10 April 2020
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:
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.
3 April 2020
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:
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.
30 March 2020
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.
27 March 2020
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
25 March 2020
Humanity faces a crisis today, and we struggle to find the right way to deal with it, to solve it, to live meaningfully within the constraints it imposes. You might think I’m referring to coronavirus, but it’s actually climate change that’s on my mind. Hope Jahren, author of the incandescent Lab Girl, has a new volume out, on the unsustainability of modern Western life, and what actions we can take as individuals to lessen our negative impact on the global environment while simultaneously living richer, more thoughtful lives. It’s called The Story of More (more people, more energy, more resources, more carbon dioxide, etc.) with the subtitle of “How We Got to Climate Change, and Where to Go from Here.” Apparently derived from a university-level course on climate change that Jahren teaches, this book is more relentlessly quantitative than the deeply personal stories told in Lab Girl, but each chapter includes some tale from Jahren’s life that illustrates some connection to the topic in question. These vary between extremely apt and peripheral, but they are invariably heartfelt and poignant. Her writing, as always, is exceptionally elegant. One example of this is her description of a petroleum refinery south of New Orleans: It’s “a bizarre landscape that looks to have been co-designed by Ayn Rand and Aldous Huxley. For a full five miles along the road next to Chalmette, Louisiana, you’ll pass a massive array of smokestacks, steamstacks, and chimneys, looped together with pipes and shutoff valves, more angular than a Dr. Seuss drawing but equally fantastic.” The focus is always on the human connection, and never delves into remote, inhuman topics like atmospheric dynamics. A lot of it is about food and eating, nurturing plants that they may nurture us. It feels very grounded and profound as a result. I’d imagine that for Jahren’s lucky students, this intimate sense of our own deep connections with the wider world comes through in classroom discussions. In communicating, Jahren exhibits a disciplined love of words and allusions, connections and analogies. She impresses her perspective with countless calculations that she has performed herself from a diverse suite of data sources (an extended appendix to the book reviews these sources, enabling readers to explore the numbers on their own). All told, the book doesn’t “land” emotionally with the same intensity as Lab Girl, but it’s less of a memoir and more of a “personal textbook.” I could very easily imagine this volume as one of a triad of readers for an Environmental Geology course: Along with John McPhee’s The Control of Nature and Elizabeth Kolbert’s The Sixth Extinction, The Story of More would serve there to round out an understanding of the human relationship to nature with an emphasis on personal opportunity and responsibility. Recommended, particularly the audiobook, which Jahren herself reads at perfect pace and with vital emphasis.
20 March 2020
We are living in surreal times. It hardly seems possible, but a week ago this evening, I drove down the Las Vegas strip with my students, ogling at the glitz and spectacle and crowds. Now, a mere 7 days later, Vegas has been shuttered, and it’s been shuttered for days. We traveled freely through California and now a week later, everyone in the state is ordered to stay home. What a week it’s been! Ever since I arrived home, my family and I have been in self-imposed self-isolation. It seems our Death Valley trip was the last face-to-face academic thing that happened at the College prior to the unprecedented transition to 100% online instruction for the remainder of the semester.
So let’s take comfort in the routine of the good old Friday fold, and look back to pre-lockdown days in the field.
Eight days ago, I drove through Titus Canyon with my students, which manifested in last week’s Friday fold, and also gives us some smaller scale structures this week. There aren’t a lot of places to pull over in Titus Canyon, so these are all “drive-by” photos (and hence they all lack a proper sense of scale; mea culpa), but I think you’ll enjoy them as a glimpse into the highly deformed strata of the overturned Corkscrew Syncline in lower Titus Canyon:
Looking up through the skylight:
Some kink folding:
And these recumbent isoclinal folds really took the cake; at first glance they just look like bedding, but there are fold hinges near the center of both of these photos:
Example # 1:
Example # 2:
Hope you and your loved ones are safe. Please stay home. Please wash your hands.
