Steve Fetter, former dean of public policy at the University of Maryland, came to NOVA to speak at our first annual Climate Change Symposium in 2008. He was our "headliner" act. Now, I learn from the University of Maryland alumni magazine Terp that Steve is now an assistant director in the White House's Office of Science and Technology Policy. Congratulations Steve!

Labels: climate change, maryland, meetings, politics

Today I took a group of students to Sideling Hill, a syncline in western Maryland. Here are a few photos from the trip. All photos by my iPhone, via Facebook (which is why the quality is lower than my usual standards):

The group all kitted out at the Sideling Hill Visitor's Center (which was closed due to budget cuts in Maryland):


Jared points out fast-weathering shale layers betwixt slower-weathering sandstone layers:


Diamictite outcrop on the far western side of Sideling Hill:


More diamictite... enigmatic sediments...

Labels: maryland, nova, primary structures, sediment, structure, teaching, valley and ridge, weathering

Yet five more of the maps I scanned from my recently-entered-the-public-domain copy of Vernon Quinn's book A Picture Map Geography of the United States. As before, clicking on the image will take you to a bigger version of the map. Enjoy!

Labels: art, books, connecticut, maps, maryland, new york, oregon, washington

Following on from Sunday's post showcasing new outcrops seen recently along the Billy Goat Trail, here's a cool ptygmatically-folded quartz vein I saw:



Can't quite make it out? The boulder's kind of weathered, so let me highlight it for you:


...and a close-up of the left side, which is better exposed:


That's all I noticed that was new this time around... but next time I'm sure there will be something else. The Billy Goat Trail is the gift that keeps on giving...

Labels: maryland, metamorphism, piedmont, structure

Went for a hike on the good old Billy Goat Trail last Sunday and saw this beautiful outcrop. I love it how every time I walk that trail, I see something new and blog-worthy. Here you see the metagraywacke of the Mather Gorge Formation getting squished and squeezed under conditions of partial melting. Granitic magma (light-colored rock) is leaking out, while the foliated mafic residue (schist chips) are getting strung out and boudinaged under conditions of mountain-building. This granite yeilds late Ordovician isotopic ages (Taconian Orogeny, ~460 Ma).

Seeing an outcrop like this reminds me of making cheese: squeezing the liquid whey (felsic magma) out from the solid curds (higher-melting-temperature solid minerals like those comprising the 'schist chip' boudins). As orogenic forces squeeze from the sides, granite oozes out the top.

I love that there are outcrops where this process is caught in freeze-frame: not all the granite escaped from its migmatitic source rock here; instead the process stopped before it was complete, and through the luck of uplift and exposure by the probing erosion of the Potomac, we get a glimpse of a fundamental process in making the Earth look the way it does. A single outcrop shows rocks that were oceanic sediments, then became metamorphic schist, and now are were transitioning to igneous granite! That's pretty wild. We have caught the rock cycle red-handed.

Labels: analogies, granite, igneous, maryland, metamorphism, piedmont, primary structures

PALEONTOLOGICAL SOCIETY OF WASHINGTON

Maryland in the Miocene: Paleoenvironmental History of the Calvert Cliffs
Susan Kidwell, Williams Rainey Harper Professor of Geology
Department of Geophysical Sciences, University of Chicago

Wednesday, Sept. 16, 2009
7:00 p.m., in the Cooper Room, National Museum of Natural History (10th St. and Constitution Ave. in NW Washington, DC)

Meet in the Constitution Avenue lobby at 5:00 p.m. if you wish to join the PSW members for dinner at the "Elephant and Castle," NW corner of 12th & Penna. Ave., NW

Non-Smithsonian visitors will be escorted to the Cooper Room at 6:30 and 6:55 p.m.

Labels: dc, fossils, maryland, meetings, miocene, psw, smithsonian

An article in today's Post explains more.

Labels: coastal plain, maryland, plants

Unannotated photo:


Photo with quartz veins outlined, highlighting boudinage and parasitic folding:


Photo with vein quartz boudins and folds highlighted in yellow:


Sketch interpreting stresses that produced these structures:


This nice example of ~horizontal shortening and ~vertical stretching is seen in metagraywacke muscovite schist with hydrothermal quartz veins, near Potomac, Maryland. It is located on the C&O Canal, just upstream from the bridge going to Olmstead Island and the Great Falls overlook.

Labels: art, maryland, piedmont, structure

Yesterday, I lead a NOVA field studies trip to the Billy Goat Trail, and we were pleased to see that the recent rains had plumped up the big patch of Opuntia (beavertail) cactus near the boulder of Seneca Sandstone. These are native cacti which grow on poor soils in the area. These soils are poor because periodically the Bear Island strath (bedrock terrace), where the Billy Goat Trail is located, is scoured by the Potomac River's floods. These cacti are growing essentially in pine and juniper needles on top of bare rock (metagraywacke). What a beautiful sight!

Labels: maryland, piedmont, plants

And now, a few images from April's Environmental Geology class field trip. We made three stops: (1) a large coal-fired power plant in Maryland, (2) Westmoreland State Park in Virginia to look at coastal erosion, and (3) Prince William Forest Park in Virginia to look at pyrite emplacement and acid mine drainage.

Here's one of the bluffs on the Potomac River at Westmoreland:

Note the recent pile of breakdown in the middle of the bluff where all the water seepage is, and also the orange trail as soil from the uppermost bluff has marked another mass wasting event's passage down to the river.

These are Miocene-aged sedimentary layers known as the Calvert Formation, part of the Coastal Plain. In places, the gray clay has been altered along fracture surfaces, as shown by these orange stripes criss-crossing one another. My toes for scale:


The students spent some time searching for fossils: this is an area where lots of shark teeth are found. We didn't have much luck, but after a long cold winter, it was nice to be standing in the warm sunshine and water:


At Prince William Forest Park, we hiked down to the Cabin Branch Pyrite Mine to look at the massive denudation there due to acid mine drainage, and we also spent some time poking around for treasures, in this case chunks of pyrite:


We had better luck than at Westmoreland...




...But of course we were in a national park at Prince William, so we left the pyrite where we found it. (Westmoreland, in contrast, allows you to keep any fossils you find in loose sediment: that figures, eh?)

I'd like to say that the group of students I had in Environmental Geology this past semester was terrific, one of the best groups I've worked with in a long time. Maybe it was because the class was discussion-focused, or maybe it was the cookies we ate every Tuesday night, but it was a great experience for me, and I'm looking forward to teaching the course again. Thanks, everyone, for making it so much fun!

Labels: coastal plain, environmental, field trips, maryland, miocene, nova, ore, piedmont, virginia

I saw Ray Stanford, an enthusiastic amateur paleontologist, speak last month at a meeting of the Paleontological Society of Washington.

It was my first PSW meeting, and I got a warm welcome from PSW president and University of Maryland paleontologist Tom Holtz, who gave a specific shout-out to NOVA Geoblog, encouraging the ~30 attendees to check it out. (If you're arriving as a consequnce of that endorsement, welcome!) Four of my Honors students joined me for the talk. Just getting to go behind the scenes at the Smithsonian is a treat in itself. From the Easter Island moai in the Constitution Avenue lobby of the museum, we were escorted through labyrinthine passageways to the Cooper Room. Our route brought us past immense fossil collections, cossetted away in row after row of cabinets. It was enticing, and made me resolve to arrange a special tour there sometime for the Honors students.

