I spent yesterday on Corridor H in eastern West Virginia’s Valley & Ridge province. The rocks here are a mid- to upper-Paleozoic set of strata that record the switch from post-Taconian passive margin sedimentation into Acadian clastic deposition, and then everything is deformed by Alleghanian folding and thrusting. I found myself taking photographs of the … Read more
The Friday fold can be found in a boulder of gray chert layers on Black Sands Beach, at Marin Headlands in California.
In keeping with the Arizonarific theme of this week’s posts (thanks to my participation in the 2018 Structural Geology and Tectonics Forum), I thought I would wrap up my ‘geology of the Phoenix area‘ posts with a walk I took on my last day there. This was to what Google Maps calls “Hayden Butte,” but … Read more
The scenic arch of Dore Holm (“Door Island”) in Shetland shows off the most efficient way of breaking a slab of rock. The island’s shape is a reflection of the parsimonious nature of natural deformation.
A basalt flow in Iceland shows both enticing pahoehoe and fractures with a Y-shaped intersection pattern. Comparisons to bread loaves and east Africa suggest a reason why.
Time for another virtual field trip on the Geologist’s Grand Tour of the United Kingdom: the most famous outcrop in the world. Today, we visit Siccar Point, Scotland. You’ve probably already seen photos of this place – they usually look something like this: To those who aren’t familiar, here’s what going on: There are two … Read more
Want a geological irony? Here’s one! You’re looking at a rounded boulder of Cushendun Conglomerate, a Devonian “Old Red Sandstone” unit (Cross Slieve Group) exposed at Cushendun Caves, Northern Ireland, U.K. The irony lies in the repetition of history – a tumbling environment of high water energy, rounding cobbles and boulders and depositing them, in … Read more
Check out the argillite boulder in the left midground of this GigaPan, which I’ve showed here before. It was taken at the Icefields Center parking area in Jasper National Park, Alberta: link There, you’ll find some lovely orange lichens, some iron oxide staining, some graffiti, and a fair number of sub-aligned glacial striations. Also, at … Read more
Good morning. Here are two images from last March’s “Border to Beltway” field trip to West Texas, on the north flanks of the Cristo Rey laccolith. Specifically, these are Cretaceous strata of the Anapra Sandstone, looking at the bedding plane of the rocks. Cutting across bedding are a series of fractures (joints) that have been … Read more
Callan’s Rockies field course students document faulting and jointing in Red Rock Canyon, Waterton Lakes National Park, Alberta.
My favorite rocks are those that tell multiple stories – rocks that are “palimpsest” with subsequent “chapters” of their biography capable of being teased out, based on different features to be observed in the rock. Click to enlarge What can we see in this small sample of the Silurian-aged Tonoloway limestone, from Corridor H, West … Read more
As noted previously, I live in a regional scale fold: the differential erosion of the Massanutten Synclinorium has produced the ridge of Massanutten Mountain, which separates the Fort Valley from the Shenandoah and Page valleys on either side. The Fort is “fort” like because the strata which underlie it are relatively friable, soluble, or otherwise … Read more
Our three-day karst theme wraps up today with a visit to Natural Bridge, Virginia, an impressive sight: I went to Natural Bridge early last week to give a talk to a group of Road Scholars (an Elderhostel-like program) about the Snowball Earth. Part of my compensation for the talk was a night’s lodging at the … Read more
Yesterday we examined primary sedimentary structures (including trace fossils) at an outcrop of Devonian-aged Brallier Formation turbidites between Deerfield and West Augusta, Virginia. Today, we’ll zoom in on the tectonic structures at the site: folds, faults, and joints. Remember, you don’t have to take my word for it. You can explore it for yourself in … Read more
Another scene from the South Page Valley Martinsburg outcrop featured here last week: a slightly mud-bedecked example of plumose structure. This plume occurs within a single graded bed (turbidite) of the Martinsburg Formation. It gets younger (paleo-up) to the right. The joint propagation that the plumose structure records began somewhere vertically above the area of … Read more
Today, we return to my field trip from last week, for a look at an odd outcrop of the Ordovician-aged Edinburg Formation: Note the car key with green lanyard, to provide a sense of scale. It’s folded, as the yellow bedding traces show in this annotated version: But what really caught my eye about this … Read more
Yesterday, I took five new GigaPans at Thoroughfare Gap, a water gap where Broad Run cuts through Bull Run Mountain, the eastern limb of the Blue Ridge Anticlinorium at my latitude. The rocks here are the Cambrian-aged Chilhowee Group, with bedding tilted moderately to the east during Alleghanian mountain-building in the late Paleozoic. To the … Read more
A USGS colleague shows Callan a bizarre fold outcrop in the Conococheague limestone of the Boyce quadrangle, Virginia.
Callan & his students visit an outcrop on the Icefields Parkway in Alberta, showing a variety of white veins cutting dark rock.
Everything’s bigger in Texas, even the footprints…