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Author Topic:   Evidence that the Great Unconformity did not Form Before the Strata above it
Faith 
Suspended Member (Idle past 767 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 196 of 1939 (753512)
03-20-2015 11:42 AM
Reply to: Message 195 by PaulK
03-20-2015 10:32 AM


Re: The Reformers on Science
Genesis 1 was not written solely for people with knowledge of modern astronomy or cosmology.

Genesis 1 was written by and originally for people with an ancient Middle Eastern geocentric cosmology.

Genesis, like all the Bible, was written for all people in all times in all cultures with all degrees of knowledge about everything.

In relation to the cultures of its day it was written mostly as an answer to the idolatrous religions of all the different peoples, which it answers with a flat declaration of the one true God as Creator of everything. Cosmology is a very very small part of its concern.

Genesis 1 is strongly consistent with ancient Middle Eastern cosmology.

Genesis 1 has very little interest in cosmology at all.

It begins with the Primordial Ocean. It lacks any concept of the Earth as a planet, seeing it as a few areas of dry land, set in the Ocean. It lacks even the idea that the moon only reflects light from the sun.

None of this is about cosmology, or any particular culture's point of view, it's about how God created everything.

If Genesis 1 is intended to communicate accurate information about the physical universe or even how it was created it does rather a poor job of it.

I'll let the Creator know your objections to His work. But again cosmology is not of any importance in Genesis 1.

Why, then, should anyone assume that Genesis 1 was intended by God to convey information about the physical universe at all ?

Because it's God's Word and whatever it says about the physical universe is true. But I don't think it has ANY aim at providing a scientific description of anything whatever.

Edited by Faith, : correct quote code


This message is a reply to:
 Message 195 by PaulK, posted 03-20-2015 10:32 AM PaulK has replied

Replies to this message:
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PaulK
Member
Posts: 17181
Joined: 01-10-2003
Member Rating: 2.5


Message 197 of 1939 (753517)
03-20-2015 12:05 PM
Reply to: Message 196 by Faith
03-20-2015 11:42 AM


Re: The Reformers on Science
quote:

Genesis 1 has very little interest in cosmology at all.

That's a very weird statement. And quite obviously untrue.

quote:

None of this is about cosmology, or any particular culture's point of view, it's about how God created everything.

And that is also obviously untrue. You've got the Primordial Ocean right there in Genesis 1:2 That IS cosmology, and it IS an important part of the view of the world held in the Ancient Middle East.

quote:

I'll let the Creator know your objections to His work. But again cosmology is not of any importance in Genesis 1.

I'm not objecting to anything that God has done. I'm pointing out that it seems pretty clear that God DIDN'T do what you claim.

quote:

Because it's God's Word and whatever it says about the physical universe is true.

That's what you say. It's not what the Bible says.


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 Message 196 by Faith, posted 03-20-2015 11:42 AM Faith has not replied

  
NoNukes
Inactive Member


Message 198 of 1939 (753546)
03-20-2015 1:45 PM
Reply to: Message 186 by Faith
03-19-2015 10:45 PM


Re: The Reformers on Science
NoNukes writes:

The few geocentrists you find around today are Protestants and Catholics who consider themselves to be Bible fundamentalists.

Yeh, so?

Yeah, so it supports my argument that geocentricism is not just Catholicism or Romanism or whatever you want to call it. People can and do reach that conclusion by reading the Bible, and it is highly likely that the Biblical writers also had the same view of the universe. Modern geoncentrists get to that conclusion despite the fact that they don't have Ptolemy's influence to blame and despite having all of modern science to draw on. They reach those conclusions because the universe 'looks' geocentric unless you look at it hard and because the Bible says the universe is geocentric. And by hard, I mean employing the science that was available at least by the 17th century. And some visual evidence (namely as the phases and sizes of Venus which cannot be explained using a geocentric model), has been visible to mankind for his entire history.

Edited by NoNukes, : No reason given.


Je Suis Charlie

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

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
Member
Posts: 3884
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001


Message 199 of 1939 (753611)
03-20-2015 11:30 PM


From another topic
From here:

Faith writes:

Edge writes:

Well, it doesn't have to, I suppose, but it probably did. First of all, the development of a schist (with a platy foliation) is dynamothermal, meaning that there was deformation along with heating. If the intrusion caused the schist development, then there should be some geometric relationship of the intrusion to the orientation of the foliation. That does not appear to be the case.

