These days, I'm engaged in the lovely process of rediscovering the geologic record of Shenandoah National Park. This 'rediscovery' was prompted by the recent Virginia Geological Field Conference based at Big Meadows. While I wasn't able to attend in person (I was in Yosemite that weekend!), colleagues like Pete Berquist and John Weidner were there, as well as three of my Rockies students from last summer. They've all shared their perspectives on the conference with me, and John loaned me a copy of the field guide to the conference. This guide, authored by other colleagues like Chuck Bailey of William & Mary and Scott Southworth and Bill Burton of the USGS in Reston, makes for great reading. I'd link to it so you can read it too, but it's not online.

The guide led me to the revelation that there is a new geologic map of the park and the surrounding area that was published earlier this year by the survey. This map* is authored by Chuck, Scott, and Bill, along with their peers at the survey and other institutions. Why wasn't I informed? (Just kidding) It's a beautiful work of art and science. I'm having the NOVA duplicating services team print me out a copy this week.

The new insights offered by the map (and the VGFC field guide) include the fact that the oldest rocks in Shenandoah National Park are diverse and complicated. It used to be that geologists considered these rocks to be a granite gneiss called "the Pedlar Formation," which was intruded in places by younger granitoid plutons. Modern work in the park has revealed that it's more complicated than that. There are a dozen or more separate rock units comprising what the pros are now calling "the basement complex." These rocks are distinguishable based on texture, mineralogy, and age. (These newer, more precise ages are one of the key advances of recent work by John Aleinikoff of the USGS: the granitoids and their metamorphic successors have crystallization ages ranging from 1,183 Ma (+/-11 Ma) to 1,028 Ma (+/- 9 Ma).

I've updated my Shenandoah web page to reflect the new preferred terminology plus these new dates. More updates to come -- I've got many new tidbits of inspiration from reading the 100+ page write-up that accompanies the new map. The web page, like all of my web pages, is a work in progress. Nothing makes that clearer to me than a steaming helping of fresh science!

When I was out in the park last weekend, I found this new outcrop of the basement complex, which shows some of this intriguing diversity:


Annotated version:


The outcrop is on the hike over Bearfence Mountain, described (and mapped) in the new VGFC field guide. It's a granite gneiss, partially altered to unakite (the plagioclase and pyroxene in the graniotid reacted in the presence of water to generate epidote. A pronounced foliation is cut by no less than 3 separate sets of fractures, two of which are filled in with fibrous quartz, and another by something dark. The granitoid formed during the Mesoproterozoic Grenvillian Orogeny, and was deformed later in that same episode of mountain building. The fractures formed at some point after that: just when, I can't say. Vein sets 1 and 2 are infilled with apparently identical compositions, which would be consistent with them being contemporaries. Vein set 3 has something else lining its fractures. At first I thought it was just mildew, but Elli suggested some mineralogical possibilities. Vein set 3 does not show the same amount of dilation as the other two sets. Cross-cutting relationships show vein sets 1 and 2 cross-cutting vein set 3, which suggests I was too hasty in labelling them in my photo. "3" is the oldest; "1" and "2," despite their names, are younger. Maybe they're related to Neoproterozoic breakup of Rodinia, or Alleghanian mountain-building, or uplift? So many mysteries...

More to come on this topic, surely, as I get re-introduced to my local national park.
__________________________________________
* Southworth, Scott, Aleinikoff, J.N., Bailey, C.M., Burton, W.C., Crider, E.A., Hackley, P.C., Smoot, J.P., and Tollo, R.P., 2009, Geologic map of the Shenandoah National Park region Virginia: U.S. Geological Survey Open-File Report 2009–1153, 96 p., 1 plate, scale 1:100,000.

Labels: blue ridge, conferences, granite, igneous, metamorphism, national parks, proterozoic, shenandoah, structure

Yesterday, we had a joint NOVA-University of Pittsburgh at Johnstown field trip to Shenandoah National Park. It was a great day of examining new rock outcrops and old treasured favorites. UPJ is responsible for one of the only departmental student-centered geology blogs that I am aware of, Mountain Cat Geology. A couple of weeks ago, igneous and metamorphic petrology professor Elli Goecke contacted me about local rock options, and I invited her crew to team up with the NOVA GOL 135 field course to check out Shenandoah. [Geoblogger small world: Elli studyed under Kim Hannula in Vermont!]