The point of the talk was Stanford's immense collection of fossil dinosaur tracks (and at least one apparent mammal track which is quite large: raccoon-sized at least, with apparent dinosaur skin impressions right next to it). It used to be thought that Maryland only had Triassic/Jurassic fossil tracks, from the Newark Supergroup rift valleys that opened up during the breakup of Pangea / opening of the Atlantic Ocean. Stanford has made a real scientific breakthrough by demonstrating that there are early Cretaceous-aged tracks in the area too.

None of his Cretaceous-aged tracks are collected in situ. Instead, he finds them all as "float" (weathered-out loose blocks) in streams draining exposures of (what I infer to be) the Patuxent Formation. (He didn't specifically mention source formations that I heard during the talk.)

He's found a ton of stuff! Actually,if I'm being literal, he's found tonS of stuff! And he stores it all in his living room! He recently had the foundations of his house reinforced because he has so much STUFF. Hundreds of tracks, and other fossils, too. Whoa! This guy does not play by the same rules as most folks.

There were a lot of coprolites mentioned, including:

• a 98-pound coprolite (!)
• a coprolite with a dinosaur footprint in it
• a dinosaur footprint with a coprolite in it

He also shared what he claimed were skin textures preserved in tracks. Some were self-evident, and I readily accepted them as valid. However, others weren't visible to the naked eye, and he only "demonstrated" them with Photoshopped images wherein the contrast dial was turned up to 11 -- I think this "technique" generated patterns that resembled skin impressions, but when I looked at the fossil itself, they were nowhere to be seen. I am dubious about this particular claim.

The talk gave me lots to think about, but not so much about dinosaur lifestyles or anatomy so much as the role of amateurs in science. Here's a guy with boundless enthusiasm, and he's finding stuff that the books literally said didn't exist. His efforts have resulting in expanding Maryland's Mesozoic paleontological record into the Cretaceous, and he's found all sorts of stuff that's super-duper interesting, like that mammal track.

Stanford was profiled last year in Geotimes magazine, before it switched its name to EARTH. Discovery News also ran a story about his findings. Interestingly, when Googling his name for this blog post, I also came across some other wacky stuff he's involved in, including UFO's. This definitely jibes with the lack of scientific rigor that I perceived in his presentation. (Quote from the interviewer: "In the 1970s, Stanford was the moving force behind the Association for the Understanding of Man (AUM) and Project Starlight. The former an attempt to decipher the UFO enigma by psychic means, the latter using advanced scientific instruments.")

So, having learned this, what do I make of his paleontological data? The best I can come up with is to trust my own eyes and view his claims open-mindedly but with the traditional scientific filter of skepticism. I accept the coprolite data; I found it self-evidently convincing. The skin-texture data? Not so much. The UFO stuff? Don't get me started...

Labels: coastal plain, cretaceous, culpeper basin, fossils, maryland, meetings, mesozoic, museums, psw, science and society, smithsonian

The other day I mentioned the Setters Schist.

Here's a couple of cobbles of the same formation, but lower stratigraphically than the stuff we saw on the University of Maryland petrology trip. The basal Setters has beautiful metamorphic tourmalines lying willy-nilly within the plane of foliation:







According to Mindat.org, "the general formula for this group may be written:

• A = Ca, Na, K, or is vacant (large cations);
• D = Al, Fe²⁺, Fe³⁺, Li⁺¹, Mg²⁺, Mn²⁺ (intermediate to small cations - in valence balancing combinations when the A site is vacant);
• G = Al³⁺, Cr³⁺, Fe³⁺, V³⁺ (small cations);
• T = Si (and sometimes minor Al³⁺, B³⁺);
• Y = O and/or OH; and
• Z = F, O and/or OH."

Note the constant there: boron! ...A lot of boron! Three boron atoms per unit cell... These metamorphic rocks have a sedimentary protolith. Where did the pre-metamorphic sediments get all that boron from?

Any ideas?

Labels: geology, maryland, metamorphism, minerals, piedmont

After we had collectively collected a hundred pounds of samples from Mineral Hill, the final stop on the University of Maryland petrology trip was in scenic Ellicott City, Maryland, where we visited the Ellicott City Granodiorite (map to outcrops).

Like everything else on this trip, the ECGD is intimately tied in with the Taconian Orogeny (late Ordovician; caused by the collision of ancestral North America with a volcanic island arc in the Iapetus Ocean basin). However, unlike the Port Deposit Tonalite we looked at early in the trip, this one crystalized from magma at 435 +/- 15 Ma (U/Pb in zircon). It is not only much younger than the PDT, but it's also pretty young even for the Taconian Orogeny, which reached its peak around 460 Ma.

It's more potassic than the Port Deposit Tonalite, as these K-spar 'megacrysts' show:


This potassium feldspar 'megacryst' shows internal growth laminations, as small mafic bits got caught up in the growing feldspar crystal, which consumed and included them:

Not only does this help us see how the feldspar crystal's habit is a reflection of its internal structure, but it's also an example of the principle of relative dating by inclusions, expressed in a single mineral crystal! Pretty cool.

As with the PDT, xenoliths may be seen in the ECGD:


Parts of it are equigranular, and parts of it are highly foliated:


And of course my eye is always drawn to the structures, like these small faults offsetting dikes of granite which cross-cut the ECGD:




The real prize with the Ellicott City Granodiorite is to view first-hand the magmatic epidote it bears:


Most epidote is metamorphic. However, as Zen and Hammerstrom (1984) showed that epidote could also crystalize from a late-phase magma as the melt interacted with hornblende at high pressures (8 kbar; roughly 30 km depth). You'll note in the photo above the intimate association between the epidote and the hornblende. (I'm not super-confident on my titanite identification, by the way; this rock also bears similar-looking allanite. Please correct me if I'm clearly wrong.) E-an Zen has guest-posted to this blog before, and once upon a time he tasked me with searching for magmatic epidote near Haines, Alaska, in 2006. I didn't find any, but it did pique my interest. So it felt good to be able to finally see some of this rare beast. I was surprised to find it locally, considering the the original magmatic epidote paper referred mainly to west coast plutons from California to Alaska. I was also suprised because of the tremendous depth of crystallization it implied: 30 kilometers down? Wild! I collected a sample for the NOVA lab.

Thanks again to Rich Walker and Roberta Rudnick for graciously hosting me on this trip. I learned a lot, and I'm greatful for the opportunity to expand my local outcrop knowledge.

_________________________________________________________________

Reference:
E-an Zen and Jane M. Hammarstrom (1984). "Magmatic epidote and its petrologic significance." Geology, September 1984. Volume 12, no. 9, p. 515-518. DOI: 10.1130/0091-7613.

Labels: alaska, maryland, metamorphism, minerals, structure, xenoliths

Done with the Cockeysville Marble and fortified with chocolate malts from the Twin Kiss, we ventured on to "Mineral Hill," interpreted as a paleo-black-smoker site from the deep Iapetus. This is a zone of mafic and ultramafic rocks that have been metamorphosed and also mineralized with a suite of sulfide minerals, including pyrite, chalcopyrite, bornite, covellite, and carrollite (in fact, this is the type locality for carrollite). Presumably it was a SedEx-type deposit in the Iapetus Ocean basin. It is geographically associated with the Baltimore Mafic Complex, which is most readily interpreted as a dismembered slice of the Iapetus oceanic lithosphere (that is, an ophiolite). As the Iapetus closed during the Taconian Orogeny, it was accreted to North America and metamorphosed.

The petrology students start picking up pieces from the massive pile of tailings in search of treasures:


Talc shist (soapstone) with malachite:


More of the same:


I forget what this one was, but I loved the "spray" pattern of its bladed crystals:


Chrysotile asbestos:


Pyrite:




And lots and lots of magnetite! These are some of my refrigerator magnets stuck to it:


One more stop to go: the Ellicott City Granodiorite...