As to the burial origin of the foliation, if that is due to the Paleozoic section being deposited, then the foliation should be closer to vertical. In fact, IIRC, there are some folds in the schist, which would suggest some kind of lateral compression.

I wonder if you would be so kind as to translate these paragraphs into simple English for us mentally challenged YECs? I would really like to have some idea what you are talking about.

First of all, I think Edge had an error. I think a sentence above should have been "As to the burial origin of the foliation, if that is due to the Paleozoic section being deposited, then the foliation should be closer to horizontal". The greatest pressure is perpendicular to the foliation.

The metamorphism of the schist require heat and high pressure. The non-metamorphism of the overlying sediments requires the lack of heat and high pressure. The sediments were not there when the schist metamorphism happened.

http://en.wikipedia.org/...s#Early_Paleoproterozoic_basement:

CORRECTION - The above link was to the wrong location in the article. Below is the correct location.

http://en.wikipedia.org/...shnu_Basement_Rocks#Upper_contact:

quote:
The upper contact of the Vishnu Basement Rocks is a major unconformity between it and either the Tonto Group or Unkar Group that resulted from uplift and the deep erosion, by at least 25 kilometres (16 mi), of the Vishnu Basement Rocks and any overlying strata. In the case of the unconformity between the Vishnu Basement Rocks and the Unkar Group, studies of the underlying Vishnu Basement Rocks indicate they were uplifted from a depth of about 25 kilometres (16 mi) to a depth of about 10 kilometres (6.2 mi), between 1.75 and 1.66 Ga, and from a depth of about 10 kilometres (6.2 mi) to the weathered surface on which the Bass Formation of the Unkar Group accumulated – between 1.66 and 1.25 Ga.

And that unconformity is a nonconformity - It is sediments on top of basement metamorphics and intrusives.

Now the above quoted is a bit muddled.

But, pressure means deep burial. Per my interpretation of the above quoted, what became the Vishnu Schist was once buried under approximately 25 kilometers of other material (The summit of Mt. Everest is about 9 kilometers above sea level). Perhaps that interpretation is wrong. But if so, that means that 25 kilometers of material was eroded off before the deposition of any of the currently overlying sediments.

Before I researched this a bit, my WAG (wild-ass-guess) was that at least 10 kilometers of burial was required for the metamorphism to happen. That's still an Everest height of sediment that had to have been eroded off, before the depostion of the Unkar Group. And that takes time, and that's before any of the sediments were deposited, which requires more time. Not going to happen in 6-10,000 years.

Moose

Edited by Minnemooseus, : Fix quote box. I don't use [quote] much.

Edited by Minnemooseus, : Corrected a link. Had been to the wrong place in the right article.

Edited by Minnemooseus, : Neglected to include a closing " mark.


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edge
Member (Idle past 1029 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 200 of 1939 (753615)
03-21-2015 12:02 AM
Reply to: Message 199 by Minnemooseus
03-20-2015 11:30 PM


Re: From another topic
First of all, I think Edge had an error. I think a sentence above should have been "As to the burial origin of the foliation, if that is due to the Paleozoic section being deposited, then the foliation should be closer to horizontal. The greatest pressure is perpendicular to the foliation.

Heh, heh... rough day to day. Yes, I was thinking that the forces would have been vertical. If I can edit that, I shall.

The metamorphism of the schist require heat and high pressure. The non-metamorphism of the overlying sediments requires the lack of heat and high pressure. The sediments were not there when the schist metamorphism happened.

Exactly. And they are close enough in space that there should be some effect on the Paleozoic section.

And that unconformity is a nonconformity - It is sediments on top of basement metamorphics and intrusives.

Also true. However, I think that nonconformities are a subset of unconformities.

This message is a reply to:
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Faith 
Suspended Member (Idle past 767 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 201 of 1939 (753618)
03-21-2015 12:19 AM
Reply to: Message 199 by Minnemooseus
03-20-2015 11:30 PM


Re: From another topic
The metamorphism of the schist require heat and high pressure. The non-metamorphism of the overlying sediments requires the lack of heat and high pressure. The sediments were not there when the schist metamorphism happened.