Together, the sixteen of us checked out evidence for the two Wilson Cycles recorded in the rocks of Virginia's Blue Ridge province, and had a pleasant time hiking around and enjoying unparalleled fine weather. Unfortunately, November means the days are short, and we had the sun set on us before we got to the final stop (at Signal Knob Overlook). We took a group photo there: see if you can spot who's a NOVA person and who's a UPJ person...


The annotated version, to show who's who:


Thanks for a great day in the field, everyone!

Labels: blogs, blue ridge, field trips, national parks, nova, pennsylvania, shenandoah, virginia

On his popular science blog Pharyngula, PZ Meyers has a regular series of posts called "I get email," (example) wherein he discusses e-mails he gets. I get e-mail, too (as I'm sure, so do other science bloggers of all stripes). Here's one I got the other day from Brian, a recent graduate from one of my many almae matres (oh yeah, I took Latin). I post it here in case anyone else is wondering the same thing:

I have a simple question for you... I was out at the Pimmit Run-Potomac
confluence collecting rock samples with that awesome chlorite/pyrite/garnet
assemblage and I encountered a couple pieces of unakite float. I'm just
wondering about its provenance. Your blogs seem to indicate that unakite is
typically found in situ farther west in the Shenandoah which would be a pretty
long way to travel (and pretty cool too!) although I believe there is Antietam
around Mather Gorge so I guess it's not impossible; unless it was
anthropogenically relocated which would be much less cool. A little insight
would be greatly appreciated so I can wow my friends when describing what is now the piece de resistance in my fish tank.

So I wrote back with this (links are additions, since I'm blogging it):

Yes, you could certainly have found some Blue Ridge unakite as float in the Potomac Gorge. I've seen many other Blue Ridge Formations as float on the bedrock terraces of the Potomac: Catoctin Formation, Harpers, Weverton, Antietam (like you mentioned), and something that looks a hell of a lot like the Old Rag Granite. I've found well-rounded bituminous coal cobbles, too! I've found unakite further out, in the Coastal Plain, as well as blue quartz (which is unique to the Blue Ridge). So I think it's quite likely you could have found some unakite.

Anyone else have any questions? Like PZ, I could make this a regular series. The more local and the more geo-centric, the better.

Labels: blue ridge, coastal plain, i-get-mail, metamorphism, piedmont, rivers, sediment

Here's two pictures of quartz I took with my new toy, a Nikon camera/microscope/digital-picture-stitcher-togetherer. More to come, clearly. Click on each image to make it bigger.

Conchoidal fractures at the tip of a quartz crystal:

Blue quartz, a distinctive mineral that's found in Virginia's Blue Ridge province:

The blue color is apparently from inclusions of ilmenite and rutile...

Purty, huh? No sense of scale, though. Tough!

Labels: blue ridge, minerals, weathering

This is another photo from Saturday's hike. Unakite is rumored to be the 'state rock' of Virginia, though it's not in the state code. Regardless of its official status, it sure is a distinctive sight: An epidotized granitoid, unakite is identified by the distinctive pairing of pistachio-green epidote and pink potassium feldspar. There's some grey/purple quartz there too. In the mid-Atlantic states, it's only found in the Blue Ridge geologic province. Here, on the trail below Dark Hollow Falls in Shenandoah National Park, my friends and I encountered this lovely boulder of unakite bearing a vein of milky quartz.

The original granitoid was Grenvillian in age, about 1.1 billion years old. Presumably the metamorphism took place during Alleghanian mountain-building, between 300-250 million years ago. Unakite has been quarried in Virginia for use as a building stone, and can be seen as tiles on the first terrace of the steps leading from the National Mall up to the southern doors of the Smithsonian's National Museum of Natural History in Washington, DC.

Labels: blue ridge, dc, igneous, metamorphism, minerals, museums, smithsonian, virginia

A funny coincidence transpired a couple of weeks ago. I posted about "Amygdules!" and so did Andrew. We were both so excited by these cool primary igneous structures that we added an exclamation point to our post titles. Over the weekend, I found some more. These are in Dark Hollow, in Shenandoah National Park, above the falls. Pretty sweet, eh?