Labels: appalachians, maryland, metamorphism, minerals, ophiolites, ordovician, ore

We are now halfway through our documentation of the University of Maryland petrology field trip. As a reminder, we've already seen the Port Deposit Tonalite and the Setters Schist. Today, we meet the Cockeysville Marble.

The Cockeysville is famed in some quarters because of its role in the construction of the Washington Monument. The upper portion (most) of the monument is made of this rock, although it is a purer (higher CaCO3 content) marble than we see here at this outcrop near the Hunt Valley Shopping Mall. Really, this is more of a marble gneiss.

Rich and Roberta talk with the students about this new rock:


The Cockeysville Marble has a well-developed foliation at this outcrop. Impurities in the limestone protolith (probably clay) have metamorphosed into muscovite mica:


Whether these foliations reflect bedding is an open question in my mind. Here's a look at how the outcrop is weathering out. Lovely, just like a limestone in the way it's dissolving away:


It's reasonably coarse-grained:


Here's two close-ups of the stringers of muscovite mica:




Some structural geology was also apparent. Here for instance, is a fault/shear zone


...And here's a fold. It's an overturned fold; Note how the foliation dips at two different angles, though in the same direction:


Still can't see it? Okay, let me help:


The sharp-eyed among you probably noticed the boudinage on the left side of the fold. Here's a portrait of the most prominent boudin:

The most mica-rich domains acted relatively stiffly under deformation, while the calcite-rich domains flowed more easily.

I also found a surface decorated with slickenfibers (crystal fibers growing aligned in small spaces along the surface of a fault):


... and a close-up, so you can see that the opposite block of rock was moving from the bottom of the photo towards the top. Running your finger over this outcrop from bottom to top would feel relatively smooth, while running your finger over it from top to bottom would feel rough as your fingertip would catch on the little mineral "steps":


The Cockeysville is a lovely marble. But we needed lunch at the Twin Kiss drive-in. The day was advancing, and refueling became a serious issue. And then? On to Mineral Hill...

Labels: marble, maryland, metamorphism, structure

Yesterday, I showed you the Port Deposit Tonalite, stop #1 on the University of Maryland's annual ig/met pet trip. Today I'll share pictures of the next stop. We voyaged to the Hunt Valley Shopping Mall, where a lovely exposure of the Setters Schist can be found.

It's a lovely example of a classic-looking muscovite schist:


It is also chock-full of garnets! Millions and millions of them....

Some are small:


Some are medium:


Some are large:


Some are fresh:


Some are weathered:


Some are weathered-out:


There's also staurolite present:




Here's a nice big chunky staurolite:


In one localized zone, we also see some very big, rather lovely kyanite:




...Awesome! I love this suite of metamorphic minerals!

The Setters Schist is a highly metamorphosed pelitic rock (meaning that its protolith was clay-rich). It was presumably metamorphosed in the late-Ordovician-aged Taconian Orogeny, like everything else in the Mid-Atlantic Piedmont.

Next up, another member of the Glenarm Series, the Cockeysville Marble...

Labels: appalachians, maryland, metamorphism, minerals, ordovician, piedmont

Today, I present a guest post from my student Hope W., who described her experiences visiting the Chalk Point Generating Station in Maryland on our Environmental Geology field trip the weekend before last. The essay is posted here with her permission. Enjoy! -CB

The Chalk Point Generating Station is a coal burning power plant owned by the Mirant Corporation. Our guide during our tour was Greg Staggers, the plant manager. There were three main subject areas that Mr. Staggers talked to us about: power generation, the economic supply and demand, and environmental regulations and precautions.

Power Generation:
Mr. Staggers explained how the station has two different types of units. They have steam units and combustion units. Mr. Staggers described how the two different types of units are designed. He said that the steam units are like giant boilers, and that the combustion units are like jet engines. The plant has four steam units and seven combustion units, both types use fossil fuels to produce energy. Mr. Staggers explained how when power is first generated it is at too high of a voltage to be safely used by the public in homes or offices; and how the current has to be run through various lines to transformers and substations in order to be brought down from 20,000 volts (the level generated) to 110-220 volts (the level used in homes and offices.) Mr. Staggers pointed out the transformer field we drove past on the way in on the aerial photograph of the plant explaining that that’s where the process of conversion begins.

In response to Sophia's question about why the plant was built next to the water, Mr. Staggers explained the complex system for using water from the river to cool the equipment in the plant. As he talked in depth about this system he described how ideas improved through time and experience, as well as environmental regulations which lead the plant to finding more efficient and ecological ways of utilizing the river water. Later on when we took our tour through the plant we had the opportunity to see the some pipelines that the river water runs through. The water runs through the pipe-lines to cool the steam that is emitted during the power generation process. When the river water is released back into the river from the plant it has picked up no chemicals, and has only increased in temperature by approximately 20°F.

Mr. Staggers told us about four of the units that get run; units 1 and 2 which are combustion units and units 3 and 4 which are steam units. When running at full capacity units 1 and 2 operate at 90% efficiency, burn 2.5 million pounds of coal per hour, and use 14 megaWatts of the energy produced to operate; and when units 3 and 4 are running at full capacity the burn 650 gallons of oil per minute. Mr. Staggers informed us that the enormous pile of coal we saw on our way in would last for 45 days if the plant were running at full capacity.

Economic Supply and Demand:
In the 1990's the system was deregulated, which basically means that the power generation, wholesaling of the utility, and the supply distribution were all split up. So when the Chalk Point station produces energy they sell it to PJM a 'middleman' who will then sell it to the suppliers like Dominion Power etc. who then sell and distribute the supply to the public. I mentioned the transformer field earlier in this paper in reference to the generation process, but the transformer field has economic implications as well. The transformer field is also where the producers pass of the ownership of the energy to the middleman.

Mr. Staggers explained the bidding system for establishing the market value for each day. In the bidding system if you are over producing you get paid the difference in price from your morning bid in real time. During the tour we got to see the control rooms where the market price rates were being adjusted in real time. In response to Dustin's question about how they know when to produce Mr. Staggers explained how the middle men suppliers make that call based on the morning bids and the actual demand by the public, when the suppliers make the decision about production levels they call the plant to inform them of how much they need to be producing.

In terms of the national economy coal is the cheapest in explicit costs, in equivalent quantities the price for coal is 1/3 that of oil and natural gas prices, which is why more than 50% of the U.S.'s power is generated by coal. In terms of the local economy the Chalk Point station produces a 500 thousand volt ring around D.C. It is estimated that in the next five years 1 million homes will be added to the market that the Chalk Point station caters to.

The demand for coal is influenced by seasonal changes which gives it a cyclical demand. Callan asked if the increased attention on alternative methods of energy has affected the demand for coal in terms of reduction. Mr. Staggers said that no such change has been apparent and that the cyclical trend has followed a predictable pattern.

Environmental Regulations and Precautions:
Mr. Staggers told us about the regulations the plant has been mandated to conform to, as well as what the plant has done of their own accord for the sake of the environment. Some of the changes that the plant made in the past include setting up new stack facilities in 1982 because of environmental regulations. When the clean air act was passed in 1992 brought down their level of pollutants they were releasing into the atmosphere from 1.4 to .7 Further regulations such as; the separated overfire air controls in 2000, selective auto-catalystic reduction in 2007, and selective catalystic reduction in 2008 brought the pollutant rate down to .06. All of the methods above have dropped total output capacity by some amount.