In my scenario they were and there is no reason to suppose the intense heat reached to that level, especially if the entire region was soaked in Flood water as I hypothesize that it was. The blocks of tilted Supergroup also weren't metamorphosed, I assume for the same reason, but I still think the Vishnu contains the rubble from the Supergroup that is no longer in evidence AS Supergroup. Oddly, one of the layers of the Supergroup is metamorphosed, the Shinumo quartzite. Enough heat and pressure for that without affecting the others? I don't know but that's the lines I'm thinking along.

http://en.wikipedia.org/...shnu_Basement_Rocks#Upper_contact:

The upper contact of the Vishnu Basement Rocks is a major unconformity between it and either the Tonto Group or Unkar Group that resulted from uplift and the deep erosion, by at least 25 kilometres (16 mi), of the Vishnu Basement Rocks and any overlying strata.

Am I reading this right? Is this talking about erosion caused by the abrasion between lower and upper rocks?

And that unconformity is a nonconformity - It is sediments on top of basement metamorphics and intrusives.

So, on top of the basement metamorphics and intrusives the contact with the sedimentary strata is a nonconformity, but on top of the tilted Supergroup it's an angular unconformity? Is that the idea?

But, pressure means deep burial. Per my interpretation of the above quoted, what became the Vishnu Schist was once buried under approximately 25 kilometers of other material (The summit of Mt. Everest is about 9 kilometers above sea level). Perhaps that interpretation is wrong. But if so, that means that 25 kilometers of material was eroded off before the deposition of any of the currently overlying sediments.

How would that compare with my Young Earth interpretation of three miles (about 5 km?) of sedimentary layers burying the Vishnu as it formed into schist. On this scenario only the upper two miles of that strata were then eroded away as the canyon was cut and the Grand Staircase as well. Three miles of sedimentary weight not enough "deep burial" to form schist?

Before I researched this a bit, my WAG (wild-ass-guess) was that at least 10 kilometers of burial was required for the metamorphism to happen. That's still an Everest height of sediment that had to have been eroded off, before the depostion of the Unkar Group. And that takes time, and that's before any of the sediments were deposited, which requires more time. Not going to happen in 6-10,000 years.

Unless it's all soaking in a handy-dandy worldwide Flood that then recedes, washing away a two-mile depth of those upper strata as described above. That shouldn't take more than a few months, with then some years after that to lithify the strata into rock etc. Meanwhile the Vishnu should have become schist under all that pressure plus the heat from the magma beneath, IMHO.

Edited by Faith, : No reason given.

Edited by Adminnemooseus, : Fixed link. The bad version had been copy/pasted from an erroneous link in the Moose message - Also, to get the full form of the link one must use "peek" to get the full text.


This message is a reply to:
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Replies to this message:
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Minnemooseus
Member
Posts: 3884
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001


(1)
Message 202 of 1939 (753622)
03-21-2015 2:01 AM
Reply to: Message 201 by Faith
03-21-2015 12:19 AM


Sorry, but there's so much wrong here
The quotes are piling up, but it seems necessary.

Faith writes:

Moose writes:

The metamorphism of the schist require heat and high pressure. The non-metamorphism of the overlying sediments requires the lack of heat and high pressure. The sediments were not there when the schist metamorphism happened.

In my scenario they were and there is no reason to suppose the intense heat reached to that level, especially if the entire region was soaked in Flood water as I hypothesize that it was. The blocks of tilted Supergroup also weren't metamorphosed, I assume for the same reason, but I still think the Vishnu contains the rubble from the Supergroup that is no longer in evidence AS Supergroup. Oddly, one of the layers of the Supergroup is metamorphosed, the Shinumo quartzite. Enough heat and pressure for that without affecting the others? I don't know but that's the lines I'm thinking along.

As Edge said in the previous message, there's no way to shut off the metamorphism, especially that radically, at the contact. The sediments would have shown some signs of pressure and heat effects.

The schists etc. structures and compositions (see http://en.wikipedia.org/wiki/Vishnu_Basement_Rocks) are not compatible with a Supergroup protolith (pre-metamorphism form).

Re: Shinumo Quartzite - Unfortunately, that name does not require metamophism. It means that the quartz sandstone is so well silica cemented that the rock can break through the sand grains, rather than just between the grains. Besides, you're not going to get metamorphism there, without also getting metaphophism in the neighboring sediments.

Faith writes:

http://en.wikipedia.org/...shnu_Basement_Rocks#Upper_contact:

Moose writes:

The upper contact of the Vishnu Basement Rocks is a major unconformity between it and either the Tonto Group or Unkar Group that resulted from uplift and the deep erosion, by at least 25 kilometres (16 mi), of the Vishnu Basement Rocks and any overlying strata.

