Where on (Google) Earth #196?

Having no blog of my own, Ron has kindly agreed to post my entry for WoGE #196. Schott rule applies here as these landforms are quite unique and diagnostic. Please post coordinates and a brief explanation of their significance. Happy sleuthing.


Post time: 3/23/2010, 05:10 Central Daylight Time (USA).

Where on (Google) Earth #196.

Day #81 Deskcrop: Tigerton Wiborgite Porphyry

The ~1475 Ma Tigerton Wiborgite Porphyry outcrops near the Embarrass River in the Wolf River Batholith of east-central Wisconsin. This rock has a phaneritic porphyritic texture – rapakivi textured K-feldspar megacrysts in a phaneritic granitic groundmass. I wish I had a stained slab to show you the dramatic sodic rims on these big K-spars, but I’m afraid you’ll have to use your imagination.

Tigerton Wiborgite Porphyry

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Day #80 Outcrop: The Whaleback

As it happens, the very first GigaPan I ever made was of the folds exposed in the east face of the Bear Valley Coal Mine, near Shamokin, Pennsylvania. That GigaPan was stitched from about a dozen hand-held shots, before I owned a GigaPan robot, and barley met the minimum size threshold of 50 megapixels.

This past summer I had the opportunity to get back to the mine and shoot a much larger GigaPan in the mine with a brand new GigaPan Epic 100 robot. This time, I also composed a shot that captured not only the beautiful anticline-syncline pair in the east wall of the mine, but also the pièce de résistance for any geologist visiting the mine – the Whaleback. This remarkable anticline – exposed by strip mining of anthracite coal – is a Mecca for structural geologists.

The GigaPan below is over 5 gigapixels in size and composed of 1320 individual input images – it took over an hour and a quarter to shoot. The old version of GigaPan Stitcher crashed every time I tried stitching this image, but the recently updated GigaPan Stitch 1.0 software was able to finish the job in merely 7 hours.

I know there are some very detailed diagrams in the literature of the small scale structural features of the Whaleback (e.g., joints). I’m eager to learn whether my structural geologist colleagues think there’s enough detail in this GigaPan to make this image useful for teaching more than just basic structural concepts. If so, I’d be eager to work with you to develop web-based exercises around this GigaPan.


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Day #79 Outcrop: West Castleton Fold

For this weekend’s outcrops I’m going to revisit the localities of my first two GigaPan images.

The West Castleton Fold is a justifiably famous fold in the slate belt of Vermont. The outcrop (which does seem to be a natural exposure) presents a vertical face through the axial region of a syncline in the Poultney Formation. Among the highlights of this outcrop are the beautiful bedding-axial planar cleavage relationships, as well as some lovely ptygmatic folds (below).

Ptygmatic Folds

West Castleton Fold

Unfortunately, the lighting was not as good when I revisited this outcrop last summer, though this time I had the GigaPan robot and was able to make a MUCH more detailed GigaPan (almost 100x more pixels).


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Thus endeth “Slate Week” – time to head west…

Spring Cleaning: My Updated Geoblogosphere Blogroll

Some time ago WordPress lost track of the original Geoblogosphere Blogroll I had compiled in the sidebar. It’s probably just as well, because it was getting fairly outdated, given the general churn rate among geoblogs.

Today I got the urge to update my geoblogosphere blogroll – this time as a static page linked from the menu bar just below my header. Its a task that’s eaten much of the day, though I’m glad to have it updated (at least for now). I’ll try to keep it up to date, but will almost certainly fail to do so.

The page is organized in three sections, each ordered alphabetically. I’m pleased to say the largest section is the Active Geoblogs, followed by the Mothballed/Deprecated Geoblogs, and finally those that have passed into the Ether. Why do I maintain a list of mothballed/deprecated blogs? Two reasons: first, some blogs come back to life (I know from personal experience); and second, there’s still good value in all of the archived older material on many of those sites – just because it isn’t new doesn’t mean it isn’t interesting.

Active, I should hasten to add, is a relative term here – I’ve loosely used about a six month cutoff for the most recent (geology related) blog entry. Some folks post on a daily basis and many post much more sporadically. I have made no effort to distinguish these, nor any effort to subcategorize the geoblogs by their area of emphasis. That would probably be a useful next step, but don’t hold your breath waiting for me to do it. I am going to maintain a limited blogroll down on the right sidebar of my blog for the handful of these blogs that I personally consider “Must Reads”. Both geoblog lists are necessarily subjective – I don’t read a lot of paleo blogs because my interest is more in the hard-rock geology fields – please don’t be offended. However, if you think I’ve missed an important blog or you’re just getting started in geoblogging and want me to take a look at your blog feel free to comment on this post and I’ll take your input under advisement.

