First one to identify this animal* (photographed with my new microscope) wins a GEOLOGY ROCKS bumper sticker... Width of photo is about 2 cm.


* Note, not the entire animal is shown.

Labels: contest, fossils

Yesterday, I asked you, "What is the origin of these red polka-dots on this apparently white sample?"



And I gave you a hint that this cobble was photographed at the "half drumlin bluff" site I detailed the previous day! And the fact that the word "apparently" was in italics was also a hint.

Well, here's the deal -- this is a red cobble, with a white coating. I think Paul said it was the Oswego Formation, a fine-grained reddish sandstone. I think what's going on here is that all the limestone powder in the till is readily dissolving during rain storms, and the dissolved calcite gets carried along in solution, flowing over and around larger clasts like this cobble. Then, as it dries out, it begins to precipitate a coating of calcite all over everything (maybe with entrained clay and silt particles too?). Then along comes a little sprinkle of rain, and individual raindrops splash away this encrusting solution from little circular areas, revealing the red rock beneath. I saw this same phenomenon on several cobble and boulder lithologies, not just the red ones.

What do you think? Plausible?

Howard came pretty close in the comments (though this is the top side of the cobble, not the underside), and as the sole guesser, I reckon that entitles him to the prize. Howard, send me your mailing address if you want a bumper sticker.

Labels: contest, new york, sediment

A quick contest:



What is the origin of these red polka-dots on this apparently white sample?

Hint: this cobble was photographed at the "half drumlin bluff" site I detailed yesterday!

First one to answer correctly is entitled to a free "GEOLOGY ROCKS" bumper sticker!

Labels: contest, new york, sediment

Yesterday, I asked you to see what you see here:


And today, I shall tell you what I saw...

Here's what it reminds me of:

...An Olenellid trilobite (slightly deformed)!

Here, I'll sketch it for you:


Garry Hayes came closest to my vision by suggesting the foam pattern resembled Marella splendens, Walcott's "lace crab" of the Burgess Shale.

Labels: art, arthropods, contest, fossils, structure

Just back to DC after a lovely week up in upstate New York, enjoying the scenery, hiking, and geology. Here's a little treat for you: a foam pattern on a stream, en route to Big Slide Mountain in the Adirondacks. What does it look like to you?


...I'll tell you what it looks like to me, tomorrow...

Labels: contest, new york

A couple of days ago, I asked for someone to tell me the geologic history of this boulder, in correct chronological order. To make it easier, I labeled the relevant rock units with letters. I promised that the first person to post the correct sequence of events in the comments would win a GEOLOGY ROCKS bumper sticker.



From first to last, the correct sequence of events is X, D, R, M, F.

Thomas Donlon got it right! Congratulations, Thomas -- I'll mail you a bumper sticker.

So let's delve into more detail: what actually happened with this rock?

First, a mafic source rock was weathered, generating chunks of rock "X." Then those clasts were mixed in with a bunch of sand and mud to generate the graywacke that makes up most of the boulder. This was later metamorphosed (not shown with a letter) to generate rock "D." Later, rock "D" with inclusions of "X" was split open, and granitic magma intruded into that fracture to make the dike labeled as "R." Later still, another cross-cutting event took place, cutting across everything that had come so far, to generate the vein of milky (hydrothermal) quartz labeled as "M." Finally, these rocks were uplifted and exposed, and various fractures, including "F," liberated this boulder from its source area. Now it is free, adrift on the Chain Bridge Flats, and posing for geologists. The final event was me discovering and gracing it with a quarter before snapping its portrait.

Labels: contest, dc, geologic time, piedmont

Inspired to give those Californians a run for their money with their cool examples of relative dating exercises, I took this photo last week down at Chain Bridge Flats, the westernmost corner of Washington, DC:



Your assignment, should you choose to accept it: tell me the geologic history of this boulder, in correct chronological order. To make it easier for you, I've labeled the relevant rock units with letters here. (The letters were chosen randomly, and do not by their alphabetic nature imply any sort of order. Note that "F" is the fracture surface defining the planar outer edge of the boulder.) First person to post the correct sequence of events in the comments area below wins a GEOLOGY ROCKS bumper sticker.



Answer in a couple of days. Good luck!

Labels: contest, dc, geologic time, piedmont

A couple of days weeks ago, I posted three photographs (reproduced below) and asked you to explain them. My sincere apologies that I haven't gotten the answers up sooner... it's been a crazy time. I've been swamped. And the explanations are not brief. Anyhow...

Here are my explanations -- and the winners for the contest!

A

This is a kink band that got reactivated fault. The tectonic stresses acting on these rocks changed over time, and with them deformation took different paths.

This kink band occured in an area of highly foliated metavolcanic rocks, which developed their transposed foliation (running left to right across the photo) due to transpression in the late Mesozoic. The orientation of the kink bands suggests that the second generation of deformation (the kinking) was caused by a maximum stress oriented at an angle of ~30 degrees to foliation. (see Figure 56, page 100 of my geology master's thesis). Some of the resulting deformation was taken up by (See Figure 52, page 95 of my geology master's thesis) kinking. If the second generation of deformation (kinking) were directed parallel to the foliation, we would expect to see conjugate pairs of kink bands, both at the same angle to foliation. But that ain't what we see... we see kinks in only one angular relationship to foliation. This tells us that the maximum stress (sigma-1 in part C of the diagram below) must have been coming in at an angle of about ~30 degrees to the foliation:


Later, those kink bands/faults were reactivated under a third generation of deformation, which then allowed those fault surfaces to open "void spaces" which instantly filled with whatever fluids were available. In this case, that appears to have been a quartz-saturated water, which filled in the void space with a deposit of milky quartz.

Winner? Kim came closest -- and also pointed out that this story is reinforced by looking around the area at similar exposures which show the same story. Kim, you win a bumper sticker!
_________________________________________________________________

B

This is a strained metaconglomerate, and it provides a nice case-study in strain localization.

This photo speaks volumes to me, because my geology master's thesis was a "real life" check on the predictions of a forward numerical model. My advisor wanted to try and understand the development of lineation in shear zones (ductile faults) via computer modeling. So he came up with a cool model that made predictions about the orientation of lineation relative to foliation and relative to the shear zone's boundaries, and he sent me out into the real world to see if real shear zones played by those rules. And the two didn't match up perfectly.

One issue that may contribute to the lack of agreement between the Sierra Crest shear zone system and modeling predictions is that models distribute strain systematically across a shear zone, whereas it is instead localized in natural systems. The shear zone is itself a localization of strain, of course. The question is, 'how local?' In other words, at which scale(s) is strain being accommodated? Possible triggers for strain localization are many: rheological contrasts between lithologies (Nadin and Saleeby, 2004), variations in temperature or fluid flux (due perhaps to proximity to an intruding magma body) (McCaig, 1984; O'Hara, 1988; Tobisch et al., 1991), variations in stress (due perhaps to salients of wall rock which project into the shear zone or the presence of resistant blocks inside the shear zone), presence of fluids, and / or pre-existing structural heterogeneities. For whatever reason, certain areas within a shear zone may accommodate more strain than neighboring areas. Shear localization may occur on many scales.

Photo B above shows cm-scale localization of strain as small pebbles in a metaconglomerate wrap around a larger, central, less deformed clast. Pebbles immediately across strike from the large clast are more deformed than pebbles along strike from the large clast (i.e. those in the rigid clast's 'pressure shadow'). As a result, the orientations of the long axes of the surrounding pebbles (i.e. lineation) occur in a variety of orientations, a condition also seen in traces of the foliation. On a shear-zone-segment (km) scale, strain localization may be noted in the appearance of pods of relatively undeformed rock surrounded by well-foliated and lineated rock more typical of the shear zone. In the Gem Lake and Mono Pass segments of the Sierra Crest Shear Zone system, for instance, lozenge-shaped pods of clast-rich volcanic breccia (See thesis Figures 14, 15, and 21) were far less deformed than neighboring rock. The implication is that the deforming portions of the shear zone 'flowed' around these pods of more resistant material.

Winner? Growing Tedium came closest, though nobody wrote about the strain localization.
_________________________________________________________________

C


I took this last photograph because it demonstrates well the relationship between bedding and foliation in these rocks. Bedding runs from the lower-left of the outcrop towards the upper-right. But within those beds, you'll notice that all the clasts are elongated vertically into elliptical shapes (ellipsoidal in three dimensions). That's because these rocks got squeezed from the sides when they were hot enough and under enough pressure to flow into new shapes. At this location, deformation played a light enough touch that we can still see relict bedding, but in most of the Sierra Crest Shear Zone, the rocks are much more pervasively deformed: they exhibit a transposition foliation, where no traces of their primary structures can be still be seen. So in some ways, Photo C is the opposite of Photo B: it's a zone of lesser deformation surrounded by a zone of greater deformation: a less-disturbed pocket of rock in an area defined by its disturbed rocks.

