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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8 May 2020

Friday fold: Wills Mountain Anticline

Eric Fulmer (who pitched in with last week’s Friday fold) returns this week with another treasure. He writes,

I was in Hopeville, WV a couple of years ago. The entire area between Cabins and Hopeville is a real joy (geologically and recreationally) as some of the most resistant rocks of the Mid-Atlantic Appalachians are folded and exposed in quick succession and with great relief. I am particularly fond of seeing the western-most exposure of Tuscarora Sandstone in the Wills Mountain Anticline along the North Fork Gap.

The Wills Mountain Anticline is a much larger structure than the Hopeville Anticline and the most obvious member of the antiform is the resistant Tuscarora Sandstone. North Fork Mountain (south of North Fork Gap) is essentially the eastern limb of the anticline and resistant Tuscarora forms white cliffs along the crest of the mountain for miles. The western limb of the anticline includes nearly vertical beds of the same unit plunging directly into the earth; Seneca Rocks are equivalent rocks further to the south.

Click to enlarge

Click to enlarge

The best view that I have seen of the Wills Mountain Anticline is from the first ridge of North Fork Mountain Trail (northern trailhead). The path winds up the mountain and then takes you to a fabulous viewpoint across the North Fork Gap towards New Creek Mountain, where the Tuscarora Sandstone can be followed from east to west across the entire anticline. The drop into the gap is also quite dramatic for the East Coast.

Highly recommended for a long day trip or overnighter.

Once again, thanks to Eric for contributing a fold. Other readers are welcome to do the same. Just drop me an email.

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6 May 2020

The Broken Land, by Frank L. DeCourten

You might think that the last two months would have been a good time for reading, given the social isolation and stay-at-home orders. But that hasn’t worked out to be the case for me. The stresses of the pandemic, new and different work responsibilities, new homeschooling responsibilities, ongoing textbook writing and an impending move for my family have all conspired to gobble up my time, and there’s been very little time left over for reading books. I managed perhaps 2 or 3 pages per day. I started Frank DeCourten’s The Broken Land before I went to Death Valley in early March. But I didn’t finish it until this morning. It was good. It’s a comprehensive summary of Great Basin (Basin & Range) geology: outcrops, locations, events, and interpretations, accompanied by anecdotes and DeCourten’s own hand-sketched illustrations. I found it an excellent compilation, and I’ll keep it on my shelf for the rest of my career, for the next time (hopefully) that I’m lucky enough to return to the Basin & Range. One distinctive aspect to the book is that each chapter opens with a personal story about some experience DeCourten has had on a geological field trip. These are an attempt to draw the reader in toward the experience of geological explorations in the area. I found them familiar enough and therefore engaging, but I’m increasingly conscious that they may not appeal to everyone – they are the experiences of a able-bodied white male professor, and I wonder how they would land with any other audience. Unfortunately, I’m the wrong person to make that call. My gut tells me that the book would have been stronger without them, though. Overall, the geological content is solid and comprehensive and useful. It’s a valuable resource for anyone seeking a better understanding of how the Basin & Range came to be.

And now: Onward to the next book! Hopefully I’ll have more reading on which to report before another two months elapse.

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1 May 2020

Friday fold: Hopeville Anticline

Reader Eric Fulmer has contributed a fold as a balm for the end of another week of COVID-19 self-quarantine. Check it out:

Eric writes,

I was in Hopeville, WV a couple of years ago. The entire area between Cabins and Hopeville is a real joy (geologically and recreationally) as some of the most resistant rocks of the Mid-Atlantic Appalachians are folded and exposed in quick succession and with great relief. I am particularly fond of seeing the western-most exposure of Tuscarora Sandstone in the Wills Mountain Anticline along the North Fork Gap. Immediately next to Hopeville (Harman’s Cabins, just off of WV-55), a textbook anticline of Oriskany Sandstone is exposed where the “North Fork of the South Branch of the Potomac” cuts through the Hopeville Anticline. The hinge line is high up the hill side and the western limb plunges into the earth at a ~35 degree angle. The competent sandstone forms a nice cliff face and exposes easy to identify bedding layers across the outcrop. Decent views of the entire anticline can be found from the Cabins Assembly of God upper parking lot.


Thanks Eric!
Happy Friday to all.


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24 April 2020

Friday fold: The geologic map of Pennsylvania

This is such a gorgeous map:

Link 0.43 Gpx GigaPan of a geologic map by Berg, T.M., Edmunds, W.E., Geyer, A.R., Glover, A.D., Hoskins, D.M., MacLachlan, D.B., Root, S.I., Sevon, W.D., and Socolow, A.A., (1980)

I’ve been organizing a bunch of geologic maps this week for my Historical Geology students, and this is one of the most beautiful. I merged the two halves of the map that were available online and posted the result on GigaPan, which allows students to zoom in and out to various interesting parts of the map. To me, the contrast between the tightly-folded Valley & Ridge and the broader folds of the Allegheny Plateau is striking – and gorgeous!

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17 April 2020

Friday fold: Episode 14 of “Rock du jour”

I’ve been making a little daily video series over the past couple of weeks about rocks I have at my home – a quarantine-driven focus on the samples at hand around the house (as well as a few local outcrops). In many of the videos, I’m joined by my son, who know goes by the title “Mini-Professor,” though in this one from a few days ago (14th in the series), I fly solo:

I offer that one here now, since it features a folded rock, and today is Friday. I owe you that!

