6 October 2015

Can you spot the contact?

There’s a formational contact in this photo, and for many years, I misplaced it completely. Let’s see how well you do: can you spot it?


Submit your answers by downloading the photo (right click; ‘save as’), drawing on the contact, saving your annotated copy, and then posting your version in the comments.

Need more data? Try exploring this GigaPan of the site:

Answers tomorrow.

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5 October 2015

Trace fossils in the Juniata and Tuscarora Formations

Route 33 in Pendleton County, West Virginia cuts across the lower Paleozoic stratigraphic section. I went there this past spring on a sedimentology and stratigraphy field trip with the GMU sed/strat class. The trip was orchestrated by professor Rick Diecchio.

Here are some scenes from two of the stops – the upper Ordovician Juniata formation (red sandstones and shale intepreted as Taconian molasse) and the overlying Silurian Tuscarora Formation (thick quartz arenite equivalent to the Massanutten Sandstone).


The conformable contact between the two units is discernible at one point along the road, but what I would like to call your attention to today are some trace fossils from the two formations. In the Juniata, the planar bedding is cross-cut by deep Skolithos tubes, which Rick interpreted as an indication that the critters which lived in this area really needed to retreat from the high flow regime which deposited the planar bedding.


Same sample, with the contrast dialed up a bit, so the bedding and Skolithos stand out better:


In the Tuscarora, there were more bedding plane parallel traces, such as these Arthophycus:


Because of the relatively coarse substrate (sand, not mud), the fine details of the Arthrophycus (bumps and ridges) weren’t preserved especially well, but if held at the right angle to the light, a few of them emerged as discernible:


This will be the penultimate post from that field trip… I’m almost out of photos!

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2 October 2015

Friday fold: cherts at Mount Diablo, California

My former student James O’Brien recently moved out to the left coast, and posted some photos earlier this week of a hike he took at Mount Diablo State Park in the mountains east of the San Francisco Bay area of California.

There are some classic-looking Franciscan cherts exposed there, as these folded examples show:



Seeing these pictures reminded me of the “GoSF” series I wrote last time I went to the AGU Fall Meeting (in 2010). I’m planning to attend the meeting again this year, and look forward to spending some time reacquainting myself with some of these rocks while in San Francisco.

Thanks for sharing the photos, James! Happy Friday, everyone.

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26 September 2015

A History of the World in Six Glasses, by Tom Standage

standage This week’s book was a survey of human history, from the dawn of civilization to the Cold War, of the various ways that societal, health, political, technological, and economic factors drove the adoption of various beverages, and how the presence of those beverages in human society generated ripples of cause and effect, propelling advances and turns of history that led us to the world we live in. It’s a prime example of one of my favorite genres of book: the “microhistory” that uses a novel perspective to explore some aspect of history. Other exemplars include Salt by Mark Kurlansky, or Bananas by Virginia Scott Jenkins. Really, Standage’s book is six (or seven) microhistories in one, arranged in roughly chronological order from the Fertile Crescent of Mesopotamia where fermented gruel turned to beer, to the rise of classical civilizations in Greece and then Rome, places where wine was the drink of choice, to the embrace of distillation to make spirits, and the full blooming of the spirit making business in the New World, to the role of coffee and coffeehouses in the Enlightenment and the era of world exploration, and then a survey of tea from ancient China and India through Colonialism (including, of course, the role tea taxation played in triggering the American colonists’ revolution against Britain). Finally, with World War II and the rise of American “Imperialism,” Standage turns his attention to Coca-Cola. An epilogue explores the role of bottled water in the modern industrialized/developed world. It’s a fascinating, well-written book, full of connections at which I never would have guessed, and it really gave me an appreciation for the sweep of history that I never got in high school history classes, reading from relatively dry (pun intended) textbooks. I felt like the pacing of the book was particularly well-balanced: each topic was discussed exactly the right amount of time, without feeling like it was overemphasized. As with most of my ‘reading’ these days, really I listened to the book on my commute – a lovely time of uninterrupted concentration. There’s a great quote from the theoretical physicist Richard Feynman in his Lectures on Physics that Standage’s book reminds me of. At the risk of overwhelming this brief review, I’ll quote it here:

