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Author Topic:   Growing the Geologic Column
Percy
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Posts: 19077
From: New Hampshire
Joined: 12-23-2000
Member Rating: 3.2


Message 211 of 740 (734239)
07-27-2014 7:20 AM
Reply to: Message 178 by herebedragons
07-26-2014 2:09 PM


I touched on this in Message 210, see if you agree.

--Percy


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Percy
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Posts: 19077
From: New Hampshire
Joined: 12-23-2000
Member Rating: 3.2


Message 212 of 740 (734240)
07-27-2014 8:26 AM
Reply to: Message 193 by Faith
07-26-2014 7:00 PM


Interspersed Volcanic and Sedimentary Layers
Hi Faith,

The Columbia River Basalt Group in the western US (mostly Washington state) consists of basalt layers from volcanic lava flows interspersed with sedimentary layers. Here's a diagram of the layers at Hanford Reach along the Columbia River. It shows basalt layers from lava flows interspersed with sedimentary layers:

Here's a good description of how these layers formed from http://hugefloods.com/Basalt.html:

Hundreds of eruptions--each separated by thousands of years--leave us with a unique record of conditions millions of years ago. During periods of volcanic inactivity, water would accumulate in depressions, sediment would accumulate in valleys, and wind would deposit dust. Soil layers would develop and forests and grasslands would flourish. Plants and animals would appear. The next cycle of lava flows would would abruptly terminate their existence, but preserve a fossil record.

Here's a couple images - unfortunately the websites didn't note which specific layers these are. I did dig a little trying to find images with some labeling, but no luck. Maybe someone else can find some labeled images:


But the bottom line question for you is why you wouldn't expect volcanic lava (basalt) and tuff layers (both igneous layers) between sedimentary layers. What is to prevent a volcanic eruption in a region where sediments are being deposited? Even in a global flood a volcanic eruption could occur, leaving behind pillow lava, something I mentioned before that also occurs in the geologic column.

--Percy


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herebedragons
Member (Idle past 71 days)
Posts: 1513
From: Michigan
Joined: 11-22-2009


Message 213 of 740 (734241)
07-27-2014 8:28 AM
Reply to: Message 210 by Percy
07-27-2014 6:57 AM


Re: Layer / Sill
"Stratigraphic column" has two definitions... the other calls it a "structural column", meaning the rocks just as they are without regard to how or when they got there. I think this second definition of "stratigraphic column" is the definition that feels best to HBD and myself.

Statigraphic column or sequence works for me. I guess it does make sense that geological column should refer to the relation of the sequence to the time scale. Just a subtle difference.

That words are just labels means you can't use definitions to infer how the world really works,

I have always hated arguments about definitions but couldn't really put my finger on exactly why. I think you nailed it! I think it has a lot to do with why these discussions get so confusing sometimes.

as if geologic columns could only be constructed during global floods.

I too got the impression that she was trying to suggest this by definition.

But what we observe happening in all low lying regions around the world today (mostly sea floor) is the creation of a time ordered sequence of sedimentary and igneous layers, the very definition of a geologic column.

In her defense, I think that what we observe happening today DOES look strangely different than what we see in the rock record. But to me it highlights the fact that it takes lots of time (as well as specific circumstances) to convert these unconsolidated sediments into recognizable rock units. We just don't see it happening year by year as it would have had to happen in a global flood. If that were the case, we would have rock units under the Mississippi Delta that were only a couple hundred years old or so and new ones forming all the time.

HBD


Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for... I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca

"Nothing is easier than to persuade people who want to be persuaded and already believe." - another Petrarca gem.

Ignorance is a most formidable opponent rivaled only by arrogance; but when the two join forces, one is all but invincible.


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JonF
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Posts: 5610
Joined: 06-23-2003
Member Rating: 2.9


Message 214 of 740 (734242)
07-27-2014 9:30 AM
Reply to: Message 205 by Faith
07-27-2014 12:14 AM


It's a unique place, though, and really it's less like igneous layers between sedimentary layers than sedimentary layers between igneous layers since the area is a huge volcanic province.

OK. So you were wrong when you claimed no such thing existed. And there's no difference between "igneous layers between sedimentary layers" and "sedimentary layers between igneous layers"; they are just igneous layers followed by sedimentary layers followed by igneous layers...

Of course it's not unique. From Geochronology of the pre-KBS Tuff sequence, Omo Group, Turkana Basin (all but the abstract is paywalled) here's the stratigraphic sequence near Lake Turkana (nee Rudolph) where many hominid fossils are found:

Note that tuffs cannot be intrusive.

From How do we know the ages of fossils and fossil-bearing rocks?, explaining that it's non-intrusive igneous layers that are used (mostly) to date sedimentary rocks:


caption: Ash layers from ancient volcanic eruptions are found in many sedimentary rock deposits.
(Again ash layers cannot be intrusive)

And from Strangers in a Strange Land: Tuff luck, it's all your fault, so don't be an ash about it (you really should click that, it has a simple and great explanation of why that black layer isn't intrusive):


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JonF
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Posts: 5610
Joined: 06-23-2003
Member Rating: 2.9


Message 215 of 740 (734243)
07-27-2014 9:33 AM
Reply to: Message 205 by Faith
07-27-2014 12:14 AM


It's a unique place, though, and really it's less like igneous layers between sedimentary layers than sedimentary layers between igneous layers since the area is a huge volcanic province.

OK. So you were wrong when you claimed no such thing existed. And there's no difference between "igneous layers between sedimentary layers" and "sedimentary layers between igneous layers"; they are just igneous layers followed by sedimentary layers followed by igneous layers...

Of course it's not unique. From Geochronology of the pre-KBS Tuff sequence, Omo Group, Turkana Basin (all but the abstract is paywalled) here's the stratigraphic sequence near Lake Turkana (nee Rudolph) where many hominid fossils are found:

Note that tuffs cannot be intrusive.

From How do we know the ages of fossils and fossil-bearing rocks?, explaining that it's non-intrusive igneous layers that are used (mostly) to date sedimentary rocks:


caption: Ash layers from ancient volcanic eruptions are found in many sedimentary rock deposits.
(Again ash layers cannot be intrusive)

And from Strangers in a Strange Land: Tuff luck, it's all your fault, so don't be an ash about it (you really should click that, it has a simple and great explanation of why that black layer isn't intrusive):


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edge
Member (Idle past 45 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 216 of 740 (734245)
07-27-2014 12:30 PM
Reply to: Message 193 by Faith
07-26-2014 7:00 PM


Re: Blackrock Escarpment is all volcanic
Back on the other thread somebody did post pictures of lava layers that really look like lava layers between sedimentary layers but are not layers that were deposited within the sequence but as they all turn out to be, intrusive layers, sills.

Well, since we were discussing the Grand Canyon, the obvious example to satisfy you would be the Cardenas Basalt.

The Cardenas Basalt is stratigraphically described by Wikipediea as:

Unit of: Unkar Group
Underlies: Nankoweap Formation
Overlies: Dox Formation
(http://en.wikipedia.org/wiki/Cardenas_Basalt)

Further:

The basal contact of the Cardenas Basalt with the underlying Dox Formation is ... Thus, the contact between the Cardenas Lavas and the Dox Formation is conformable and interfingering. This indicates that sands were still being deposited when the first lavas erupted and that deposition occurred during the transition from the accumulation of Dox Formation to Cardenas Basalt.[3][4][9]

The contact between the Cardenas Basalt and the overlying Nankoweap Formation is an erosion surface that is a disconformity or even a slight angular unconformity. Locally, the contact is a low relief erosional surface associated with a thin weathering zone developed in the lavas of the Cardenas Basalt.

And here is a cross setion showing the relationships:

Edited to add: I just noticed how this diagram shows the erosional unconformity between the Temple Butte and the Muav. Also, notice the presence of dikes and sills along with the Cardenas lava.

Edited by edge, : No reason given.


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edge
Member (Idle past 45 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 217 of 740 (734246)
07-27-2014 12:46 PM
Reply to: Message 213 by herebedragons
07-27-2014 8:28 AM


Re: Layer / Sill
In her defense, I think that what we observe happening today DOES look strangely different than what we see in the rock record. But to me it highlights the fact that it takes lots of time (as well as specific circumstances) to convert these unconsolidated sediments into recognizable rock units. We just don't see it happening year by year as it would have had to happen in a global flood.

In order for Walther's Law to be in effect, you must have changing sea levels and this only really happens on a scale of geological time.
If the Atlantic Ocean transgressed across New Jersey and into the mid-west, you'd see layers precursive to those Faith is talking about.

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hooah212002
Member (Idle past 161 days)
Posts: 3183
Joined: 08-12-2009


Message 218 of 740 (734247)
07-27-2014 12:58 PM
Reply to: Message 201 by Faith
07-26-2014 10:28 PM


Re: Layer / Sill
Just because you are geologically ignorant doesn't mean your question hasn't been answered over and over. and over. and over.

Organic life is nothing but a genetic mutation, an accident. Your lives are measured in years and decades. You wither and die. We are eternal, the pinnacle of evolution and existence. Before us, you are nothing. Your extinction is inevitable. We are the end of everything.

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edge
Member (Idle past 45 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 219 of 740 (734248)
07-27-2014 1:06 PM
Reply to: Message 194 by JonF
07-26-2014 7:05 PM


Re: Layer / Sill
Are you actually arguing that all igneous layers are intrusive?

Apparently that is the case. Faith seems to require that all deformation and volcanism and plate tectonics(?), occurred after the fludde. So, if there is an igneous body in the sedimentary sequence, it must have been intruded.

This, of course, is at odds with geological observations.

Tuffs are not intrusive. And it's quite possible to determine when a lava layer is not intrusive.

It is weird to some people that igneous rocks can actually span the gap between intrusive and sedimentary. In fact, probably most volcanic rocks are, to some degree, 'sedimentary'. They come under the general term 'pyroclastic' and 'reworked' (for lack of a better term).

I will say that volcanic stratigraphy is ... er, challenging at times; especially if you are not working with 'flood basalts' (not to be confused with The Fludde). That may be the reason that they are often not shown in generalized 'geological columns'.


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edge
Member (Idle past 45 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 220 of 740 (734249)
07-27-2014 1:14 PM
Reply to: Message 189 by Faith
07-26-2014 6:12 PM


Re: The Bronx Diagram Reconstructed
But it would sure be nice if just once in a while somebody responded to something like that reconstruction effort I drew, with something like "Wow, yes, now I see it, that's really brilliant how you put all that together," instead of the predictable denigration like how I supposedly "took liberties" with it and how there are really four or five tectonic events there (which I don't see at all) and so on.

Well, just on cursory review, you ignored the fact that there is an angular unconformity between the Stockton Formation and the units beneath it. It also appears that you ignore several fault surfaces. As a first attempt by a novice, maybe it's not too bad.

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Faith
Member
Posts: 33872
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.2


Message 221 of 740 (734256)
07-27-2014 3:06 PM
Reply to: Message 220 by edge
07-27-2014 1:14 PM


Re: The Bronx Diagram Reconstructed
In my own diagram of it I ignored the angular unconformity but I didn't ignore it in my description to HBD right above it. There's a difference between ignoring it and thinking it's best understood as I showed it in the diagram.

