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#17618 - 03/02/06 12:45 PM Re: Shawangunk radio essay text [Re: Mike Rawdon]
RangerRob Offline
Carpal Tunnel

Registered: 06/06/00
Posts: 3764
Loc: Ulster County, NY
How about we save everybody the headache and just call it nice rock. Nice rock....niiiiice rooock.....

RR

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#17619 - 03/03/06 12:36 AM Re: Shawangunk radio essay text [Re: RangerRob]
Frank Florence Offline
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Registered: 01/05/00
Posts: 528
Loc: moved to Bend
Sorry, RR, it's winter and the lack of climbing is wearing on some of us. So in lieu of that activity, and even as I agree that it is a nice rock, either to look at or climb on, I'll happily rag on some more about its classification.

If I understand Timbo's argument correctly, he doesn't want to call this rock a quartzite because the original sediment wasn't well sorted, that is, it contained a variety of grain sizes. Yup, it does, and that permits the term conglomerate, specifically a quartz pebble conglomerate. He contrasts the Gunks' rock to the quartzite at Devils Lake and Seneca, two examples of more well sorted material, that is, with more uniform sand-grain sized original sediment. He could have also mentioned the quartzite at the back end of Lake Louise, another exposure with uniform sized original grains that a lot of climbers are familiar with.

What we have at the Gunks is a silicified rock, that I still think is well described by the term quartzite (or orthoquartzite) precisely for the reason Oenophore mentioned that also has a good number of pebbles in it. The advantage of using this nomenclature is that it indicates the tough, tight character of the rock. Calling the Gunks a conglomerate emphasises the range of particle size, but doesn't indicate the extensive cemetation that's taken place.

Maybe if I was writing a technical paper I'd call the rock orthometaconglomerate. Jeez, I hope DW never puts that in a guidebook! And if Yorick had called it that in his report, I'll bet people would have tuned him out right there. Only dweeby geo-types like Timbo and myself would parse out the true sense of the word to figure out what it implied in terms of rock composition and subsequent process of lithification.

Final points: Timbo, you said that the different sized sediment grains had different sources. Why? What supports that conclusion? And isn't the Tuscarora (Seneca's rock) actually a a distal equivalent of the Gunks' rock? Both were deposited in essentially the same transitional environment during the Silurian, as I understand it. (Please correct if this is wrong.) The only real differences are that the Tuscarora is more well sorted and then later was metamorphosed into quartzite during tectonic events. The lumpier Gunks outcrops are still horizontal and presumably were flushed with silica-rich groundwater as a consequence of these same events.

RR, you still with us?

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#17620 - 03/03/06 03:20 AM Re: Shawangunk radio essay text [Re: Frank Florence]
GymClimbingPoser Offline
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Registered: 03/20/01
Posts: 285
Loc: Logan, UT
Have I ever told this board how glad I am that I didn't go into geology?
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#17621 - 03/03/06 11:32 AM Re: Shawangunk radio essay text [Re: Frank Florence]
oenophore Online   confused
Carpal Tunnel

Registered: 09/24/01
Posts: 5962
Loc: 212 land
To the geologists posting on this thread I'll address my wonder: why is that formation so quartzite-like in some places and not in others?
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#17622 - 03/03/06 04:41 PM Re: Shawangunk radio essay text [Re: oenophore]
Timbo Offline
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Registered: 12/23/99
Posts: 694
Loc: Delaware
Quote:

To the geologists posting on this thread I'll address my wonder: why is that formation so quartzite-like in some places and not in others?




Differences in deposition environent when the sediments were being deposited and differences in pressure and temperature when the material was being buried.

You can see this on a less regional scale in any streambed. Check out the different sediment sizes in riffles versus pools, outer edge of turns versus inner, etc.

I did some more looking and there are several references that refer to rock as conglomerate and several that refer to it as quartzite conglomerate. So Mr. Rawdon can refer to it as quartzite conglomerate if he chooses; however, the material contains numerous grain sizes and is by definition conglomerate, not quartzite. So, quartzite conglomerate is OK, quartz conglomerate is OK, plain vanilla congomerate is OK, but it is not currently a quartzite.

I say lets give it a few million years and it might erode, lose all those nasty quartz pebbles, regroup, and metamorphose into a quartzite.
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#17623 - 03/03/06 04:59 PM Re: Shawangunk radio essay text [Re: Timbo]
GeeVee Offline
Auto Reply

Registered: 11/14/00
Posts: 4403
Loc: Brooklyn, NY
I say lets give it a few million years and it might erode, lose all those nasty quartz pebbles, regroup, and metamorphose into a quartzite.

Would that be impacted by the build-up of chalk on the rock?
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So long as you can boogie you ain't too old.

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#17624 - 03/03/06 05:02 PM Re: Shawangunk radio essay text [Re: Timbo]
oenophore Online   confused
Carpal Tunnel

Registered: 09/24/01
Posts: 5962
Loc: 212 land
So Mr. Rawdon can refer to it as quartzite conglomerate if he chooses; however, the material contains numerous grain sizes and is by definition conglomerate, not quartzite. So, quartzite conglomerate is OK, quartz conglomerate is OK, plain vanilla congomerate is OK, but it is not currently a quartzite.

As close to consensus as we'll get; I'll take it.
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#17625 - 03/03/06 09:21 PM Re: Shawangunk radio essay text [Re: oenophore]
pedestrian Offline
Pooh-Bah

Registered: 08/05/02
Posts: 2244
Loc: a heavily fortified bunker!
According to the Wikipedia article, portions of the Shawangunk caprock are in fact sandstone. I certainly can't disagree. Just look at parts of the Mac Wall, Yellow Wall and Lost City.


Edited by pedestrian (03/03/06 09:21 PM)

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