This is a sample from the teaching collection at George Mason University: The swirly folds exhibited by this quartz vein reminds me of von Karman vortices. Happy Friday! For me, it’s the last day of classes of the spring semester at NOVA, though GMU is still in session for a couple more weeks. I’m grateful … Read more
The Friday fold is a contorted chert sample from Turkey.
The Friday fold is glimpsed from Google Earth. Atop a valley glacier in south-central Alaska’s Kenai mountain range, a fold of “transverse moraine” displays parasitic folds.
Spotted this one a week ago today, when I was out exploring north of the Rocky Islands with my GMU Structural Geology students…
Cretaceous calcarenite layers, folded along the coast of Spain (?). From the repository of geological images hosted by the European Geological Union, Imaggeo. I was reminded of Imaggeo earlier this week, and it’s a great place to go browse around for cool photos of geological things. It could use a better search interface, but oh … Read more
At last weekend’s northeastern / north-central GSA meeting in Pittsburgh, David Saja of the Cleveland Museum of Natural History presented a talk entitled, “Geometric Analysis of Folded Greywacke Layers from Pacheco Pass, California.” [Abstract link] In addition to the standard PowerPoint presentation that 99% of GSA speakers use, David also brought in some hand-samples (what … Read more
More from Mount Washington, New Hampshire: some folds in the Madison Member of the Littleton Formation (schist) along the auto road near Cragway Springs (just past 5 miles up; see map below): IMAGE SOURCE The folds are asymmetrical, with long west-dipping limbs, and shorter east-dipping limbs. Happy Friday!
Another fold seen in the Catoctin Formation, where last week we encountered a very different style of folding — chevrons overprinting Catoctin foliation. Here, we instead have a light colored vein that appears to have been buckled into a semi-ptygmatic form. The trace of the foliation in the Catoctin is discernible, too. Enjoy your Friday!
Last Sunday morning, two of my former GMU students, Aaron and Alan, led a hike for the GMU Geo-Club to Thoroughfare Gap, a water gap in the Bull Run Mountains of Virginia’s eastern Blue Ridge province. I’ve mentioned the Weverton Formation structures we saw there, and a nice example of a hackle fringe in previous … Read more
Here’s your Friday fold, straight from the canyon of the Jefferson River, near Cardwell, Montana. Perspective is to the south. East is on the left; west is on the right. Bigger version This is right next to the outcrops of LaHood Conglomerate that I mentioned earlier this week. My Rockies course co-instructor Pete Berquist and … Read more
The Friday fold takes us to some high-grade metamorphic rocks in the Piedmont of northern Virginia.
Today’s edition of the Friday fold is a cross-section: Doesn’t look too spectacular, does it? — “Why, it’s just a bunch of strata folded into anticlines and synclines,” I’ll bet you’re thinking. But no… it’s actually more complicated than that. We know it’s more complicated by examining geopetal primary structures in the strata. Geopetal structures … Read more
The Friday fold is a series of strata underwater near California’s famed “Mavericks” surf break.
This week’s edition of the “Friday fold” takes us to Route 55 in West Virginia, to deformed Appalachian strata of the Valley and Ridge province. A few bonus structures are also shown — some ripple marks, slickensides, and pencil cleavage.
Norwegian structural geologist Haaken Fossen contributes two incredible images for this week’s Friday fold: a pavement of drastically-shortened banded iron formation from Minnesota, and a trio of three white granitoid dikes, buckled within a gneiss from the Jotun Nappe, in the Norwegian Caledonides. Gorgeous images of gorgeous folds, with links to the rest of Fossen’s collection.
The weekly example of a fold is especially… “cool” this week.
The Friday fold visits the French Broad Massif of North Carolina’s Blue Ridge province.
Today’s Friday Fold comes to us via Pete Berquist of Thomas Nelson Community College in Hampton, Virginia. Check it out: Pete explains what’s going on here: I cannot provide an exact location but this is within the Mars Hill Terrane (MHT), which is an distinctive swath of Mesoproterzoic basement extending ~50 km x 100 km … Read more
Sometimes you find folds in funny places, like the side of a monastery. Guest fold from Maitri.
For the structural geology fans among AGU’s readership, enjoy the weekly installment of the Friday fold.