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Author Topic:   Exploring the Grand Canyon, from the bottom up.
IrishRockhound
Member (Idle past 1787 days)
Posts: 569
From: Ireland
Joined: 05-19-2003


Message 211 of 260 (436773)
11-27-2007 1:55 PM
Reply to: Message 210 by jar
11-26-2007 10:56 AM


Re: Read it and Nankoweap
Once again, Wikipedia is our best friend.

quote:
Sedimentary rocks are formed because of the overburden pressure as particles of sediment are deposited out of air, ice, wind, or water flows carrying the particles in suspension. As sediment deposition builds up, the overburden (or 'lithostatic') pressure squeezes the sediment into layered solids in a process known as lithification ('rock formation') and the original connate fluids are expelled.

Sediment gets dumped in a spot. As more and more gets dumped there, whether by air, ice, wind or water, the stuff on the bottom gets compacted. All the air/water gets squeezed out, and eventually after it gets reeeeeeally well crushed, it solidifies into rock.


This message is a reply to:
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jar
Member
Posts: 28433
From: Texas!!
Joined: 04-20-2004
Member Rating: 2.6


Message 212 of 260 (436779)
11-27-2007 2:20 PM
Reply to: Message 211 by IrishRockhound
11-27-2007 1:55 PM


Re: Read it and Nankoweap
I guess I'm just old, but why does one formation end up sandstone, another shale or mudstone?


Aslan is not a Tame Lion
This message is a reply to:
 Message 211 by IrishRockhound, posted 11-27-2007 1:55 PM IrishRockhound has not yet responded

Replies to this message:
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Jazzns
Member (Idle past 1262 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 213 of 260 (436784)
11-27-2007 3:09 PM
Reply to: Message 212 by jar
11-27-2007 2:20 PM


Re: Read it and Nankoweap
I guess I'm just old, but why does one formation end up sandstone, another shale or mudstone?

Its all about the size of the particles which relate to the energy, or lack thereof, which is transporting the particles.

It takes more energy to transport a particle of sand than it does a smaller particle of silt even if they are made from the same material. So up high in a mountain stream, water and wind will pick up sand and silt both and carry them away.

Near a beach though, the energy of the wind and water is much lower and so sand which makes it there goes no further, but silt can continue on.

Silt that makes it out into deeper and deeper water will eventually hit the point where there is little to no energy to keep in moving so it will settle out.

The different force of weathering energy at different geographic locations basically sorts material out over the course of its transport. One only needs to look at how energetic a mountain stream is compared to the mouth of any of the great rivers to see the effect.


Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)
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jar
Member
Posts: 28433
From: Texas!!
Joined: 04-20-2004
Member Rating: 2.6


Message 214 of 260 (436787)
11-27-2007 3:19 PM
Reply to: Message 213 by Jazzns
11-27-2007 3:09 PM


Re: Read it and Nankoweap
Okay, let me try describing it and see how close I come.

If we looked at the rocks and asked about how the materials that got there might have been transported, we could relate material laid down to how active the transport method was by size of particulate.

From most to least active we would see:

  1. sandstone
  2. siltstone
  3. shale
  4. mudstone

Is that correct?


Aslan is not a Tame Lion
This message is a reply to:
 Message 213 by Jazzns, posted 11-27-2007 3:09 PM Jazzns has responded

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Jazzns
Member (Idle past 1262 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 215 of 260 (436791)
11-27-2007 3:40 PM
Reply to: Message 214 by jar
11-27-2007 3:19 PM


Re: Read it and Nankoweap
From most to least active we would see:

1. sandstone
2. siltstone
3. shale
4. mudstone

I think that list looks right. I forget exactly which is smaller shale or mud.

There is some above sandstone though, IRH can help me with the exact correctness of this but it goes.

