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Author | Topic: Exploring the Grand Canyon, from the bottom up. | |||||||||||||||||||||||
jar Member Posts: 33957 From: Texas!! Joined: Member Rating: 2.0 |
Start at Message 1 sir.
Aslan is not a Tame Lion
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jar Member Posts: 33957 From: Texas!! Joined: Member Rating: 2.0 |
Sure would like for one of our
Edited by jar, : No reason given. Aslan is not a Tame Lion
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IrishRockhound Member (Idle past 3758 days) Posts: 569 From: Ireland Joined: |
Above the Dox formation is the Cardenas Basalts. Volcanic rock, i.e. lava flows. Much of what you get from google on it conisists of demented creationist honking about how the dating for this series is inaccurate or whatnot.
Here's a quick description I managed to dig up: "The Cardenas Lava is the name given to a series of basalt and basaltic andesite flows and sandstone interbeds that are above the Dox Formation, but below the Nankoweap Formation. The Cardenas Lava is only exposed in the eastern part of the canyon, where it ranges from 785 feet to 985 feet in thickness. The contact between the Cardenas Lava and the Nankoweap Formation is an unconformity. An unknown amount of the Cardenas Lava was removed before the deposition of the Nankoweap." Sandstone and basalt, hmmm. Periodic coastal volcanic eruptions?
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jar Member Posts: 33957 From: Texas!! Joined: Member Rating: 2.0 |
Just a few questions if you please.
You say "a series of basalt and basaltic andesite flows and sandstone interbeds." For the benefit of this OLD mind, does that mean the Cardenas layer is actually a whole series of layers? What does "Andesite flows" mean? Just for those following along we are approaching 200 posts and here is where we are. Aslan is not a Tame Lion
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The Matt Member (Idle past 4864 days) Posts: 99 From: U.K. Joined: |
Andesite is a different type of lava. It has a different mineral composition to basalt (less silica, most significantly), and is generally a good deal thicker, leading to steeper volcanoes and more explosive eruptions.
{Note from Adminnemooseus - Re: "(less silica, most significantly)." - The Matt is ambiguous about which volcanic type this refers to. It would refer to basalt. Andesite has more silica that basalt.} Edited by Adminnemooseus, : See note above.
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jar Member Posts: 33957 From: Texas!! Joined: Member Rating: 2.0 |
Okay, got that it is a different type of lava.
Need some more help. Can one event produce both types of flows? Edited by jar, : appalin spallin Aslan is not a Tame Lion
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jar Member Posts: 33957 From: Texas!! Joined: Member Rating: 2.0 |
It seems that the Cardenas Lava flows are between 685 and 985 feet thick.
The lower Dox formation we covered earlier is mostly shale (mud) and sandstone with indications of being made during a series growing and receding seas. It has areas that show ripple marks and also area of mud cracks. While the Cardenas Lava flows are between 785 and 985 feet thick, the Dox formation is up to 3000 plus feet thick. As we look at each of these layer we seem to find signs that each layer really was at one time at the surface; for example we found ripple marks, rain drop impressions and mud cracks in parts of the Hakatai Shale (about 400 to 100 feet thick), then the Shinumo Quartzite layers (1000 to 1300 feet thick) then the Dox formation that is a totally different set of compositions and, as stated about, ranging up to 3000 feet thick. Is that a reasonable summary so far? Aslan is not a Tame Lion
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IrishRockhound Member (Idle past 3758 days) Posts: 569 From: Ireland Joined: |
That's about right, jar.
For reference, when we talk about a formation such as the Cardenas Basalt, we're not speaking of a single type of rock. We're actually talking of a whole series of layers of rock, representing a particular depositional environment, in this case sandstone being deposited in between volcanic eruptions. In general terms, formations are divided based on the change in depositional environment, and within the formation you will have several members or types of rock which define that environment. The Cardenas Basalt has several members such as a red sandstone layer and a basalt layer. Formations are the basic units, I guess, of how you look at the rocks.