I’m not sure if we can get “normal” back at this point, but we can prevent spreading this plague to the most vulnerable members of our civilization with simple, straightforward measures. I know those simple, straightforward measures contort our lives into almost-unrecognizable shapes as we seek fulfillment of our employment duties, our educational goals, and our social desires, all mediated through electronic communications. But the priority needs to be safety and health. All else is secondary.
Be well, friends.
13 March 2020
Hi everyone, and greetings from eastern California’s Death Valley, where I’m leading a field geology course over our spring break.
I found an excellent Friday fold for you:
That’s the Cambrian-aged Bonanza King Formation, a package of limestones, as exposed in lower Titus Canyon, Death Valley National Park.
Here’s the thing: the lower part of that outcrop is Upper Bonanza King Formation, while the upper part of the cliff is Lower Bonanza King Formation… The stratigraphic sequence, in other words, has been inverted.
These beds are upside-down. They are part of the large-scale Corkscrew syncline, a recumbent fold. This is is its overturned limb.
Which means that thing on the left which looks like an anticline, is really an upside-down syncline. It’s antiformal, but really it’s a syncline, with the youngest rock in the middle, and the oldest rock on its flanks. Similarly, the fold at right looks like a syncline, but once we understand the strata have been flipped over, we recognize it to be an anticline, with the oldest layers in the middle.
So we have a synformal anticline and an antiformal syncline, side by side and utterly upside down.
Bonkers. The power of tectonics made manifest.
Happy Friday! I hope you’re healthy and neither dying of COVID-19 nor transmitting it to someone who will transmit it to someone who will die of it.
Wash your hands, eh?
6 March 2020
Today’s Friday fold is the last question on the Historical Geology midterm exam I gave today.
This is a diagram showing a cross-section through the rocks at Villuercas-Ibores-Jara UNESCO Global Geopark in Extremadura, Spain. It comes from a field guide to the region by J.J. Álvaro, S. Jensen, and T. Palacios. I stumbled across the image while searching for something else, and was immediately struck by its elegance and graphical balance, but also how it showed a deep time story with many discernible chapters. I modified their image to trim it down to what I considered to be the essential components for my own students, but I was so pleased with the story that popped out that I also posted it on Twitter today, challenging geo-students there to take a crack at deciphering the saga from the information in this cross-section. Despite likes and retweets, no one was brave enough to put forward some observations and interpretations.
Before you scroll any further down this blog post (and see my answer), see what sense you can tease out of this accumulation of lines, wiggles, and dots….
Okay, here’s what I see:
- Once upon a time, there was a deep marine basin where most of the time, mud was deposited.
- Periodically, turbidites would bring in layers of graywacke.
- At some point, either a glacier dumped a bunch of debris in, or there were some submarine landslides that resulted in an exceptionally poorly sorted deposit of diamictite. (We can’t tell from the data available here whether the clasts in that diamictite are faceted and striated or not.)
- Then there was an episode of folding and faulting, probably accompanying an episode of mountain-building. Roughly speaking, and with the diamictite acting as our marker unit, the strata were warped into what appears to be a regional antiform in structure.
- This tectonic squeezing resulted in uplift, subjecting our now-near-vertical strata to a time of erosion. The mudstone, graywacke, and diamictite layers were truncated against the ancient Earth’s surface.
- Time went by and subsidence occurred, allowing sea level to creep back up and over the site. Higher-energy fluvial or shoreline (delta) deposits were laid down. Based on the lens-shaped deposits of conglomerate within the coarse sandstone, it looks like this was either terrestrial or transitional. The base of the unit makes an angular unconformity with the layers described in steps 1-5.
- On top of that is a layer of fine-grained sandstone, perhaps indicating beach or nearshore marine deposition.
- On top of that is a layer of mudstone, going back to a more offshore setting, and…
- Topping that is a layer of limestone, dolostone, and shale – the most offshore facies yet. In total, this package represents a classic fining-upward transgressive sequence.
