31 July 2020

Friday fold: Two Mile Run Overlook

I spied an anticline last weekend while engaging in a day of solo geologizing along Skyline Drive in Shenandoah National Park. At Two Mile Run Overlook, I gazed west toward the southern tip of Massanutten Mountain, and noted what appeared to be an anticline in the Blue Ridge foothills:


And here it is in Google Maps,  with the perspective rotated to looking ~along strike to the north, and I hope you will note that (1) this anticline is not alone: there are at least four big folds here, 2 anticlines and 2 synclines, and also that (2) there are similar expressions of these folds in the ridges both north and south of the one I spotted.

There’s a ton of folds there! And based on their position in the landscape, I’m guessing this is all Antietam Formation, which should mean it’s chock full of bedding-perpendicular Skolithos trace fossils: poles to bedding for the structural geologists, I reckon. Someone should map this area in detail…

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24 July 2020

Friday fold: Totier Creek phyllite

I have moved from the Fort Valley to Charlottesville, Virginia, where next month I’ll take up a new position teaching geology at Piedmont Virginia Community College. I’m excited to be in a more progressive community with excellent food and music, and a wealth of new outdoor recreational opportunities – not to mention higher-performing public schools for my son.

But what about the rocks? I don’t know the rocks around here yet!

This is the first post of what I hope will be many, as I explore my new home region and learn about its diverse geology. Charlottesville sits at the interface between the Blue Ridge and Piedmont geologic provinces, with Triassic rift basins located a short distance along strike to both the northeast and southwest. Surely there will be lots to see and learn! Where to begin, though….?

I’m fortunate to have several friends in town, and this past week, one of them showed me a cool outcrop of phyllite. At the spillway for a dammed reservoir on Totier Creek, north of the James River near Scottsville, the outcrop is much cleaner and less vegetated than many central Virginia sites. It pleases me to find clean rocks outside!

Here’s the site in Google Maps.

Because of being periodically scoured by overflow from the reservoir, the outcrop here is pretty clean, with sparkling silver outcrop where the water is rushing over it…

…and nearby dry locations shining with a muscovite gleam:

…but the same rocks show a rusty patina at less frequently scoured locations…

… and lichen encrustation at the most infrequently-scrubbed sites:

And the foliation is folded in a bunch of different styles – open, undulating folds, tight kinks, and combinations thereupon:

Depending on the map you consult and how willing you are to extrapolate along strike, this site is mapped as “Zpm- metagraywacke, quartzose schist and melange,” “Zmg – metagraywacke,” or Pzc – Candler Formation – muscovite-chlorite-quartz-paragonite phyllite and schist, metagraywacke.” I found my visit there to be intellectually stimulating, despite oppressively brutal heat. But these were new rocks, and visiting the Totier Creek spillway was the first step toward a new appreciation of a new regional geology.

All told, there was a good amount to see, and I can envision some fun student projects to be conducted at the site: for instance, “Does the orientation of the maximum principal stress implied by the veins match that implied by the kink fold axes? If not, which one came first?” Or using the weathering levels to map out scouring histories of different parts of the outcrop; perhaps augmented by some lichenometry?

It’s exciting to think about the possibilities… hopefully our nation will be able to get this pandemic situation under control so that someday I can actually plan for field trips with students again.

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17 July 2020

Friday fold: Sandy Hollow from the air

My friend and colleague Mike Plautz sent me this photo today, from an airplane above the region east of Dillon, Montana.

I dialed up the contrast and saturation of the photo to make it “pop” a bit more, and I’m pleased with the result. Many, many geology students will recognize this site, a patch of BLM land called Sandy Hollow, adjacent to Block Mountain (just northeast of the cloud shadows). It’s a favorite mapping site for field camps. As such, I won’t say any more here about its structure; but I did want to share this wondrous site with Mountain Beltway readers. It’s too good to pass by.

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15 July 2020

Book report

A few recent reads, reviewed:

Record of a Spaceborn Few, by Becky Chambers

The third science fiction novel in the Wayfarers series, this piece examines the culture of the Exodus Fleet, a group of big spaceships that contain most of the human population of Earth, running their own society with a principle idea being that they run a self-sufficient operation, meeting the needs of their populace in place, and running a closed ecological loop, recycling the dead to make soil, to grow new food to feed the living. As with Chambers’ previous books in the series, the beauty and delight of the novel comes in its explorations of character, with a brand new cast of people, most of them human, thinking about what it means to be human when you live in a human society that’s not on its planet of origin. As with A Closed and Common Orbit, the second novel in the series, I missed the plethora of aliens described in such fun Star Wars-level of detail in the original book, The Long Way to a Small, Angry Planet, but at this point I’m hooked on Chamber’s realization of a diverse, inclusive future for our flawed species, and there’s just enough alien in there to keep it spicy.

