25 October 2019

Friday fold: Identity of a BIF

Darrel Cowan steps up with the Friday fold again this week: this time it’s a polished slab, mounted on a wall indoors at the University of Washington’s Department of Earth & Space Sciences; an elegant and informative piece of décor:

…and with Darrel for scale:

It’s so reflective that glare is a bit of an issue in photographing it!

Here, I’ll zoom in on the un-glare-besmirched portion of the image:

Here’s another view:

Darrel wants your help, gentle and geologically-informed reader. He writes,

When we moved into our renovated building in 2006, the contractors had left spaces in the walls to mount six polished rock slabs. I found and chose the BIF and my brother and I gave it to the department. The slab is about 4 x 8 feet. The red layers are chert, and the gray, magnetite with possibly some hematite. The folds are awesome, and one can easily see the different behavior of the chert and magnetite. The wholesale slab merchant calls it “Iron Red” and claims it came from India, although they could not substantiate its origin.

BIFs are present in many Precambrian terranes. A colleague suspects the slab it “itabirite” from Brazil. Can anyone more positively identify the source?

Can you all help Darrel out with a positive ID on this beautiful BIF?


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18 October 2019

Friday folds from the Foreknobs Formation


That’s my seven year old field assistant showing off the shape of a syncline in shale, siltstone, and fine sandstone of the Foreknobs Formation, a Devonian nearshore package of clastic sediment in the Valley & Ridge Province of eastern West Virginia.

Want to see something freaky for Halloween? Photoshop can make it happen:

Ewwww. Creepy!

Another shot of the same fold, with a thick massive sand above a thicker black shale, from across the road (and no tentacle-armed boy for scale in this one):

My son and I took a field trip on Monday out to Corridor H, in Grant and Hardy Counties, West Virginia. There, a new highway has cut into folded and faulted strata of the Paleozoic section. Today’s Friday fold ensemble comes from an outcrop of Foreknobs that I’d never previously bothered to stop at. It was a delightful reminder that, despite dozens of trips to Corridor H over the years, there are still surprises lurking in these road cuts…

Here are some more folds we saw:

All these photos are taken of south-facing outcrops (note how well lit they are in the low October noon light), so our perspective is looking to the north. So west is to the left, and east is to the right. Once that orientation is mentally established, we note that the west-dipping limbs are much shorter than the east-dipping limbs. This asymmetry is found throughout the Valley & Ridge province: the folds are said to have a westward vergence. This indicates the tectonic transport direction: during deformation, these sedimentary layers were shoved from the east toward the west.

Here, my field assistant slugs some iced tea:

…but behind him is a small overturned, breached anticline, a little fault propagation fold:

A similar overturned fault propagation fold, with the bonus of a decent little cleavage fan developed on the axis of the fold, on the lower part of the most prominent resistant layer:

Let’s take a closer look:

Annotations here, with yellow showing cleavage in the shale/slate on the bottom of the siltstone layer, and the green on the upper surface of the siltstone, showing outer arc extension on the siltstone’s extended upper edge.

Here’s a small thrust fault doubling a siltstone bed for a few inches of overlap:

And I’ll conclude with a shot that lacks a proper sense of scale, as I shot it full zoom across the highway of the higher berm of the roadcut, on the other side of the road:

It’s a delight to go out in the field with my son. He really engages with the exploration now, finding rocks he thinks are cool (“This one is a perfect triangle!”) as well as helping me search for key features. We’ve been doing this a while now, and I look forward to future field work with him.

Happy Friday to you and your family field assistant!

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11 October 2019

Friday fold: Watern Cove

On the seaward edge of southeastern Newfoundland’s Avalon Peninsula, there’s a special place called Mistaken Point, where fossils of ancient soft animals are preserved in abundance. On my way there this summer, I crossed over a small creek running into Watern Cove. This is what it looked like as we approached:

Closer up, you can see a nice ~monocline cropping out: an symmetric fold with two ~horizontal portions on either side, and one central limb in an attitude of steep inclination:

Here is my six-year-old field assistant approaching the outcrop:

Here is the view from the other side of the channel:

This fold is important, because on its steep limb, it exposes some of the fossil-bearing layers of the Mistaken Point Formation. Here’s that same view orientation, but see if you can pick out the fossils on the bedding-plane outcrop in the foreground:

My field assistant reaches out, and connects with his distant Neoproterozoic relatives:

These creatures boggle the mind with their unfamiliar forms, their nonstandard senses of symmetry:

There’s a huge thing (fossil??) in this shot, something like a meter and a half long before it’s truncated by the raw right edge of the outcrop. Its narrow end is ~10 cm below the tip of the pencil:

What a site for paleontology! And we have the structure to thank for exposing this amazing scene. Jay Kaufman made a GigaPan of the outcrop if you want to try exploring it on your own:

Fortunate find for fossils, eh Friday friends? Felicitations to the folding for this fine frontage!

