In last week’s Friday fold, I featured this image… …which prompted commenter Lynn David to ask, What’s going on to the west side of that red/green rock cored syncline in #2? It looks like some sort of disconformity but then I looked closer (and man, does that rock redden up) and it appears that the … Read more
Found these lovely places over the past few weeks while searching (unsuccessfully) for Where On (Google) Earth? scenes… Click on any of them to make them bigger.
Picked this one up the summer before last and took its portrait without recording too much else about it. There’s a small fault in there towards the bottom too. Sorry I forgot to mention it. My fault… Happy Friday! A light rock for “black Friday,” eh? Hope you had a happy Thanksgiving.
Quartzite, shattered and healed and shattered again and again and again. It’s cataclasite, seen in the North Carolina Piedmont and inferred to be Mesozoic in age due to its brittle style of deformation.
Callan attends the Geological Society of Washington’s fall field trip, examining the relationship between grape-growing and the underlying geology of two provinces in northern Virginia: the Blue Ridge and the Valley & Ridge. With GSW compatriots, Callan visits Hume Vineyards in the Blue Ridge basement complex and North Mountain Winery in the Shenandoah Valley. This is part I.
Grab your coffee and join Callan & Lily for a stroll along the quartzite cliffs of Hermanus, South Africa. Bedding, cross-bedding, joints, faults, veins, folded veins, and faulted veins all await you there in the morning light.
A showcase of geologic structures observed between downpours of rain at Floe Lake, Kootenay National Park, British Columbia. Cleavage, bedding, folds, faults, and strain are all presented for the discerning structural reader’s edification and titillation.
Another batch of out-the-airplane window photos from March, on my flight from Reno, NV, to Minneapolis, MN. I looked out the window and saw a form that seemed familiar…. A slightly higher-contrast exposure: I was focused on that asymmetric mountain range in the distance. Is that the Tetons? And Jackson Hole to their east? I … Read more
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 … Read more
Another shot from my pre-GSA structural geology field trip to the Superior Craton last fall, up in southern Ontario, Canada. The image shows slickenlines coated with brownish fault gouge and oxide staining, cutting through a high-potassium granite (see fresh surface at upper left). The slickenlines are little gouged grooves where asperities (bumps) on the block … Read more
I got this note via email last week. Hi Callan, First of all, congratulations to your blog. It is just great. I would like to contribute to your “Friday fold” section. A few words about myself. I am born in Austria and did my BSc and MSc at the Montanuniversitaet Leoben. In September 2011 I started … Read more
When are sedimentary layers also faults? …When the slab-like layers slip over and under one another during the act of folding. Structures traditionally confined to faults show up on the bedding plane in these circumstances. Callan shares a shiny example from West Virginia in the form of an animated GIF.
Slickenlines (fault grooves) and fault polish on a chunk of sandstone in far western Texas.
A few shots from a week ago today, when my students and I were exploring the White Mountains of eastern California, just west of the Deep Springs Basin…
Why are these people smiling? photo by Yvette Kuiper Because they are structural geologists, and they are psyched to be at an extraordinary outcrop: This is a famous pavement outcrop of polyphase-folded banded iron formation (BIF) near Soudan, Minnesota. I went there last fall before the annual meeting of the Geological Society of America, on … Read more
Callan reviews the geology of the superlatively auriferous Witwatersrand Supergroup of South Africa, and then zooms in on a distinctive marker bed near the base of the sequence. The deformation in this particular banded iron formation (BIF) is an aesthetic wonder, as this suite of images reveal. The layer outcrops in the heart of urban Johannesburg.
The Friday fold is found on a newly-opened section of road in West Virginia. Join Callan in checking out some synclines and associated faults in the Devonian-aged Brallier Formation.
Okay – in spite of numerous distractions (see every other post so far this week), it’s time to return to the pre-GSA Minneapolis structural geology field trip. Our final stop of the second day in the field was a series of folded up mafic metavolcanics. I’ve got some photographs of them. These mafic volcanics were … Read more
By local prodigy Hannah Holland, elementary school student: Click through to make it bigger and see some details. Nice work, Hannah! Very impressive, and thanks for sharing!
The Friday fold is a gorgeously deformed “duplex structure” in Mesozoic limestones of southwestern Montana.