The Sparrow, by Mary Doria Russell

A novel of interplanetary civilizations meeting, but also a novel about humans’ spiritual connection to the cosmos. The set up is that an astronomer discovers a signal from another species, living on a planet near Alpha Centauri. He shares the information with his friends, one of whom is a Jesuit priest. The Jesuit communicates the finding to his superiors, and they bankroll a modern “mission” to the planet, to explore God’s creation in the same way the Jesuits sent themselves into some of the more remote corners of the Earth. The assembled team includes both the ecclesiastical crew (three more priests get added in) as well as the circle of the astronomer’s friends, many of whom have much deeper levels of character development than him. At the center is Emilio Sandoz, the priest who feels a calling from God to engage on this journey. The novel is told in alternating chapters: both the “real-time” story unfolding on Earth, within an asteroid that they retrofit as a spaceship, and on the distant planet, which we learn is called Rakhat as well as the story told in reflection and interrogation, forty Earth years later, as Sandoz returns to Earth and Rome, and is asked to explain why everyone else is dead, and what happened to his hands (stretched out into uselessly elongated form) and why his spirit is broken. It’s a powerfully written novel, with many strong characters, thoughtful explorations on our place in the universe, and the trauma of violence on our lives.

The Two-Mile Time Machine, by Richard Alley

Penn State glaciologist/climatologist Richard Alley wrote this book as a popular account of his scientific work decoding past climatic variation (including abrupt climate change) from ice core data, particularly from Greenland. It’s an account of the how and the why of drilling through the Greenland ice sheet for information about the past, and how that ice sheet formed. The latter half of the book is a description of what that ice core information has revealed about the past few million years of climate history on our planet. In particular, focus is given to the North Atlantic, and changes in oceanic circulation that result in changes to sedimentation and isotopes. The great strength of Alley’s writing (and his general science communication) are his imaginative analogies, which feature many more hits than misses, and force the reader to think about Earth processes from a fresh perspective. Reading this has been on my list of things to do for years; I’m glad to finally have managed to make it happen.

Lone Traveller, by Anne Mustoe

This is a “bicycling around the world” travel book (a favorite genre of mine) but it’s not structured as a “first I went here; then I went there, and finally I made to this other place,” as she did with her breakout travelogue, A Bike Ride. Instead, the structure of this book is thematic: what she packed, how she dealt with bureaucrats, how she found shelter, how she dealt with wild animals and predatory men. As such, it’s more like a conversation over tea with the protagonist, when a prompt leads to a series of anecdotes connected by a common thread: “But tell me, weren’t you ever scared?” “Well, there was this time in China when…” etc. In book form, I’m not sure it works as elegantly as in spoken conversation; I like my books to have a narrative arc to them, and the structure of a travelogue is familiar and uncomplicated and comfortable, but I can also appreciate why as an author Mustoe made the call to organize things differently. I’m sure it was more engaging to write for her when the vast year+ of experiences in the world were considered in terms of notable lessons that cluster around the most common queries an experienced traveler gets from those who are curious about exploring the world as a solitary woman.

Binti, by Nnedi Okorafor

A novella set in the future about a Himba girl (from what is today Namibia or Angola), who scores well on an exam and gets a free ride to the galaxy’s best university, but she has to leave her family and home to go. She retains an important practice from her culture: the use of otjize, a mix of oil and clay that is kneaded into the hair and spread over the skin. This traditional practice is a soulful connection to her sense of self, despite her nontraditional path – but it also acts as a shield against envenomation by jellyfish-like aliens that attack her “schoolbus” ship as it crosses interstellar space. Binti also brings with her an object she found in the desert back home, which turns out to allow her to translate the medusae’s language, something no other human has been able to do. This puts a unique person into a unique position in the history of the galaxy. Is Binti up to the task? She is.


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10 July 2020

Friday fold: Candigliano River, Italy

Reader Michael Hiteshaw spotted some amazing folds this week while watching Kayak Session TV on YouTube.

Though there’s a dramatic arc of “saving” a deer, both Michael and I felt our eyes drawn to the canyon walls where there are gorgeous folds in several sizes and shapes, with an emphasis on chevron folds:

The video description on YouTube reads:

Fabulous action by whitewater kayaker Fabrizio “Gass” Capizzo who saved a deer from drowning while paddling with friends on the Candigliano river near San Marino in Italy. The funny part is he almost cares more about the deer than his fellow paddler who swam… 🙂
Thanks for alerting me to this one, Michael! Happy Friday to all.