The plant has also put up two boundary nets to protect fish from the areas where hot water is released and two more boundary nets as well as a fine mesh screen to prevent the fish from getting sucked up into the pumps for the cooling system. The plant has many systems in place to reclaim energy where they can to avoid waste, such as how they use residual heat from the coal burning process to heat the incoming air from its current temperature to be closer to the temperature required for being used as an infuser in the combustion process. The plant is in the process of building a "scrubber" which will reduce the sulfur emissions by 98%. The method this "scrubber" will use will allow the plant produce and collect gypsum which the plant will sell for its use in drywall. The plant also has a system set up to collect ash by a precipitation method; the ash collected is also sold for its use in drywall.

The plant has continuous emissions monitors which monitor emission levels of CO2, SO2, and NOx. The data from the monitors is sent quarterly to the State and the E.P.A. In the control room Callan asked a question about the plant's ppm output of CO2. Mr. Staggers said that measure by percentage and he did not know the output in ppm . This discussion lead to a very clear statement by Mr. Staggers that he wasn't convinced that it really made a difference. Mr. Staggers informed us that the plant's output of CO2 is 12% of flue gas volume, which Callan calculated to be 120,000 ppm. From Mr. Staggers' point of view as a producer of a commodity it is hard to see much else besides bottom line explicit costs. This was not his position out of greed, but out of responsibility to keep the company running so he has a job to provide for his family, and his employees as well. On the other hand, scientists cannot escape the implicit costs of CO2 emissions.

There needs to be a level headed discussion in a neutral setting were the two groups can learn to understand each other and start to cooperate. We as individuals and a nation must step up and set the example. When we start working together we will create the safe harbor necessary for understanding and cooperation to grow and flourish.

Labels: coal, energy, environmental, maryland, nova, oil, teaching

Yesterday, I was fortunate enough to be able to tag along on the University of Maryland's petrology field trip, to five locations in Maryland showcasing a variety of igneous and metamorphic rocks. I'd like to thank Rich Walker and Roberta Rudnick for allowing me to come along on the excursion, and UMD graduate student Ryan Kerrigan for alerting me to the trip's interesting rocks in the first place. They have a crew of enthusiastic students, and some cool outcrops!

Our first stop was in northern Maryland's Cecil County. Along the banks of the Susquehanna River, just upstream from the I-95 bridge, is an abandoned quarry of the Port Deposit Tonalite.

Here's Rich and Roberta leading us into the quarry:


UMD students examine the semi-overgrown outcrops of the tonalite:


Tonalites are kind of like granites, except they have only very low amounts of potassium feldspar. This particular tonalite has a magmatic crystallization age of 515 Ma (U/Pb in zircon) and a metamorphic age of 490-480 Ma (Rb/Sr in biotite). Close-up of the rock's texture:


ADDITION: Kim notes in the comments that I didn't draw an explicit connection between the metamorphism and the metamorphic foliation that is so prominent in this photo. She's right: The wavy linear pattern you see in this photo is produced by minerals aligned by differential pressure. Squeeze the rock "top to bottom" and you produce a foliation that runs "left to right."

On the basis of isotopic evidence, the Port Deposit Tonalite is interpreted to have formed as an igneous pluton offshore of ancestral North America, underneath an island arc in the Iapetus Ocean. Later, subduction brought the island arc into contact with North America, triggering the Taconian phase of Appalachian mountain-building.

Here's a closer look at the texture and mineralogy. You can see some k-spar present here, though this was not a common mineral to see at the outcrop...


There were some nice xenoliths present, indicative of the host rock into which the PDT intruded:


Here's a quartz vein cutting through the tonalite. You'll notice that the vein is emplaced approximately perpendicular to foliation, suggesting the same maximum stress which imparted the foliation also extended the rock parallel to the foliation place, opening up fractures that when then fill with the most mobilizable minerals available (in this case, quartz):


If you look closely, you'll see that the fracture which opened up in the tonalite to allow this vein to be emplaced has a ragged edge (not a clean break):


Next up: the Setters Schist...

Labels: appalachians, cambrian, granite, igneous, maryland, metamorphism, ordovician, structure, teaching, xenoliths

PALEONTOLOGICAL SOCIETY OF WASHINGTON

Maryland's Lower Cretaceous Vertebrate Tracks and Trackways
by Ray Stanford, Maryland Track Project

Wednesday, April 15, 2009
7:00 p.m., in the Cooper Room, National Museum of Natural History
10th St. & Constitution Ave. Meet in the Constitution Avenue lobby at 5:00 p.m. if you wish to join us for dinner, at the Elephant and Castle, NW corner of 12th & Penna. Ave., NW

Non-Smithsonian visitors will be escorted
to the Cooper Room at 6:30 and 6:55 p.m.
Remaining Date for 2008-2009 Season: May 20

Labels: cretaceous, fossils, maryland, psw, smithsonian

Here's some photos from today's Physical Geology class field trip to the Billy Goat Trail. It actually snowed on us a little bit... cold! My student Luke O'Neil took all of these, hosted on his Facebook page, and this is an experiment to see if I can post Facebook photos on my blog... keeping my fingers crossed...

Migmatite:


Il profesore showing tilted tree trunks (knocked in a downstream direction during floods):


Folded graded bed in metagreywacke:


Students circle around an exotic boulder of the Catoctin Formation greenstone (from the Blue Ridge province); the boulder was transported downstream by the ancestral Potomac River when it was flowing on the Bear Island strath, before incision and abandonment of the former river bottom to become a bedrock terrace:

Labels: field trips, geology, maryland, national parks, nova, piedmont, rivers, teaching

The backlog of photos from my hikes several weeks ago still looms. I've showed you exotic cobbles, migmatites, graded beds, flood debris, and boudins, now for some folds...

As with the others, these are images from the Maryland Piedmont, along the Billy Goat Trail in C&O Canal National Historical Park.

Here's two repeats that fall, Venn-diagram-like, into the overlap area between the "graded beds" theme and the "folds" theme:




Now for some fresh, never-before-seen images:







(that's a fold cut twice oblique to its axis, resulting in an elliptical outcrop pattern).

Tiny folds:


Folds in one direction (top to bottom); boudinage in the perpendicular direction (left to right):


Found this one on the side of a cliff I probably should not have been scaling:


That's all for now... have a good Tuesday!

Labels: igneous, maryland, metamorphism, national parks, piedmont, primary structures, structure

Last week, I updated my field trip photo page with a fresh batch of images from last spring's Field Studies in Geology course to the Billy Goat Trail. Here are the new shots:












All photos are by Kevin Mattingly, NOVA photographer.

Labels: field trips, maryland, nova, piedmont, teaching

Audio (and video) to share the sound of springtime froggies calling, along the Berma Road trail in C&O Canal National Historical Park:

Labels: amphibians, maryland

Labels: maryland, structure

Picking up where I left off last week with cool new pictures of rocks from the Billy Goat Trail, today we examine igneous beasties...

As you may have picked up from previous posts on this blog [e.g. here], the rocks of the Piedmont province are essentially the mangled remains of an ancient ocean basin: deep sea sediments, oceanic crust, volcanic islands, even microcontinents -- and all were crushed between North America and Africa during the mountain-building that closed the Iapetus Ocean and formed the supercontinent Pangea. Along the Billy Goat Trail, Piedmont rocks are exposed that started off as deposits of mud and dirty sand, but then were metamorphosed during mountain-building. From the bottom of the ocean to the center of a mountain belt: that forces rocks to change. In some places, they heated up so much that they began to melt.

When rock partially melts, but then the melt crystallizes in places (i.e., it doesn't completely drain out of the source rock), we call it a migmatite. The Billy Goat Trail has some spectacular exposures of migmatite. Here's three shots from the downstream end of the trail:







If migmatitic rock rips open while it is in this partially-molten state, that generates cavitites that the fluid magma flows into and fills. Here, for instance, you can see a rip in the foliated migmatitic metagraywacke that is filled with granite.


