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Offline Bass

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Geology Question of the Week
« Reply #100 on: 11/01/2008 01:05:46 »
as to the red sandstone, its very common in the uk,  because we used to be on and around the equator, at around 50  degrees we were in a desert environment. the action of the sun made the rock much darker red in colour and the green has got to be copper because green marks arent left by any common tree from  the tertiary when the climate was that of a desert...the sandstone deposited in the uk has laminations if found on a grand scale.. the fact that the red sandstone has laminations ( deposited in dunes ) means that a tree could not survive in a sand environment alone.  its got to be from the element. it wouldnt be discolouring, because in sandstones the only form of discolouring is bleaching, where by the action of water removes the oxide and leaves it white !
Sorry, I just couldn't leave this alone.
The red coloration in sandstone is from ferric (oxidized) iron, which precipitates and is fairly insoluble in oxidizing surface conditions. 
I only wish that all the green sandstones/mudstones were copper- that would make my job of finding copper deposits much easier.  The green coloration is most commonly ferrous (reduced) iron. 
Red sandstones do NOT require heat or a desert environment to form.  Many sandstones are formed underwater-  the red color only indicates that the rock contains iron.  Reds are common in desert environments because the rocks are generally much more deeply oxidized.
I have been in sandstone-hosted uranium deposits which occur right at the redox boundary- the rocks are red on one side of the boundary and green on the other.
 

Offline Bass

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« Reply #101 on: 11/01/2008 01:14:02 »
the rockies are running along the conservative plate boundary known as the san andreas fault, or the massive tear in the ground between the american plate and the pacific plate.so it is a plate boundary. theyre stil growing because the plates are active
Check your geography- the Rockies are approximately 1000+ kilometers (600+ miles) from the plate boundary/San Andreas Fault.  You have to cross the Coast range, the Great Valley, the Sierra Nevada mountains and the Great Basin before you reach the western edge of the Rockies.
 

Offline Karen W.

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« Reply #102 on: 11/01/2008 01:31:06 »



Any idea?? This is probably too easy BUT spec-tack-u-ler


That is very cool!
 

Offline JimBob

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« Reply #103 on: 13/01/2008 03:45:55 »
Why do hills and ridges form at a 60° angle to a strike slip fault?

If you can draw a diagram it would be even better. (Some readers are not well versed in the language of geology.) An example would also be nice.
« Last Edit: 13/01/2008 03:47:30 by JimBob »
 

Offline Bass

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« Reply #104 on: 15/01/2008 06:18:33 »
In a word "strain ellipse" (oops, two words)

Will draw funny circles when time allows.
 

Offline JimBob

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« Reply #105 on: 15/01/2008 20:03:43 »
My most gracious thanks, kind sir.
 

Offline Karen W.

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« Reply #106 on: 18/01/2008 03:26:48 »



Any idea?? This is probably too easy BUT spec-tack-u-ler


That is very cool!

It reminds me of an agate.. how they get that milky look over the top of the base color and then the shiny spots!
 

Offline Evie

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« Reply #107 on: 07/10/2008 19:28:05 »
I couldn't help but see some visual similarities...



Quote
How did these layers of red cliffs form on Mars? No one is sure. The northern ice cap on Mars is nearly divided into two by a huge division named Chasma Boreale. No similar formation occurs on Earth. Pictured above, several dusty layers leading into this deep chasm are visible. Cliff faces, mostly facing left but still partly visible from above, appear dramatically red. The light areas are likely water ice. The above image spans about one kilometer near the north of Mars, and the elevation drop from right to left is over a kilometer. One hypothesis relates the formation of Chasma Boreale to underlying volcanic activity.
http://antwrp.gsfc.nasa.gov/apod/ap081006.html
 

Offline frethack

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« Reply #108 on: 08/11/2008 00:35:50 »
Maybe from crustal extension???  I have a friend who is a planetary geologist and an expert on Mars...Ill have to ask him and see what he says.
 

Offline Bass

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« Reply #109 on: 24/12/2008 05:05:30 »
What are these stripes from??  (This will be way to easy for JimBob).

 

Offline frethack

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« Reply #110 on: 24/12/2008 15:37:31 »
At first glance, it almost looks like conjoining glaciers with medial moraines, but I dont think the white is ice (very little ice in the mountains).  It looks like evaporites...maybe halite or gypsum.

So Im gonna take a very random guess...

Evaporites from runoff (maybe from a salty playa lake) moving over either inclined strata or an antiform/synform that has differentially weathered.
 

Offline itisus

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« Reply #111 on: 30/12/2008 05:06:57 »
It looks big, in a wide mountain valley with no stream, looks like a glacier, the shadows fit medial moraines, and it is supposed to be easy, so it must be a glacier.  I would bet my geology degree if I had one, which I don't because I couldn't figure out anything in the field.
 

Offline frethack

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« Reply #112 on: 30/12/2008 15:26:29 »
The valley is certainly glacial, but at first the moraines looked FAR too large in comparison with the glacier.  Also, there doesnt appear to be much of a source for flow, as none of the cirques that can be seen are full (which might explain the anemic looking glacier).