I hereby give them two exclamation points. Let's see if anyone else can come up with two-exclamation-point-worthy examples of amygdules...

Labels: basalt, blogs, blue ridge, falls, igneous, primary structures, proterozoic, shenandoah

Our third Rockies training hike took place Saturday. Six of us hiked White Oak Canyon, in Shenandoah National Park. It was about an eight mile loop, with six big waterfalls on it. There were a lot of plungepools where other hikers were swimming.

There wasn't an astounding amount of geology on the trail: it was mostly Catoctin Formation, with a few outcrops of underlying Grenvillian granitoids. A few nice amygdules; no columns.

The waterfalls sure were purty, though. Here's Jason at the uppermost falls (86 feet tall):


Me departing from one of the lower falls:

Photo by Chris McMahon

I got home tired and sore from this hike -- it was a good time, but I slept well last night as a result!

Labels: blue ridge, falls, geomorphology, national parks, proterozoic, shenandoah, virginia

Amygdules (mineral deposits filling extrusive vesicles) in the Neoproterozoic-aged Catoctin Formation meta-basalt, Shenandoah National Park, Virginia.

Labels: basalt, blue ridge, igneous, primary structures, proterozoic

A little follow-up to this morning's post of pictures from the Garth Run high-strain zone. A short distance away is the Quaker Run high-strain zone, which I visited in spring of 2003 with my geology graduate advisor, Dazhi Jiang, and two other structure students from the University of Maryland, College Park. Here's a beautiful sample of the mylonite I collected then:

Labels: appalachians, blue ridge, metamorphism, structure

I took my Structural Geology students on a three-day field trip this weekend to examine outcrops in the Blue Ridge and Valley & Ridge geologic provinces. Here's a few photos of the team at our first (of four) field study areas, the Garth Run high-strain zone:

Examining the structure and taking strikes and dips:






Fabric elements cross-cutting one another:


Mylonitic fabric:


Foliation wrapping around a feldspar porphyroclast:


This is kind of interesting: a big pancake (oblate ellipsoid) of blue quartz, with a potassium feldspar in the middle:


And if you zoom in close, you can see that the feldspar porphyroclast is broken in the middle (along the plane of cleavage) with non-blue quartz filling in the gaps:


I think this blue quartz likely formed in the pressure shadow of the resistant feldspar porphyroclast during flattening strain, and eventually that feldspar began to brittlely deform, extending in the direction of minimum principal stress.

Quite a bit of variation across strike:


The students found some nice euhedral garnets too, though this was a block of float from upstream, and not intimately associated with the high-strain zone itself:


More tomorrow, from Field Study Area #2...

Labels: blue ridge, field trips, igneous, metamorphism, structure, teaching, valley and ridge

Almost a week after the field trip to Old Rag Mountain, and the Facebook-hosted pictures keep trickling in. Here's some shots by NOVA student Eileen Lodovichetti, and an ensuing discussion of feeder dikes and supercontinent breakup.

Here's a shot of the upper reaches of Old Rag, showing the characteristic spheroidal weathering of the Old Rag Granite and the relative lack of trees on top:

photo by Eileen Lodovichetti

...And here's a shot that Eileen took which shows the interior of one of the weathered-out feeder dikes we had to hike through on our way to the summit. You can actually see the classic geoprofessorial arm-waving caught in blurry motion!

photo by Eileen Lodovichetti

This is one of the coolest things about hiking Old Rag: after scrambling up on top of spheroidally-weathered granite domes, you drop into these tabular "hallways." The astute observer will note that the floor is made of a fine-grained, dark-green-colored rock, quite distinct from the light-colored, coarse-grained granite that makes up most of the mountain. These are dikes of metamorphosed basalt that intruded the granite during the breakup of the supercontinent Rodinia in the Neoproterozoic era of geologic time.