Am I reading this right? Is this talking about erosion caused by the abrasion between lower and upper rocks?

Erosion is the removal of material. If the lower rock/upper rock contact had undergone intense fault activity, I think you would have ended up with as substantial zone of mylonite. Or at least some evidence of fault activity, which there is none.

Faith writes:

Moose writes:

And that unconformity is a nonconformity - It is sediments on top of basement metamorphics and intrusives.

So, on top of the basement metamorphics and intrusives the contact with the sedimentary strata is a nonconformity, but on top of the tilted Supergroup it's an angular unconformity? Is that the idea?

As Edge said in the previous message, a nonconformity is a variety of unconformity. But it is a variety that implies a lot of erosion having happened. The other unconformity is an angular unconformity.

Faith writes:

Moose writes:

But, pressure means deep burial. Per my interpretation of the above quoted, what became the Vishnu Schist was once buried under approximately 25 kilometers of other material (The summit of Mt. Everest is about 9 kilometers above sea level). Perhaps that interpretation is wrong. But if so, that means that 25 kilometers of material was eroded off before the deposition of any of the currently overlying sediments.

How would that compare with my Young Earth interpretation of three miles (about 5 km?) of sedimentary layers burying the Vishnu as it formed into schist. On this scenario only the upper two miles of that strata were then eroded away as the canyon was cut and the Grand Staircase as well. Three miles of sedimentary weight not enough "deep burial" to form schist?

You would not go from high grade metamorphsim to little or no metamorphism at the contact that is the nonconfromity. Not even if the lower rocks were dry, and the upper rocks were water saturated.

Faith writes:

Moose writes:

Before I researched this a bit, my WAG (wild-ass-guess) was that at least 10 kilometers of burial was required for the metamorphism to happen. That's still an Everest height of sediment that had to have been eroded off, before the depostion of the Unkar Group. And that takes time, and that's before any of the sediments were deposited, which requires more time. Not going to happen in 6-10,000 years.

Unless it's all soaking in a handy-dandy worldwide Flood that then recedes, washing away a two-mile depth of those upper strata as described above. That shouldn't take more than a few months, with then some years after that to lithify the strata into rock etc. Meanwhile the Vishnu should have become schist under all that pressure plus the heat from the magma beneath, IMHO.

Wild fantasy, not supported by any geologic study. You're invoking a "Magic Flood", that has no relationship to geologic processes.

Moose

General reading: http://en.wikipedia.org/wiki/Metamorphism

Edited by Minnemooseus, : Autotyped "know" instead of "no". Also added general reading link at end.


This message is a reply to:
 Message 201 by Faith, posted 03-21-2015 12:19 AM Faith has replied

Replies to this message:
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Faith 
Suspended Member (Idle past 767 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 203 of 1939 (753627)
03-21-2015 3:53 AM
Reply to: Message 202 by Minnemooseus
03-21-2015 2:01 AM


Re: Sorry, but there's so much wrong here
Not to worry, it will all fit together eventually.

Just this for now:

The schists etc. structures and compositions (see http://en.wikipedia.org/wiki/Vishnu_Basement_Rocks) are not compatible with a Supergroup protolith (pre-metamorphism form).

So some say. I'll have to look it up again but one source who studied the Vishnu says it is made up of a huge range of different rocks. I ran across this earlier and mentioned it in one of these recent threads, guess I'll have to find it.

Re: Shinumo Quartzite - Unfortunately, that name does not require metamophism. It means that the quartz sandstone is so well silica cemented that the rock can break through the sand grains, rather than just between the grains. Besides, you're not going to get metamorphism there, without also getting metaphophism in the neighboring sediments.

Not at all unfortunate. It would solve the puzzle if you were right but everything I've found calls it a metamorphic rock requiring heat and pressure, such as this Google page:

Quartzite (from German: Quarzit) is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts

Its presence between nonmetamorphic rocks needs another explanation apparently.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.


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herebedragons
Member (Idle past 180 days)
Posts: 1517
From: Michigan
Joined: 11-22-2009


(2)
Message 204 of 1939 (753629)
03-21-2015 8:31 AM
Reply to: Message 203 by Faith
03-21-2015 3:53 AM


Surface of the Unconformity
everything I've found calls it a metamorphic rock requiring heat and pressure

Shinumo Quartzite

quote:
Red-brown, purple, and gray, cliff-forming sandstone. Includes four undivided informal members as defined by Daneker (1975)... All members cemented with silica, making sandstone as hard as metamorphic quartzite, but unit is not metamorphosed.