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9 October 2019

Book report

I’m way behind in writing about writing, but I’ve read a decent number of books (or listened to them) over the past few months. I apologize to each of these authors for lumping all these reviews into a single blog post, but this has collectively been on the back burner for months, and I’ve decided to finally push them all out there at once. I’m going to wipe the slate clean, or else I’ll never catch up!

Here are the highlights of my past half a year of reading:

Underland, by Robert Macfarlane

A masterpiece of passionate writing about the world’s deeper spaces. Macfarlane is a gifted, assiduous writer who savors choice words and descriptions that walk the line perfectly between spare/economical and luxuriant. In this substantial collection, he explores caves, sinkholes, mines, laboratories, abandoned subway tunnels, graves, root/mycelium networks, moulins, and other “underland” spaces, seeking insights that come from the depths of the planet. The locations visited vary tremendously – some are natural, some anthropogenic, and some are an eerie amalgam of both. The people Macfarlane meets along the way, his guides and friends, plus new random acquaintances are a curious mix of calm, zany, driven, and adventurous. There are many, many wonderful moments in Underland, but my favorite is the chapter wherein Macfarlane spends a week traversing Paris underground, through abandoned spaces. At one point, he’s surrounded by a particularly tight passage, hemmed in as if in a coffin, when suddenly he’s very uncomfortably massaged by a train passing over his skull, inches away, violently vibrating the stone just above his tightly constrained body. It’s an extraordinary moment, described with such detail that I get a sensation of claustrophobia just recounting it. Truly a wonderful book.

Spirals in Time, by Helen Scales

Mollusks. Shells. More than you knew. The author is a marine biologist with a passion for malacology. She uses Spirals in Time to recount all sorts of fascinating aspects to seashells, from their chemistry to their architecture, their evolution, and the edible animals inside. She covers marine conservation and ocean acidification, but more so celebrates the beauty and intrigue exemplified by mollusk shells of every conceivable variety. This leads some interesting places: to a female-driven oyster economy blooming in the Gambia, the very-nearly-lost art of spinning fabric art from the anchoring fibers of certain shells (called byssus) in Italy, biomimicry studies for human needs, and an examination of the wholly odd argonauts, which I feel everyone needs to know more about. This book feels like a good companion for Danna Staaf’s Squid Empire. Every chapter is a tidy, thoughtful essay, and the whole book that results is quite a delight.

The Moon, by Oliver Morton

On the 50th anniversary of the Apollo Moon landings, Morton has taken the time and attention to draw together everything lunar into one book. It’s at once a history of the Moon, thinking about the Moon, the exploration of the Moon, the naming of its features, and its depiction in popular media like books and comics and film. There are parts of this book that I didn’t find personally compelling, but I could see how they would appeal to certain segments of the population – the popular culture stuff seem irrelevant to my purview. But other parts are astoundingly great, deliciously written. There’s a four page section on the formation of the Moon, the collision of proto-Moon Theia with proto-Earth Tellus, told in the context of the geological timescale: the one-moment transition between the Chaotian Eon (the condensation of the pre-solar nebula and accretion of the planets) and the Hadean, when “Earth” history proper begins. This is so good, with its descriptions of mountains hanging down from the sky, of oceans reaching out and merging, of the tremendous massive violence of it all, that I actually indulged in reading it out loud verbatim to my NOVA students the other day. It is astonishingly vital science writing.