Here's one of my former Field Studies in Geology students, Mike Nelson, pointing out a similar dike along Skyline Drive, in the main part of the park:


Basically, the story goes like this: Around 1.2 to 1.0 Ga, continental fragments amalgamated into a supercontinent called Rodinia. In Virginia, this is recorded in the rocks of the Blue Ridge province, where the basement consists of granitoids (granites and related rocks) and metamorphosed granitoids (gneisses, mylonites). Among the youngest of these is the Old Rag Granite, which intruded the Pedlar Formation granite gness around 1.0 Ga.

Later, Rodinia broke apart, resulting in an extensional tectonic regime and mafic volcanism. Fractures opened up in the Old Rag Granite and funneled mafic magma towards the surface. Massive eruptions of basalt blanketed the landscape. The resulting layers of basaltic lava are known as the Catoctin Formation. At Old Rag Mountain, we can see some of the plumbing that led to these flood basalt eruptions: these are feeder dikes, because they "fed" the eruption above them.

Because the dikes (which were metamorphosed to greenstone during ~300 Ma Appalachian mountain-building) weather more rapidly than the Old Rag Granite, they are typically recessed into the landscape. That's what makes the "hallways" in the photograph above. Here's two more images, showing these weathered-out feeder dikes:



Check out how there's moderately-developed columnar jointing extending across the dike. These columns form perpendicular to the cooling front, and the dikes would have lost their heat out the sides. In horizontal lava flows, the heat is lost from the top and bottom surfaces, so you get vertical columns. Here, a vertical dike produces horizontally-oriented columns. Hikers appreciate these "steps" as they squeeze through the dikes on their way up the mountain.

Here's a map of part of Shenandoah National Park:


Please ignore the "hover" instructions at the lower right. I've reproduced the "hoverable" image below. Key: the orange is the Pedlar Formation. The pink is the Old Rag Granite, and the green is the Catoctin Formation. Feeder dikes of the Catoctin are shown as green lines.

Now, let's take away the map, and just preserve the orientation of the feeder dikes. This will tell us the overall tectonic stretching direction:
Various plate reconstructions show either Amazonia or the Congo craton offboard of Virginia at the time Rodinia broke apart and the Iapetus Ocean began seafloor spreading. I've illustrated it here as the Congo, but that might be wrong.

So: the hike up Old Rag is great exercise, and offers scenic views, but for those willing to consider the rocks and how they got there, it's an insightful view into the tectonic past.

Lastly, here's a lovely, well-developed weathering rind on the Catoctin meta-basalt (greenstone). When the dark green rock adjusts to the conditions at the Earth's surface, it breaks down, resulting in the tan/"buff" color on the outside. You're watching the rock "rot" from the outside surface, working its way inward:


More on the geology of Shenandoah National Park can be seen at this page on my website.

Labels: appalachians, basalt, blue ridge, field trips, metamorphism, mountains, national parks, nova, plate tectonics, shenandoah, structure, weathering

Last weekend, I took a group of students, mostly from NOVA but also 3 from GMU, up to hike Old Rag Mountain in Shenandoah National Park.

Here's a Google Map showing the terrain (and trails, which is a cool new addition to the already cool Google Maps):


The crew discusses debris flow deposits in the forest on the way up the mountain:

photograph by Charlie Corrick

The first spot where we get a nice view out over the valleys below:

photograph by Charlie Corrick

Spheroidal weathering in Catoctin Formation greenstone:

photograph by Jared Fortner

Spheroidal weathering in granite (the Old Rag Granite, 1.0 Ga):

photograph by Charlie Corrick


photograph by Charlie Corrick

Student Jared atop a spheroidally-weathered boulder of the Old Rag Granite:

photograph by me

Grain-size differences in the Old Rag Granite (balanced atop my leg):

photograph by me

Non-foliated Old Rag Granite (showing lovely "blue quartz"):

photograph by me

And the foliated version of the Old Rag Granite:

photograph by me

Labels: appalachians, basalt, blue ridge, field trips, geology, granite, igneous, mountains, national parks, nova, structure, weathering

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

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

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

At the DGMR Blue Ridge / Valley & Ridge Symposium the other week, we had a productive hour-long brainstorming session about unresolved issues in the geology of those two physiographic provinces.