1. Breccia - Large and jagged pieces of rock mixed in with sizes of particles all the way down to silt sized. (there is nothing preventing smaller particles from sticking around with bigger ones)
2. Conglomerate - Large pieces of rock that are rounded off usually indicating that they were transported at least a little bit.
3. Sandstone
4. Siltstone
5. Shale
6. Mudstone


Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)
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jar
Member
Posts: 28433
From: Texas!!
Joined: 04-20-2004
Member Rating: 2.6


Message 216 of 260 (436794)
11-27-2007 4:10 PM
Reply to: Message 215 by Jazzns
11-27-2007 3:40 PM


Next the Chuar Group
The next group up is the Chuar Group. From what I gather it is yet another major change from the lower Nankoweap and made of at least two major formation.

What can you tell me about the Chuar Group other than that it is almost a mile think?


Aslan is not a Tame Lion
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bluescat48
Member (Idle past 1540 days)
Posts: 2347
From: United States
Joined: 10-06-2007


Message 217 of 260 (436796)
11-27-2007 4:18 PM
Reply to: Message 215 by Jazzns
11-27-2007 3:40 PM


Re: Read it and Nankoweap
from Wikipedia:

φ scale

Size range(metric) Size range(approx. inches) Aggregate name
(Wentworth Class) Other names
< −8 > 256 mm > 10.1 in Boulder
−6 to −8 64–256 mm 2.5–10.1 in Cobble
−5 to −6 32–64 mm 1.26–2.5 in Very coarse gravel Pebble
−4 to −5 16–32 mm 0.63–1.26 in Coarse gravel Pebble
−3 to −4 8–16 mm 0.31–0.63 in Medium gravel Pebble
−2 to −3 4–8 mm 0.157–0.31 in Fine gravel Pebble
−1 to −2 2–4 mm 0.079–0.157 in Very fine gravel Granule
0 to −1 1–2 mm 0.039–0.079 in Very coarse sand
1 to 0 ½–1 mm 0.020–0.039 in Coarse sand
2 to 1 ¼–½ mm 0.010–0.020 in Medium sand
3 to 2 125–250 µm 0.0049–0.010 in Fine sand
4 to 3 62.5–125 µm 0.0025–0.0049 in Very fine sand
8 to 4 3.90625–62.5 µm 0.00015–0.0025 in Silt Mud
> 8 < 3.90625 µm < 0.00015 in Clay Mud
>10 < 1 µm < 0.000039 in Colloid Mud

Clastic sedimentary rocks, such as breccia or sandstone, were formed from rocks that have been broken down into fragments by weathering, which then have been transported and deposited elsewhere.

Clastic sedimentary rocks may be regarded as falling along a scale of grain size, with shale being the finest with particles less than 0.004 mm, siltstone being a little bigger with particles between 0.004 to 0.06 mm, and sandstone being coarser still with grains 0.06 to 2 mm, and conglomerates and breccias being the coarsest with grains 2 to 256 mm. Breccia has sharper particles, while conglomerate is catergorized by its rounded particles. Arenite is a general term for sedimentary rock with sand-sized particles.

It appears that mudstone can be the same as siltstone & shale just different mineral content


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JB1740
Member (Idle past 3295 days)
Posts: 132
From: Washington, DC, US
Joined: 11-20-2007


Message 218 of 260 (436805)
11-27-2007 4:52 PM
Reply to: Message 211 by IrishRockhound
11-27-2007 1:55 PM


Re: Read it and Nankoweap
I'm coming in to this late and for that I apologize. This might not
be critical to the point at hand, but it does help to understand the
difference between various sedimentary materials From the perspective
of a geologist, there is no real appreciable difference between rock
and sediment. Beware the wikis of the world. A rock is an
aggregate of minerals. No lithification component is needed. I
have seen rocks containing dinosaur fossils that are 67 million
years old but which are hardly cemented at all and can be pulled
apart with your fingers. In reality a pile of sand is a rock as it is
an aggregate of minerals (sand grains are usually grains of
individual minerals). The important thing to think about when
contemplating sedimentary rocks is the process of formation.
This is what it's all about. Whether or not the rock is lithified is
of tertiary importance at best.
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jar
Member
Posts: 28433
From: Texas!!
Joined: 04-20-2004
Member Rating: 2.6


Message 219 of 260 (437001)
11-28-2007 12:45 PM
Reply to: Message 218 by JB1740
11-27-2007 4:52 PM


Re: Read it and Nankoweap
Welcome to the thread and thanks for reminding us.