But it is a glacier...and not evaporites.  Your geology degree is safe itisus  ;D

Its the Kennicott Glacier at Wrangell-St. Elias National Park in Alaska.  Here is an aerial view:

« Last Edit: 30/12/2008 15:32:59 by frethack »
 

Offline JimBob

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« Reply #113 on: 30/12/2008 19:02:37 »
What are these stripes from??  (This will be way to easy for JimBob).


Wanna make a bet - I didn't think it looked like ice at first glance. Was considering the weathering of an emergent thrust sleet.  But convergent glacial outflow and the resulting medial moraines was obvious after I checked out the glacier Grasshopper came up with.

DOH!

« Last Edit: 30/12/2008 19:04:57 by JimBob »
 

Offline Bass

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« Reply #114 on: 30/12/2008 22:26:40 »
Frethack- I'm impressed. Not only did you come up with the right answer, you even found the right glacier.  I visited this area several decades ago- I'm sure the glaciers were more extensive then than now.  Was intrigued at how the glacier seemed to be more than half medial moraine material.

Least you can do now is explain to non-glaciologists what medial moraines are and how they form.
 

Offline JimBob

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« Reply #115 on: 30/12/2008 23:45:56 »
Frethack- I'm impressed. Not only did you come up with the right answer, you even found the right glacier.  I visited this area several decades ago- I'm sure the glaciers were more extensive then than now.  Was intrigued at how the glacier seemed to be more than half medial moraine material.

Least you can do now is explain to non-glaciologists what medial moraines are and how they form.

Now you can see why I chose to be his Kung Geo Master. He isn't too dumb for being from Houston.
He impresses me over the phone, I hired him sight unseen.
 

Offline frethack

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« Reply #116 on: 31/12/2008 03:28:44 »
Thank you Bass for the compliment, and thank you JimBob for the almost compliment...hehehe

One thing JimBob forgot to mention is that Im also stubborn and pigheaded.

Anyway...glaciers begin in cirques (technically snowfields...but we'll start from the cirque), bowl like depressions in a mountain range that collect snow and ice.  As a glacier forms it grinds out a larger and larger cirque.  Heres an example:



As the cirque fills, the snow is compacted to firn, and then finally glacial ice and then spills over and joins with other glaciers from other cirques.  A glacier is never still, and constantly flows, albeit slowly (from a few mm to a meter or more a day, depending on snow supply and relief), as it is being replenished at its head in the cirque.  As the glacier flows it grinds down the rock around it, widening its valley, and transporting this ground material as a moraine, or a bank of till that lies on either side of a glacier.  Here is a photo:



Moraines contain everything from silt sized particles to boulders.  There are five main types of moraines:  Lateral moraines that form at opposite sides of a glacier, terminal moraines that form at the farthest extent that the glacier has travelled, recessional moraines that are deposited when the glacial ice flows faster than the cirque and snowfield can replenish (the glacier begins to recede), ground moraines which are fine silts (glacial flour) left across most of the glacial valley, and medial moraines that are formed by the lateral moraines of two joining glaciers...heres another picture!



Normally the moraines arent quite as large as what Bass has posted, and the adjoining glaciers usually push the tilled material upward as the ice connects at the base like this:



But the glacier that Bass posted is likely in recession and has long dropped its moraine material and now flows between it.  This is conjecture...not totally sure on that one.
« Last Edit: 31/12/2008 03:31:30 by frethack »
 

Offline Bass

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« Reply #117 on: 31/12/2008 18:06:32 »
Love the illustrations, Frethack- nice explanation.
 

Offline JimBob

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« Reply #118 on: 01/01/2009 15:54:53 »
You think he has been cribbing from "Holmes", Bass? I can't find my copy. Hummmmm...???
 

Offline frethack

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« Reply #119 on: 01/01/2009 17:05:42 »
If I get the chance to do my graduate work at University of Wisconsin - Madison, I would love to study glaciology and Quaternary climate. 

Holmes?  I assume its a text, and if it covers glaciers...I want it! hehehe

 

Offline frethack

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« Reply #120 on: 05/01/2009 01:23:21 »
Ill give it a go this time.  An easy one to begin.

How is this structure formed? (bonus points if you get the name, location)

« Last Edit: 05/01/2009 01:32:08 by frethack »
 

Offline Bass

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« Reply #121 on: 05/01/2009 03:26:56 »
(Mumble t%ww@@beedle))^^ soft rockers grumble)

Is that bedrock (as in "in place")?
 

Offline frethack

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« Reply #122 on: 05/01/2009 03:45:59 »
Youre on the right track...nope...not bedrock.
 

Offline JimBob

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« Reply #123 on: 05/01/2009 13:09:06 »
Formed by karsting. I have seen similar formations in Central Texas but this could be a scene from any temperate karsted region in the world.
 

Offline frethack

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« Reply #124 on: 05/01/2009 17:01:48 »
Nope...not karsting.  The slump in the center looks like it may have been, but no dice!
 

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