21 July 2017
My friend Ander Sundell at the College of Western Idaho is the source of today’s Friday fold. I don’t have much detail on it, other than that it’s from somewhere in Sardinia, but I think you’ll find it visually striking:
There appears to be a cleavage that runs ‘horizontally’ from left to right across this image, aligned with the axial surface of the folds. I’m guessing that the strongly-contrasting light and dark layers are a primary feature such as sedimentary bedding. If I get more details, I’ll update this post.
Guest submissions of Friday folds are always welcome. Thanks for contributing, Ander!
18 July 2017
I’ve just finished three weeks of travel in Italy, and I was absolutely delighted to read this terrific book by Walter Alvarez while I was there. Alvarez is famous the world over for being the nucleus of the team that proposed an extraterrestrial meteorite impact as the cause of the end-Cretaceous extinction, prompted to that bold hypothesis by the discovery that the clay seam marking the boundary between the Mesozoic and Cenozoic portions of the Scaglia Rossa limestone near Gubbio (the “K/T boundary”) contained anomalously high levels of iridium. But Alvarez didn’t set out to drive a stake into the heart of uniformitarian doctrine. In his career, he hasn’t focused on mass extinctions or meteorite impacts. Instead, in The Mountains of St. Francis, he tells the story of the less celebrated aspects of his career, working on the geology of Rome, then moving afield to the Apennine Range, the mountainous “backbone” of Italy. It was in attempting to match up the foraminiferid fossil record of the Scaglia Rossa with the record of paleomagnetic reversals (The “Rossa” in Scaglia Rossa means “red,” referring to the color that results from a decent amount of magnetic iron in these strata), an important exercise in bolstering the stratigraphic toolkit, that Alvarez stumbled onto the K/T boundary iridium anomaly. Along the way, over decades of Italian fieldwork with his wife Milly and a host of colleagues, he explores basic geological concepts for the lay reader, ideas very familiar to readers of blogs like this one, but in a new, thoughtful, patient, and creative way (and therefore worth reading for that reason alone). In so doing, he makes The Mountains of St. Francis into a calm, insightful introductory text to geology: with concepts discussed ranging from superposition to to turbidites to thrust faulting to delamination to the Messinian Salinity Crisis. Foundational research in many disparate branches of geology happened in this mountain range, and Alvarez is an appreciative, contemplative guide to exploring it. The title of the book comes from St. Francis of Assisi, whom Alvarez examines in the first chapter, including the first mention of the Scaglia Rossa in describing the lovely pink limestones used to construct the Basilica of St. Francis in Assisi, where the saint is buried.
So the book is simultaneously a memoir of a career’s worth of research, a travel guide to Italy, an layperson’s introduction to geological thinking, and a primer on the geologic history of central Italy. It’s unique in trying to serve all these purposes simultaneously, but I think it works. It was exactly the sort of book I wanted for the sort of trip I was taking.
During my Italian travels, I visited both the K/T boundary at Gubbio and the Basilica of St. Francis in Assisi. My experiences at both places were enriched as a result of having read Alvarez’s book. If you are traveling to central Italy and you are a geologist, this is the book to read. It’s highly recommended in that case. If you have no plans to ever go to the Apennines, I’m not sure it will read quite as smoothly, as there’s lots of local flavor that may seem alien until you come to Italy yourself. With that caveat, I highly recommend it.
The K/T boundary at Gubbio:
The pink Basilica of St. Francis in Assisi:
The Scaglia Rossa exposed in Assisi’s building stones, with my Lonely Planet for scale:
17 July 2017
Jorge Cham will likely be known to most of the folks who read this blog as the cartoonist behind the spot-on examination of grad school called Piled Higher and Deeper / PhD Comics. If you’ve read this comic, you’ll know that Cham’s visual style is simple and engaging, and his sense of humor is terrific. In a new book about the unknown territory of physics that we still need to nail down, he teams up with Daniel Whiteson, a physicist. The two of them explore issues like dark matter and gravity in a lighthearted but enthusiastic and informative way. It’s a delightful book to read, with a heavy dose of jokes – I’d guess the ratio of science to silliness to be around 3:1, which is probably too much for the physicists out there, but just right for the rest of us who are trying to wrap our minds around relativity. There are cartoons on almost every page, some instructional and some mere gags. From the expansion of the universe to the moment of the Big Bang, to distinguishing subatomic particles, it’s a treat. I appreciated the emphasis on the history of scientific thinking on these varied topics – it helped me re-tread the intellectual thought paths trod by the pioneers in physics. I also appreciated the way the authors occasionally took a “time out” to emphasize that we readers should sit still for a moment and just think about how mind-blowing some of their conclusions are. There is much that is non-intuitive about our universe. Highly recommended.