I only attended the Blue Ridge session, and with the blessing of the conference organizers, I'd like to share the results of our ruminations here:

Unresolved issues in Blue Ridge Geology

General Outcomes:
Participants would like to see this as a start to a new state geologic map for 2015.
Participants would like have follow-up workshops to discuss these issues in detail.
Participants would like to develop research needs proposals on these key topics.

Specific Issues:
1. Ramp separating the Cambro-Ordovician carbonates from the rock of the Blue Ridge
a. What is its position?
b. Is it "thick" skinned?
c. Can field work (alone) resolve this?
d. What is its age?
How might this question be resolved?
A. Detailed geologic mapping at 1:24,000 scale across the Blue Ridge / Valley and Ridge transition
B. Applying geophysical techniques such as
a. Seismic reflection
b. Gravity studies
c. Reprocessing old data and reassessing old interpretations
C. LIDAR

2. Working out the problems with the Blue Ridge nomenclature and unit and fault correlations
a. Issues with variability in terminology and correlations across Virginia and between Virginia and North Carolina.
b. Map distribution of faults along the Blue Ridge - need to correlate their timing and extent
How might this question be resolved?
A. Detailed geologic mapping at 1:24,000 scale along the Blue Ridge (N/S) and across the Blue Ridge (E/W).
B. Models for the Blue Ridge need to be presented, discussed and synthesized.
C. Developing a basement "tool kit" for Late Proterozoic rocks: Since we can't afford to date every rock, there is a need for key characteristics for each unit to be agreed upon and applied in the field.
D. Expunge archaic terms and agree upon an appropriate vocabulary.
E. Regular focus group meetings and field meetings are necessary to resolve these issues.

3. When did the Blue Ridge develop its topographic relief?
a. Timing?
b. Is it in a steady state?
c. What is the history of the various erosional surfaces throughout the BR's evolution?
d. How does this correlate with the other physiographic provinces?
How might this question be resolved?
A. Detailed geologic mapping at 1:24,000.
B. Utilize low temperature chronometers such as U/Th/He at a sufficiently detailed spatial scale.

4. Role of the Mesozoic system in the Blue Ridge story and geometry.
How might this question be resolved?
A. Detailed geologic mapping at 1:24,000.
B. Need more geophysical studies.
C. Examine the effects/association of these fractures with water
D. Examine the relationship between features and mineral resource deposits
E. More detailed fracture studies are needed
F. Compare and contrast the Mesozoic rifting with previous rifting cycles
G. A seismic risk assessment needs to be done.

5. Mylonites in the Blue Ridge
a. Triclinic deformation
b. Palinspastic restoration of the Blue Ridge in 3 dimensions.
c. Oblique convergence in Thornton Gap area.

6. Is there an unconformity between the Catoctin and the overlying sedimentary units?

7. New mica ages and their implications for deformation timing
a. Is this related to thrusting sequence?
b. Ages in the Swift Run and Weverton ages were likely the maximum temperature. Deeper rocks likely represent cooling ages.

8. Issue with the cover sequence west of the Blue Ridge - just where is the PreCambrian / Cambrian boundary?
a. Middle of the Chilhowee group?
b. Is all of the Chilhowee group Cambrian in age?
c. Is it in the Lynchburg formation?

9. Are there any Ediacaran fauna in any of the Neoproterozoic sediments?

10. There is a need to reconstruct paleoenvironments in the Blue Ridge
i.e. Mt. Rogers' glacial deposists, etc.

11. Paragneiss story
a. What is the time/temperature path these rocks took?
____________________________________________________

Again, I'd like to thank Amy, Matt, Laurie, and the rest of the dedicated staff of the Division of Geology and Mineral Resources for organizing the symposium and following up with this break-out session digest. Everyone I know who was there felt it was really useful. Facilitating discussions like these between geologic researchers is a key function of a robust state geology agency, and it chagrins me to think there will be less of this in future years due to the recent budget cuts.

What do you think of this list? Are these the most important issues in Blue Ridge geology? What would you add or refine?