Here's how I interpreted this outcrop in my thesis:



Winner? Again, Growing Tedium came closest, by referencing the long axes of these clasts and the "bands" (bedding planes) which run through the outcrop at a 60-degree angle to the long axes. GT, please send me an e-mail with your mailing address, and I'll put your bumper sticker(s) in the mail to you ASAP.

Thanks to everyone for playing, and my sincere apologies for taking this long to get the answer up. (Is it apparent why it took me a while, now that you've read through this whole thing?) I've got a new, simpler contest planned for later in the week.
__________________________________________________________________

McCaig, A.M., 1984. "Fluid rock interaction in some shear zones from the Pyrenees." Journal of Metamorphic Geology 2, 129-141.

Nadin, E.S., and Saleeby, J.B., 2004. "Localization of shear along a compositional discontinuity: the Proto-Kern Canyon Fault, Sierra Nevada, California." GSA Annual Meeting Abstracts: Denver 2004.

O'Hara, K., 1988. "Fluid flow and volume loss during mylonitization: An origin for phyllonite in an overthrust setting, North Carolina, U.S.A." Tectonophysics 156, 21-36.

Tobisch, O.T., Barton, M.D., Vernon, R.H., and Paterson, S.R., 1991. "Fluid-enhanced deformation: Transformation of granitoids to banded mylonites, western Sierra Nevada, California, and southeastern Australia." Journal of Structural Geology 13, 1137-1156.

Labels: california, contest, structure

Answers tomorrow... Only three entries so far... There's still room for another winner or two...

Labels: california, contest, structure

Callan is a busy boy these days working on his science education master's. But... (mainly through discussions in my Structural Geology class at George Mason University) I've been reminded of some of the cool stuff I saw when I did my geology master's thesis in the high Sierra of California. Here's a couple of neat images from my field work that ought to convey some of the magic of doing structural geology in the "Range of Light."

The challenge I now put to you: explain what's going on in these images. I've labelled them "A," "B," and "C" for easy reference. Winners get a "GEOLOGY ROCKS" bumper sticker. One winner per photo -- whoever comes closest to describing the geology most completely & accurately.

A


B


C


Just a taste of the magic that a summer of field work imparts... :)

Answers in a couple of days...

Labels: california, contest, structure

NASA's Earth Observatory runs an invaluable public service with its "Image of the Day" series. Now they've got a decade's worth of images, and they want to know which of 50 finalists you think is the best. Go and vote (so hard to choose!), and on April 29, they will reveal the winner.

My personal choice? I'll bet you think it looks familiar... It's this one:

Labels: contest, satellite imagery, websites

What's going on here?


(Michelle Arsenault of NSF for scale)







First person to answer correctly wins a "GEOLOGY ROCKS" bumper sticker!

Labels: contest, plants

At the end of every issue, The New Yorker runs a cartoon caption contest. Readers write in with captions they think would be funny. Here's a cartoon I just drew and submitted for the December issue of EARTH, only to learn that they weren't featuring granite countertops in that issue after all (because they already ran a story on that topic in the current issue.)

So here's my challenge for you: Come up with a caption for this cartoon. I'll post the three captions I came up with after 24 hours or so.

Have fun. The geo-geekier, the better... Here's the cartoon:

Labels: art, contest, granite, humor

Take this opportunity to view the contestants and then cast your vote for the Freakiest Fish.

And... While we're talking about fish, check this out.

Labels: contest, fish

Yesterday I noted that there's an interesting pattern to be seen as one crosses DC's Duke Ellington Bridge:

After sharing these photos yesterday, I posed question for you: What's up with the coloration of these exposures? Why are they black on top and white on bottom? It's the same rock (Indiana limestone), so why the difference in color?

The answer has two parts. First, the calcite (calcium carbonate) which comprises the limestone is sitting out there in the air, and is subject to rain and what-not. Some of that rain has sulfuric acid in it, and that dilute sulfuric acid reacts with the calcite, producing a thin layer of gypsum (calcium sulfate). Those itty-bitty crystals of gypsum have bladed habits, and those bladed crystals are really good at trapping soot and dust. So while the calcite underneath isn't as effective as a soot-trap, the thin layer of chemically-altered gypsum on the surface of the blocks rapidly accumulates dark-colored particulate matter.

So that explains the dark color, but what about the lighter-colored lower portions? Is it simply that they aren't exposed to as much acid rain? Perhaps because they're further down on the "outcrop"? Nope... though that's clearly a consideration (note the thin white vertical lines below some of the stars), it wouldn't explain the abrupt transition from dark colored above to light-colored below. So: what gives?