15 July 2017
I collected only a single rock on my summer travels in France and Italy. (Those of you who know me will realize how extraordinary this low number is!)
It’s a flow-banded rhyolite from Vulcano, in the Aeolian Islands north of Sicily a few weeks ago. It contains porphyritic vesicular basalt xenoliths.
I featured a similar sample on Twitter yesterday on the occasion (supposedly) of “International Rock Day”:
— Callan Bentley (@callanbentley) July 14, 2017
Here’s a GIGAmacro of my “keeper” sample:
Link 1.46 Gpx GIGAmacro by Callan Bentley
And here’s a 3D model of it:
14 July 2017
It’s Friday, and I’m back in the States after a wonderful month of traipsing around Europe. I spent the final 5 days of my journey with my friend Alan Pitts of the University of Camerino, examining the geology of Le Marche, a province in central-east Italy. One of the sites we saw was this cliff of chevron-folded layers of limestone + limy shale. The unit is the Scaglia Rossa, which spans the Cretaceous-Paleogene boundary in the Apennines. The folding probably dates to the Miocene, which is the age of the turbidites in the neighboring Camerino Basin, which was orogenically-initiated.
They are beautiful, and remind me strongly of similarly aged and deformed chert layers at Marin Headlands in California.
These charismatic structures were chosen for the front cover of Ernesto Centamore’s and Giovannie Deiana’s La Geologia Della Marche, a volume on the geology of Le Marche:
Happy Friday, all!
7 July 2017
Thermopolia are basically the street food stalls of the ancient Roman world. They are distinctive because they have a counter/storefront that contains embedded enormous terra cotta vessels. The surface of the counter is often decorated with slabs of marble. Some of these marbles bear folded internal layering.
Here’s a fine example from Herculaneum, though there are many others at Pompeii.
Coin for scale — or is it to pay for a snack of some nice squid fritters???
23 June 2017
I was in southern France last week, exploring an awesome suite of caves cut into the Causses limestone plateau.
My family and I took an afternoon to paddle a canoe down 5 kilometers of the Célé River. While floating along, we spied a gentle, open fold in the limestone layers that crop out along the banks.
This low-amplitude fold is highlighted with the “horizontal” reference line of the river’s edge.
It’s a little anticline/syncline pair, a pleasing sight for a structural geologist floating through a landscape of relatively undeformed rocks…
16 June 2017
I spent last weekend at the National Association of Geoscience Teachers’ Eastern Section meeting, based out of the Community College of Baltimore County in Catonsville, Maryland. One of the two field trips I took headed out to the western Piedmont, Blue Ridge and Valley & Ridge provinces of western Maryland. On that trip, we took a tour of Crystal Grottoes, a commercial cave south of Boonsboro. I was impressed at how deformed the carbonates were there. The alternating limestone/dolostone strata appear to have flowed like toothpaste squeezed from a tube.
These are Cambrian-aged limestones of the Tomstown Formation, which were deformed (folded and cleaved) during the Alleghanian phase of Appalachian mountain-building. The style of folding is reminiscent of another example from an equivalent structural position much further south. In this example, cleavage is parallel to the axial plane of the folds. I found it interesting that I could keep track of my ‘compass’ orientation in the cave by the angle between bedding and cleavage, and their dip direction. These rocks have attained a fundamentally pervasive fabric as a result of the overthrusting of the Blue Ridge on top of the easternmost Valley & Ridge: a tectonic “grain” that these lucky layers could never have hoped for when they were deposited in calm Cambrian seas.
9 June 2017
Check this out: is it a fold?
Annotated to show the 3D expression of the ‘bed’ (left) and cross-sectional view (right):
Here’s a 3D model of the outcrop to better convey its shape:
This is in the same sandstone unit I blogged about on Tuesday with the apparent soft-sediment deformation. This could be another example of the same general class of pre-lithification structures, or it could be an optical illusion. Again it’s hard for me to make the call since the folded “layer” is the same composition as the layers above and below, yet if folded, it shows a significant rheological contrast. I don’t get it.