Arts of Living on a Damaged Planet, edited by Anna Tsing, Heather Swanson, Elaine Gan, and Nils Bubant

This is an odd collection – a series of essays and speeches and articles about a very wide variety of topics, all supposedly united under the idea of a changing world, an altered biosphere, what we’re going to do about it, and what our cultural response is to these changes. The editors have grouped these contributions into two broad themes: “ghosts” and “monsters,” and I reckon one could claim that the book is cleverly designed with two front covers and no back cover. It ends in the middle. There are some very strong pieces in the book(s), and some that I found very weak and turgid. One of the best was an essay by the developmental biologist Scott Gilbert about how every biological idea we have of individualism is a mistake – on every level of scale, he demonstrates examples the show “individualism” to be a lie, and instead give support to the idea of the cooperative entity dubbed a “holobiont.” That’s an exceptional piece, and one I’ll set aside for future Historical Geology classes to read. The worst read like parodies of academic treatises in the humanities – full of highfalutin jargon that uses lots of syllables to convey very little meaning or insight. I won’t name names, but some of the essays were painful to read. A couple of famous contributors include Ursula K. Le Guin and Dorion Sagan (whose mother and frequent collaborator Lynn Margulis is celebrated in the “monsters” half-book).

Hot Carbon, by John Marra

This is an account of the discovery of different isotopes of carbon, and how they can be used as tools to track different Earth system processes. In particular, the author is keen on exploring 14C, and specifically its utility in understanding nutrient cycling in ocean plankton. I appreciated the historical story that dominates the first part of the book (the discovery and isolation of 14C) more than the latter part of the story (about the author’s own research on oceanic productivity), but it was all useful and informative.

This America: the Case for the Nation, by Jill Lepore

An examination of nationalism, and how it’s distinct from ‘the nation.’ What is a nation? How does a nation gain its identity? What is America’s history of nation-identity, and of nationalism? What’s the essential story of America, and where do we go from here, the rather wretched situation we find ourselves in now, with nationalism on the rise, particularly white-supermacist nationalism? Lepore, a historian at Harvard and a staff writer for the New Yorker, has written a taut little history here, one that illuminates our current situation with a fresh look at its historical underpinnings. She argues that America’s best story is our constant work towards increased justice and increased equality, prevailing again and again against forces that seek to minimize and oppress. Our national identity should be progress, not perfection, as Jameela Jamil recently put it. The arc of moral history bending toward justice is the national identity we should embrace, owning our flaws and faults, and working to ameliorate them, to fix our failings and work toward a national identity that is fully inclusive and inherently fair. Thought-provoking and inspiring.

The Mueller Report

Yep, I listened to the whole thing. It’s a free download on Audible, and a tour de force of meticulous evidence gathering and organization. There are two volumes, one about Russian interference in the 2016 presidential election, and a second about whether President Trump committed obstruction of justice. I’ll briefly comment on the latter, though there is much important and worthy detail documented in the former. Mueller and his team chose not to issue a formal prosecution decision on the obstruction question, apparently in accordance with a long-standing rule at the Justice Department that you don’t prosecute sitting Presidents or even formally declare their criminal activity (if any) to be criminal, since such a declaration could interfere with their Constitutionally mandated duties. So there’s neither an official denunciation nor an exoneration. But there are hours and a hours of documenting and interpreting actions that in any other citizen would be seen as obstruction of justice. It’s utterly damning, even if Mueller doesn’t ultimately officially seal the deal by saying “Therefore, I conclude we should prosecute the President for obstruction.” When considered in the context of the past week’s news, it’s more relevant than ever.

Autonomous, by Annalee Newitz

A novel set in the future with global warming, sentient robots, mind-altering drugs, and well-meaning individuals vs. nefarious government agents. Enjoyable, imaginative, and a bit uncomfortable, as one of the characters develops a sexual relationship with one of the robots. The most interesting part to me what how Newitz describes the robots communicating with one another, nonverbally, exchanging packets of information. That was something truly new and different for me, creative and insightful for understanding the inherent otherness of a non-human intelligence. Newitz is a founding editor of the futurism-focused io9, and the author of another novel of high acclaim, The Future of Another Timeline, which I just bought and look forward to reading. I like the way she thinks, and I anticipate reading everything she writes!

