17 March 2016
Here are two views of a single anorthosite cobble, collected in the Adirondack Mountains of upstate New York:
Raw, natural surface:
Slabbed and polished surface:
As you zoom in and explore these GIGAmacro images, see if you can find the delicate little “necklaces” (reaction rims) of garnet wrapping around the few isolated pyroxenes!
15 March 2016
Today I’ll share a few photo highlights from last Friday’s trip: a field review of the new geological map of the Timberville, VA quadrangle, by Matt Heller and Randy Orndorff. I’ve previously shared three 360° panoramic “spherical photos” from the trip. Today, the pictures will be the old-fashioned kind. One of the first stops was to a fault zone, where Cambrian carbonates were thrust over shales of inferred Ordovician age. Here’s a look at some of the shales:
Tracing out bedding (in yellow) reveals some structural complexity, with tight folding and probable faulting, as seen here:
On one slab of shale, I found a graptolite fossil:
Contrast dialed up a bit so it’s easier to see:
I passed this on to the mappers in case it could help identify the unit more precisely. (Edinburg Formation?)
Nearby, there were several of these striking scarlet cup fungi:
Here’s the fault surface itself, with Randy pointing out deformed rocks in the footwall:
Though this fault is expressed topographically as a “wall,” it’s not a scarp. This is a case of differential weathering, where the footwall shales are more easily etched away by the stream, and so the hanging wall carbonates stand proud of the landscape.
Our next stop was at Brock’s Gap, where we looked at the transition from the late Ordovician Martinsburg Formation (turbidites) into the overlying Oswego Group sandstones. Here’s a nice example of a graded bed in the Martinsburg:
Because graded bedding looks different at the bottom of the bed than the top, it can be utilized as a ‘geopetal’ indicator – a clue about ‘which way was up’ when these strata were deposited. This is very useful thing to know when you’re doing geologic mapping. At Brock’s Gap, the strata are vertical or slightly overturned, younging to the west.
There were tectonic structures to behold, too. Here’s a folded turbidite, showing more fracturing on the outer part of the arc than the inside.
This is typical of the folding of relatively competent layers – outer arc extension is accommodated partially by cracking. The cracks are subsequently filled with mineral deposits – and then they are veins.
Some Skolithos were spotted in the Oswego:
We then climbed up onto North Mountain, and were examining slices of rock that had galloped all over each other (“horses”) along the North Mountain Fault system. I learned a new clue for locating a fault in this heavily vegetated land: look for travertine suddenly appearing the creeks!
Travertine is freshwater limestone with a distinctive spongy appearance. It’s a common feature in creeks in Virginia’s Valley & Ridge province where the creek gains some of its discharge via the groundwater, and the groundwater has been in the business of dissolving subterranean limestone before flowing out at the surface. Faults act as preferential fluid flow pathways, shunting this CaCO3-rich water into the creeks, where agitation makes it precipitate out, building up ledges like the ones in the photo above.
Next up: Devonian mudrocks and turbidites…
Here’s a fold in a unit that I think we agreed must be the Marcellus/Needmore:
We entered the Brallier Formation, and saw some nice examples there of overturned cross-bedding, indicating these strata have been tectonically inverted.
Here’s the same photo with bedding annotated in yellow, and several spots circled in black where you can see clear truncating relationships:
Another example, on a fresher surface:
DGMR geologist Anne Witt serves as a sense of scale for a folded and faulted section of Brallier shales:
I think I see at least three small “horses” (ponies??) there – with nice drag folds on the top of the one directly in front of Anne:
Another Brallier stop showed a wall of folded turbidites:
These folds had horizontal axial surfaces, so we would classify them as “recumbent” (tectonically “lying on their sides”):
Another one, with a breeding colony of Appalachian tires for scale:
As I was writing up this blog post, I noticed that cleavage also has a ~horizontal orientation:
Finally, we climbed out of the Devonian (Acadian) “flysch” and into the “molasse”: redbeds of the Foreknobs or Hampshire Formation, though it was hard to make the call which one it was at this particular outcrop. There were some nice ripple marks there, though.