A poet once said, “The whole universe is in a glass of wine.” We will probably never know in what sense he said that, for poets do not write to be understood. But it is true that if we look in glass of wine closely enough we see the entire universe. There are the things of physics: the twisting liquid which evaporates depending on the wind and weather, the reflections in the glass, and our imagination adds the atoms. The glass is a distillation of the earth’s rocks, and in its composition we see the secrets of the universe’s age, and the evolution of the stars. What strange array of chemicals are in the wine? How did they come to be? There are the ferments, the enzymes, the substrates, and the products. There in wine is found the great generalization: all life is fermentation. Nobody can discover the chemistry of wine without discovering the cause of much disease. How vivid is the claret, pressing its existence into the consciousness that watches it! If our small minds, for some convenience, divide this glass of wine, this universe, into parts — physics, biology, geology, astronomy, psychology, and so on — remember that nature does not know it! So let us put it all back together, not forgetting ultimately what it is for. Let us give one more final pleasure: drink it and forget it all!

I feel that after reading Standage’s book, every time I brew a cup of coffee or crack open a beer, I’m tapping into an immense flowing vein of history. These beverages are “liquid artifacts” (his phrase) and by continuing to consume them today, we participate in human civilization. It’s a heady form of secular communion, re-enacting countless acts of beverage consumption through the past 10,000 years, bringing our species from hunter-gatherers to the sort of place where we can write blog posts about books about the intermingling of beverages and history.

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25 September 2015

Friday fold: Macro GigaPan of Archean gneiss, Spanish Peaks, Montana

I don’t think I’ve featured this sample here before… It’s a lovely gneiss from near the trailhead for the Spanish Peaks, near Ted Turner’s Ranch in the Gallatin/Madison Range in southern Montana, not too far from Big Sky. Have fun checking it out in this macro GigaPan:


Happy Friday to all.

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22 September 2015

New LiDAR of the Fort Valley & surrounding area

My colleague Dan Doctor (USGS) just shared some new LiDAR imagery of my neighborhood. Check it out:


There are some amazing things to be seen in this image.

For instance, check out the change in the course of Passage Creek where it exits the Fort Valley – it goes from a deeply incised morphology to a broad, braided plain:


Speaking of the creek, I can make out both natural levees and old river terraces in this area of the image:


It’s really striking how sedimentary strata can be traced out through the forested mountainsides due to slight differential weathering:


And the same differential erosion of the strata of the Massanutten Sandstone exposed at Mudhole Gap reveal the structure of Green Mountain to be an anticline:


Outside the Fort Valley, the parallelism between ridge-perpendicular fractures and the long “arms” of the meanders of the North Fork of the Shenandoah River show up nicely, and this abandoned meander is exquisitely preserved:


Perhaps most intriguingly, I found an odd set of perfectly flat little circles on the northwest side of the ridge of Massanutten Mountain:


What are these things? They are almost the perfect size for campsites, but they are out in the middle of nowhere in the George Washington National Forest. I’ve visited one of these in person, and am deeply curious at why there are so many, including so many on the same contour. Any ideas?

It’s great fun to explore this image – there’s a wealth to be learned, and probably a lot to be discovered by poking around in it. Let me know if you find anything particularly neat!