Further away from the source rock, mobilized magma can fill in planar fractures that cut across older rocks of many varieties. These cracks are filled in with magma that cools into igneous rocks, and we call them dikes. Here is a new dike I discovered on my hike last week: a vertical dike of granite about one foot thick, cutting across non-migmatitic metagraywacke:


Here's a granite dike cutting amphibolite; weathered out in high relief:


Same dike, from a slightly different angle (I leaned over to the left), to show how it pokes up above the amphibolite like a little wall:


Metamorphosed (some epidote present) granite dike cutting amphibolite:


These fractures didn't open up wide enough to admit large volumes of fluid (either magma or hydrothermal solutions), but there was some fluid flow along them. How do we know? The rock immediately adjacent to each crack weathers out in high relief, suggesting a higher proportion of stable, tough minerals (like quartz). [We've seen this before.] The base rock here is fine grained amphibolite.


Contact between a small granite pluton (or a large dike?) and neighboring amphibolite:


Tension gash in amphibolite, filled in with a mix of potassium feldspar and quartz:


Xenoliths of foliated biotite-rich rocks which I interpret to be metagraywacke that has had all its felsic melt expressed from it, then ripped off by the growing granitic magma chamber (stoping) and dropped into the magma (relatively low temperature, so the biotite doesn't melt), and rotating around to new orientations which do not match the regional foliation orientation. I'm seeing these as shreds of the 'depleted' migmatitic source rock...


Closer-up of these xenoliths #1:


Closer-up of these xenoliths #2:


Another cool thing I saw on last weekend's hikes was pegmatite. Pegmatites are present where there is a particularly watery magma. Water, the universal solvent, helps act as a courier, ferrying atoms around to where growing crystals can access them and add to their bulk. As a result, pegmatites are characterized by really large crystals. These potassium feldspars are highlighted by lichens which grow at the interface between the feldspars and the surrounding milky quartz:


Those same black-colored lichens can also highlight the cleavage planes of the feldspars:


Another big-ass K-spar:


...and another:


I love this stuff. Hope you enjoy these igneous treats as I much as I enjoy sharing them.

Labels: igneous, maryland, metamorphism, piedmont

It's getting to be springtime... and that means field trips!

My first field trip of the semester is tomorrow: my friend David Dantzler has organized a trip to look at stratigraphy and structure out on a new highway in West Virginia. I'm supplying half a dozen Honors students and a NOVA minivan, but David's handling the content. And of course, I'll be on hand to comment on "teachable moments." Looking forward to it.

Other trips upcoming this semester: Billy Goat Trail (x4!), Massanutten Mountain, Old Rag Mountain, Washington DC walking tour, and a weekend-long structural geology trip to the Blue Ridge and Valley & Ridge provinces. I love field trips; really they were the aspect of majoring in geology that appealed to me the most - the fascination with Earth processes took longer to develop.

See you in the field!

Labels: blue ridge, field trips, maryland, nova, piedmont, teaching, valley and ridge, virginia, west virginia

I mentioned seeing some cool stuff when I went hiking on the Billy Goat Trail last weekend.

One of the things that really caught my eye were multiple new exposures of graded bedding. These rocks began as deposits of sediment offshore from a volcanic island arc: they consist of turbidite deposits that were then squished and squeezed as that volcanic island arc collided with eastern North America during the closure of the Iapetus Ocean. As a result of this, they were metamorphosed and deformed. But in a few places, you can still see the relict graded beds that originated through the settling out of turbidity currents.

Here's some images:

I count four or five here:





A nice central fault zone displaced the central block downward:




This one is a little more subtle...


Here's one that's been turned upside down (by tectonics):


And there were also some folded examples:




A close-up of the hinge of this folded graded bed:


Pretty cool, eh? The only problem is these samples aren't on the Billy Goat Trail itself, which means I'll really never be able to show them to students except in photographs...

Labels: geology, maryland, metamorphism, national parks, piedmont, primary structures, sediment, structure

Ladies and gentlemen, spring has arrived in the Washington, DC region. It is sublime. I'm very grateful that it's my spring break this week because even though I still have a ton of work to do, I've had the opportunity to get outside every day and enjoy a bit of the weather.

This weekend, I got up early both days and headed out the the Billy Goat Trail, a rugged hiking trail along the Potomac River's gorge about 12 miles upstream from DC. I departed from the trail itself both days, which was great because it brought me to places I hadn't seen before. I found a lot of cool new structures and rocks! Over the next few days or weeks, I'll be sharing some of those images with you, but for today, I figured I'd show you some 'soft' imagery, just to celebrate the fun of being outside on a hike on a lovely day. ...and wearing short sleeves, no less!

Here's a shot of typical scenery along the Billy Goat Trail. This is looking upstream:



One of my side-trips off the trail... because the water level was pretty low, I was able to get to some islands that are often inaccessible. This is the channel between the Rocky Islands (downstream of Great Falls, upstream of Mather Gorge):



This land is all part of the C&O Canal National Historical Park. Here's a spot where rains from Tropical Storm Hanna breached the wall of the C&O Canal, allowing its water to drain downward into the Potomac. Because the canal's towpath was located there, the Park Service has constructed a temporary path which detours around the breach:



I saw some good birds on my hikes there. Red-tailed hawks, double-crested cormorants, Canada geese, mallards, belted kingfishers, pileated woodpeckers, red-bellied woodpeckers, tufted titmice, chickadees, robins, blue jays, and great blue herons. Also, both local species of vultures: the turkey vulture and the black vulture. This is a black vulture (note the black, not red, head):



Here's some tracks: theropod dinosaurs? ...or great blue heron? You be the judge:



Here's a cool fish skull I found:



Of course, it wasn't all scenery, birds, and fish. There were rocks, too. I took a lot of rock photos, and you'll get to see them all in due course... But for now, let me start you off with the tame stuff. Here's some cobbles I encountered along the hike...

Cobble of the Seneca Sandstone (Triassic arkose) showing a mudchip rip-up clast:



Tilting it a bit, you can see other mudchips too:



Cobble of cement containing Seneca chunks:



Cobbles of quartzite of the Antietam Formation showing Skolithos 'worm' tube trace fossils:



I love these Skolithos tubes. It's hard not to love them, and they're everywhere around here. Like the Seneca cobbles, they come from source areas to the west (Culpeper Basin & Blue Ridge, respectively), and were transported to the Maryland Piedmont by the ancestral Potomac River.



My favorite Skolithos-bearing quartzite cobble:



...And the same cobble, end-on:



More to come, tomorrow...

Labels: birdies, blue ridge, culpeper basin, fish, fossils, maryland, national parks, piedmont, sediment

For those of you who missed it, here's video of Mike Tidwell's talk at NOVA last Thursday.

Labels: action, climate change, global warming, maryland, nova, podcasts and vodcasts, politics, virginia

Because he's coming to campus tomorrow (Thursday), last weekend I watched Mike Tidwell's movie We are all Smith Islanders. It's a 35-minute long documentary about how climate change is effecting the states of Maryland and Virginia, and the District of Columbia. Though it is a political document (and not a scientific documentary), I think it's a worthwhile enterprise because it connects the global to the local. We hear a lot about climate change, but when someone actually walks through Ocean City, Maryland, pointing out what three feet of sea level rise would look like, it fosters a connection based on shared landmarks.

Thanks to archive.org, you can actually watch the movie in low resolution on the Internet. Google video also keeps a copy available.

