15 February 2012

Colluvium-choked channel in cross-section

Posted by Callan Bentley

After seeing the contact of the Campus Andesite with Western Interior Seaway sedimentary rocks (Cretaceous in age), we moved a bit on down the line, and saw this disconformable contact between the Cretaceous shales below, and a bouldery sedimentary breccia above. Note the concave-up shape of the contact to the left of Elizabeth Nagy-Shadman (of Pasadena City College, California): that’s probably an old river channel scoured into the shale bedrock, then filled with what appears to be colluvium…

Another perspective on the same outcrop: