23 July 2015

Purcell Sill, layer-jumping

Posted by Callan Bentley

After reading the post last weekend about the discordant offshoot of the Purcell Sill, Rich Gashnig (post-doc at Georgia Tech) sent me a few photos he shot at Piegan Pass (at the head of a side-canyon adjacent to the one containing Grinnell Glacier). They show the Purcell Sill leaving one stratigraphic horizon and jumping to another, with the intermediate zone of Helena Formation limestone bending to accommodate the different positions:



In addition to the main, obvious jump at left-center, there are two other offsets (one,perhaps, apparent offset) further to the right:


Thanks for sharing, Rich!