4 December 2015

Friday fold: interference patterns on Elba

Samuele Jæger Papeschi shares one more fold with us:

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some deformation here… type III (Ramsay…) interference pattern in Cretaceous calcschists… Cavo, Elba Island
Awesome! I hope everyone has a great Friday.

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1 December 2015

Which way’s up? Check cavity fills.

When snail shells are deposited in a bunch of sediment, they serve as tiny architectural elements, with a “roof” that protects their interiors. Any sediment mixed into the shell’s interior will settle out (more or less horizontally), and then there will be empty space (filled with water, probably) above that. As burial proceeds and diagenesis begins, that pore space may be filled with a mineral deposit, such as sparry calcite.

Here is an example from a gastropod rich horizon within the Mississippian-aged Reynolds Limestone member of the Mauch Chunk Formation, exposed on Corridor H, West Virginia:

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(There’s another example on the far right of the photo, below the letter “t” in “sediment”.)

The sediment (lime mud) is yellowish gray and granular. The sparry calcite is gray to white and crystalline, continuous with the shell material.

This “cavity fill” structure (where the snail shell is the cavity being filled, partly by entrained mud and partly by diagenetic crystallization) serves as both a paleo-horizontal “level” and a geopetal structure (indicating which way was up when the sediment was deposited).

It’s a cool thing to find – it helps geoscientists orient themselves in outcrop spacetime.

Okay, now try applying the concept to this one: Can you see the same structure?

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Scroll down to see if you were right…

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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(Photo ‘up’ is geopetal ‘up’ in this case, too.)

A macro GigaPan example, from the Permian-aged Hueco Limestone of west Texas:
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And another, more subtle, locality unknown:
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30 November 2015

Slump in progress on Corridor H

I was out on Corridor H last week, looking at rocks with my Honors student, and on the way back from the field work, I noticed this:

cor_H_slump_650Click to enlarge

That’s a fresh slump scarp running across a slope that is gradually sliding downhill. (The left half of the image is moving down relative to the right.) To judge from the rip-rap-filled culverts, this slope must have a previously-documented history of instability, which the highway department attempted to control, but didn’t succeed.

I’ll keep my eye on it in the months to come and let you know how it develops.

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23 November 2015

Seveneves, by Neal Stephenson

7evesAt first, I thought the titular Seveneves referred to fragments of the Moon. It blows up on the first page of the novel – or disaggregates anyhow, into seven big chunks. But these start knocking into one another, breaking off smaller pieces, and these bang into each other, making more pieces.

Soon, there are a lot of pieces.

Spoilers galore follow, as I feel obligated to outline the scope of the story: The mathematics of making a lot of pieces from the seven originals is a scientific problem that catches the interest one of the main characters, a PR-savvy astronomer who’s clearly modeled on Neil DeGrasse Tyson. He runs the numbers and finds that the system of moon fragments’ auto-catalyzing fragmentation will go exponential about two years after the moon broke up. This isn’t good news for the surface of Earth. Humanity has two years to get a space colony going, and stock it with enough genetic information to kick-start human civilization some thousands of years in the future after the “Hard Rain” ceases and the surface of the planet becomes habitable again.

The politics and the logistics of who to save kick in, and basically everyone pitches in, trying to make this project a success, since the future of the human race and life on Earth hinges on it. The novel is set in the here and now, and Facebook and Twitter figure into the plot. By the time the Hard Rain begins to fall and >7 billion people (and every other form of life) on the surface are killed, about a thousand folks are in orbit in a hastily-constructed “Cloud Ark,” centered on the former International Space Station. One of them is a stowaway – the conniving President of the United States, a woman who instantly starts sowing discord in the rank and file. There’s a daring mission (by an Elon Musk like character) to bring a comet into the Ark for fuel, and various other instances of serious problem solving. Each of these challenges is addressed frankly and in detail, with plenty of exploration of perigee and apogee, ΔV and the physics of living in zero gravity amid near constant bombardment by cosmic radiation. The first two-thirds of the book has a lot of discussion of orbital mechanics. You should know that going in, and you should also know that it’s not boring. While the technical problems can be solved to greater or lesser degrees, the human problem (of how to get along) is presented as a constant. People make moves, other people respond, and there are deaths. Soon, there are waaaaaaaaaaaaaay fewer people left than is in any way acceptable, but one of them is a geneticist, and her lab equipment survives, and after a brief discourse on parthenogenesis and heterozygosity, we see her plan for furthering the human species – essentially, one of each of the surviving women is author of a ‘race’ of future humans.

