Thursday, May 7, 2009

Tweeting the Eureka Quartzite

Eureka Quartzite, with cave, on a hill above Ely, NV


A Geological Conversation, on Twitter, about the Eureka Quartzite (April):

aboutgeology: @sfoxx OK, why is the Eureka Qtzite such a familiar name? What's it signify? 7:02 PM

sfoxx: @aboutgeology It's an unusual siliclastic break in the middle of the Ordovician in an otherwise carbonate depositional environment. Eustacy. 7:03 PM

sfoxx: @aboutgeology Actually, it's a very nice marker horizon, a very pretty rock, and quite widespread in central and eastern Nevada! 7:04 PM

sfoxx: @aboutgeology Have you written about the Eureka Qtzite? 7:06 PM

clasticdetritus: @sfoxx @aboutgeology re Eureka Qtzt - and an extremely important stratigraphic marker in the region too, if I remember correctly 7:07 PM

clasticdetritus: @aboutgeology @sfoxx re Eureka -- doh, sfoxx, you just said that before I did ... need to read other tweets before tweeting 7:08 PM

sfoxx: @clasticdetritus @aboutgeology Very important. And I've been reading it may have correlations into Mexico, and even on the east coast 7:10 PM

sfoxx: @clasticdetritus Oh, well! :) 7:10 PM

sfoxx: @clasticdetritus There have been a bunch of conodont studies in the rx above and below the Oe; it seems to be bounded by unconformities. 7:13 PM

rschott: @sfoxx Just how metamorphosed is the Eureka Quartzite? Is it truly a quartzite or just a quartz arenite? Maybe even friable? 7:16 PM

sfoxx: @rschott It's totally non-friable, except maybe in places near the bottom, though I've never seen it that way. May be an orthoqtzite. 7:32 PM

aboutgeology: So it's a big, clean quartzite in the middle of a fat Ordovician carbonate sequence. A pulse of stored sand? What's its provenance? 7:33 PM

aboutgeology: With unconforms above and below? Is it involved in thrusting as a coherent block? 7:37 PM

rschott: @aboutgeology @sfoxx Any idea when it was metamorphosed? Are the carbonates above and below it marbles? Gotta collect me some! Roadtrip! 7:37 PM

sfoxx: @aboutgeology @rschott I read just now that the source is the Peace River Arch in B.C. http://tr.im/iH8m 7:38 PM

sfoxx: @rschott @aboutgeology Gee Whiz! Yes, come get some. It should be in the upper plate of the Roberts Mountain thrust. Below overlap sequence. 7:40 PM

rschott: @sfoxx @aboutgeology A-ha, I figured George Gehrels would have done some detrital zircon work on it. Neat stuff! 7:41 PM

sfoxx: @rschott @aboutgeology When? Ortho - soon after depn? Un/dis conformities are regional, not always obvious in otcp. (I didn't notice!) 7:42 PM

aboutgeology: @sfoxx That talk says no, the Peace R Arch zircs are supplemented by local zircs in Idaho and NMex. 7:42 PM

aboutgeology: Ordovician paleogeography: http://tinyurl.com/ctg5dq 7:44 PM

sfoxx: A very nice rock, you all-everyone-should have some. The Oe above my house here is almost completely bx'd and changes thickness rapidly. 7:45 PM

sfoxx: @aboutgeology So it has a source to the north, but then local sources as well 7:46 PM

aboutgeology: @sfoxx Do you have a photo up of the Oe? 7:48 PM

sfoxx: @aboutgeology Oh, okay, they were finding new evidence from the long-standing Peace R Arch idea. 7:48 PM

aboutgeology: @sfoxx So the zircs point to a regional, Cordilleran pulse of unroofing, not just one Canadian arch? 7:50 PM

sfoxx: I have a couple pics of the Oe @aboutgeology @rschott This one: http://tr.im/icoX And this old one, mostly a fault: http://tr.im/iHac 7:52 PM

aboutgeology: Aha, not orogeny but eustasy given East US equivs: http://tinyurl.com/ch3tkk 7:53 PM

aboutgeology: @sfoxx Pretty pix! A clean, massive qtzt. Is it distinctive in hand specimen? 7:55 PM

sfoxx: @aboutgeology Exactly, which is why there may be a correlation to other siliclastics on the east coast, although I don't have the ref handy. 7:56 PM

sfoxx: @aboutgeology It's generally distinctive from the Prospect Mtn Qtzite in being much cleaner, lighter. And there aren't v. many others. 7:58 PM

sfoxx: @aboutgeology Actually, that last abstract you cited was the ref I was thinking of! 8:00 PM

sfoxx: I have some great photos of the type section, type area of the Eureka Quartzite! It's right on Highway 50 west of Eureka a ways. 8:02 PM

sfoxx: @aboutgeology The Oe rt above our house has an interesting arch in it, from erosion along the intersection of high&low angle fault-joints 8:17 PM

aboutgeology: @sfoxx No wonder there's no type section, it was named in 1883: Geolex - http://tinyurl.com/dhhvym 8:20 PM

sfoxx: @aboutgeology It had a broad type area, which was redefined to Lone Mountain in 1956 by Nolan [no, by Kirk in 1933]. I think that's the defacto "type section." 8:23 PM

sfoxx: Nolan et al, 1956: http://pubs.er.usgs.gov/usgspubs/pp/pp276 8:25 PM

clasticdetritus: @rschott @aboutgeology @sfoxx re Oe -- dang, you guys did some serious tweetsearch ... I need to catch up! 8:34 PM

sfoxx: @clasticdetritus Tweetsearch, I like that. I had been doing some research off and on during the day, @aboutgeology does research v. fast! 8:37 PM

rschott: @aboutgeology @sfoxx @clasticdetritus The Eureka Quartzite discussion is a prime example of how Twitter can be genuinely useful for geology. 8:37 PM

sfoxx: @rschott Tweetsearch, @clasticdetritus called it! 8:39 PM

Reference:
Kirk, Edwin, 1933, The Eureka quartzite of the Great Basin region: Am. Jour. Sci, 5th ser., v. 26, p. 27-44.

The GeoTweeters:
@aboutgeology
@clasticdetritus
@rschott
@sfoxx

4 comments:

Anonymous said...

Cool! We have an equivalent (or at least homotaxial) quartzite here in the Canadian Rockies, called the Mount Wilson Formation. I always thought it was peculiar that there should be a massive dump of quartzite plunk in the middle of a (mostly) carbonate succession; but I had no clue that it was so widespread. The type section is in Banff Park, but I've never seen it close-up.

--Howard (Calgary, AB)

ReBecca Foster said...

Now I feel really out of touch. I just found out my mom has a twitter account also. I do not have one lol.

Silver Fox said...

Thanks for the input, Howard, and the link to the Lexicon of Canadian Geological Units. Would be interesting to compare hand samples!

ReBecca, I'm considerably more out-of-touch with the blogging world recently, and I find it hard to reconcile the twit thing with the blogging I want to do (but don't do). If you join, be sure to let me know!

ReBecca Foster said...

I have not been keeping up with my blog much either recently, since I have not been home much. If I ever jump into twitter I will let you know!