aboutgeology:
@sfoxx OK, why is the Eureka Qtzite such a familiar name? What's it signify?
7:02 PMsfoxx:
@aboutgeology It's an unusual siliclastic break in the middle of the Ordovician in an otherwise carbonate depositional environment. Eustacy.
7:03 PMsfoxx:
@aboutgeology Actually, it's a very nice marker horizon, a very pretty rock, and quite widespread in central and eastern Nevada!
7:04 PMsfoxx:
@aboutgeology Have you written about the Eureka Qtzite?
7:06 PMclasticdetritus:
@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 PMaboutgeology: 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 PMaboutgeology: With unconforms above and below? Is it involved in thrusting as a coherent block?
7:37 PMrschott:
@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 PMsfoxx:
@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 PMsfoxx:
@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 PMsfoxx: 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 PMsfoxx:
@aboutgeology So it has a source to the north, but then local sources as well
7:46 PMaboutgeology:
@sfoxx Do you have a photo up of the Oe?
7:48 PMsfoxx:
@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 PMsfoxx: 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 PMaboutgeology: 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 PMsfoxx:
@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 PMsfoxx:
@aboutgeology It's generally distinctive from the Prospect Mtn Qtzite in being much cleaner, lighter. And there aren't v. many others.
7:58 PMsfoxx:
@aboutgeology Actually, that last abstract you cited was the ref I was thinking of!
8:00 PMsfoxx: 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 PMsfoxx:
@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 PMaboutgeology:
@sfoxx No wonder there's no type section, it was named in 1883: Geolex -
http://tinyurl.com/dhhvym 8:20 PMsfoxx:
@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 PMsfoxx: Nolan et al, 1956:
http://pubs.er.usgs.gov/usgspubs/pp/pp276 8:25 PMclasticdetritus:
@rschott @aboutgeology @sfoxx re Oe -- dang, you guys did some serious tweetsearch ... I need to catch up!
8:34 PMsfoxx:
@clasticdetritus Tweetsearch, I like that. I had been doing some research off and on during the day,
@aboutgeology does research v. fast!
8:37 PMrschott:
@aboutgeology @sfoxx @clasticdetritus The Eureka Quartzite discussion is a prime example of how Twitter can be genuinely useful for geology.
8:37 PMsfoxx:
@rschott Tweetsearch,
@clasticdetritus called it!
8:39 PMReference: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
