23 July 2012
Salt casts from Purcell (Belt) Supergroup rocks, Waterton National Park
Posted by Callan Bentley
I’ve previously mentioned the lovely salt casts that can be found in Mesoproterozoic argillites of the Belt (“Purcell” in Canada) Supergroup of the Canadian Rockies (including the North American portion of the Canadian Rockies: Glacier National Park and the Sevier fold and thrust belt immediately south of it).
When I led my Rockies field class students over Alderson Pass / Carthew Summit in Waterton Lakes National Park, Alberta, last week, we found some more. Here are a few field photos of these lovely indicators of past hypersaline conditions:
(Scale on pencil is in centimeters.)
… and further in still…
My student Cameron found the greatest quantity of casts on a single slab:
For this feat, I awarded him 13,000 bonus points. Looking closer at this same slab:
Here’s the spot to look for these samples if you’re in Waterton – but remember that you cannot collect samples in a national park: Take only photos and leave the salt casts there for future hikers to see and wonder about.
The hopper-shaped crystal in the third specimen is the clincher. Beautiful examples!
In sample #2, I really like the way the salt crystal made little wrinkles as it expanded into the surrounding mud…
Gotta love the Belt. A petrologist I know said that he would’ve become a sedimentologist had he gone to Glacier National Park and seen the Belt when he was in college.