You are browsing the archive for folds Archives - AGU Blogosphere.
16 August 2022
Callan shares a few outcrops from coastal Maine, part of the Avalonia terrane that accreted to ancestral North America during the Acadian Orogeny. They are volcaniclastic rocks, coarse and fine, and showing both overprinting kink bands and cross-cutting basaltic dikes.
1 July 2022
A quick Friday fold that I observed last month in a boulder of riprap at Chippokes State Park in Surry, Virginia. I have absolutely no idea where this rock was quarried; but it doesn’t look like anything I’m familiar with in Virginia, so maybe the Baltimore Mafic Complex??? Anyhow, it’s not native to the Coastal Plain, but it shows a pleasing fold train of green and gray amid the black …
24 June 2022
Happy Friday! Here are some kink-folded metasediments from Virginia’s Lynchburg Group to help usher in the weekend.
29 May 2022
The Lost Coast of northern California shows geological evidence of deep sea turbidity current sedimentation, tectonic accretion during Mesozoic subduction, and then isostatic uplift interacting with shoreline erosion. Check out a few photographs taken by Callan’s wife on a recent backpacking trip through the region.
15 April 2022
A guest contribution for the Friday fold, from reader Christian Gronau: Christian reports that this is located on the North side of Hwy.11, 20 miles east of Saskatchewan River Crossing, Alberta. Eastern foothills of the Canadian Rocky Mountains. Faulting and folding in Early Cretaceous Luscar Group sediments. Typical repeating sequence of sandstone, siltstone and coal. Thanks for pitching in, Christian! Happy Friday to all!
12 November 2021
Happy Friday, all! Two shots today from my friend Joe up in Vermont. He sends these from the Champlain Valley, at a place called Raven’s Ridge. It looks like an alternating series of sandstones and shales, arched into an anticline, perhaps during the Acadian Orogeny (??). According to the Nature Conservancy’s website, porcupines live in this anticline, which is called “The Oven.” Looks like most of the strata around there …
25 June 2021
Inside the Blue Ridge (in an 1850s-era railroad tunnel), Callan finds folds and boudinage that formed during Appalachian mountain-building.
11 June 2021
It’s Friday! Adam Forte, a geology professor at LSU, posted this image yesterday on Twitter: It’s a box of sheets of newsprint, stored vertically and ignored for a while, now rotated 90° so we’re looking at a cross-sectional view. To me, this is an excellent example of a physical analogue modelling experiment (albeit inadvertent) that demonstrates the process by which kink folds form. The key parameters to get this distinctive …
7 May 2021
On his way to get his COVID vaccine, Callan visits a new outcrop showing folded and faulted strata of the Neoproterozoic Lynchburg Group.
16 April 2021
Friday means folds –
This week, we head to the Colorado Rockies for a butterfly-like presentation of a ptygmaticly folded granite dike within biotite schist.
26 March 2021
It’s Friday, and it’s been a few Fridays since I offered you a fold. Let me make up for that with five Friday folds today, all from the incredible collection of free 3D models by Sara Carena on Sketchfab. Sara is a senior scientist/lecturer in Geology at Ludwig-Maximilians University in Munich. [sketchfab id=”f424c677140147138f25d15b5c9a1718″ start=”0″ spin=”” controls=”0″] [sketchfab id=”79f5e7be0c7f4e5397cf2158fcce1dd4″ start=”0″ spin=”” controls=”0″] [sketchfab id=”58f60e9e9aab4e919b0b7be442d23b66″ start=”0″ spin=”” controls=”0″] [sketchfab id=”79b2a04061634c188df31ef26954fd56″ start=”0″ spin=”” …
5 February 2021
Here’s a good sample, another one I inherited from Declan de Paor when he retired from Old Dominion University. It’s an interesting sample – I guess I’d call it a graphitic clay shale, but it’s surprisingly lightweight, so I’m not super confident that’s right. The bedding surfaces are glossy and slick, indicating some flexural slip between the layers. In terms of composition: It’s too beautiful to cut up and make …
15 January 2021
Earlier this week, I was alerted to an online photo collection from the Alaska Division of Geological and Geophysical Surveys. For those of us who are feeling the lack of field work over the past year, it’s pleasant to browse through them and get a taste of backcountry Alaska. Many of the photos are shot on old slide film, but that kind of adds to the “Alaskaness” of them in …
13 November 2020
A quick “Friday fold” that is expressed in three dimensions – “stairstep” style folds deforming a bed of Tonoloway Formation dolostone…
9 October 2020
Looks like we’re sticking with the U.K. for Friday folds, for the time being… This lovely beast comes to us from Torcross, via Danny Stubbs, who shared it on Twitter this past week. That’s from the Meadfoot Group of slates, cross-cut by quartz veins. In this follow-up image, Danny shares that sometimes the quartz veins have enjoyed some folding too: Happy Friday to all.
2 October 2020
For the Friday fold this week, we travel to Northumberland, U.K. for this beautiful fold pair: Robert McKibbin posted this image on Twitter this week, and graciously allowed me to feature it here. Thank you Robert! Happy Friday to all.
11 September 2020
A hilly region of Cornwall, U.K. features beautiful folding, and a fuzzy field assistant!
7 August 2020
I went on a day of field work last week to Corridor H, West Virginia, to help make drone-based photogrammetric 3D models of the huge outcrops there. One site we stopped at is this beautiful V-shaped syncline in Devonian-aged Helderberg Group limestones. Click to enlarge Here are two layers traced out: Here is a GigaPan that Alan Pitts shot of this outcrop several years ago, when it was a bit …
31 July 2020
I spied an anticline last weekend while engaging in a day of solo geologizing along Skyline Drive in Shenandoah National Park. At Two Mile Run Overlook, I gazed west toward the southern tip of Massanutten Mountain, and noted what appeared to be an anticline in the Blue Ridge foothills: Annotated: And here it is in Google Maps, with the perspective rotated to looking ~along strike to the north, and I …