What we are trying to do in this thread is as the title suggest, slowly work our way up formation by formation from the current bottom of the Grand Canyon. So far we are still down in the basement and what we are trying to do is actually describe that hands on aspect of each layer.

The important thing to think about when
contemplating sedimentary rocks is the process of formation.

That is what we are looking for, with the understanding that dating should be avoided for now.

Try and think of this thread as a view as it might have been seen several hundred years ago, long before things like radiocarbon dating were known.


Aslan is not a Tame Lion
This message is a reply to:
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JB1740
Member (Idle past 3295 days)
Posts: 132
From: Washington, DC, US
Joined: 11-20-2007


Message 220 of 260 (437004)
11-28-2007 12:51 PM
Reply to: Message 219 by jar
11-28-2007 12:45 PM


Re: Read it and Nankoweap
Jar, Roger that. I'll take a gander through and see if there have been any questions asked that I can answer or if there is anything I have to contribute.
This message is a reply to:
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jar
Member
Posts: 28433
From: Texas!!
Joined: 04-20-2004
Member Rating: 2.6


Message 221 of 260 (437005)
11-28-2007 12:54 PM
Reply to: Message 220 by JB1740
11-28-2007 12:51 PM


Re: Read it and Nankoweap
Great, please hang around because once we cover these last few formations in the Super group we get to the exciting questions of how they got tilted and where so much of them went?


Aslan is not a Tame Lion
This message is a reply to:
 Message 220 by JB1740, posted 11-28-2007 12:51 PM JB1740 has responded

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JB1740
Member (Idle past 3295 days)
Posts: 132
From: Washington, DC, US
Joined: 11-20-2007


Message 222 of 260 (437013)
11-28-2007 1:49 PM
Reply to: Message 221 by jar
11-28-2007 12:54 PM


Re: Read it and Nankoweap
That's good...I don't spend that much time thinking about the Proterozoic.
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JB1740
Member (Idle past 3295 days)
Posts: 132
From: Washington, DC, US
Joined: 11-20-2007


Message 223 of 260 (437017)
11-28-2007 2:08 PM
Reply to: Message 217 by bluescat48
11-27-2007 4:18 PM


Re: Read it and Nankoweap
It appears that mudstone can be the same as siltstone & shale just different mineral content

Yes for siltstone versus mudstone (mud and silt are grain-size classifcations)...no for these two versus shale. Mudrocks (e.g., mudstone and siltstone) are distinguished from shale by virtue of shale being fissile. Fissile means that a hand sample of shale tends to be comprised of many very thin laminae which are parallel to bedding (bedding is very roughly analogous to the amount of sediment laid down during one sedimentation event--one event more or less equals one bed). You can think of laminae as just very very fine beds (again rough analogy). So where as mudrocks are bedded sedimentary rocks, shales are bedded and laminated sedimentary rocks. For most of the discussion we're likely to have here, we don't really need to worry about the differences between mudrocks and shale and we can think of them as roughly equivalent (although in reality they form under slightly different conditions and thus are different rocks).

Did that make sense or was it more confusing than helpful?


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bluescat48
Member (Idle past 1540 days)
Posts: 2347
From: United States
Joined: 10-06-2007


Message 224 of 260 (437019)
11-28-2007 2:24 PM
Reply to: Message 223 by JB1740
11-28-2007 2:08 PM


Re: Read it and Nankoweap
I was referring to the size of the aggregate
This message is a reply to:
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JB1740
Member (Idle past 3295 days)
Posts: 132
From: Washington, DC, US
Joined: 11-20-2007


Message 225 of 260 (437022)
11-28-2007 2:28 PM
Reply to: Message 224 by bluescat48
11-28-2007 2:24 PM


Re: Read it and Nankoweap
If talking about just grain size then basically...yep.
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