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19 June 2020

Friday fold: Scaglia Rossa chevrons at Lago di Fiastra

My friend Alan Pitts is orchestrating a virtual field camp for George Mason University this summer, utilizing outcrops in central Italy’s Apennine Mountains. Here’s a 3D model he just posted of one of the most impressive outcrops there: the chevron folds in the Scaglia Rossa limestones at Lago di Fiastra. I featured the site as a Friday fold 3 years ago when Alan took me there in person, but this gives a much fuller picture of the site:

by alanpitts on Sketchfab

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5 June 2020

Friday fold: Harbledown Island

Reader Christian Gronau writes with this Friday fold contribution:

Greetings from Cortes Island, BC – at the opposite end of the Strait vis-a-vis Lopez Island.

Your Mountain Beltway blog is always of interest, and I have been following it for several years by now. Thank you for putting the effort into this worthwhile website.

Quite regularly your posts elicit “echoes” and make me go back to some of my own geological notes and photographs. The Lopez Island tension gashes are exquisite in their elegance and classic simplicity.

A little further north again from Cortes Island lies Harbledown Island, eponymous of the Harbledown Formation (Early Jurassic sediments, often fossiliferous). The west of the island has a bay called Parson Bay, eponymous of the Parson Bay Formation (Late Triassic, also fossiliferous) – making this geographical area one of rare distinction as well as historical complexity (early 20th century stratigraphic work).

The attached photograph shows part of an extensive stress zone in Parson Bay limy shales, looking remarkably similar to the image of your last “Friday Fold,” though a bit more complex and, perhaps, confusing. I thought you might be interested in seeing it:

That’s a lovely outcrop photo, Christian! It has many of my favorite features: a multi-chapter story (i.e., it’s a palimpsest rock), good structural geology, a well-placed sense of scale, and a lack of vegetation, barnacles, and/or anthropogenic detritus. A very pleasing sight to contemplate at the end of a rough week.

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29 May 2020

Friday fold: Lopez Island tension gashes

Darrel Cowan returns with a Friday fold for you! He writes with these

awesome fractures. They formed in slightly metamorphosed sandstone on Lopez Island in the San Juan Islands, Washington. The rocks are probably Late Jurassic-Early Cretaceous in age and part of the Lopez Structural Complex [I can give a reference for the setting: GSA SP 221]. The sandstone exhibits a weak foliation imparted by dissolution and reprecipitation of quartz; the quartz in the fractures is evidence of the role of fluids.

You can interpret what we see. I tell my students that these formed in a localized shear zone, even if the boundaries are not expressed in the outcrop, which is glacially polished and striated, by the way. I challenge my students to infer the sense of shear and to explain why the fractures are sigmoidal and thicker in the middle [they kept opening while rotating and extending their wings outward!]. The youngest tips are oriented at 45° to the boundaries of the shear zone, as predicted.

I’ve wanted to go back and visit these outcrops, but access on Lopez is extremely difficult. Someday, after covid-19.

Best wishes to all. On several levels, the Friday fold feels like a frivolous indulgence in such dark times for the nation, but perhaps its a reminder of the sort of content that acts as a beacon of normalcy. It’s the content I would prefer to focus on, were pandemic disease, racial injustice, culture war, environmental degradation, and looming facist oppression not occupying my thinking instead.

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22 May 2020

Friday fold: Anticline in Glacier National Park

Working on a virtual field experience for Glacier National Park this weekend, I came across this amazing GigaPan of a portion of central Glacier by Joe Giersch of the USGS:

What really struck me about it is that big arc of white rock (quartzite, no doubt) within the lower green argillites of the Appekunny Formation… Just left of center. Zoom in and see if you can find it!

I saw that and thought, “Ooh! A fold!” But then I thought that perhaps it was just a trick of the outcrop: i.e. a curved landscape intersection a planar bed, as in the false syncline I noted in Titus Canyon. To corroborate, I looked to adjoining ridges. And…sure enough, it can also be seen in the next ridge over to the right, highlighted by vegetation.

I found the place in Google Maps, and shifted the perspective so I was looking along strike of the anticline’s axis:

Because the fold trends north-northwest, and the valleys run east-west, you can see it appearing in cross section on at least three ridges there! Here’s a link on Google Maps to get this same view, should you care to poke around there yourself.

Sure enough, on the Whipple (1992) geologic map of the park, there’s an anticline mapped at that location:

A little virtual geological discovery for me… What an amazing place; I miss it pangfully.

Whipple, J.W., 1992, Geologic map of Glacier National Park, Montana: U.S. Geological Survey, Miscellaneous Investigations Series Map I-1508-F, scale 1:100,000

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15 May 2020

Friday fold: Argentinian turbidites

Zoltán Sylvester brings us this Friday’s fold:

And there’s more where that came from:

These are deepwater strata of the Lower Cretaceous Rio Mayer Formation, exposed near Lago Argentino, Argentina, south of the lake’s northwest “arm,” about here. They were deformed so exquisitely during Andean mountain-building.

Zoltán is a talented photographer, and you should check out more of his work here.

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