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21 September 2015

Assassination Vacation, by Sarah Vowell

vowell Time for my book report: This week, I read (well, listened to) a fun history of the assassination of three American presidents. Yes, it’s simultaneously about political murder and is a fun read (well, listen). This is because of the author’s ideal mix of snark, intelligence, and obsession with the three stories discussed herein: the assassination of Lincoln, McKinley, and Garfield. She doesn’t get into Kennedy’s assassination – perhaps because we see Kennedy as “of a different era” than the other three men – a man of relatively recent history, as compared to relatively distant history. Or perhaps it’s because Robert Todd Lincoln, Abraham Lincoln’s son, wasn’t in Dallas when Kennedy was shot – and that doesn’t fit the pattern of the other three. One of the fascinating things I learned by reading (listening to) this book is that Robert Lincoln was a bit of a hex, an ‘angel of death’ when it comes to presidential assassinations: he was present at each of the other murders. Vowell also reveals crazy tangential connections between these historical events and everyday features of our lives – everything from “House of Cards” type political intrigue and the unlikely ascension of Teddy Roosevelt, to unionization and Oneida teapots. I first became familiar with Vowell’s work when a decade ago I listened each week to the public radio program “This American Life,” where she made occasional reports – quirky audio essays that are fully in keeping with the way she writes in her books. In Assassination Vacation, she travels to many spots up and down the eastern part of the United States, from upstate New York to the Dry Tortugas in Florida, a kind of pilgrimage that prompts reflection on the people who made decisions that altered the course of history. She describes these peregrinations with a unique voice, and I mean that literally – you will be familiar with it if you have seen the excellent movie The Incredibles, for it is Sarah Vowell who voices the teen-aged daughter Violet. As I get older, I find myself drawn more and more to human history, in a way I never was as a teenager or college student. The twists and turns of past events have wrought the landscape in which we now live, and it’s increasingly interesting to me to learn why things are the way they are, and the pivot points on which the social juggernaut has turned. Vowell’s book is an excellent, enlightening, entertaining examination of presidential assassination, but in exploring the antecedents and consequences of each plot, she has enlightened me to a rich and detailed portrait of the America of more than a century ago. Recommended.

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14 September 2015

Awesome field trips at GSA Baltimore meeting

Hi everyone,

As the deadline for early registration for the annual meeting of the Geological Society of America nears, I’d like to call your attention to a suite of awesome field trips exploring mid-Atlantic region geology. If you’re traveling to the east coast for the first time for GSA, or if you’ve never ventured beyond the Smithsonian and NSF conference rooms, then you should consider one of these trips as an insight into a rich geologic heritage. While there are many terrific sounding trips on the docket, these three are being offered by my colleagues and me:


Trip Description
The Neoproterozoic era was a time of vast change as the Earth experienced dramatic climatic and paleoceanographic shifts involving global ice ages (a.k.a. Snowball Earth), the evolution and diversification of the earliest animals, and tectonic upheaval associated with the breakup of the Rodinian supercontinent. Neoproterozoic rocks in the central Appalachian Blue Ridge bear witness to the dynamism of that era. This field trip will examine Cyrogenian to Ediacaran sedimentary and volcanic rocks formed along the southeastern margin of Laurentia and currently exposed in central and northern Virginia. Planned stops include glacial diamictites, rift-basin sequences, post-glacial red beds and cap carbonates, as well as plume-related (?) tholeiitic flood basalts. Research during the past two decades has revealed much about the enigmatic Neoproterozoic rocks of the central Appalachians. This field trip will afford an opportunity to discuss advances, consider unanswered questions including the significance the Paleozoic structural and metamorphic overprint, and place these rocks in a better global framework. Field trip participants will visit locales in the Blue Ridge foothills as well as in scenic Shenandoah National Park.

Trip Description
This two-day field trip will focus on the Paleozoic tectonic and eustatic history and depositional environments of the Appalachian Foreland Basin as interpreted from selected exposures of Cambrian through Pennsylvanian strata in the Blue Ridge, Valley and Ridge and Allegheny Plateau Provinces of western Virginia and eastern West Virginia. We will see evidence of major events in the history of eastern Laurentian North America, from the rifting of Rodinia up-section through the Taconic and Acadian clastic wedges and the intervening periods of relative tectonic calm during which carbonate deposition was widespread in a variety of environments from deep shelf to sabkha. The final stop will be at the base of the Alleghanian clastic wedge. Emphasis will be on some of the more prominent stratigraphic transitions, and how these are interpreted in terms of corresponding tectonic and/or eustatic events including the Sauk, Tippecanoe I and II, and Kaskaskia sequences and their bounding discontinuities. A highlight of the trip will be stops at several of the extensive and superb new exposures along the recently constructed Corridor-H, U.S. Highway 48 in the Appalachian Development Highway System.