Or, if you'd prefer it in higher resolution (on DVD), you can find it at the NOVA library.

Labels: action, climate change, dc, global warming, maryland, movies, nova, politics, virginia

President Obama is acting to (potentially) improve the fuel efficiency of cars manufactured in the United States. The official announcement will apparently come later today, but somehow the newspapers always find out first.

Meanwhile, Virginia's budget shortfall has led to the elimination of pollution inspectors, which means that instead of the usual inspection of 1400 sites in the Commonwealth this year, the reduced staff will likely get to 800 or so. In Maryland, by contrast, the article describes how the governor is actually increasing funding for the oversight of power plants. An interesting contrast from two Democratic governors (one of whom is now moonlighting as the head of the DNC).

PS - My Prius is less efficient in the cold. I've been hovering between 46.5 and 47.0 mpg for the past couple of weeks. Brrr.

Labels: energy, environmental, maryland, news, oil, prius, virginia

One of my favorite hiking and geologizing destinations, the Billy Goat Trail (in C&O Canal National Historical Park) was the site of a gruesome discovery Saturday: a dead body! More here from MSNBC. Hat tip to Michelle A. for the prompt notification.

UPDATE: Same info, but from the Post.

Labels: field trips, maryland, news, piedmont

Recently, Andrew Alden compiled a list of state minerals and state rocks. A quirky piece in today's Washington Post explores what Maryland is urging its citizens to do with their state fish: eat them. The story also, somewhat randomly, includes a limerick composed by Virginia's former governor and current senator, Mark Warner:

We have a state dog and a fish and a bird.
And of the fossil I'm sure you have heard.
So why not a bat?
What's wrong with that?
The state beverage is no more absurd.

For some reason, I hear this limerick in my head in Carl Kasell's voice...

Labels: birdies, critters, fish, fossils, mammals, maryland, politics, virginia

Strange Maps has an interesting piece up today about where West Virginia came from (as a state): turns out it was all about the Civil War. The accompanying map shows the original proposed name for West Virginia, "Kanawha," as well as a proposed demarcation between Virginia and Maryland that trended along the western margin of the Blue Ridge physiographic province. If this boundary had come to pass, Virginia would have gotten the Valley & Ridge province, but Maryland would have retained the Blue Ridge, Piedmont and Coastal Plain.

Labels: blogs, blue ridge, coastal plain, history, maps, maryland, piedmont, valley and ridge, virginia, west virginia

According to a study by the Washington Post, our area's electricity consumption dropped by a small but perceptible amount in the first nine months of 2008, as compared to 2007. The article linked to above describes the sources of data as being a mix of home audits in Arlington County, Virginia (40 out of 89,000 total), government figures for the number of miles driven on local roads, and utility billing information. Overall, the Post estimates a 2% reduction for the study period in 2008 as compared to the previous year. Now, the question is, Why? By their reckoning, it's likely to be a mix of increased consciousness of "green" energy practices, increased use of compact fluorescent light bulbs, and perhaps most importantly: mild weather.

One thing I can say about that lattermost factor: this year, 2009, is so far not really of the "mild weather" variety. It's dang cold here!

Labels: dc, energy, environmental, maryland, news, virginia

Following the success of last year's Climate Change Symposium, this year NOVA will host Mike Tidwell, the dynamic director of the Chesapeake Climate Action Network, for a talk on global warming and what college campuses can do about it. Mr. Tidwell has a reputation as a terrific speaker, so I'm really looking forward to his talk.

He will be speaking at 11am on Thursday, February 5, in the Ernst Community Cultural Center Theater (CE building) on the Annandale campus of Northern Virginia Community College. The event is free and open to the public. I encourage you to attend if you're in town. A booksigning will follow in the Theater lobby.

Labels: climate change, global warming, maryland, meetings, nova

Last week was field trip week for me. I led trips to the Billy Goat Trail on Tuesday and Thursday, and to Washington, DC, on Saturday.

On the Physical Geology field trip to the Billy Goat Trail, we saw rocks like amphibolite, metagraywacke, and migmatite:







Hope and Ana checking out the migmatite:


The group poses with the migmatite, to show how close anatexis is to their hearts...


Jane examines lamprophyre in a weathered-out dike:


Noting the characteristics of metagraywacke:




Traversing 'Pothole Alley'... Joel looks chilly...


Our lunch spot... Alex pretends to dive into the Potomac River...


Traversing 'The Traverse':


On the Historical Geology field trip to DC on Saturday, we were amused to find a jack-o-lantern that had facial hair resembling mine...



But that's not all! We also saw some geology. While you can get a more complete picture at my "DC Rocks" webpage, I'll post a few new photos of new outcrops here...

Here's a nice slab of granite (very angular) set in metagraywacke matrix (metamorphosed accretionary wedge complex)...


Here's two members of the Georgetown Intrusive Suite, showing the (earlier) gabbro stoping xenoliths into the (later) granite:


I love field trips. I love seeing my students light up at being outside, at getting a handle on the stuff we talk about all semester in class. I think field trips are super duper important.

Labels: dc, field trips, granite, igneous, maryland, metamorphism, nova, piedmont, teaching, xenoliths

Labels: maryland, meetings

What're you doing on Friday? There are two excellent-sounding earth science seminars inside the Beltway: The University of Maryland Geology Department's weekly seminar, and the American Meteorological Society's monthly seminar for policy makers. Both events are free and open to the public. AMS is at 10am, UMD at 11am. You can't do both -- you must choose...

AMS: Friday, September 26, 2008New Time - 10:00 AM - 12:30 PM
Dirksen Senate Office Building, Room G50 Washington, DC

Accelerating Atmospheric CO2 Growth from Economic Activity, Carbon Intensity, and Efficiency of Natural Carbon Sinks

What is the relationship between economic activity and CO2 growth? What is carbon intensity and how does it relate to economic activity? What are the trends in CO2 growth, carbon intensity, and changes in the efficiency of natural reservoirs to store carbon? How does the growth in CO2 compare to the various estimates of CO2 growth contained in the most recent IPCC assessment of climate change? What is permafrost and what is the extent of permafrost thaw in the Arctic? Is permafrost thaw a response to global warming and if so, what is the future likely to hold? Will permafrost thaw result in the release of additional CO2 into the atmosphere from Arctic soils? If so, what is the impact likely to be on global warming? How much carbon is stored in Arctic soils? Assuming that the Arctic continues to warm well above the global average, what is the likely fate of that soil carbon and how might it influence climate in the future?

Public Invited; Buffet Reception Following

Moderator: Dr. Anthony Socci, Senior Science Fellow, American Meteorological Society

Speakers:

• Dr. Josep (Pep) Canadell, Executive Director, Global Carbon Project, Commonwealth Scientific and Industrial Research Organization (CSIRO) Marine and Atmospheric Research, Canberra, Australia
• Dr. Vladimir Romanovsky, Geophysical Institute, University of Alaska, Fairbanks, A
• Dr. Howard E. Epstein, Department of Environmental Sciences, University of Virginia, Charlottesville, VA

Program Summary

How Fast is Atmospheric CO2 Growing and Why, and Does it Suggest Ways to Mitigate Climate Change?

The increase in atmospheric carbon dioxide (CO2) is the single largest human perturbation of the climate system. Its rate of change reflects the balance between human-driven carbon emissions and the dynamics of a number of terrestrial and ocean processes that remove or emit CO2. It is the long term evolution of this balance that will determine to a large extent the speed and magnitude of climate change and the mitigation requirements to stabilize atmospheric CO2 concentrations at any given level. Dr. Canadell will present the most recent trends in global carbon sources and sinks, updated for the first time to the year 2007, with particularly focus on major shifts occurring since 2000. Dr. Canadell’s research indicates that the underlying drivers of changes in atmospheric CO2 growth include: i) increased human-induced carbon emissions, ii) stagnation of the carbon intensity of the global economy, and iii) decreased efficiency of natural carbon sinks.

