You are browsing the archive for 2011 July.
30 July 2011
On my hike to the Burgess Shale earlier this week, we encountered some great geology as well as paleontology. For instance, consider this rather epic alluvial fan, spilling out of the Presidential Range to the northwest of Fossil Ridge and Mount Burgess, and rapidly filling the Emerald Lake basin. Here’s a Google Map link to the location.
29 July 2011
Folded quartzofeldspathic vein in amphibolite, Wyoming Terrane basement complex, Montana.
28 July 2011
Here is a trio of concentrically-zoned chert nodules in Mississippian Castle Reef Dolostone, exposed at Sun River Canyon, Montana, just downstream from the roadside outcrop of the French Thrust: If you look closely at the lowermost of the three chert nodules, you’ll see it’s been split and offset by a small fault. Here are close-up portraits of all three, concluding with the most interesting one (the deformed one): Hope all …
25 July 2011
All my Rockies students would agree. Just sayin’.
To follow up to my Cascade Canyon post, here’s a gigapan of the scene:
Dave Lageson of Montana State University and I ran into each on our respective field trips sometime last year outside of the Two Medicine Dinosaur Center in Bynum, Montana, and he told me that I had to go check out the Swift Dam area, a little ways northwest of the town of Depuyer. So, a year later, finding myself in Depuyer (as one does), I finally did. One thing I …
22 July 2011
That’s my Rockies co-instructor Pete Berquist, in the regulation uniform of an orange down vest, holding a subtly-folded slab of sandstone (it’s a very slight “S”), rescued from amid the shaley wastes of the Blackleaf Formation, the Cretaceous aged sedimentary rocks beneath the Lewis Thrust on the Blackfoot Reservation, just east of Glacier National Park. It’s cool to go check out these strata of the Western Interior Seaway, and see …
15 July 2011
Today, the Friday fold is a fake! Looks like a nice set of asymmetric antiforms and synforms, right? But it ain’t! It’s naturally wiggly; primary not tectonic. The photo shows nothing more than differential erosion of hematite that was deposited by groundwater in permeable sandstone. It’s Liesegang banding! These hematite blobs are in the sandstone at Giant City State Park, south of Carbondale, Illinois. Several are cylindrical in form, presumably …
12 July 2011
Stylolites (pressure solution seams) in limestone of Mississippian age, exposed on the side of a rounded boulder in Hyalite Canyon, Gallatin Range, Montana. These stylolites, like most, are bedding-parallel, and thus most likely formed due to the weight of the overlying rock. Calcite, the dominant mineral, goes into solution under pressure, and insoluble material, like organic matter and clay, accumulates along the dissolution surface, producing a dark, wiggly line. Here, …