Labels: blue ridge, conferences, geology, virginia

I spent this past Friday (12/12) at a symposium put on by the Virginia Division of Geology and Mineral Resources, in Charlottesville, Virginia. This excellent branch of our state government just had their budget disproportionately slashed, but they aren't letting it bring them down. In fact, they're breaking new ground in their unparalleled service to the geological public. In honor of the groundbreaking Virginia geologist Tom Gathright (who was in attendance), they organized a day of scholarship and conversation about recent advances in the geology of the Blue Ridge and Valley & Ridge physiographic provinces.

Rick Diecchio (of George Mason University) and I drove down together, getting up at the unholy hour of 5am in order to get there on time. Once there, we trundled past their excellent outdoor rock garden (about which I will post tomorrow), and inside to join the gaggle of more than a hundred geologists from the USGS, Virginia universities and community colleges, transportation agencies, environmental agencies, and the DGMR itself.

The morning session consisted of a series of talks about the Blue Ridge. We heard from Bob Millici (USGS), Scott Southworth (USGS), Chuck Bailey (W&M), Mark Carter (DGMR), Bill Henika (Virginia Tech), and Karen Rice (USGS). I won't post any of the juicy data details we heard, for fear of spilling any unpublished beans, but there was some cool stuff we learned about. There was also a poster session in the well-appointed library. Pete Berquist (Thomas Nelson Community College) and I had lunch out in the rock garden, where I chatted with three undergrads from our alma mater.

The afternoon session was given over the the Valley & Ridge province. We heard from Scott Eaton (JMU), Steve Whitmeyer (JMU), Dave Weary (USGS), Randy Orndorff (USGS), Joel Maynard (Virginia Department of Environmental Quality), and Wil Orndorff (Virginia Department of Conservation & Recreation, Division of Natural Heritage).

My favorite part of the day, though was a break-out session to discuss unresolved issues. There were three break-out groups: one for water issues, one for the Valley & Ridge, and one for the Blue Ridge. I went to the Blue Ridge one, and really enjoyed this unique setting. I mean, here I am in a room with a bunch of people who spend the majority of their professional time trying to understand how the Blue Ridge got put together, and we're just brainstorming together, thinking about big unknowns, big gaps in our understanding. The DGMR staff is compiling these results, and once they're distributed out to the participants, I'll post them here on NOVA Geoblog. We've been asked to share the results. Since there were two geobloggers in the room (me and Chuck), we reckoned that's a quick way to disseminate some of our ideas.

I'd like to thank the DGMR for putting on such a great meeting, in particular during such lean and uncertain times. The day was positive, affirming, and valuable on many levels. Readers, remember that you (yes, you) can still write to the governor and other state officials to protest the crippling 75% reduction in the DGMR staff.

Labels: blue ridge, conferences, geologists, meetings, valley and ridge, virginia

The Virginia Community College System (VCCS) organizes conferences occasionally where faculty in different disciplines can get together. This weekend was the "peer conference" for the natural and physical sciences. It was held at the lovely mountain resort called Wintergreen, in central Virginia's Blue Ridge Mountains.

Here's a map of the area:

That's the Shenandoah Valley on the left (part of the Valley & Ridge province), the Blue Ridge in the middle (running from NE to SW), and the Piedmont province on the far right. Wintergreen is a bit SW of Charlottesville.

The conference was fruitful and interesting. I enjoyed getting to meet a bunch of the other VCCS geology faculty and discussing what we want to do in the future in terms of supporting one another and professional development. I gave a talk about new technologies in geology instruction, which included information about the geoblogosphere and other sundry web resources I use. My colleague Erik Burtis at NOVA-Woodbridge led us on a cool "field trip" to Glacial Lake Missoula, via Google Earth.

I spent a lot of time talking with Pete Berquist, from Thomas Nelson Community College, discussing next summer's Regional Field Geology of the Northern Rocky Mountains course. We laid out a series of goals for the students, and created a tentative itinerary. Pete and I took a great hike at the end of the first day, poking around in the rocks and watching the sun set over those gorgeous mountains. Friday evening, there was a cool astronomy session, where Ed Murphy from UVA showed us the Ring Nebula, the Andromeda Galaxy, and assorted other stuff in outer space. He had a great laser pointer that extended a green laser line up about 80 feet into the sky... Very useful for pointing things out. Low light levels in the forested mountains meant excellent stargazing. Saturday morning, Bill Warren of Lord Fairfax Community College gave a good talk about the global energy crisis, and potential solutions. I picked up a few good resources there that I'll use next semester in teaching Environmental Geology. And then when the conference concluded, there was a geology "hike" out to look over the landscape. By driving us to a couple of different overlooks, Doug Coleman of the Wintergreen Nature Foundation showed us spots where we were able to look east into the Piedmont, and west into the Valley & Ridge. Pretty cool, though we didn't look too closely at the actual rocks exposed there. Fortunately, I have an inclination to do that on my own... as you'll see below:

Catoctin Formation greenstone (meta-basalt), showing chlorite-rich portions (left) and epidote-rich portions (right). Quarter for scale.


More Catoctin, the volcanic breccia layer. Lots o' epidote. Quarter for scale.


Is this a quartz vein or a granite dike?
At first glance, it appears to be your standard hydrothermal quartz vein full of milky quartz, but then you'll notice that it's not just quartz. There are also two crystals of orthoclase feldspar in there. (The dark shapes are just empty holes & shadow, not mafic minerals.) I pointed this phenomenon out before, but I'll state it again: I think that hydrothermal quartz veins and granite dikes are not separate phenomena, but points along a spectrum of composition. Quarter for scale.

Looking southeast towards the Piedmont:


Looking northwest towards the Valley & Ridge:

Labels: appalachians, blue ridge, conferences, igneous, metamorphism, piedmont, valley and ridge

On Saturday, I took a group of NOVA summer school students to Shenandoah National Park to look at some rocks. We had great weather, and saw evidence of Grenvillian mountain building, the breakup of Rodinia, and the transgression of the Sauk Sea. A real crowd-pleaser was an outcrop of what was once columnar basalt (the Catoctin Formation). I say "was once" because the basalt has been metamorphosed to greenstone, and the columns have been squashed into more lathe-like shapes.

Here's a few photos of the columns:

All four photos by Nicole LaDue (NSF). Thanks Nicole!

Labels: blue ridge, field trips, primary structures, shenandoah, teaching

While toodling along the web on some other business this week, I stumbled across this publication by the Virginia Department of Mines, Minerals, and Energy.

I had no idea that there were any diamond finds in Virginia. But apparently there are, scattered across three different physiographic provinces!

On Thursday's excursion, Chris and I tried to find the "Front Royal Peridotite," one of seven locations mentioned in the DMME publication. It's a single dike which crosses State Road 626 southeast of Waterlick, Virginia. But to no avail! There were no outcrops visible on either side of the road, and there was a dense little cluster of houses bearing manicured lawns. Bummer. That would have been cool.

I'll try and visit a couple other localities mentioned in the report over the next year or so, and hopefully I'll find some of these igneous source rocks, though I don't hold out much hope of actual diamonds.

Labels: blue ridge, diamonds, minerals, piedmont, valley and ridge, virginia

This weekend, I took a backpacking trip in Shenandoah National Park. Thought I would share a few photos today: scenery first, geology second...

Here's the view looking east from Skyline Drive:


The temperature difference due to elevation was striking. It was still early spring up on the top of the mountains, on Skyline Drive:


...But down below, it was green and lush (and sodden with pollen!):


I camped out for two nights near Corbin Cabin, and did a day-hike around Thorofare Mountain on Saturday, visiting this waterfall at lunchtime:


The geology of Shenandoah National Park is interesting: it records the assembly of the early supercontinent Rodinia at about a billion years ago, and then the breakup of Rodinia about 600 million years ago. The first event recorded is the generation of granite gneisses and granites due to the Grenville Orogeny. The oldest unit in the park is the 1.1 Ga Pedlar Formation, a granite gneiss. There's a slightly younger granite which intrudes it called the Old Rag Granite (~1.0 Ga), but I didn't see any outcrops (or float blocks) of it, so I'll not mention it further. There's a thin, patchy sedimentary cover called the Swift Run Formation deposited directly atop the granite gneiss and granite, providing a nonconformity surface. Atop that is a series of volumnious tholeiitic basalt flows: these mafic extrusions record the breakup of Rodinia and the opening of a new ocean basin: the Iapetus. In many places in the park, you can see "feeder dikes" of the Catoctin cutting through the older plutonic and metaplutonic rocks (see image below). There are also some sedimentary rocks layered atop the Catoctin (the Chilhowee Group), recording the transgression of the Sauk Sea on the North American platform. But I didn't encounter any good outcrops (or float blocks) of them on this trip, so I'll stick to the tectonic story: the Pedlar Formation shows us Rodinia getting put together, and the Catoctin Formation shows us Rodinia breaking apart. Later metamorphism due to Appalachian mountain-building resulted in changes in both of these rocks (development of "blue quartz" in the Pedlar, and the Catoctin metamorphosed to greenstone).