ABE: Here's what I said to HBD in Message 181:

OK, my reading was, maybe still is, that the yellow, red, green and brown (Stockton formation) were all layered one on top of the other, and then the sill intruded between the brown and whatever was above at that time. The blue gneiss below represents some kind of upward force that distorted them all, folding them all at that central point, the red Manhattan and the green Hartland being eroded away over that central area and remaining only on either side, the Stockton and the sill also being eroded away but remaining only on the left, and whatever was above the sill being eroded away completely. I see the brown Stockton layer with the Palisades sill above it shifting as a unit to the left as the area to the right of it pushes upward, and retaining its straightness because the sill magma acts as a kind of glue. Otherwise it could be interpreted as an angular unconformity with respect to the lower rocks (abe; But this would have had to occur before the central upward force occurred so that it would have deposited horizontally, but this may be what makes it all appear as a unit since that formation is no more displaced than the Manhattan and the Hartland, if you follow me./abe) After all that occurred but not long after, the fault up through that formation occurred.

What I was trying to say is that since it would have had to deposit horizontally on the angular section, it would have to have been deposited before the tectonic pressure that uplifted that whole central area, which is probably the cause of the angular section anyway, meaning it probably didn't exist when the Stockton formation was deposited. So there was no angular unconformity until the tectonic upheaval that shifted that part of it to the left and eroded away the rest of it.

Also, as I've been looking at cross sections by the hundreds lately I've seen the amazing variety of ways faults shift the layers relative to each other, so that the angular unconformity doesn't look like anything special, just another way the strata got moved around.

So that's why I ended up drawing it as I did.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.


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Faith
Member
Posts: 33872
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.2


Message 222 of 740 (734260)
07-27-2014 3:38 PM
Reply to: Message 216 by edge
07-27-2014 12:30 PM


Re: Blackrock Escarpment is all volcanic
I've read this through a number of times, and I know you've posted on it many times before, but right now I can't figure out why it can't be a sill. Would you please explain that again. Thanks.

abe: the "erosional surface?"

Or, since volcanic ash has been coming up, could it be that?

Edited by Faith, : No reason given.


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Faith
Member
Posts: 33872
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.2


Message 223 of 740 (734261)
07-27-2014 3:45 PM
Reply to: Message 215 by JonF
07-27-2014 9:33 AM


Are you saying that all these layers are volcanic ash or welded tuff?

And, what that would mean is that it was airborne rather than a flow, right?

Edited by Faith, : No reason given.


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edge
Member (Idle past 45 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


(1)
Message 224 of 740 (734263)
07-27-2014 4:02 PM
Reply to: Message 222 by Faith
07-27-2014 3:38 PM


Re: Blackrock Escarpment is all volcanic
I've read this through a number of times, and I know you've posted on it many times before, but right now I can't figure out why it can't be a sill. Would you please explain that again. Thanks.

abe: the "erosional surface?"


If a contact has been eroded, then it was one time at the surface. If a lava is deposited at the surface, both the lower and upper contacts would show evidence of erosion.

We live on an erosional surface, also known as an unconformity.

Or, since volcanic ash has been coming up, could it be that?

Believe it or not, we have learned how to tell lava flows from volcanic ash.

This message is a reply to:
 Message 222 by Faith, posted 07-27-2014 3:38 PM Faith has responded

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edge
Member (Idle past 45 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


(1)
Message 225 of 740 (734264)
07-27-2014 4:19 PM
Reply to: Message 223 by Faith
07-27-2014 3:45 PM


Are you saying that all these layers are volcanic ash or welded tuff?

The ones so-labeled are. In the bottom picture the whole outcrop is what we call a single 'cooling unit' or the product of a single eruption. If it is thick enough, the interior remains semi-molten and forms a glass such as obsidian. The word 'vitrophyre' means that it is a glass with some crystals in it.

And, what that would mean is that it was airborne rather than a flow, right?

Yes, but it did flow, though maybe not very far. Think of it like a turbidite similar to the ones we see in sedimentary rocks, just occurring in the atmosphere instead of the ocean. Ash flows are quite dangerous and kill a lot of people because they can outrun a vehicle.

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