Geoblogger meetup at the Thirsty Bear – AGU, Dec. 2008
Bonus Points – Can you match the geobloggers with their blogs?

Day #78 Deskcrop: Black Slate with Framboidal Pyrite

For my final slate deskcrop of the week (I’m holding a few in reserve for the future) I present to you the black Hatch Hill Slate. (Or, as Sandra “Boo” would have it: not black, but dark charcoal grey.) The deskcrop below has some nice jointing cutting its slaty cleavage.

Black Hatch Hill Slate

Turn the sample on its side to reveal a small fold nose.

Fold Nose

Finally, from the same outcrop and very near the deskcrop above we have some rather spectacular musket ball-sized pyrite framboids with spectacular pressure shadows. What do you think of that, structural geologists? Pretty nice, eh?

Pyrite Framboids with Pressure Shadows

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Day #77 Deskcrop: Red Slate

The Indian River Slate is truly one of the more beautiful slates that’s quarried in the New York/Vermont region. It’s rich red color suggests strongly oxidized iron. In addition, this slate is a somewhat more siliceous slate (in the field we commonly referred to this as a more “delicious” slate) and tends not to break as brittlely as the Metawee Slate.

Once more I’m not certain of where this specific sample was collected, but I’ve located it just east of the bridge over the Indian River in East Poultney, Vermont where I’m quite certain it crops out, since it was in the heart of my group’s field camp final mapping project area. A stone’s throw from this locality is the historic building where Horace Greeley got his start as a newspaperman. Once we’ve gotten through this week’s slates I promise we’ll “Go West”, young men and women.

Indian River Red Slate

Indian River Slate (Another View)

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Day #76 Deskcrop: Green Slate with Pyrite Cube

Happy St. Patrick’s Day! I have something of a tradition of celebrating this holiday in rocks, so it should come as no surprise that I saved a green sample for today’s deskcrop. (It’s actually a promising sign that this is only the third of those ten deskcrops to be featured so far this year – I might actually be on pace to get all the way through this year in deskcrops and outcrops!)

Today’s deskcrop is another piece of Metawee slate, but green this time, and with a pyrite cube porphyroblast to stand in for the pot o’ gold. The pyrite is consistent with the green color of the slate in that each is indicative of reducing conditions of deposition. This cube is remarkably euhedral and lacks pressure shadows, suggesting an origin that postdates the development of the slaty cleavage in this sample. Once again, the locality of this sample is a bit fuzzy in my mind, so I’m locating it at one of the many slate quarries in the general neighborhood of it’s actual origin.

Green Slate with Pyrite Cube

Pyrite Cube Crosscutting Slaty Cleavage

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Day #75 Deskcrop: Maroon Slate with Reduction Spot

Today’s slate deskcrop is a “roofing tile-quality” piece of maroon Metawee slate with an elliptical reduction spot. The reduction spots presumably originated when organic matter caused reduction of iron in a small spherical region of the shale protolith. When these slates were deformed and metamorphosed the reduction spots were also deformed, and as such, they can be used as strain markers. One of the NSF-REU funded undergrad summer research projects I was part of took measurements of the three principle axes of these reduction spot strain ellipsoids. I’d point to the abstract, but it seems GSA doesn’t have meeting abstracts from prior to 2001 online. D’oh!

Green Reduction Spot in Maroon Slate

Another thing that one can see nicely in this sample is the reflection of light off the cleavage surface. If you look closely in one of the higher resolution versions of this photo you might even to be able to detect a hint of a second (crenulation?) cleavage.

Light Reflecting off Slaty Cleavage

I have to admit that I’m not 100% sure which quarry this particular deskcrop comes from. I’ve elected to locate it at a quarry that exposes plenty of Metawee “tailings” – no doubt some of which display reduction spots with this texture.

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Day #74 Deskcrop: Maroon Slate

This week I’m kicking off a review of a couple different varieties of slate from the slate belt in western Vermont and eastern New York. I know this area well because it was the final mapping project during my three tours of duty on the Colgate Geology Summer Field Camp (the “OC”) – once as a student and twice as a TA.

Today’s deskcrop is a piece of maroon Metawee slate. The Metawee Formation is one of the most abundantly quarried in this region and has both green and maroon varieties, commonly both within the same quarry. The colors arise from differing oxidation states of iron – maroon or red is more oxidized and green is relatively reduced. These colorful varieties are both quarried for use as roofing slates. There’s really nothing particularly remarkable about this piece – I just wanted to establish a baseline theme for some of the variations coming later this week.

Maroon Slate

Maroon Slate (side view)

Explore this and all of my 2010 Deskcrops and Outcrops in Google Earth!