Fast forward 5,000 years. The final third of the book examines the results, specifically the return to Earth mid-way through the terraforming effort put into effect by the descendants of the Seven Eves. Once there, they find to their surprise that they aren’t alone. As the various strands of humanity become reacquainted, there is some static, and again some awful behavior, as well as some positive connections and unexpected outcomes. I’ll avoid going into too much. That part of the book feels like a typical science fiction novel, so the plot is perhaps more important than the set-up.

But what sticks with me about the book is the set-up – the first two thirds of the book that posit this extraordinary circumstance, and examine how we would deal with it. If we knew the planet would be totally lethal in two years, and would remain uninhabitable for five millennia, how would we act? What would we do? This, to me, is the most interesting thing about Seveneves – its examination of the real-world fallout from that initial extraordinary premise.

I enjoyed the book. I don’t read much science fiction, but this held my attention, and I’ll seek out more from the author, Neal Stephenson. It would make a great movie.

Here’s a review from NPR that speaks to my experience reading it – in particular, the balance Stephenson seems to get just right about explaining things completely but without letting your attention span down.

I found out about the book from the Don’t Panic Geocast, which reviewed it alongside The Martian. I’d say The Martian was the better book, but it’s kind of comparing apples and really complicated oranges to say that. They are both worth reading.

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20 November 2015

Friday fold: recumbent limestones of coastal Grosseto

Samuele Jæger Papeschi not only provided this week’s Friday fold, but he also serves as its sense of scale:
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According to Samuele, these are:
folded metalimestones in Punta delle Rocchette, Grosseto. This are pretty interesting transected folds, showing about 10 degrees of foliation dip in respect to their axis
Thanks for sharing, Samuele, and happy Friday, all!

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19 November 2015

A little geologic history before breakfast

While in Baltimore for the GSA meeting a few weeks ago, one morning (on my way to breakfast at Miss Shirley’s), I walked past a building and saw some cool geological features in the building stone used to face its exterior.

It was a coarse reddish limestone, at first glance kind of similar to “Tennessee Marble” such as may be seen on the interior of the National Air and Space Museum in Washington, DC, or the exterior of the National Museum of American History. It had lots of fossil chunks in it, including this crinoid:

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Primary features such as bedding were clearly discernible, as well as mottled zones of what appeared to be bioturbation:

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Here’s a zone that may represent primary sedimentary texture (rip-up clasts) or may be a little fault breccia:

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There were also some clear tectonic overprints, including a pressure-solution-induced cleavage, marked by the accumulation of dark-colored insoluble material on the cleavage surfaces:

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You can see how the pressure solution changed the shape of the crinoid, not so much by the elliptical cross-section, but by the flat upper left surface, parallel to the trace of cleavage:

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Here is another nice example of bedding / cleavage relations in this lovely building stone:

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So the overall story recorded by these slabs is: first, deposition of lots and lots of skeletal fragments of invertebrates (CaCO3) in an ancient, relatively high energy (coarse grain size) marine setting (based on the fossil content). It may have resembled a scene offshore from modern Florida. At times, the accumulation rate must have been moderate to slow (in order to get enough time for the bioturbation to occur). Periodically, storms may have pummeled these shallow waters (as hurricanes mash into Florida today) in order to make the rip-up clasts. Later, after lithification, the rock was squeezed under some sort of differential stress, oblique to bedding. This triggered pressure solution of the calcite, and allowed shortening of the fossils parallel to σ1, as well as the development of cleavage. Was this a tectonic compression? Maybe – if the bedding stayed in its original horizontal orientation. However, if the strata were rotated by 30° or so post-deposition, compaction under the force of gravity alone could explain the development of pressure solution seams ~parallel with horizontal, but oblique to bedding. Because I don’t see any of the “bed of nails” style of stylolites that are typical of such gravitational compaction (in say, the “Tennessee Marble”), I’m going with the tectonic cleavage interpretation as my leading hypothesis.