New Estimates of Carbon Storage in Arctic Soils and Implications in a Changing Environment

The Arctic represents approximately 13% of the total land area of the Earth, and arctic tundra occupies roughly 5 million square kilometers. Arctic tundra soils represent a major storage pool for dead organic carbon, largely due to cold temperatures and saturated soils in many locations that prevent its decomposition. Prior estimates of carbon stored in tundra soils range from 20-29 kg of soil organic carbon (SOC) per square meter. These estimates however, were based on data collected from only the top 20-40 cm of soil, and were sometimes extrapolated to 100 cm. It is our understanding that large quantities of SOC are stored at greater depths, through the annual freezing and thawing motion of the soils (cryoturbation), and potentially frozen in the permafrost.

Recent detailed analysis of Arctic soils by Dr. Epstein and his colleagues found that soil organic carbon values averaged 34.8 kg per square meter, representing an increase of approximately 40% over the prior estimates. Additionally, 38% of the total soil organic carbon was found in the permafrost.

A total of 98.2 gigatonnes (1015 grams) of carbon is estimated to be stored in the soils of the North American Arctic tundra. An area-based estimate for the entire Arctic suggests the presence of approximately 160 gigatonnes of carbon. The annual increase in atmospheric carbon dioxide is roughly 2% of this amount, so small changes in Arctic carbon storage could have substantive impacts on atmospheric CO2. The future of this stored carbon is, however, largely uncertain in the face of a changing Arctic environment. Climate change and resulting increasing temperatures in much of the Arctic could increase the decomposition rates of soil organic carbon (producing atmospheric CO2), and increase permafrost thaw, which would expose more soil organic carbon for decomposition. On the other hand, increasing temperatures could also lead to greater sequestration of atmospheric CO2 by tundra vegetation. Actual changes will be the result of complex interactions between processes that sequester carbon and those that release it.

Past, Present and Future Changes in Permafrost and Implications for a Changing Carbon Budget

Presence of permafrost is one of the major factors that turn northern ecosystems into an efficient natural carbon sink. Moreover, a significant amount of carbon is sequestered in the upper several meters to several tens of meters of permafrost. Because of that, the appearance and disappearance of permafrost within the northern landscapes have a direct impact on the efficiency of northern ecosystems to sequester carbon in soil, both near the ground surface and in deeper soil layers. Recent changes in permafrost may potentially transform the northern ecosystems from an effective carbon sink to a significant source of carbon for the Earth’s atmosphere. Additional emissions of carbon from thawing permafrost may be in the form of CO2 or methane depending upon specific local conditions.

Dr. Romanovsky will present information on changes in terrestrial and subsea permafrost in the past during the last glacial-interglacial cycle and on the most recent trends in permafrost in the Northern Hemisphere. He will further discuss the potential impact of these changes in permafrost (including a short discussion on potential changes in methane gas clathrates) on the global carbon cycle. Dr. Romanovsky’s research suggests that permafrost in North America and Northern Eurasia shows a substantial warming during the last 20 to 30 years. The magnitude of warming varied with location, but was typically from 0.5 to 2°C at 15 meters depth. Thawing of the Little Ice Age permafrost is on-going at many locations. There are some indications that the late-Holocene permafrost started to thaw at some specific undisturbed locations in the European Northeast, in the Northwest and East Siberia, and in Alaska. Future projections of possible changes in permafrost during the current century, based on the application of calibrated permafrost models, will be also presented.

The next seminar is tentatively scheduled for October 10, 2008.
Topic: Ecosystem Health in a Rapidly Changing Climate

Please see the AMS web site for seminar summaries, presentations and future
events: http://www.ametsoc.org/seminar

For more information please contact:
Anthony D. Socci, Ph.D. Tel. (202) 737-9006, ext. 412 socci@ametsoc.org

UMD: 11:00am - 12:00pm at 1121 Computer Science Instructional Center

Internal flow and extrusion of the Greater Himalayan Slab, Mount Everest Massif: a tour of the world's highest rocks
Dr. Rick Law from Virginia Polytechnic Institute and State University

If you are interested in meeting with Dr. Law please sign up online. You also may delete an appointment from this page. Please join the faculty and students for refreshments in the Geology Building foyer at 10:30 am.

Seminar series web page for UMD-College Park Geology.

Labels: climate change, CO2, geology, global warming, maryland, meetings

Yesterday morning, I took a jaunt with a local amateur geologist, Owen P., to go look at some outcrops in streambeds in and adjacent to Silver Spring, Maryland.

Owen wanted me to look at these surfaces, our local unconformity between foliated metamorphic rocks of the Piedmont below, and unconsolidated sediments of the basal Coastal Plain above (cell phone for scale):
The lower rocks are metagraywacke schist of the Sykesville/Laurel Formation (different aspects of the same thing, as far as I am concerned, and not worthy of two different formation names). They were metamorphosed during the Taconian ("Taconic") Orogeny, ~460 million years ago. These rocks were then eroded, and new sediments deposited on top of that eroded surface -- this is an unconformity like the ones I posted about over the past couple of days out in Wyoming and Arizona.

My host thought the layer above the unconformity might be tsunami deposits associated with the Chesapeake Bay bolide impact at 35.5 million years ago. However, that's not what I saw. Instead, the high proportion of angular quartz, and the fact that it was clast-supported rather than matrix supported, suggested to me that the upper layer was a gravel deposit from this very stream. It was good for me to see such a collection of angular clasts atop the unconformity -- on hilltops in DC, I'm used to seeing the Potomac Formation in this position. It's a Cretaceous-aged river deposit, with a real mix of sand, clay, and well-rounded (mainly quartzite) cobbles.

Another look (with cell phone for scale):


After I explained why I didn't buy the tsunamite hypothesis, but encouraged him to keep looking, Owen took me to another cool location, on Northwest Branch (a creek) just outside the Beltway at Burnt Mills Park. Here's a location map:


There, we found an outcrop of migmatitic metagraywacke very reminiscent of the one I visited on Four Mile Run in Arlington, VA, in March of this year. Cutting down, Northwest Branch has exposed a complex of clearly metasedimentary, clearly granitic, and not-so-clearly transitional migmatitic rocks. It's pretty cool, and not only because some of the potholes went all the way through the rock, making wormhole tunnels that a geologist can (and will) crawl through...


I found a couple of cool igneous contacts. Here's a dike of granite cutting through metagraywacke. I like this outcrop because it shows that these things are in fact filled-in cracks, and cracks have a propagating edge, a tip. Most granite dike exposures don't show this fracture edge, but this one does. In spite of the graffiti, it's a good look at that process caught in the act.


And here's a nice example of cross-cutting relationships. Host metagraywacke (notice the pebble-sized clasts of various lithologies in the upper left) is cut by two granite dikes: first a finer-grained, darker-colored one, and then by a coarser-grained, lighter-colored one. Beauty!


Thanks to Owen for showing me these outcrops -- I appreciate the interest and the invitation!

Labels: granite, maryland, metamorphism, migmatite, primary structures, sediment

Picking up where I left off yesterday, in describing Saturday's field trip out to western Maryland:

2:20pm: We exit Interstate 68 and go south on a dirt road for about ten or twelve miles. This road takes us through the Green Ridge State Forest, and I can tell the students are wary of it. I love a good dirt road, and this one even shows outcrops in the road surface -- resistant sedimentary layers tracing across its rutted, potholed surface. The sun comes out, and I roll down the window, relieved that the weather has finally broken.