The Uninhabitable Earth, by David Wallace-Wells

Holy cow. What a book. A pull-no-punches account of global warming’s negative impacts. The first line is “It’s worse than you think,” and it just gets grimmer and grimmer from there. An astoundingly bleak, alarming account of the climate crisis. Many authors who write about global warming are fearful of being branded “alarmist” by the forces of denialism, and more to the point, are concerned that they not push their point so far that their readers/listeners become fatalistic or resigned to a diminished, hollowed-out future world. After all, we write about the negative side of unchecked climate change precisely because we want to motivate people to act so we can avoid it. But most writers are intentional in emphasizing hope for the future. But this book is different, because it eschews that approach and strives to face the worst news head-on. Wallace-Wells actually got labeled “alarmist” by climate scientists for a 2017 article he wrote of the same name that appeared in New York magazine (his ‘day job’). I’m not sure how many of the errors they cited made it into the book version, but I know that he has been justifiably taken to task over recent misleading tweets, wherein he sloppily extrapolates looming dire predictions from what appears to be a weak understanding of the science. That said, I found The Uninhabitable Earth a compelling read, and appreciated several key points that it drove home: (1) that warming is happening fast, it’s happening now, and it’s hurting people today, (2) that heat alone is a major problem, irrespective of its influence on rising seas or melting ice: heat is an exacerbating variable with an amplifying influence on conflict, misery, and crime, and (3) that the governmental/economic/social system we have in place now is really not all equipped to cope with a problem like global warming. It’s a very sobering read.

Amity and Prosperity: One Family and the Fracturing of America, by Eliza Griswold

A dark, fascinating accounting of being poisoned by industrialization in southwestern Pennsylvania. Amity and Prosperity are towns, but as the story unfolds, the names become double entendres, as cash flows in to this rural area, but unequally, creating newly rich residents, and others who suffer horribly as conniving companies suppress information flow while permitting the flow of ethylene glycol, arsenic, benzene, and other contaminants into the local water supply. Prosperity pits those with money against interests that threaten their prosperity, and amicable relations between neighbors suffer as a result. This is a classic American story: the corporate interests, the patriotism-infused extraction of natural resources, the individuals whose personal harm is enabled by a hidden partnership between private industry and the government agencies responsible for regulating that industry. By a careful portrait of the Haney family and their interconnections with other residents of Washington County, Pennsylvania, Griswold personalizes the story of ‘fracking gone wrong,’ and methodically chronicles the history of their afflictions, corporate stonewalling, medical insights, legal sleuthing, and moments of personal serendipity that collectively comprise a saga for our times. The husband and wife legal team representing the plaintiffs are amazingly dedicated, and accomplish great good with no financial rewards at all. It’s meticulously reported, and Griswold deserves the Pulitzer Prize she won for nonfiction for her work here. In the final pages of the afterward, the court case (Haney v. Range) is settled out of court, not very satisfactorily from the sound of it. In some ways, that lack of a final legal decision works, since (a) it’s nonfiction, and that’s really where things ended up, frustrating though it is for the reader who wants justice to be served, and (b) also because there is no legal precedent established, philosophically it leaves open the question of what we as Americans will do with information like this, wherein we discover that the cheap, low-carbon, homegrown natural gas from tracking carries with it a cost in human health for people who don’t deserve to bear it. Recommended.

Wanderers, by Chuck Wendig

An epic novel by a talented author. Wendig is someone I discovered via Twitter, where he posts pithy, inspiring admonitions each day, and frequently slings humor at our dark national political situation. (As I recall, it was his progressive politics that drew me to follow him.) His interests are comfortably similar to my own: nature, Star Wars, food (he loves apples!), equality under the law, and sanity in federal governance. I read the first of his Miriam Black novels last year, and found it engaging, but Wanderers got a lot more buzz, and now that I’ve read it, justifiably so. This is a story about the end of the world, artificial intelligence, climate change, epidemic disease, and the current moment in American culture and politics. It is a story of humans caught in a circumstance where white nationalism meets a deadly white fungus, with spooky and deadly consequences. In terms of the human population being obliterated, it resembles Stephen King’s The Stand, but one thing that always stuck in my craw about King’s disease-that-ends-the-world novel is the heavy religious aspects to it. Wendig has a couple of devout characters in Wanderers, which I think is utterly appropriate considering ‘who America is,’ but the resolution to the plot isn’t a glowing hand of God coming down to squish the bad guy. Instead, there are twists and turns aplenty, and a surprising conclusion. I really enjoyed reading Wanderers, as it was simultaneously an escape from the dismaying current political situation in the United States and a reminder of how bad it could get with racist militias and conservative religious media if a life-threatening phenomenon were to unfold. I found it sobering, scary, and gleeful in equal measure.