Gosh! Contemplating all that was better than coffee to wake a person up. I continued on my walk to breakfast thoroughly invigorated. One great thing about cities is they have lots of cool rocks on display, almost everywhere you look!

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18 November 2015

Beach sand of coastal Maine

You could use a macro GigaPan of some pretty sand, I think.

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That’s sand from near Acadia National Park, in Maine. Exploring it, you can find both small chunks of Acadian granite, and green rods that are sea urchin spines. It’s fun – check it out.

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17 November 2015

Hitting a nerve with popular posts

I blog here a few times a week, when I can manage it. Mostly I focus on new things I discover on field trips, advances in geologic imagery, and structural geology.  I get about 500 readers per day. But occasionally I write about other things, like creationism or current events disasters like earthquakes, and those posts garner a lot more attention. They get shared and reshared and spread out. My most popular posts to date have been about the big Japanese and Virginia earthquakes, a post about climate change vocabulary, “Words matter,” and that testy exchange with Discovery Institute staffer who got upset with me when I wouldn’t let his boss use my photograph in his book.

Speaking of climate change, a post last week on crossing the 400 ppm CO2 threshold for good got a lot of attention. People care about climate change.

The Twitter reaction surprised me: ~1600 people tweeted a link to the post. About 7500 people per day visited the post, and if I’m to believe the Facebook statistics, 14,000 people “liked” the post. This means “The last days of sub-400 ppm CO2” is solidly in the ranks of my all-time top five most popular posts:

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It seems that there are three potential topics for a post on Mountain Beltway to go viral: (a) there’s a natural disaster, (b) the post is about creationism, or (c) the post is about climate change. None of my structural geology posts get anywhere near the amount of attention these other topics do – go figure! Human interest in disasters like the Tohoku earthquake is readily comprehensible: it’s a current event, and people are dead because of it. We all want someone knowledgeable to help us understand events like that. Creationism and climate change denial are the two most prominent forms of pseudoscience/antiscience in modern American discourse, and so discussing them is of interest to a lot of people. Most of the attention I got for those posts was positive, but going viral elicits negative commentary too. People have strong opinions on climate change and evolution. You get the good, and you get the bad. Compare and contrast:

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I guess some people are always going to be negative, or aggressive in their demeanor (one called me a “climate cultist”), and others won’t say anything at all unless it’s positive. By far, the feedback has been mostly good, and that makes me feel good. I feel as if I’ve managed to write something useful about something important. I articulated the situation clearly enough to convey the urgency and concern I feel, and the factual and logical basis for that concern. That apparently resonated well with thousands of readers. Awesome! I feel like I’ve contributed, and that’s a good feeling. I wonder whether it means I should do more climate science blogging, or counter-creationism blogging, or current events blogging. It’s something to ponder… Friday folds are never going to go viral like these other topics…

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16 November 2015

“Making North America,” episode 3: Human

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The PBS series NOVA has a new three-part series called “Making North America” that premiered two weeks ago. Hosted by the director of the Smithsonian Institution’s National Museum of Natural History, Kirk Johnson, the series explores the tectonic assembly of terranes that resulted in the bedrock of the continent, the panoply of diverse creatures that have dwelled here in the past, and the human prehistory of our continent. I was given press access to review the episodes in advance. I have been covering them one by one. Today, we’ll take a look at the final offering, “Human.”