3:00pm: We arrive at the C&O Canal's Paw Paw Tunnel, in Maryland just north of the Potomac River and the town of Paw Paw, West Virginia. ("Paw paw" is a native tree in the custard apple family with a lovely fruit also called a paw paw. They're delicious, if you can find one the raccoons haven't already claimed.) Paw Paw is the site of the most pronounced entrenched meanders seen along the length of the Potomac River. These exaggerated loops suggest an old age river system, but they are "locked" at the bottom of deep canyons, which suggests a young river system. The usual interpretation is that the Potomac is a rejuvenated river system: it was "old age," equilibrated to base level and meandering actively, but then base level dropped and it incised to a deeper level, maintaining the meandering shape even though the meanders no longer actively squiggle from side to side.

3:10pm: At the upstream end of the tunnel, we discuss the Brallier Shale (Devonian), and note the angle of the bedding here, which is tipped into the Canal's valley: ideal for landslides. When C&O Canal engineers came to the Paw Paw Bends, they faced a tough choice: construct the canal to parallel the river around its multiple entrenched meanders, or carve a tunnel through a mountain made of this stuff. They opted for the tunnel, saving 6.5 miles of Canal length, but the digging of the tunnel took 14 years!



Because the weather is good, we decide to hike over the mountain first and then walk through the tunnel on the return trip. The hike gives us views of some of the meanders' loopy shapes:



We don't see a whole lot else on the hike, but it feels good to stretch the legs.

4:oopm: We reach the Tunnel Hollow, a long linear valley on the downstream side of the tunnel. Signs of the morning's torrential rains are everywhere in the form of increased runoff. For instance, we see a large stream emerging from the base of a talus slope, flowing across the path and into the canal:



Heading up the Tunnel Hollow, we are greeted with the sight of numerous waterfalls arcing down into the valley:





Here, the layers of the Brallier Formation dip into the Tunnel Hollow, again presenting the potential for slip between the layers, and suddenly big slabs of rock dropping down into the valley. We note the "pins" holding these unstable sheets of rock in place:



4:20pm: My favorite thing about the Tunnel Hollow is the world class exposures of slickensides there. During Alleghenian mountain-building, these sheets of shale slid over one another, as a deck of cards will buckle when squeezed. Sliding between the layers ground grooves into the rock face, and also deposited mineral fibers alligned in the direction of sliding.





4:40pm: Lastly, we got to the downstream end of the Paw Paw Tunnel itself, where multiple waterfalls were cascading down onto the towpath. A fine mist fills the air, and catches the beams of sunlight. There's a nice anticline exposed just above the tunnel archway, and usually I have students climb up the stairs (on the left) to check it out up close. However, today a waterfall was landing on the stairs!







Four of us decided to go for it anyhow, just for the thrill of passing through a waterfall. Several (smarter) students who chose to stay down below pulled out their video cameras and recorded parts of our folly. Here's one showing the climb: (Unfortunately it's both silent and taken "sideways" and I'm not video-savvy enough to know how to fix it in either regard.)



Here's another video of the four of us (Nicole, Jan, Dave, and me) up on top:



4:35pm: Time to enter the tunnel. Flashlights come out, and we begin to walk through the Paw Paw Tunnel. It's a remarkable feat of engineering. It's 3/5 of a mile long, and pitch black. We walk along the towpath, where mules once pulled barges up and down the C&O Canal. It's nice and cool in there, like a cave.

5:10pm: We load up in the vans and depart the Paw Paw Tunnel. It takes a full two hours to drive back to Annandale, so we get rolling. We cross West Virginia, and then work our way east across Virginia. Several students nod off, while others discuss geology and travel along the way.

7:12pm: We return to the Annandale campus. Adios, estudiantes! The NSF crowd (Michelle and Nicole) and I retire to the Auld Shebeen in Fairfax for some Boddington's and Gaelic tunes. It's been a long day; we've covered a lot of ground and seen some cool stuff. Time for a pint!

As with yesterday's post, all photos are by Nicole LaDue, NSF. Thanks, Nicole!
Videos are courtesy of Amy Bertsch and Dean Kauffmann.

Labels: field trips, maryland, stratigraphy, structure, teaching, valley and ridge

Saturday morning, 6am: I roll out of bed and check the weather. Storms forecast for Hancock, Maryland, where I'm due to be leading a field trip that day. Hmmm. But based on the radar animation, it looks like they're going to hit hard from 10-11am or so, and then ease off for a bit before hitting hard again later in the day.

6:15am: Making coffee, with Lola the cat underfoot. I check the weather again, and convince myself that the timing of the rain will work for our trip's timetable. I decide to go for it.

7:00am: I call Dale Shelton (of the Maryland Geologic Survey) at home and confirm that it's okay if we go out on the outcrop if it's merely wet, but we can't go out if it's actively raining.

7:15am: I e-mail the students, confirming that the trip is a 'go.'

8:15am: "Bye, Lola!" I leave DC and drive out to Annandale. Once on campus, I gather up a few items (first aid kit, whiteboard, topographic maps), and then go out to the parking lot where students are gathering.

9:00am: We depart campus and head northwest.

9:45am: We leave the Piedmont and cross into the Blue Ridge province.

10:03am: We leave the Blue Ridge province and cross into the Valley and Ridge province (though there are a number of Marylanders who persist in calling it the "Ridge and Valley").

10:15am: The rain hits, hard. Windshield wipers on. Behind the wheel, I grimace. Hope it passes...

10:56am: We pull in to the Sideling Hill Visitor Center. Other cars containing other students are there already. We meet up and head indoors.

Sideling Hill is a massive roadcut in western Maryland. If you've ever seen it, you'd remember it. I won't go into all the geological details here, because (due to the rain) we didn't see them all. But if you're interested, you can read in more detail about Sideling Hill on my website. Long story short: We've got some early Mississippian strata here, derived from the weathering of the Acadian highlands to the east, deposited at the edge of the Kaskaskia epeiric sea. Then they were folded up during Alleghenian mountain-building.

12:00pm: After reviewing some of the salient details inside the Visitors Center where it was warm and dry, we ventured out into the rain and wind. Fortunately, a pedestrian walkway over the highway gave us a decent vantage:





Even from this limited vantage, we are able to observe and interpret some interesting features. For instance, check out the differential weathering of the shale vs. sandstone layers here on the eastern side of the outcrop. We likened this to other examples of differential weathering, like at Monument Valley, Arizona.



We also got a good view of what an oxbow lake looks like when viewed in cross-section. Note how this paleo-channel cuts into the layers beneath it, and is filled with a plug of dark shale, indicating low-energy, low-oxygen conditions.



2:00pm: After giving up on our chances to get out on the first berm of the outcrop, we depart the Sideling Hill Visitor Center, but pull over a short distance down the road to examine the diamictite on the western side of the roadcut. In drizzle, and shouting over the traffic, we discuss the multiple origins of diamictites:



2:10pm: On the road again, headed for our second destination, the Paw Paw Bends...

(More on that tomorrow)

All photos by Nicole LaDue, NSF. Thanks, Nicole!

Labels: field trips, maryland, stratigraphy, structure, valley and ridge

When she sees a geologic map of the eastern U.S., my cat Lola attempts to impress me by lining herself up with the trend of Appalachian structure. While noble in intent, she's not especially accurate. In the photo below, you can tell that she's off by about 20 degrees. Based on this, I conclude that cats have no natural instinct for structural geology. She can't use a Brunton compass, either.

Labels: geology, humor, lola, maryland