Have you given any more thought as to how the Shinumo Quartzite could protrude through the Tapeats and be overlain with Bright Angel Shale?

Shinumo Quartzite

quote:
Making up Cheops Pyramid above the Shinumo are the Paleozoic Bright Angel Shale, Muav Limestone and Temple Butte Formation, concealed for the most part beneath a good deal of talus, capped by a steep walled prominence composed of Redwall Formation. The normally ubiquitous Tapeats Sandstone is missing from below the Bright Angel Shale where hard, resistant quartzites and sandstones of the Shinumo eroded to a hilly topography with highs poking through and pinching out the much later deposited and subsequently eroded Paleozoic Tapeats.

Below is a photo of Cheops Pyramid marked up with the different strata present.

At first I wondered about the brown band at the top of the Shinumo Quartzite thinking it looked much like Tapeats Sandstone. However, the upper unit of the Shinumo is characterized as:

quote:
Finally, the upper member of the Shinumo Quartzite is composed of reddish brown and locally purple sandstone and an overlying well-cemented gray quartzite

And it has weathered almost identically as the formation below. The Tapeats would be much softer than the Shinumo and I would expect it to weather noticeably different.

ABE: (I could be wrong about the Tapeats in this photo. It may actually be Isis Temple in the background where the Tapeats is missing - a little confirmation from someone else would help)

Structures like this are really difficult to find adequate pictures to illustrate the phenomenon. As you can see, they are massive! We often need to rely on descriptions from people who have studied these up close. Edwin MacKee published "Cambrian History of the Grand Canyon Region" in 1945. Mac Kee has done extensive work studying the GC long before the internet. His books are difficult to come by, you have to go to a library in the dust, old books section. However, this book is available on Google Books as a free e-book.

quote:
“These monadnocks of the Cambrian plain may be compared with the Baraboo ridges of Huronian quartzite which by virtue of their homogeneity and hardness still stand as prominences which have weathered repeated cycles of erosion.” The maximum height of these monadnocks in the Shinumo quadrangle he gives as 600 feet. Schuchert,” after visiting an area farther east, refers to hills up to 700 feet, and Wheeler and Kerr “’ describe one north of Grand Canyon Village which rises approximately 800 feet above the base of the Tapeats sandstone. Wheeler and Kerr, moreover, call attention to the fact that at the start of Cambrian deposition these hills must have been still higher, because their upper parts were subsequently continuously reduced by erosion during the time involved in the deposition of some hundreds of feet of marine sediments - pg. 119

Regarding the "Weathering of Ep-Algonkian Surface" (Ep-Algonkian surface is the name used for the surface that would become the Great Unconformity) MacKee summarizes the work of Robert Sharp (1940)

quote:
The principal points are as follows:
1. Weathering of the Archean rocks has extended downward 10 to 12 feet in many places and as far as 50 feet below the surface in some places.
2. Weathering of Algonkian rocks has been slight, presumably because they are composed of minerals that have already survived at least one cycle of weathering.
3. Mineralogical changes in the weathered zone of the Archean rocks involve elimination of feldspars, biotite, and other iron-bearing minerals, and a notable development of iron oxides. Another result of weathering is a large increase in the percentage of insoluble residues.
4. Residual enrichment causing an increase in iron oxide is progressive upward toward the erosion surface.
5. Locally a regolith which consists of a foot or two of structureless, extensively weathered detritus grades upward into basal Cambrian sediments and downward into less weathered Archean rock.
6. Boulders of decomposition consisting of cores of relatively unaltered rock, residual after weathering along fractures and joints, are locally present beneath the true regolith.
7. The weathered material of the regolith probably should be classed as intrazonal or azonal soil, but some of the most maturely weathered detritus may be normal soil. A considerable but unknown amount of it probably was removed by waves as the Cambrian sea advanced.
8. At two localities, features interpreted as being due to surficial creep have been noted in the weathered zone at the base of Pre-Cambrian monadnocks. - pg. 121

Each of these points is strong indication that the Great Unconformity was once exposed to the surface prior to Paleozoic sediment deposition. If you have questions as to why they are problematic for continuous sedimentation, please ask and we can discuss further.