Trip Description
Washington, D.C. provides a world-class showcase for a diverse collection of American building stones, architectural styles, and landscape development and use—all situated in the internationally renowned area of the National Mall. This four-mile walking tour (intended for students and teachers) considers more than 22 National Mall buildings and monuments made of igneous, sedimentary, and metamorphic rock—formed during roughly 3.5 billion years of Earth history and erected during 220 years of American history. We will examine the lithology (macroscopic and thin section), provenance, structures, paleontology, facies interpretation, geologic history, architectural and political significance, and material degradation (weathering) of many classic American building stones (about 25), as well as the few exotic, foreign examples (e.g., Carrera marble). Local landscape evolution will be placed in geological context, and extend through the architectural design plans of L’Enfant (1791), Downing (1851), and McMillan (1902)—ending with recent flood-mitigation efforts in view of projected sea-level rise.

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12 September 2015

New GigaPans from Team M.A.G.I.C.

Hampshire Formation outcrops on Corridor H, West Virginia:
link (Marissa Dudek)

link (Callan Bentley)

Faults in the Tonoloway Formation, Corridor H, West Virginia:
link (Marissa Dudek)

Conococheague Formation, showing stromatolites and cross-bedding:
link (Callan Bentley)

link (Jeffrey Rollins)

Tiny folds and faults, from a sample I collected somewhere, sometime… oh well, it’s cool regardless:
link (Robin Rohrback-Schiavone)

Fern fossil in Llewellyn Formation, St. Clair, Pennsylvania:
link (Robin Rohrback-Schiavone)

Cross-bedding in sandstone:
link (Robin Rohrback-Schiavone)

Ammonite #1
link (Robin Rohrback-Schiavone)

Ammonite #2
link (Robin Rohrback-Schiavone)

Marine microfossils collection slide
link (Robin Rohrback-Schiavone)

East Sheep Canyon, Sheep Mountain Anticline, Wyoming:
link (Jeffrey Rollins)

Folded foliation on the Billy Goat Trail, Maryland:
link (Marissa Dudek)

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4 September 2015

Faults aren’t lines

A new post on GeoSpace, a sister blog here at the AGU Blogosphere, calls attention to a new study by Simon Lamb and colleagues on the plate-boundary fault running through New Zealand’s South Island, the Alpine Fault. The post is apparently taken and lightly adapted from a press release on the Victoria University of Wellington website, where it was authored by a “communications adviser.”

I call your attention to it here today because the post uses the phrase “fault line” no less than five times to describe the Alpine Fault:


I have an issue with this. Faults are not lines. They are fractures, and thus more closely approximate the geometry of planes. Lines are one dimensional. Planes are two dimensional. In reality, faults are not perfect planes either – they have three-dimensional features such as grooves, asperities, jogs, and – the exact point of this research – dip angles that can twist, warp, bifurcate, merge, or otherwise vary.

The place where the “plane” of the fault intersects the “plane” of Earth’s surface should be called a fault trace. It is not a perfect line because it almost always wiggles a bit, due to variations either in the fault’s shape, or the shape of Earth’s surface, or both. If the phrase “fault line” is ever used, it should only be invoked in this strict sense – as a synonym for “fault trace.” But even then, it’s going to make me wince.

The phrase “fault line” is a particular pet peeve of mine, for precisely the reason identified by Dr. Lamb in this post – an individual could think “the fault line” (fault trace) is way over there, but in reality, the fault is a planar feature, which could dip underneath that individual’s location. Trading the language of planar 2D geometry for 1D lines masks this perception, and thus contributes to misunderstanding and risk.

So the Lamb, et al. (2015) paper demonstrates as its key point that the Alpine Fault is not a line. Yet the primary author is quoted three times as saying “fault line.” What’s up with that?

