would it not be a layer? How about an intrusive layer?

I don't think Faith meant to say that an intrusive layer is not a layer. I think what she really meant to say is what most of us already accept, that an intrusive layer is not part of the geological column, that it is instead an intrusion into an already existing geological column. She just misstated things in her Message 169 where she claimed an intrusive layer isn't a layer at all.

--Percy

Edited by Percy, : Correct the message link.


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 Message 174 by herebedragons, posted 07-26-2014 1:25 PM herebedragons has responded

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 Message 178 by herebedragons, posted 07-26-2014 2:09 PM Percy has responded
 Message 184 by Faith, posted 07-26-2014 5:20 PM Percy has responded

  
Percy
Member
Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


Message 183 of 740 (734190)
07-26-2014 5:16 PM
Reply to: Message 179 by Faith
07-26-2014 3:01 PM


Re: Why can't geologic columns grow today?
Faith writes:

If the geologic column is already there beneath the recent depositions that would be true enough but just the accumulation of sedimentary layers in itself isn't.

You're just repeating your assertion that the accumulation of sedimentary layers atop a geologic column of sedimentary layers does not add to the geologic column, which isn't what I was hoping for. As I explained, to convince other people you need to provide facts and arguments in support of your position. What makes the sedimentary layers forming today somehow separate from the geological column beneath them?

You have a similar sort of problem with your other claim that no sedimentary layers were laid down before the flood. But weathering of higher regions produces sediments that are carried to lower regions where they are deposited as sediments. What facts and arguments support the view that there was no erosion or sedimentation prior to the flood?

I'm going to give up on this subject and go back to former ways of trying to make what I think is the same basic point.

Is that a point about sedimentary layers growing the geologic column? Which is the topic of this thread?

...it's just that the layers I happen to be talking about ARE thick and extensive, covering huge areas...I try to keep the focus on these because they are the ones that get associated with the Time Scale, are called by names of the Time Scale.

Sounds like a different topic.

--Percy


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 Message 179 by Faith, posted 07-26-2014 3:01 PM Faith has not yet responded

  
Percy
Member
Posts: 20334
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.1


(1)
Message 191 of 740 (734201)
07-26-2014 6:23 PM
Reply to: Message 180 by Faith
07-26-2014 3:30 PM


Re: lava layers versus sills
Faith writes:

In fact you aren't going to get the kind of layer out of this that you get with the sedimentary depositions, with their fairly flat horizontality and fairly tight contacts. You'd get a very lumpy surface for the next sedimentary deposit, not a neat flat contact at all.

As has been pointed out many times, boundary interface topology varies all over the map, from the very flat to the very lumpy to the interbedded to anything that follows the physical laws of nature.

You know, if a volcanic eruption during the Flood would produce layers of pillow lava, which would be very irregular. You can see from this image where the name comes from. Note how irregular is the surface of pillow lava:

Lava from surface volcanoes doesn't form pillow lava. If the lava is thick it will form a rough surface, but very hot lava will run like water and form a smooth surface over broad areas, but even typical lava fields like this are only modestly uneven. The imperfections are on the order of a few feet. In a diagram it would be drawn as perfectly flat:

Looking at nice neat diagrams you might after a while get the feeling that boundary interfaces between layers must be sharply defined and flat, but anyone who has read as extensively in geology as you've claimed would have to know this isn't true.

In actual fact this sequence has not yet been demonstrated to have occurred anywhere. If it did the upper surface of the layer, the contact with the sedimentary deposition above it, would be lumpy...

There is no requirement that they be lumpy, but they can be lumpy, and we have images of "lumpy" boundaries between layers, as in this image of the Blackrock Escarpment that Hooah used earlier:

That is not shale, by the way, that is "welded tuff" interspersed with the lava flow layers...This isn't an example of volcanic layers interspersed with sedimentary layers.

Oops, you're correct. I'll try to find a sequence of interspersed volcanic and sedimentary layers for you.

That picture hooah posted that you reposted here is absolutely undecipherable to me. If that is all lava between sedimentary layers, however, HOW IS IT NOT AN INTRUSIVE, A SILL?

Because it isn't a sill. Sills have certain distinctive characteristics, such as melting both the upper and lower contact rocks extensively, and it displays the characteristics of having cooled from the boundary contacts toward the interior. The caption for that image of the Blackrock Escarpment in Idaho tells you that the volcanic layers are rhyolite and I believe the interspersed layers are tuff.

--Percy


This message is a reply to:
 Message 180 by Faith, posted 07-26-2014 3:30 PM Faith has responded

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