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
I saw this large, chunky stylolite this summer somewhere along the trail from Takkakaw Falls to the Walcott Quarry of the Burgess Shale (in Yoho National Park, British Columbia). I like the way weathering has highlighted its form.
Driving west from Calgary, your first evidence of entering the Canadian Rockies’ Front Ranges is the startling sheer cliff of Yamnuska, north of the Trans-Canada Highway: Yamnuska’s shape is a function of differential weathering of the two rock units that make up the mountain: Cambrian Eldon Formation limestone, and Cretaceous shales of the Brazeau Formation. … Read more
Remember our examination of buckle folding versus passive folding in the Chancellor Slate (cleaved limy mudrock) of eastern British Columbia? Well, here’s another example: There’s so much awesomeness going on in that image, it’s hard to know where to start. The prominent black thin layers are buckled in a very boxy, asymmetric way. In places, … Read more
What can a little squiggle in a rock tell us? Stylolites in West Virginian limestone cut across the bedding plane, implying Alleghanian tectonic stresses.
Here’s something fun: Click to enlarge Those strata are Silurian-aged Tonoloway Formation carbonates. There are plenty of dessication cracks to be seen, as well as salt casts, among the layers exposed. But more eye-catching at this distance is the faulting that disrupts the high-contrast layers… Both (apparent) normal and reverse faults can be seen in … Read more
Another guest Friday fold from Howard Allen: View looking north at Mount Lyautey, on axis of the Lyautey Syncline, from Aster Lake trail, Peter Lougheed Provincial Park, Alberta. Rocks are carbonates of the upper Mount Head Formation, Carboniferous (Mississippian). Photo taken in 1981.
Here’s a little scene along Route 340 / 522, north of Front Royal and south of Double Tollgate, Virginia, in the Shenandoah Valley: The rock here is limestone and shale of the Edinburg Formation, a late Ordovician unit that records the transition from passive margin sedimentation to the increasingly ‘dirty’ clastic influence of the Taconian … Read more
While in West Texas over spring break, the “Border to Beltway” students took a hike up McKittrick Canyon, in Guadalupe Mountains National Park. This is part of the famed Permian reef complex, the deep reservoir of Texas’s rich endowment of oil. Here, the reef comes to the surface. In fact, it pokes up a good … Read more
Ooids are fish-roe-shaped-and-sized spherules that result from the chemical precipitation of calcite from supersaturated water. Here are a few nice examples from Monday’s field trip.