Anyway, you are not likely to find a lot of details on these features on the web except as what you might call the "Old Earth Party Line." Edwin Mac Kee spent his whole career studying the Grand Canyon, analyzing it and writing about it. Details about WHY he came to his conclusions could be found in his books. Those that have studied the region close up and in detail have determined that the Great Unconformity is an erosional surface and not a slip fault (which is more like what it would be if the basement rocks rotated underneath the Paleozoic formations).

HBD

Edited by herebedragons, : subtitle

Edited by herebedragons, : disclaimer

Edited by herebedragons, : new link to image


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.


This message is a reply to:
 Message 203 by Faith, posted 03-21-2015 3:53 AM Faith has replied

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herebedragons
Member (Idle past 180 days)
Posts: 1517
From: Michigan
Joined: 11-22-2009


(3)
Message 205 of 1939 (753637)
03-21-2015 9:44 AM
Reply to: Message 201 by Faith
03-21-2015 12:19 AM


Re: From another topic
So, on top of the basement metamorphics and intrusives the contact with the sedimentary strata is a nonconformity, but on top of the tilted Supergroup it's an angular unconformity? Is that the idea?

4 types of unconformities.

Keep in mind that the unconformity itself is the solid black line that represents a period where there was not continuous deposition. Also note, that it is interpreted to mean "missing time" but what it actually represents is a time when deposition was not continuous - in other words, deposition paused, with or with out subsequent erosion. (however, erosion is pretty much inevitable at the surface and the presence of an erosional surface would be an indication that an unconformity exists). So there is actually no "missing time" but simple no deposition.

Does that help clear things up?

Also note that there is nothing in that definition that defines long periods of time. Deposition could have paused for 1 minute between flood waves or 1 million years during an uplift. To determine time frames we would need to look at processes. But I suggest that we just focus on determining IF the Great Unconformity is really an unconformity or is it something else.

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.


This message is a reply to:
 Message 201 by Faith, posted 03-21-2015 12:19 AM Faith has not replied

Replies to this message:
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edge
Member (Idle past 1029 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 206 of 1939 (753642)
03-21-2015 11:14 AM
Reply to: Message 203 by Faith
03-21-2015 3:53 AM


Re: Sorry, but there's so much wrong here
So some say. I'll have to look it up again but one source who studied the Vishnu says it is made up of a huge range of different rocks.

Yes, some of which are not found in the Supergroup.

I ran across this earlier and mentioned it in one of these recent threads, guess I'll have to find it.

If that's what it says, it doesn't help you.

Not at all unfortunate. It would solve the puzzle if you were right but everything I've found calls it a metamorphic rock requiring heat and pressure, such as this Google page:

The term 'quartzite' is often used loosely, but if you want to be precise, many quartzites are actually 'quartz arenite', and meteamorphic quartzite are termed 'orthoquartzite'.

The term 'quartz arenite' is derived from the main component (quartz) and arenite, a Latin term for a rock with sand-sized grains. In some literature, these can be called orthoquartzites, a confusing term which usually refers to the metamorphic rock quartzite, though most metamorphic quartzites are diagentically fused from quartz arenites. The term "quartzose sandstone" can also be used for a quartz arenite.(http://en.wikipedia.org/wiki/Quartz_arenite)

This is how I was taught many years ago and it's only coming back to me now as I look up these terms.

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edge
Member (Idle past 1029 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


(2)
Message 207 of 1939 (753644)
03-21-2015 11:27 AM
Reply to: Message 204 by herebedragons
03-21-2015 8:31 AM


Re: Surface of the Unconformity
This is an excellent post. Thank you for tracking all of this down.

I especially enjoyed this part:

Regarding the "Weathering of Ep-Algonkian Surface" (Ep-Algonkian surface is the name used for the surface that would become the Great Unconformity) MacKee summarizes the work of Robert Sharp (1940)