- Then another episode of compression happened, folding all these layers into a big synform.
- Once again, this uplifted the edges of some of the layers to the surface, where they were eroded.
- Again, subsidence and/or sea level rise (during the Ordovician, according to the explanation) brought deposition back to the site, resulting in the “Base” Formation. An angular unconformity exists now between the base of the Base and the underlying high-angle strata.
- Based on truncation of some of the upper layers of the Base Formation against the overlying unit, I’m guessing there was another round of erosion.
- Deposition resumed anew, with layers of quartz sand, also during the Ordovician. This makes an unconformity with respect to the underlying Base layers.
- Then there was a little bit of folding (pretty subtle), again effecting all layers, but most noticeable in the non-horizontality of the Ordovician package.
- Then faulting down-dropped the northeast side relative to the southwest.
- Then (or perhaps accompanying #16) uplift brought it all above the surface, where erosion went to work again, breaking down the mountainous outcrop and laying down temporary (?) deposits of Recent debris.
Whew! What a tale. I can’t wait to someday see these rocks in person.
5 March 2020
What if geologists studied more than just Earth processes and history, but also how to go back in time and manipulate that history? That’s the job of the “cultural geologist” who is the flawed protagonist of Annalee Newitz‘s novel The Future of Another Timeline. (I’ve previously read her book Autonomous, and enjoyed it. I see her as a leading thinker about futurism’s intersection with feminism.) In TFOATL, the main character, Tess, lives in a United States that oppresses women even more than the current one does. Abortion is illegal for instance, but Harriet Tubman was a Senator. The book is set partially in the near-future (2022) and also in the early 1990s, but also in 1893/4, as well as the early and late Ordovician period of geologic time. Plus one of the characters comes from the distant future, a few hundred years down the line, bringing some intriguing technology with her. Tess is part of a group of female geoscientists who are working to edit the past so that women of the future can live freer lives. They are battling followers of a smut-obsessed U.S. Postal Service special agent, intent on subjugating women for all time. The action ranges from the World’s Fair in Chicago to suburban Los Angeles’s punk rock scene to the ancient city at Petra, Jordan, as well as the desolation of Flin Flon, Manitoba. An interesting feature of all these times and places are the “Machines,” time travel devices that are natural features associated with the Precambrian cratons of most continents – except the one at Petra (‘Raqmu,’ the site’s original name, is used instead), which is apparently a master Machine that controls the others. Humans can tap a rhythm into the Machines to go back in time, but they cannot go further forward than their present, and they cannot visit the same time twice. It’s weird to think of time travel as being a natural phenomenon, thought these wormhole-generating spots, though maybe they were made by alien intelligences in the deep past. The possibility is raised and set aside. It doesn’t matter: if they exist, people will use them, and pursue their own agendas accordingly. Geoscience takes on whole new levels of significance in such a world, and readers of this blog will be tickled to see that the fictional American Geophysical Union of the novel has a library in Raqmu, where geoscientists from across human history meet in the year 94 CE to compare notes on their edits in upstream and downstream in the timeline. (Take that, Fall Meeting!) As various characters go to various times and spawn new and divergent timelines, it gets dizzying to try and keep track of it all. Ultimately though, the good gals win, and manifest a future where collective action results in women having control over their own bodies. A warning: there are some scenes of real nasty violence and one of sexual abuse. The novel is by turns inspirational, fantastically creative, righteous, and extremely unsettling. I’ve never read anything quite like it.
28 February 2020
The Friday fold is a lovely little sandbox analogue model by Prof. Marco Martins-Ferreira, who posted it on Twitter this week:
As deformation proceeds, you can see the layers develop folds that then morph into faults, shoving deeper layers atop more shallow strata. As a bonus, you can hear Marco’s baby cooing in the background!
Here’s a stabilized, sped-up version, courtesy of Anna Williams:
Happy Friday, all!