7 June 2017
I have some questions for you. You answers determine whether you’re ready to begin talking about climate policy.
- Do you believe that carbon atoms exist?
Do you believe that carbon can bond to oxygen?
Do you believe that the bonding of carbon to oxygen is an exothermic reaction?
Do you believe that exothermic reactions make heat?
Do you believe that heat can be used to boil water?
Do you believe that boiling water can be used to turn a turbine?
Do you believe that the turning of a turbine can make electricity?
Do you believe that people can utilize electricity?
Do you believe therefore that people are motivated to find carbon atoms and react them with oxygen?
Do you believe the carbon atoms continue to exist after the electricity is generated?
Do you believe that the accepted method of disposing of the oxidized carbon atoms is to throw them into the air?
Do you believe that the oxidized carbon atoms in the air tend to stay there for a while?
Do you believe that these carbon atoms bonded to two oxygen atoms (CO2 molecules) are invisible to visible wavelengths of light, but opaque to infrared light with wavelengths 2.7, 4.3 and 15 micrometers (µM)?
Do you believe that CO2 having this selectively transparent property results in a finite positive quantity of energy remaining on Earth rather than being radiated to space?
Do you believe that heat is the agent of temperature change?
Do you believe that a sufficiently large finite positive quantity of extra energy remaining on Earth will raise its average temperature?
Do you believe that a higher global temperature could have negative effects?
Your answer to all of these questions should be “yes.” If it were not so, your beliefs would run counter to what we have verified about the physics and chemistry of the Earth system.
Finding yourself at odds with physics and chemistry is a bit unsettling. You might ask yourself why you should have such a state of mind.
You might ask yourself, “What would it take for me to change my mind on these questions?”
My list of questions is incomplete. I haven’t specified the size of the “sufficiently larger finite positive quantity of extra energy.” I haven’t indicated the level of the increase of the planet’s average temperature where negative effects become negative enough to matter in the grand scheme of things.
And there are other questions to be asked at the end, like
- Do you believe that a higher global temperature could have positive effects?
- Do you believe that policies exist for reducing average global temperature that might be a boon for society?
- Do you believe that policies exist for reducing average global temperature that might be a cost for society?
Again: yes, yes, yes.
These sorts of binary queries help frame a survey of possibilities for the future. Our goal is to get to the point where we can then ask some more open-ended questions, like
- Do the positives outweigh the negatives, balance them precisely, or do the negatives outweigh the positives?
- Do the answers to the previous question apply equally to all people? To all ecosystems?
- How much should we pay per year to keep some of that oxidized carbon out of the air?
- Where are we going to put it?
- What strategies would be wise to prevent harm to ecosystems as a result of the oxidized carbon we opt to leave in the air?
- What strategies would be wise to prevent harm to humans as a result of the oxidized carbon we opt to leave in the air?
- Which humans will we prioritize protecting?
- Which negative effects demand the greatest attention to ameliorate?
- Which positive effects should be most celebrated?
- Would inducing global cooling have negative effects commensurate with the magnitude of negative effects induced by global warming?
- What’s the ideal average global temperature to shoot for?
- How comfortable should we get pulling levers and steering in the planetary “driver’s seat”?
With these sorts of qualitative considerations, we venture into the realm of policy decisions. Once social priorities and economic implications are added in, the situation’s true complexity emerges. Science can help inform the answers, but it’s no longer the exclusive arbiter of valid answers. The initial chain of “yes” facts establishes the situation in which our species finds itself, on this, the only planet it has ever inhabited. We all have to get to that point before we start talking about policy options. Science establishes our understanding of the situation; no politics need be applied. The realm of politics should be focused on the squishier third group of open-ended questions.
Somehow the initial chain of questions have also been politicized. It strikes me as bizarre that this is so. Do I really have to ask “do you believe in carbon atoms?” and then lead a skeptic by the nose through a chain of “yes”s? The more interesting stuff is contained in the messy third set of questions. That’s the realm Oliver Morton explores in The Planet Remade, which you should read if you have any curiosity about the human-influenced future of the planet Earth. That’s the realm where our society’s attention should be focused. We need to get to a point where we can discuss those questions in a mature, honest way.