Friday fold: Cretaceous sandstone
Happy Friday, everyone!
folds
Tipping your tension gash
Tension gashes are small veins that open up when rocks get stretched. Often, they are arrayed en echelon with respect to other tension gashes, all oriented in the same direction. Here is a sample of tension gashes I found this summer in rip-rap (i.e., not in situ) at some building site in New England. (I … Read more
Rocks of Glacier National Park
This is the second of my Rockies course student projects that I wanted to share here on the blog: it is a guest post by Filip Goc. Enjoy! -CB —————————————————————————– The Rocks around Glacier National Park, Montana: Introduction to the formations The geology around Glacier National Park is great for beginners because the area is … Read more
Friday fold: Samaria Gorge, Crete
Photo by Lily Edmon.
How to prep your pocket fold
“Pocket folds,” as my Rockies co-instructor Pete Berquist has defined them, are rock samples exhibiting folds that are small enough to stick in your pocket (and take back to your lab). Here’s a pocket fold that I found last week in the White Mountains of New Hampshire: I brought it home, and today I unpacked … Read more
Harpers Foldry
Cleaning out the backlog of photos I haven’t popped up here yet… Here’s three shots from last weekend, of folds (some kinky) which deform Harpers Formation foliation, just south of Harpers Ferry, West Virginia: The Harpers is a Cambrian-aged lagoonal mudrock, dated via Olenellus trilobites in Pennsylvania. It is part of a transgressive sequence that … Read more
New "secondary structures" display at NOVA
…. And on the other side, we have secondary (tectonic) structures, focused on folds and faults:
Crenulation lineation
Hiking last Sunday in Rock Creek Park, DC, I saw this boulder and my eye was immediately drawn to the linear pattern running from upper left towards lower right (Swiss Army knife at upper right for scale): Because that photo is not especially large, let’s zoom in a bit to two sections… Here is Photo … Read more
Using bedding / cleavage to detect overturned beds
One of my students wrote to me this morning with a question about the relationship between bedding, cleavage, and folding. He asked: I am not sure how we use the relationship between bedding and cleavage to interpret fold limbs. It seems if bedding is near vertical and cleavage is closer to horizontal, this would be … Read more
Quartz veins on Pimmit Run
Last Sunday, I took a solo hike along Pimmit Run in Virginia, accessing the valley via Fort Marcy, a Civil War fortification off of the George Washington Memorial Parkway. As always, I did a bit of geologizing along the route. One theme that emerged from the day’s photos was quartz veins. These veins form when … Read more