Exploring the Grand Canyon, from the bottom up.

Once again, Wikipedia is our best friend.

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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.

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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.

I guess I'm just old, but why does one formation end up sandstone, another shale or mudstone?

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Aslan is not a Tame Lion

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.

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Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)

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?

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Aslan is not a Tame Lion

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

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Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)

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?

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Aslan is not a Tame Lion

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

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.

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. 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.

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Aslan is not a Tame Lion

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.

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?

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Aslan is not a Tame Lion

That's good...I don't spend that much time thinking about the Proterozoic.

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?

I was referring to the size of the aggregate

If talking about just grain size then basically...yep.