It's here that context plays an important role. This is an urban location, an outcrop in the city. Like many flat surfaces in the city, it's subject to being tagged with graffiti. Periodically, the City sends along a crew to power-wash the bridge's graffitied surfaces. When they do this, they strip away not only the spray-paint, but also the gypsum and its trapped soot! Because graffiti artists can only reach so high, the city only power-washes so high, and the upper portion of the bridge "outcrop" is both unmolested by graffiti and uncleaned by the City. It records a continual accumulation of gypsum and soot, but the lower portion has its proverbial slate cyclically wiped clean!

I'm on a field trip this weekend (I wrote this post on Thursday and set it to publish while I was away), so I don't know who won the prize (a "GEOLOGY ROCKS" bumper sticker!) but as soon as I get back, I'll settle up with the clever winner. In advance, I'll congratulate you: Nice job!

Labels: contest, dc, limestone, minerals, sediment

To walk from the Woodley Park neighborhood of DC to my neighborhood (Adams-Morgan), you have to cross the deep gorge of the Rock Creek Valley. To do this, walk east on Calvert Street over the Duke Ellington Bridge.


My question for you: What's up with the coloration of these exposures? Why are they black on top and white on bottom? It's the same rock (Indiana limestone), so why the difference in color?

First person to post the correct answer in the comments section below gets a "GEOLOGY ROCKS" bumper sticker as a reward. Full answers tomorrow in a separate post...

Labels: contest, dc, limestone, sediment

I've got a nice tough A.W.o.G.E. for you today. Hint: it's somewhere in the Virginia Piedmont. The presence of an airplane over the photographed site may help confirm the location, once you think you've found it.

In the comments section below, be the first to name the location and why the treeless area suffers so much sulfuric acid, and you will win a "GEOLOGY ROCKS" bumper sticker.

Labels: contest, google, maps, nova, piedmont

A fresh location for the new round of A.W.o.G.E. This time we're visiting a syncline that was exposed in a roadcut about 20 years ago. I've blocked out the data source, since that could help narrow the search, and I'd also like to point out that I should have put an "s" on "geologist" in the lowermost annotation. Oops.

In the comments section below, be the first to name the mountain the roadcut goes through, and you will win a "GEOLOGY ROCKS" bumper sticker.

Labels: contest, google

I haven't put up an annotated Google Earth image in a while, so here's one. As with the previous A.W.o.G.E.'s, this is some place where I've been, annotated with a few details about the local geography and my experiences there. Note the scale bar in the lower left.

In the comments section, be the first to name the town or the prominent spit (both have the same name) and you'll win a "GEOLOGY ROCKS" bumper sticker.

Labels: contest, google

Last week, I posted my first of these images. Today I follow up with another spot in the same state as last week's A.W.o.G.E. Annotations are described in detail below. The first one to correctly identify the location wins a "GEOLOGY ROCKS" bumper sticker. The contest is open not just to my students but to the whole world (though I'm hoping someone in the U.S. wins it so I don't have to pay some outrageous postage to send the winner their bumper sticker!) Last time the winner was helped along by comparing the Google Earth image to photos on my website, but I don't have any photos of this area up on the website, so it ought to be more challenging!

Labels: contest, google

The favorite pastime of the geoblogosphere appears to be "Where On Google Earth?" (example 1, example 2, example 3) ...Who am I to buck such a trend? But I've also gotta give it my own spin: so I hereby introduce Annotated "Where On Google Earth?" The difference is that in my version, the game gives you a chance to learn something new about me (via the annotations) while exploring some cool places.

Here are your clues: (A) West of this line is a major Mesozoic batholith. Location (B) is a peninsula where I camped for a week and a half. (C) is a dam which produced the lake that the image is centered on. (D) shows a prominent shadow below a cliff formed by a Paleogene ("Tertiary") basalt flow.

Since today is my first day of classes for the semester, I'm going to make this a contest. The first of my students to deduce the location of this image by naming the lake and the mountain range that hosts it, will win a GEOLOGY ROCKS sticker. Geoblogospheroids, you can guess too, but my students are allowed to check your answers and then adopt them as their own to win the prize. It's kind of like one of those celebrity game shows, or the weekly bigwig- plays- for- a-random- person- getting- Carl- Kasell- on- their- home- answering- machine dealio on "Wait, Wait: Don't Tell Me!" The contest is open... see some of you in class in a few hours!

Labels: contest, google