Here's a massive dike (possibly a "feeder dike" feeding surface lava flows) of the Catoctin basalt cutting through the Pedlar Formation granite gneiss, just north of the Marys Rock Tunnel. Note the columnar jointing extending perpendicular to the walls of the dike:


Having covered all that, I now propose to spend the rest of this blog post showing you the variety of cobbles and boulders in my campsite. I camped at the little wedge of land above the confluence of two streams. One stream's catchment basin was Catoctin, and the other drained outcrops of Pedlar. As a result, the "float" in my camp was all either Pedlar Formation or Catoctin Formation. I'll just run through them one after another so you get a sense of the range of variety in each formation.

You'll notice that the Pedlar is sometimes coarse, sometimes fine, sometimes well foliated, sometimes not so much. You'll also notice that the Catoctin varies a lot in terms of its extrusive texture: sometimes aphanitic (fine-grained), sometimes amygdular (formerly vesicular), sometimes it even runs to volcanic breccia. All of these original lithologies have been metamorphosed to various degrees in the Catoctin, which here can be seen by comparing the amount of green in the rock. This green comes from two metamorphic minerals: chlorite and epidote. Enjoy!

Pedlar Formation:



















Catoctin Formation:

Labels: appalachians, basalt, blue ridge, granite, iapetus, metamorphism, national parks, primary structures, proterozoic, shenandoah, virginia

Last week on one of the many field excursions, I found a nice cobble of amygdular basalt. Amygdules are vesicles (bubbles in degassing lava that didn't get the chance to pop before the lava solidified into igneous rock) that have been filled in with mineral deposits. In the mid-Atlantic, most amygdules are found in the Neoproterozoic lava flows of the Catoctin Formation, from which my cobble was presumably derived. The amygdules are typically filled in with zeolites, quartz, and jasper. This one doesn't show any jasper, but the basalt still appears to be basalt, too -- whereas the Catoctin typically is metamorphosed to greenstone / greenschist. I've noticed an association between jaspery amygdules and epidote formation in the metaingeous rock.

As with Skolithos-bearing Antietam Formation quartzite cobbles, clasts of the Catoctin deposited in the river gravels atop the Piedmont/Coastal Plain unconformity indicate a Blue Ridge provenance for the cobbles, and therefore a eastward-flowing river to deposit them 100 million years ago.

I took the cobble back to the lab and sliced it open on the rock saw. The brown circle in the background is a penny for scale.

Here's what the sawn surfaces look like after I sanded them down a bit and then scanned them:

Right purty, ain't it?

Labels: basalt, blue ridge, coastal plain, primary structures, sediment, virginia

Walking around the mid-Atlantic Piedmont (my home territory), we find a lot of these fellows lying around. They are cobbles of the Antietam Formation (a Cambrian quartzite from the Blue Ridge) which were weathered out and transported eastwards (~60 miles or so, as you can probably deduce from their rounding). They were then deposited as part of the Potomac Group (Cretaceous river gravels draped over the metamorphic rocks of the Piedmont; preserved today on Piedmont hilltops and as the basal layer of the Coastal Plain). The cobbles display the vertical trace fossil "Skolithos" (sometimes spelled "Skolithus"), usually interpreted as a worm burrow. Each burrow is 2-3 mm in diameter. Here I've got a few photos: a cross-sectional view, a "plan" view, and a shot of one of the boulders in a stream in Arlington, VA.

Labels: blue ridge, coastal plain, fossils, piedmont, sediment