They were so sweet that I willingly braved a thicket of thorns on an unstable shaley slope in order to get the 360° panorama of them in close-up.
(Last two photos by Nathan from UVA)
All told, it was an excellent day in the field – as you can tell from the ancillary qualities of these images, the weather was sunny and mild, and there was minimal vegetation to obscure the lovely geology.
Thanks to Matt and Randy for organizing the field review, and letting me tag along!
12 March 2016
On Friday, I participated in a field review for a new geologic map of the Timberville quadrangle in western Virginia’s Valley & Ridge province. The field trip leaders were the two lead mappers, Matt Heller (Virginia Department of Geology and Mineral Resources) and Randy Orndorff (United States Geological Survey). I brought along my new Ricoh Theta 360° camera, and made these images of three scenes during the day’s geologizing. Each image can (and should!) be explored through turning left or right, up or down, zooming in or out. Enjoy!
Randy Orndorff (USGS) explains his multi-horse model for the North Mountain Fault (juxtaposing 2 synclinoria):
Randy Orndorff (USGS) explains his multi-horse model for the North Mountain Fault (juxtaposing 2 synclinoria) – Spherical Image – RICOH THETA
Fault surface, differentially weathered to appear scarp-like, placing Cambrian carbonate over Ordovician shales:
Fault scarp (Cambrian limestones over Ordovician shales, probably), Timberville quad, VA. – Spherical Image – RICOH THETA
Ripple marks preserved on vertical strata of the Devonian Foreknobs or Hampshire Formation (gradational contact; not sure which it is):
Ripple marks preserved on vertical strata of the Devonian Foreknobs or Hampshire Formation, Timberville quadrangle, Virginia. – Spherical Image – RICOH THETA
11 March 2016
Happy Friday – it’s the end of a very busy week for me, and I hope you too are looking forward to a fun and rejuvenating weekend.
Wowzers; that’s a looker!
What are we looking at here? Joe writes:
This photo shows geologic mapper and structural geologist Greg Walsh (USGS) explaining disharmonic folding to assembled geologists on a field trip at the 2012 Northeastern Section meeting of the Geological Society of America. The outcrop is of the migmatitic Old Lyme Gneiss in south central Connecticut. Although the rock itself is latest NeoProterozoic, the prominent folds here in outcrop (that Greg is standing on) formed synchronously with the migmatization ~285 million years ago during the Permian. The folds are related to the formation of the larger Lyme Dome, during the Alleghanian orogeny in New England– the latest of the “Too Many Orogenies” (Bentley et al., 2015) cycle that culminated in assembly of the supercontinent of Pangea from collision of Gondwana and Peri-Gondwanan microcontinents with Laurentia.
I see my buddy Bill Burton (gray raincoat) was on that trip. Looks like a great exposure – wish I had been there to see it in person.
4 March 2016
Happy Friday, everyone. Today, Joe Kopera takes us to the summit of Mount Monadnock, in New Hampshire, to show us “the Billings fold.”
This locally famous recumbent fold is a favorite teaching spot on the southern face of Mt. Monadnock, southern New Hampshire’s most prominent peak. The recumbent fold deforms turbiditic graded bedding in the Devonian Littleton formation and is associated with a bedding-parallel cleavage. It’s still debated as to whether or not this fold is related to, and is itself, early nappe-style folding during the Devonian Acadian Orogeny. Look to the lower left of the fold hinge for a rotated boudin train parallel to the axial trace of the fold, highlighting the strain direction that caused the fold.
You can explore bigger versions of this image at Joe’s Flickr page. What an excellent fold – I hope to visit it in person some day. Thanks for the contribution, Joe!
Remember, any reader is welcome to submit fold imagery for this weekly feature. I welcome your contributions.
