31 October 2014
Here are four folds from the Potomac Terrane (or maybe an “exotic unit” that looks like the Potomac Terrane, butted up against the Potomac Terrane) that I saw on the 2014 Virginia Geological Field Conference back in October.
It was an overcast, rainy day, so I apologize for the relatively low quality of these images.
30 October 2014
Esteemed readership, I’ve got a mystery for you. What are these white lines, inclined consistently at a high angle to bedding? I picked up this sample below the “Wall of Death,” on the trail from Wapta Lake below Mount Wapta, en route to the Walcott Quarry of the Burgess Shale. The “zebra-striped” rock is of the Eldon Formation of the Cambrian section in Yoho National Park.
At first, I thought “cross-beds,” but they I realized that they were too high angle.
Here’s another side of this sample:
Tension gashes? But though they are indeed oriented subparallel to one another, they are so closely spaced, that doesn’t seem plausible.
Perhaps a clue can be found in the apparent void spaces filled with coarse dolomite crystals seen near the base of some of the white layers:
Here’s another example of that: Initially zoomed out for context…
…and then zoomed in for detail…
What about this idea?… Initial cross bedding creates small compositional variations on a geometrically regular scale. Then, during diagenetic dolomitization of a limestone protolith, the cross-beds are a site of preferential dolomitization. If shearing occurred simultaneously with the recrystallization, then that could change the orientation of the former-cross-beds in a systematic way. Perhaps this opens up new void spaces, which subsequently fill with coarse chemically-precipitated dolomite.
29 October 2014
I saw this large, chunky stylolite this summer somewhere along the trail from Takkakaw Falls to the Walcott Quarry of the Burgess Shale (in Yoho National Park, British Columbia). I like the way weathering has highlighted its form.
28 October 2014
Today, I thought I would share some images of lovely “textbook” glacial striations from rocks I saw in the Canadian Rockies this summer…
27 October 2014
Driving west from Calgary, your first evidence of entering the Canadian Rockies’ Front Ranges is the startling sheer cliff of Yamnuska, north of the Trans-Canada Highway:
Yamnuska’s shape is a function of differential weathering of the two rock units that make up the mountain: Cambrian Eldon Formation limestone, and Cretaceous shales of the Brazeau Formation. The Cambrian is the uppermost of the two, which is a violation of superposition, considering these are both sedimentary rocks that form on Earth’s surface. Hence, we invoke a major thrust fault here: the McConnell Thrust, named for a pioneering geologist in these mountains.
From this perspective, Yamnuska appears to be a klippe, like Chief Mountain in northern Montana, but it is not actually physically disconnected from the main mass of limestone to the west of it, so it’s not quite a klippe… yet. Give it another couple million years of erosion, and maybe we can make it happen.
26 October 2014
Good afternoon! Here are a few photos, both plain and annotated, showing the relationship between primary sedimentary bedding and tectonic cleavage in the “tectonised Stephen” Formation atop the Cathedral Escarpment (in Yoho National Park), just northeast of the Walcott Quarry where the (thicker, basinward) Stephen Formation hosts the Burgess Shale.
Weathering exploits both these planes of weakness…
Here, the cleavage is more planar at the bottom of the sample, and more curved toward the top – probably due to subsequent folding?
25 October 2014
The recently-concluded Geological Society of America meeting in Vancouver, British Columbia, was one of my best meetings ever. I gave two talks and a digital poster, supervised three student digital posters and one student group regular poster, attended and contributed to meetings on a variety of subjects, met new colleagues, reunited with old friends, and even attended some stimulating science talks. Plans were hatched, ideas refined, projects discussed.
Tuesday was a big day for me – at lunch that day, I received the Biggs Award for Geoscience Teaching Excellence from the Geoscience Education Division of GSA. I was nominated for this prestigious award by Heather Macdonald of the College of William and Mary and Bob Blodgett of Austin Community College, who appear alongside me in the photo below. Also in the photo is the (now Past) President of the Geoscience Education Division, Elizabeth Heise, of the University of Texas – Brownsville.
Heather and Bob’s citation appears in the current (hot off the presses) issue of In The Trenches (published by the National Association of Geoscience Teachers). If you read it, you’ll see I was in very good company on the awards dais. Their words were so laudatory as to verge on being embarrassing, and I was deeply honored to be seen as worthy of such high praise from such accomplished geoscience educators, from such leaders in our field.