quote:
The principal points are as follows:
1. Weathering of the Archean rocks has extended downward 10 to 12 feet in many places and as far as 50 feet below the surface in some places.
2. Weathering of Algonkian rocks has been slight, presumably because they are composed of minerals that have already survived at least one cycle of weathering.
3. Mineralogical changes in the weathered zone of the Archean rocks involve elimination of feldspars, biotite, and other iron-bearing minerals, and a notable development of iron oxides. Another result of weathering is a large increase in the percentage of insoluble residues.
4. Residual enrichment causing an increase in iron oxide is progressive upward toward the erosion surface.
5. Locally a regolith which consists of a foot or two of structureless, extensively weathered detritus grades upward into basal Cambrian sediments and downward into less weathered Archean rock.
6. Boulders of decomposition consisting of cores of relatively unaltered rock, residual after weathering along fractures and joints, are locally present beneath the true regolith.
7. The weathered material of the regolith probably should be classed as intrazonal or azonal soil, but some of the most maturely weathered detritus may be normal soil. A considerable but unknown amount of it probably was removed by waves as the Cambrian sea advanced.
8. At two localities, features interpreted as being due to surficial creep have been noted in the weathered zone at the base of Pre-Cambrian monadnocks. - pg. 121


Earlier, I have suggested that some of the material just above the unconformity consists of materials derived directly from the underlying rock. While I was reluctant to be too specific in drawing conclusions from a picture, these observations by Sharp give me a lot more confidence in my earlier musings. Nothing like actual field work to generate conclusive data. We could spend all week arguing about a photo (maybe we have...), but these observations put everything into perspective.

Each of these points is strong indication that the Great Unconformity was once exposed to the surface prior to Paleozoic sediment deposition.

This is an inescapable conclusion. Normally, it would be 'end of discussion' but I have a feeling that a certain poster is preparing a bulwark of denial.

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 Message 204 by herebedragons, posted 03-21-2015 8:31 AM herebedragons has not replied

  
edge
Member (Idle past 1029 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 208 of 1939 (753646)
03-21-2015 11:34 AM
Reply to: Message 205 by herebedragons
03-21-2015 9:44 AM


Re: From another topic
Keep in mind that the unconformity itself is the solid black line that represents a period where there was not continuous deposition. Also note, that it is interpreted to mean "missing time" but what it actually represents is a time when deposition was not continuous - in other words, deposition paused, with or with out subsequent erosion. (however, erosion is pretty much inevitable at the surface and the presence of an erosional surface would be an indication that an unconformity exists). So there is actually no "missing time" but simple no deposition.

One could say 'missing rock' that represents the passage of time.

And this also bears repeating:

Also note that there is nothing in that definition that defines long periods of time. Deposition could have paused for 1 minute between flood waves or 1 million years during an uplift.

In other words, the Great Unconformity does not necessarily represent a billion years of erosion, only a billion years of missing record. This is one of the subtleties of unconformities that people often overlook.

To determine time frames we would need to look at processes. But I suggest that we just focus on determining IF the Great Unconformity is really an unconformity or is it something else.

Yes, we should focus the discussion, at least for the time being.

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 Message 205 by herebedragons, posted 03-21-2015 9:44 AM herebedragons has not replied

Replies to this message:
 Message 209 by jar, posted 03-21-2015 11:55 AM edge has replied

  
jar
Member
Posts: 33957
From: Texas!!
Joined: 04-20-2004
Member Rating: 2.0


Message 209 of 1939 (753649)
03-21-2015 11:55 AM
Reply to: Message 208 by edge
03-21-2015 11:34 AM


Re: From another topic
In other words, the Great Unconformity does not necessarily represent a billion years of erosion, only a billion years of missing record. This is one of the subtleties of unconformities that people often overlook.

Would it not be more accurate to say that "the Great Unconformity represents at least a billion years of missing record?"

We can say that the time period would be at least as long as shown by the remaining layers of the Super Group but what is left of the Super Group is very likely not all that was there.


Anyone so limited that they can only spell a word one way is severely handicapped!

This message is a reply to:
 Message 208 by edge, posted 03-21-2015 11:34 AM edge has replied

Replies to this message:
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edge
Member (Idle past 1029 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 210 of 1939 (753652)
03-21-2015 12:21 PM
Reply to: Message 209 by jar
03-21-2015 11:55 AM


Re: From another topic
Would it not be more accurate to say that "the Great Unconformity represents at least a billion years of missing record?"

Exactly.

We can say that the time period would be at least as long as shown by the remaining layers of the Super Group but what is left of the Super Group is very likely not all that was there.

Yes, the Supergroup could be considered part of the missing record. Then, of course, we are presented with two unconformities...

I think saw that called a 'biconformity' or something like that.


This message is a reply to:
 Message 209 by jar, posted 03-21-2015 11:55 AM jar has not replied

  
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