The videos are intended to be informal, semi-goofy, and unpolished. I’m learning about video production as I go, which is interesting to me, but the resulting videos definitely are certainly not especially polished! Don’t get your expectations up too high. If you want to explore the whole “Rock du jour” series, here’s a link to my YouTube channel.

I hope you are healthy in these unhealthy times.

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10 April 2020

Friday fold: Sorrosal Falls, Pyrenees

This gorgeous image popped up in my Twitter stream this week:

That comes from Amicia Lee, who revealed that it is Cascada de Sorrosal or “Broto Falls” in the Pyrenees:

Here, cropping out some of the gaudy distractions and zooming in on the good stuff:

Amicia writes,

The[se strata] are folded turbidites deposited in the Lutetian* and deformed during the Pyrenean-Alpine Orogeny. I’m not sure on the exact timing of deformation relative to deposition. Pretty sure flexural slip was a big talking point here, but we talked about it a lot so I could be confusing outcrops! The waterfall is located here in the village of Broto on the edge of Ordesa National Park, Spain. Sorry I can’t tell you any more, if I had my notebook with me I could have told you a lot more, but as everyone is finding right now, useful things are locked away in our offices.

There is also a via ferrata route that goes up the left side and through a cave and into the gorge at the back; you can see the ladders just above the vegetation patch about half way up the cliff.

Waterfalls don’t do too much for me in general, but I’d go to see this one for the lovely folds exposed on its face!

Thanks for sharing, Amicia! This is awesome.

* An age / stage in the Eocene. It spans 47.8 to 41.2 Ma.


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3 April 2020

Friday Fold: Saudi Arabia

To Saudi Arabia for today’s Friday fold, visible here at Wadi Fatima:

Annotated to show the rough trace of bedding:

This is a contribution from Ezra Zaini. He says:

In addition to the rampant folding, the area is affected by regional faulting (Najd F.S to the north and extensional faulting related to the Red Sea to the west). The formation itself is known for alternating beds of limestones and reddish purple siliceous/lithified mudstones. It and other surrounding formations unconformably overlay Precambrian Arabian Shield with all of them being dated back to the Cenozoic. (Oligocene-Miocene is what’s been agreed upon.)

Zooming in more closely:

And annotated:

I hope you’re doing well, dear reader.

It’s been a rough week, and it doesn’t look like it’s going to get better any time soon. Vicarious armchair geology is all that’s safe at the moment, it would seem.

If you have cool folds to share, please get in touch.

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30 March 2020

Stepping-Stones, by Katharine Fowler-Billings

This memoir by one of America’s earliest female geologists is an enjoyable read about adventure and professional working conditions in the 1920s and 1930s, and up though the 1950s and 1960s. Fowler-Billings (née Fowler) led an interesting life, ranging from growing up in an urban Boston that still had a significant horse population to post-retirement conservation and environmental activism. In between, Kay was a field geologist and an educator. She was born and died in New Hampshire, but roamed the world during her active almost century of life.

Herself a product of the geology departments at Bryn Mawr (where she was a student of Florence Bascom) and the University of Wisconsin (MA in geography), and finally Columbia for her PhD (where she mapped Wyoming’s Laramie Anorthosite Complex for the first time), she inspired generations of geology students through her teaching at Wellesley and Tufts. In between, she worked as a resource geologist in West Africa, searching for gold and lead and iron and other valuable commodities in challenging conditions that she appears to have enjoyed immensely.

Much of the book is given over to recounting her travels, which is a genre I use to enjoy very much, but I find it doesn’t hold my interest as much nowadays. More interesting to me now is how Fowler-Billings navigated the various professional obstacles she encountered, with confidence and cleverness. A worthwhile read to enter the mind of a trailblazing geologist.

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27 March 2020

Friday fauxld: a false syncline in Titus Canyon

Can it really be only two weeks ago that I was geologizing in the California desert?

My students and I saw this scene in Titus Canyon, just below Leadville.

Naturally enough, we keyed into this feature specifically:

It looks like a syncline (or “synform,” as lower Titus Canyon teaches us to more carefully say)!

…But: there’s no fold here at all! It’s a trick of the outcrop surface.

These are uniformly right-dipping strata, but in some places the outcrop surface is parallel to the true dip of the strata, showing them to be most steeply inclined, and sometimes parallel to the strike of the strata, which gives their trace a horizontal expression, and everywhere else the outcrop surface is oblique to the strike and the dip at some angle, giving them an “apparent dip” that is somewhere between the true dip and horizontal:

No fold at all in this photo: it’s a faux fold, a “fauxld!”

Enjoy, and be safe and be healthy, and I hope sincerely that you and your loved ones are spared the ravages of COVID-19. I think it’s unlikely to leave any of us truly unscathed, but we’re still in the early days of the disaster.

It may seem indulgent and frivolous, but for me, the Friday fold represents a regular ritual to return to in these extraordinarily stressful times.

Here’s a handheld GigaPan of this outcrop:

Link 0.13 Gpx GigaPan by Callan Bentley

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