2 March 2016
This is the second Andrea Wulf book I’ve read in the past month. It’s a biography of a great naturalist and popularizer of science and travel writing, who at the same time is largely forgotten in the modern English speaking world. Alexander von Humboldt’s intellectual impact is vast, Wulf argues, leading to everything from Darwin’s wanderlust (and thus, to the observations that led to the idea of descent with modification through natural selection), to ecology, to environmentalism, to anti-colonialism, infographics, and even Art Nouveau. Part of this book is a fairly standard format biography, though I note that it’s very well written and quite engaging. You should probably know more about Humboldt than you do. We learn of Humboldt’s oppressive mother, his great voyage to South America, his friendships with Thomas Jefferson and Johann Wolfgang von Goethe, his theretofore-unprecedented melding of empirical fact and emotional reverence for the natural world. Another part of the book is a thoughtful, detailed examination of several case studies of Humboldt’s legacy – mini-biographies, in essence, of Darwin, John Muir, Ernst Haeckel, George Perkins Marsh, Simón Bolívar, and Henry David Thoreau. Humboldt’s ideas inspired each of these men in different ways, to strive toward greatness and help shape the world we live in today. It’s an excellent, thought-provoking survey of the age of exploration and its aftermath. From Chimborazo to Half Dome, Humboldt’s legacy is positive and (for me) greatly appreciated.
1 March 2016
I just finished an interesting book with a provocative title. How to Clone a Mammoth, by Beth Shapiro, is a readable, sober assessment of de-extinction, the idea of bringing back extinct species through a variety of techniques. She defines very clearly at the outset that the purpose of de-extinction is ecological – to restore critical / desired organism/organism or organism/abiotic environment interactions in ecosystems. It is, in other words, a potentially powerful tool in helping to solve problems with biodiversity. It is happening now, whether you approve or not, and it’s both extremely challenging and very expensive. Shapiro recounts historical efforts and societal reactions, expeditions, and lab work in great detail. She does a great job of beginning with the big picture, and then getting down into the weeds of genetic engineering. For anyone who’s captivated by the notion of glimpsing species that have vanished from the Earth, or anyone interested in biodiversity conservation, or anyone interested in molecular genetics’ cutting edge, this is a book worth reading. It’s a great choice for a companion to other contemporary works on environmental degradation, such as Elizabeth Kolbert’s The Sixth Extinction, or Gaia Vince’s Adventures in the Anthropocene. Particularly fascinating to me were the lattermost two chapters, that examine the legal and ethical ramifications of proceeding with de-extinction efforts. Are de-extincted species GMOs? Invasives? Endangered? All three? When is it the right choice to “re-extinct” a de-extinction that has gone awry? Shapiro has written a book that lacks hyperbole, and addresses these questions in clear prose. Her experience working in the field and teaching about it has resulted in an informative survey of the state of the art in this fascinating cross-disciplinary field.
26 February 2016
The British Geological Survey just came out with a new video on Siccar Point, featuring some excellent drone video of the site (in very good weather!).
In addition to the unconformity, one of the things you will appreciate about the video is an excellent end-on view of a plunging synform exposed just above waterline:
You’ll get a much better sense of its shape by enjoying the motion of the drone’s perspective. Watch the whole video here:
Top notch video! Well done, BGS. Happy Friday all.
21 February 2016
I just finished this book, about the botanical and agricultural predilections of United States ‘founding fathers’ George Washington, Thomas Jefferson, John Adams, and James Madison. Three of these farmed and gardened in Virginia, one in Massachusetts. Some were federalists, others republicans who championed the rights of the states. Some were slave owners, others not. All saw gardening as foundational to a sustainable democracy. This history examines the revolutionary war and the early years of the U.S. in the light of all things botanical, and quotes primary sources convincingly to show that the founding fathers would rather be planting trees, harvesting vegetables, and sharing seeds that governing the young nation.
The book is well written. Topically, I found it less engaging than some of my other recent reads (and even another book by Wulf, a biography of Alexander von Humboldt), but it held my attention anyhow. I was pleased to see some of my own gardening instincts reflected in decisions Jefferson made – in particular about the balance between wild and cultivated plants on one’s land. If you’re a gardener with a taste for history, this is a book for you.
19 February 2016
Happy Friday – sorry to have not shared any folds with you last week. I hope these beautiful folds in Catalina Island meta-cherts will make up for it:
As with the previous couple of Friday folds, this image is courtesy of Sarah Penniston-Dorland (University of Maryland, College Park).