Here’s what I said upon accepting the award:
It’s wonderful to be here today with you, here on Earth. You and I are fortunate to live on a very interesting planet. It’s big enough to have differentiated. This allowed the development of a metallic core, whose circulation powers a magnetic field that protects our atmosphere from erosion by the solar wind. Differentiation also provides for mantle convection, the power source driving plate tectonics. The eruption of volcanoes and gravitational acquisition of comets both yield water, and this water is critical for life. Every critter and microbe needs liquid water, and for 4.5 billion years, our planet’s surface has had the right blend of solar heating and greenhouse gas insulation to keep the water flowing. What fortune! Every move we make, every breathe we take, we rely on geology.
In my job, it is a delight to be surrounded by clever people who are largely unaware of the dynamic geomachinations that sustain them. You and I teach them to read the world. In every process, Earth generates a little clue or two. The cumulative record of these clues is a fantastic saga: from magma ocean to stromatolitic ‘slimeworld’ to Snowball Earth to Cambrian explosion and eventually the evolution of abstract thinking and human intelligence, we’ve come a long way! And we have the rocks to prove it.
You and I are the ones who get the honor of opening the world’s eyes to geoscience. We reintroduce our students to their planet, what it’s made of, how it works, how it sustains them, and how it can kill them. We provide a vital service, a job that is extraordinarily gratifying fun. For each new student, we slip a pair of geology-colored glasses onto their face, and lean back with satisfaction as they stare about in newfound wonder. Their appreciation is our greatest reward.
I’m honored to be recognized with the Biggs Award. I thank Heather MacDonald and Bob Blodgett for making the effort to nominate me. Heather and the faculty at William & Mary nurtured a familial atmosphere that drew me into geology as a very young man.They inspired me, as did many talented writers and artists. I’m grateful to my colleagues at NOVA, Geo2YC, Pearson, and every institution I’ve been lucky enough to be affiliated with. I’m most grateful to my hardworking students, too many to list here, but some of the best are here at this meeting. My wife Lily is a stalwart supporter of my many projects, but she rightfully reminds me that life is short, and work is but one facet of a full life. Sharing an appreciation of nature with our son Baxter is now the main project I want to spend all my time on.
Every person in this room is interested in geoscience education. Future students are lucky to have you to learn from. I hope you are as honored as I am to be doing this job. It is essential work for the sake of our species’ future, and for the sake of feeling at home here on the most fascinating planet in the neighborhood.
This little speech had quite a galvanizing effect. In addition to applause, several people (mostly people from the Geo2YC community) leapt to their feet and whooped out loud. The ovation was at least partly on its feet. It was really cool to see the chord my words had struck with them. Man, what an infusion of adrenaline and good will I felt. It was so nice to have my work validated in this public forum.
Later that evening, my publisher, Pearson, hosted a reception in honor of the award. Though there was a snafu with directions, those who really wanted to attend figured out where it was and made an appearance. It was a fine evening, and led to some heartfelt and heartwarming narratives from my students (six of whom were there) on the positive influence I’d had on their lives. It was humbling and astonishing to hear how significant my actions had been in determining their course through life. I thank all of them for sharing their feelings with me there – it brought tears to my eyes.
Overall, the meeting was one of the best I’ve ever been to, and I look forward eagerly to the next one – in Baltimore a year from now. GSA’s annual meeting is a highlight of my professional year.
24 October 2014
Remember our examination of buckle folding versus passive folding in the Chancellor Slate (cleaved limy mudrock) of eastern British Columbia?
Well, here’s another example:
There’s so much awesomeness going on in that image, it’s hard to know where to start. The prominent black thin layers are buckled in a very boxy, asymmetric way. In places, the layer is discontinuous, suggesting faulting or shortening via pressure solution. Note how the cleavage that emerges from the overlying and underlying more massive units warps and deflects (dominantly to the left) as it crosses the trio of high-contrast thin beds.
From a few feet away, here’s another example of more classic cuspate-lobate folding between units of different strength:
And from a few feet away in the other direction, here’s a bunch of offset thin beds, which at first looks a lot like a series of microfaults, but in fact is pretty clearly pressure solution induced dissolution of some of the (now absent) rock along the prominent pressure solution seams (distributed cleavage or stylolites):
Happy Friday to you!
17 October 2014
Here’s some folded schistocity in the schist of Santorini’s Cycladean subduction complex:
The blunt crest of the fold in the second photo appears to be a folded marble boudin. Neato!
16 October 2014
While on my blueschist quest, I noticed this boudin train exposed in the trail.
I’m not sure what exactly is being boudinaged here – only that it is lighter in color than the schist that surrounds it, as well as finer grained and less foliated (more massive). A tabular mass of fault gouge perhaps?