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RAZD Member (Idle past 727 days) Posts: 20714 From: the other end of the sidewalk Joined: |
I thought clays were also characterized by ionic polarity (like water, thus the affinity for water), while silt was not. Both, being very small particle size, settle slowly in water, and thus take a lot longer to accumulate than larger granular sediment (like sand (or shells)) when they have to settle out of the water column. http://en.wikipedia.org/wiki/Clay quote: Or am I mixing definitions: quote: Defining it by size alone seems a little arbitrary to me, especially when you can have particles above and below that limit that exhibit plasticity and particles above and below that limit that don't exhibit plasticity (or should we have 'plastic clays' and 'non-plastic clays'?). http://en.wikipedia.org/wiki/Silt quote: Another thing http://en.wikipedia.org/wiki/Clay quote: This implies that all clays take a long time to make, but I also thought that clays were formed by (mixing water with) volcanic ash? http://en.wikipedia.org/wiki/Volcanic_ash quote: Which would be a fairly rapid process for making clay (mixed with larger particles) layers, and the different size particles could be separated by erosion and different settling rates ... {abe} from Message 117 by roxrcool:
Some of the larger ash particles become clay in water? Enjoy. Edited by RAZD, : roxrcool quote compare Fiocruz Genome and fight Muscular Dystrophy with Team EvC! (click) we are limited in our ability to understand by our ability to understand RebelAAmericanOZen[Deist ... to learn ... to think ... to live ... to laugh ... to share.
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jar Member Posts: 33957 From: Texas!! Joined: Member Rating: 2.0 |
From this source. Above the Cardenas formation we find the Nankoweap. Once again we see a change in the types of rock From what little I have learned so far, several thing jump out at me. First, it mentions that the lower part of the formation has a finer grain composition than the upper. That seems to indicate that the lower layers were deposited in a less active environment than the upper. I understood that when material is transported by both water and air, the larger particles get deposited first and the finer material is held in suspension longer. If the Nankoweap had been a single event I would have expected the larger coarser material to be lower with the finer sediment towards the top. Is that reasonable? Second, they mention an angular unconformity. (see Young earth explanations for Angular Unconformities.) If I remember correctly from earlier parts of this thread, sandstone, siltstone, shale and mudstone each form under different conditions and have different compositions. Can you or another of our geologists give me a short description of each of those just as a reminder? Pictures would also help. Aslan is not a Tame Lion
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RAZD Member (Idle past 727 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Do we have a sedimentary layer without (recognizable) signs of life near the bottom of the canyon, and a layer above that ...
I thought the Bass (3a?) was above the Vishnu Schist (1a) and the schist was metamorphic, and that only leaves group 2 below (did I miss something between the Vishnu and the Bass? (and is this where the layer(s) got "pinched"?)
The Houtata Conglomerate from Message 115
Or are these two sedimentary layers, one without life one with, both in the Bass? I was not aware of any non-metamorphic sedimentary rock that did not show life. Thanks compare Fiocruz Genome and fight Muscular Dystrophy with Team EvC! (click) we are limited in our ability to understand by our ability to understand RebelAAmericanOZen[Deist ... to learn ... to think ... to live ... to laugh ... to share.
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jar Member Posts: 33957 From: Texas!! Joined: Member Rating: 2.0 |
Can we hold this for just a short while. See Message 199.
The reason is that the Bass formation will return in just a little while after we cover the last few groups and at that time it will become very pertinent. Edited by jar, : fix link Aslan is not a Tame Lion
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jar Member Posts: 33957 From: Texas!! Joined: Member Rating: 2.0 |
Are there any geologists that can help me with some issues on the Nankoweap formation?
See Message 205. I'd really like to at least work through the Super Group before we need to close this thread and even after we cover these last few formations, I have some really big questions to ask about what happened. Aslan is not a Tame Lion
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IrishRockhound Member (Idle past 3758 days) Posts: 569 From: Ireland Joined: |
quote: More or less, yes. I couldn't say 100% because I haven't actually examined the rock in detail. quote: Wikipedia has a very concise description on shales and sandstones:
Just to explain: fissility is the way that shales break into thin sheets rather than into blocks like other rocks.
So overall, the visual difference between sandstone, siltstone, and shale/mudstone is how 'gritty' or coarse they are. And mudstone and shale differ only in that shale is fissile and mudstone is not. Edited by IrishRockhound, : fixed quote box
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jar Member Posts: 33957 From: Texas!! Joined: Member Rating: 2.0 |
Thanks. That helped a lot in differentiating them.
But is there any chance I could get you to elaborate a little on how they are made? Aslan is not a Tame Lion
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