9 August 2017
Today, for your edification and amusement, I offer five new 3D models that I’ve assembled over the past few weeks from photo sets collected in the field and then fed into Agisoft Photoscan. Enjoy zooming in and out, spinning and turning them.
Orbicular granite from the Sandia Mountains of New Mexico:
Fault-bend fold in Grinnell Formation quartzite and argillite, Glacier National Park, Montana:
Glaciated bedding-plane outcrop of Mesoproterozoic stromatolites, Helena Formation, Glacier National Park, Montana:
Vesicular ventifact, Blackwaterfoot, Arran, Scotland:
Bedding and foliation in Dalradian metaturbidites, Lochranza, Arran, Scotland:
4 August 2017
While attending the Earth Educators’ Rendezvous in Albuquerque a few weeks ago, I noted these specimens on display in the halls of the Department of Earth and Planetary Sciences at the University of New Mexico:
A trio of big “pocket folds” – the perfect way to close out the workweek.
31 July 2017
After reading Passing Strange, I found myself wanting to learn more not only about Clarence King, but also about the other great surveys of the American West – those of Hayden, Powell, and Wheeler. I’ve read Powell’s account of descending the Colorado River, and I’ve been delighted this decade past to explore Hayden’s territory in the northern Rockies (but didn’t know the details of his work). Of Wheeler, I knew next to nothing. So I was glad to find there was a volume dedicated to the history of all four surveys – Richard Bartlett’s Great Surveys of the American West, published in 1962. The book is a useful compilation of each survey, its personnel, personality, adventures, and output. However, it suffers from a serious case of mid-last-century perspective. The author’s perspective is both sexist and racist. For example: early in the book, he likens exploring the west to undressing a beautiful woman. Native Americans were the original inhabitants of this “unexplored” land, and Bartlett paints them with a broad brush, sneering that they were “bloodthirsty” or “dirty, sullen, not to be trusted.” He has a similar attitude towards predatory animals – delighting in the killing of grizzly bears and describes a coyote as “a scraggly, sneaking little yellowish cur with its tail between its legs, a symbol of perpetual guilt.” Not exactly ecologically enlightened! These flaws, casually inserted in many places throughout the narrative, make for distasteful reading. It may be unrealistic of me to expect a book by a white man in the early 1960s to share the relatively egalitarian attitudes of 2017, but despite that, I found myself wincing repeatedly as I read and learned. So: caveat emptor. Coming away from reading it, I feel as though the insight i gained was tainted with a distasteful set of attitudes. This history tastes spoiled.
28 July 2017
Here’s a fun fold – I saw this hiking Siyeh Pass in Glacier National Park earlier this week:
(note the four people for scale in the upper photo – 3/4 of the way up the grassy slope.)
Here’s a closer view, with me for scale:
Happy Friday! I’m leaving Glacier today and beginning the journey home. Happy Trails!
21 July 2017
My friend Ander Sundell at the College of Western Idaho is the source of today’s Friday fold. It’s from somewhere in Sardinia, and I think you’ll find it visually striking:
The rocks here are Silurian phyllites generated from mudstones that were deposited on the floor of the rheic ocean basin. The color and grain size variation do an excellent job highlighting compositional layering. They were deformed during the Variscan Orogen, which the last phase of a composite mountain belt that ultimately formed Pangea. This photo shows an excellent example of axial planar cleavage.
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???