What have you all been reading lately? Any recommendations to share? Let us know in the comments…

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4 October 2019

Friday fold: Angel Island “IV”

Hey, let’s go back to Angel Island for today’s Friday fold. We’ve been there once, twice, thrice previously.

The rocks in question are metaconglomerates that Jess Ball and I found at first only as float on the beach at Camp Reynolds, like these two examples:

…Look at those beautiful elongated pebbles, transected by wee white veins!

Where there’s float, there may be outcrop — Sure enough, with a minute or two of searching, we found this same beautiful stretched-pebble conglomerate cropping out to the south, in cliffs along the shore.

Now let’s take a little tangent into looking at deformation within the clasts….

Here’s a close up of one of the deformed pebbles:

Note the set of fractures that are more or less perpendicular to the long axis of the thing; this implies both ductile and then brittle deformation of the clast.

More examples of the same phenomenon:

So that’s a lovely bit of deformation in a metaconglomerate, I’m sure we can all agree. But where are the folds, you may ask?

Here’s one spot – a bit of waviness that has an S-C feel to it:

What’s being folded here is the foliation, defined the shape of the deformed pebbles. Here it is, traced out:

And, in a less severe example, there’s a very slight arching to the foliation here, steeper at bottom left, shallower at upper right:

And here’s some slight warping of one of the stretched pebbles:

Note the varying orientation of the X-axis-perpendicular fractures. It almost looks like a segmented grub, undulating across the outcrop surface!

I hope you find these unimpeachably solid folds, even if they are a bit subtle. Hopefully the rest of the structure in the outcrop is icing on the cake.

Happy Friday to you!

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27 September 2019

Friday folds: O’Shaughnessy Boulevard, Glen Canyon Park, San Francisco

Last week saw me out in the San Francisco area, working on our revision to Clyde Wahrhaftig’s classic 1984 field guide, Streetcar to Subduction. One fold-o-rific locale I got to see for the first time was the west side of O’Shaughnessy Boulevard, west of Glen Canyon Park. It’s a great place to observe deformation in chert+shale interbeds of the Marin Headlands Terrane.

Now for some close-ups, including this one which shows the interbedding of the chert and shale quite well. These beds are much easier to crumple up by virtue of this mechanical layering.

And here’s a return to the same spot about an hour and a half later, when the outcrop was completely in shadow, so the lighting’s more consistent, but the rocks don’t “pop” quite as much.

(zooming in…)

The bedding there is overturned on the short limb, and the fold has become a fault!

If you want to see these outcrops for yourself, here’s a Google map link, and a link to the best outcrop in Street View. It’s walking distance from the Glen Park BART station. If driving, you might consider parking on Malta Street. That’s what we did. It would take only a couple of hours away from your AGU Fall Meeting experience to go and check out these folds. An alternative would be to participate in our pre-AGU field trip on “highlights of the Franciscan Complex,” which will be available for sign-up in October. That trip will showcase similar folds in the same rocks, seen at Marin Headlands itself.

Happy Friday; enjoy your weekend!

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13 September 2019

Friday fold: crinkled schist from Italy

AGU’s Chief Digital Officer Jay Brodsky offers up a fresh European fold for you today — and this one is on rather a smaller scale than Jay’s last Friday fold contribution

Click through for a bigger version.

These are lovely crinkly folds in highly foliated rocks. I love boxy little crenulations like these.

Jay tells me that this is from

Graines, Italy, in one of the valleys of the Val D’Aosta right by this castle.

Jay asked “What is it?” and I replied that “it looks metamorphic.” But I also made an attempt at digging deeper:

I brought up a geologic map of Italy, and draped it onto Google Earth, lining up major cities and Milan to get it positioned correctly, and then put the Castle of Graines into the search button:

… So that is this spot, and the rock type there appears to be rock type 99, “medium grade metamorphic rocks:”

Well, that doesn’t tell us too much, but these appear to be metamorphic rocks (‘scisti!’) that enjoyed deformation during Alpine mountain-building.

As always – if anyone else recognizes these lovely folds, or knows any greater detail about the geology of this region, chime in via the comments below.

Thanks — and Happy Friday!

