Friday folds: Serendipity in the White Mountains
Callan and his field studies students encounter a lesson in the White Mountains of eastern California that combines bedding, cleavage, folding, and even fossil archaeocyathids!
joints
Poleta plume paradise
On Monday, my field course students and I tried to find the Poleta folds, but I had failed to figure out in advance the best access point. Oops. That’s the way the cookie crumbles, when you’ve got big plans but not enough time to enact them with appropriate pre-planning. We had some happy exploration of … Read more
Contorted fractures in the Contorted Bed
Today, let’s zoom in on a little something I saw at the outcrop of the Contorted Bed in downtown Johannesburg, South Africa: What are these things? I only saw them at this one spot. These look to me like en echelon fractures at a high angle to bedding, that were then deformed due to dextral … Read more
Plane views
A few scenes out the left side of the airplane from when I flew from El Paso to Houston a week and a half ago… Sand dune field overprinting desert vegetation and human roadways: Outcrop pattern of horizontal strata (tracing out the contours of this hill), and the weird geometry of human road systems: More … Read more
Fractures on a seismic sign
On the campus of the University of Texas at El Paso, there is a sign for the Kidd Seismic Observatory. The sign has seen some brittle deformation of its reflective letters. I infer this due be due to differential shrinkage of the letters (relative to the sign they are attached to) in the intense Texas … Read more
A campus underlain by porphyritic andesite
The campus of the University of Texas at El Paso is a beautiful place. You can look south into Mexico, a scant half mile away. It’s got rocky hills rising up between buildings and between stadiums (stadia?), and a utterly unique campus architecture based on the Himalayan nation of Bhutan. Here’s a look at the … Read more
Tofu with hackle fringe
We were making dinner last week and took out a block of “silken” tofu* with less care than we should have, and it broke. But what a break! The fracture showed a gorgeous elliptical joint face that broken up into a twisted series of hackles along its fringe: That’s something nice homogeneous fine-grained rocks do, … Read more
What I saw there
Yesterday, I showed you this picture and asked what you saw there: Today I’ll give you my impressions. This is an outcrop of sandstone of the Table Mountain Supergroup, seen on the beach in the idyllic village of Rooiels, on the eastern side of False Bay, north of Cape Hangklip, in South Africa.The field of … Read more
Friday folds (and boudinage): Superior Craton day 3, stop 1
Today the Friday fold comes with copious bonus structures. It’s the first stop we hit on Day 3 of the pre-GSA Minneapolis field trip to examine the structural geology of the subprovince boundaries within the Superior Craton. This particular site showed granitoid dikes that had been deformed during dextral transpression into a variety of structures … Read more
Those could be pillows
More pillow-like structures, seen in the Catoctin Formation, on the west side of the Blue Ridge Parkway about ten miles south of Interstate 64. Mini Sharpie for scale – what do you think? They don’t seem to be as strongly fracture-controlled as the Stony Man area “pillows.” But dang, they sure are small… Read the … Read more