Surely the use of “fault line” in the piece was a goof-up by the “communications advisor” who wrote it, rather than Simon Lamb, the geoscientist who led the writing of the research paper? I worried because three of the five instances are within quotes attributed to Dr. Lamb. I wrote to him while I was composing this blog post to ask if he was misquoted. Or perhaps it was a case of him using “fault line” deliberately, figuring that more of the public would understand that phrase than “fault.” Or maybe “fault line” is synonymous with “fault” in New Zealand. Or –  worst case scenario –  perhaps Dr. Lamb doesn’t himself distinguish between the two. In that case, I’ll have to chalk this all up to a case of two professionals disagreeing over the proper terminology. I’ll update the post when I get new information. UPDATE: He has written back with the following response:

Dear Callan,

You are right, of course! Faults are 3-D features.

However, I’ve found that outside the geological community, the term ‘fault line’ has come to mean what we, as geologists, would call a fault. This is certainly the case in New Zealand. I think the reasons for this are that faults certainly look like lines on a map, but the term also distinguishes a geological fault from the word ‘fault’, as in ‘it is not my fault’ or an ‘electrical fault’, and finally it draws attention to the fact that we are talking about a spatial feature (albeit 3-D and not 1-D!).

In all my interviews, the journalists repeatedly used the term ‘fault line’ and I found it counterproductive to correct them as it only seemed to lead to more confusion. But if you listen to my Radio NZ interview (attached), you can see that they do appreciate the 3-D nature of it. In my first interview, I did start talking about planes and this just drew a blank, as I think in this world, where geometry is hardly taught at school any more, most people don’t know what a plane (or surface) is from a geometrical point of view!

The press release was written by the university’s media team, and we did discuss these points, but they decided to stick with ‘fault line’ in the hope of making sense to journalists, and not just drawing a blank, which would lead to a desert of interest.

But, good on you to plug away on these points!


I feel that “fault line” should never have appeared on an AGU blog. It’s my opinion that our team should have caught that before it was published and changed it to “fault.”

But wait; there’s more…

Shouldn’t a university press release about newly published research merit a link to the actual paper? This is a best practice in science blogging about new research – link to the research! The GeoSpace post added a link before publishing, and noted that the research was published in an AGU journal. But somehow I glossed over that – and went to Google instead.

I typed “g3 simon lamb alpine fault” into my browser’s Google-utilizing search bar, and got this piece by Sarah Jane O’Connor as my first hit: Stuff.co.nz Science: “Alpine Fault spreads across South Island, researchers say”

Though it too uses “fault line” terminology, this article is far superior to the UVW press release: (1) it includes a map graphic that makes the key point — not merely “rethinking” the fault but an attempt to describe the newfound aspects of its shape and structure, and (2) it links to the actual published research article.

Look at the map:


This map demonstrates in a nutshell the difference between a fault (planar, dipping, in this case steeply to the southeast in the northeast part of the island and more gently in the southwest) and a fault trace (the black line on the map). I am pleased to note the lack of the phrase “fault line” anywhere in the graphic.

However, even this gets the geometry wrong on two counts:

(a) “flattens” isn’t really as accurate as “dips more shallowly” – after all, “flat” means lacking relief. A wall can be just as flat as a floor, though one is vertical and one is horizontal.  I guess I’d let this one slide, since in popular parlance, many people equate “flat” with “horizontal.”

But then there’s (b) “a triangular shape” – not only are faults not lines, they aren’t triangles, either. You can project a fault’s presence at depth onto a map, and it may make a triangular area of the land, but the fault itself is a more-or-less planar fracture surface or collection of such surfaces. It’s not a hexagon; it’s not a square; it’s not a triangle. A perfectly developed fault in homogeneous rock that doesn’t hit the discontinuity of Earth’s surface will be more or less elliptical (an “oval”) with a 2:1 or 3:1 axial ratio, but a huge plate-boundary fault such as the Alpine Fault has a much more complicated geometry than even that ideal shape. So “triangle” is just confusing, unless you specify you’re referring to a portion of the projection of the fault’s position at depth onto the surface — and that projection abruptly stops southwest of Queenstown, something the real Alpine Fault doesn’t do in reality.

Please don’t use “fault line” when you mean “fault.”

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