Advertisement

You are browsing the archive for 2012 May.

17 May 2012

More percussion marks

Yesterday, I introduced percussion marks to this blog space. Here are some other shots of this distinctive “shatter” structure, but in a vein of hydrothermal (milky) quartz exposed on Bear Island, between the C&O Canal and the Potomac River (about right here, just west of the trail): Sometimes percussion marks are accompanied by radial fracture sets like this one… I interpret these radial fractures (sometimes with small cone-fractures at the …

Read More >>

No Comments/Trackbacks >>


16 May 2012

Contemplating the IARC-JAXA graph

One of the ~350 or so blogs I subscribe to is Arctic Sea Ice by Neven. Today, he put up a post highlighting new daily data from IARC-JAXA, a collaboration between the International Arctic Research Center (IARC) at the University of Alaska-Fairbanks and the Japan Aerospace Exploration Agency (JAXA).  Check it out. Here’s a couple of things I was struck by: The annual variation between summer and winter ice cover …

Read More >>

No Comments/Trackbacks >>


Brecciation & percussion in Antietam Formation

Further upstream from the Skolithos and the snake and the diabase rip-rap… The field review team wandered down onto a creekside outcrop of Antietam Formation. The Antietam is a quartz sandstone, with variable levels of deformation, depending on where you look. In some places, it has been gently strained with the little Skolithos tubes taking on elliptical cross sections, or the individual sand grains undergoing a moderate amount of pressure …

Read More >>

No Comments/Trackbacks >>


15 May 2012

Diabase dike in diabase

Seen in rip-rap on the side of Naked Creek, a week ago yesterday: This boulder is exotic to its current location. It is typical of medium- and coarser-grained diabase from the Culpeper Basin, a Triassic rift valley east of the Blue Ridge. The main minerals are plagioclase (light-colored) and pyroxene (dark colored).

Read More >>

No Comments/Trackbacks >>


14 May 2012

Hiking Cory Pass

Callan and his wife hike Cory Pass in Banff National Park, Canada, and encounter some geology, some solitude, and a spectacular landscape.

Read More >>

8 Comments/Trackbacks >>


13 May 2012

Virginia’s seven Shenandoahs

The word “Shenandoah” is thought to mean “daughter of the stars,” a lovely turn of phrase even if there’s no evidence for it. The name has been applied to a variety of features in the Commonwealth of Virginia. One is the Shenandoah River, and the valley in which it flows. Here’s a look at the North Fork of the Shenandoah, northwest of Massanutten Mountain: Then there is the political entity …

Read More >>

8 Comments/Trackbacks >>


12 May 2012

Ernst Cloos’ notes on the western Blue Ridge

Handwritten notes by Ernst Cloos (legendary structural geologist from Johns Hopkins University) on the area I visited last Monday on a field review of the new geologic map of the Elkton East quadrangle by Chelsea Jenkins, Chuck Bailey, Mary Cox and Grace Dawson.

Read More >>

1 Comment/Trackback >>


11 May 2012

Friday fold: boxiness in Oman

Max Arndt contributed this week’s Friday fold: (click on the image to get to a larger sized version on Max’s Flickr page) That’s the Warah Formation exposed on the Batain Coast of northeastern Oman. This is the thrust front of a thin-skinned fold and thrust belt. I think it’s just lovely! Max has a ton of other great structure photos on Flickr, he tweets, and he has a blog. Check …

Read More >>

4 Comments/Trackbacks >>


10 May 2012

Veiled geology at Naked Creek

As I mentioned, Monday had me out in the field, looking at the western Blue Ridge and eastern Valley & Ridge provinces in Virginia. This was a field review for the new geologic map of the Elkton East quadrangle by Chelsea Jenkins, Chuck Bailey, Mary Cox, and Grace Dawson. Immediately after lunch, we visited an outcrop in the middle of Naked Creek. You’ll be happy to hear that we all …

Read More >>

2 Comments/Trackbacks >>


9 May 2012

Coiled snake

Saw this fellow on Monday, coiled up next to an outcrop of Antietam Formation in Naked Creek, northwest of Elkton: It had flattened its head to make it very spade-shaped. The right eye was cloudy – perhaps snake glaucoma? Or maybe it was just getting ready to shed its skin?

Read More >>

1 Comment/Trackback >>