It begins with the Ice Age of the Pleistocene, since that’s apparently when North America was first inoculated with humans. They came from Siberia, but did they (a) climb over the Laurentide Ice Sheet, (b) wait in the great Alaskan vestibule until an ice-free corridor opened up, or (c) use boats to travel down the west coast? Kirk goes ice climbing and finds it difficult, and uses that as a visually striking rhetorical device that option “a” isn’t so likely. Option “b” is presented as the standard academic party line, but that’s a lead in to an emphasis on the preferred hypothesis, “c,” which leads us to the Channel Islands of California, where a 13,000 year old femur is explored as evidence for boat technology existing early on in the human history of North America.

So people somehow got to places like coastal California, and then they moved inland. One thing they found was critters, and part of the episode visits the La Brea tar pits in Los Angeles, and we get a taste of some fun paleontology as well as a hint of the overkill hypothesis for the extirpation/extinction of the Pleistocene megafauna. That leads us to hunting, and to Clovis points, our oldest uncontroversial archaeological evidence of humanity’s presence in North America’s interior. There’s a cool scene where Kirk makes a spearhead and then tests it against hide-covered ballistics gel.

Agriculture and soil are the next topic, presented starting at Mesa Verde, but then it goes off in a “but then the Europeans showed up” kind of way. I was delighted to see David Montgomery, MacArthur fellow and author of Dirt: the Erosion of Civilizations, show up alongside Kirk in a North Carolina tobacco field. They engage in a fun examination of the soil, and I thought it was pretty clever that they put on aprons for a faux cooking show set up, combining ingredients from jars to make soil: sand, silt, clay, organic matter, living critters, and -this caused both of them to laugh- “time” in a bottle.

The depletion of east coast soils was a matter of national security in the early days of the United States of America, and this offered a way to segue into discussing westward expansion, railroads, and the California gold rush. Kirk and a local expert travel into a mine and examine auriferous hydrothermal quartz veins there. They interpret these as the healed scars from earthquakes, which is stretching the point but probably a good approach for the show’s audience, and it’s accompanied by a lovely animation – showing a vein crystallize from the inside, with quartz nucleating on the walls and grow inward, trapping gold flakes along the way. Another cool visualization was of the old school variety: simply comparing “then” and “now” photos of Los Angeles, showing the profusion of oil wells that used to occupy that town. Even today, there are 3000 active wells in L.A. County.

Burning oil makes CO2, and global warming gets a brief mention, but it’s not dwelled on for more than 30 seconds or so. But a more palpable disaster lies waiting in the Pacific Northwest, so it’s off to Washington to examine a ghost forest and tsunami sand deposit. I appreciated the decision to say “a Pacific Ocean plate” instead of “the Juan de Fuca plate,” for the sake of simplicity. It’s an elegant choice that’s technically correct and also intuitive for the nontechnical audience. But matching this good word choice is a bad word choice – I shudder to report that “fault line” gets used at least once.

The episode concludes with a visual recap of the whole series, and a good message that geologists are useful: learning about the past helps us prepare for the future. As we look back in time, or predict what comes next, we can see that no landscape is permanent. I endorse both of those messages wholeheartedly. They encapsulate the sense of participating in the grand sweep of epic events, and this series did a good job of expressing those events.

I’ve been keeping tally with each episode of the gender ratio of the experts interviewed, and this final episode has a ratio of 6 named male experts to 2 named female experts, one of whom also appeared in episode 1. That makes “Human” the most male-skewed episode of the series (previous episodes were 5:2 and 2:2).

The episode airs in two days: on Wednesday, November 18, on your local PBS station. Check it out.

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13 November 2015

Friday fold: chevron-folded chert

Samuele Jæger Papeschi is the source for today’s fold:

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Those are:

chevron-folds in radiolarian cherts – Jurassic radiolariti fm. – Quercianella – Leghorn, Italy

Cool. They look a lot like the chevron-folded cherts near San Francisco. Same age, too.

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