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6 September 2019

Friday fold: Gonzen, Switzerland

Science writer Gabe Popkin shared two fold photos with me this week – both from near Sargans, Switzerland, adjacent to the Rhine River Valley and the border with Lichtenstein. The photos shows the mountain called Gonzen. There, Jurassic limestones crop out in a very wavy pattern:

I don’t know the geology of this area in any kind of detail, but I decided to trace out a distinctive upper surface of these limestone beds to get a better sense of what’s going on.

…The big central antiform appears to be overturned!

It occurred to me that this potentially implies some faulting, like this:

These are merely armchair speculations as I try to make sense of the pixels in the photo – but it makes me eager to go and visit the Alps to see these rocks in person! In the interest of “doing my homework” on the site in the limited amount of time I have this week, I found this paper, which seems to show at least one thrust fault on the mountain in one figure, and suggests these Jurassic limestones are part of Glarus Nappe Complex just to the southwest, which would be awesome.

If anyone reading the blog knows more about this area, please chime in below…

Thanks for sharing the images, Gabe!

Happy Friday, all.

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3 September 2019

An unconformity at Bacon Cove, Newfoundland

The last outcrop I visited in Newfoundland this summer was an angular unconformity, exposed along the shore at a place called Bacon Cove, near the head of Conception Bay:

Here, I’ve traced out the unconformity surface in yellow:

Unconformities are gaps in the geologic record – structures which juxtapose two different geologic units along a surface formed through an extended period with no rock-forming activities at that site or (more commonly) erosion, which destroys rocks at the site. At Bacon Cove, erosion was the culprit. First a green shale formed, then it was tilted to a steep angle, then it was eroded, probably along a rocky coastline much like Bacon Cove appears today, and then it was buried in dark limy sediment, sand and pebbles and mud.

Here is another view of the unconformity where the different orientations of the strata are plain:

There are additional aspects of this site that are intriguing: note the differential weathering of the one layer in the upper unit, weathering out to form a series of little hollows. Also note the prominent joint set that transects both units, indicating it was imposed after both units existed and were lithified.

One nice thing about Bacon Cove is how high-relief the unconformity surface is: there are lots of swales and bumps on it.

It’s also kind of patchy: there were spots where ancient “potholes” had been filled in with the upper limestone, and were preserved today as elliptical patches of the younger unit. Here is a spot where erosion making the modern rock surface has penetrated through to the unconformity and into the lower unit, breaking the upper unit into several patches:

Here is a place where the upper unit is particularly sandy:

There were also boulders lying around that crossed the unconformity surface – what an amazing sample this would be to have in one’s rock garden! Earlier in the trip, I was impressed by several of these on display at the Johnson Geo Centre in St. John’s.

Here are a few more shots of in situ unconformity exposures, where I’ve cleaned up the unsightly coring holes using Photoshop:


I like these because they show the presence of substantial pebbles/cobbles as inclusions in the overlying unit. In this next shot, those all appear to be locally derived examples of the older greenish shale:

The lower (older) unit here is Ediacaran in age, and is correlated with the fossil-bearing rocks at Mistaken Point. The upper (younger) unit here is Cambrian. So in the grand sweep of geologic time, there’s not a huge amount of time missing at Bacon Cove. But it was enough to take horizontally-deposited mud, turn it to rock (lithify it) , and then rotate it and lift it up to where it could be partially eroded, before it was re-submerged and buried anew.


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30 August 2019

Friday fold: Calafia State Beach

Happy Friday, good people!

We close out the workweek with a fold, and today it comes to us from Larry O’Hanlon, who manages the AGU Blogosphere.

Larry writes that he was recently in California, and…

I noticed a little fold in a sea cliff at Calafia State Beach in San Clemente. I barely managed to snap a few pictures before being pulled away by the kids. Looks like soft sediment deformation of beach sands? As it is about 100 m from the surf and maybe less than 10 m above sea level, I’m guessing this is a fairly young deposit exposed by uplift.

Here it is:

I’ve attempted to trace out bedding here, but it’s hard to do in the most tightly folded bit:

I agree that this looks like a soft sediment slump fold.

Thanks for thinking of the Friday fold when you were traveling, Larry! I hope all readers of the blog will consider snapping some fold photos when they see them during their global peregrinations…

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