21 September 2011

A Burgess plume

Posted by Callan Bentley

At the Burgess Shale this summer, it wasn’t all fun and fossils. I also saw a lovely, distinctly feather-shaped plume:

This is an example of plumose structure – the subtle branching micro-topography that forms on the surface of a joint as the fracture propagates out from its origin. The more obvious “rib” that is perpendicular to the feathery plumes represents a moment, perhaps only a fraction of a second long, when the fracture stops propagating and “tips out” (changes orientation) before propagating anew.

Plumes are typically “feathery” in the sense of an ostrich plume, but the primary-feather-shape of this concentric rib struck both the structural and the ornithological sections of my brain simultaneously. That’s a rare occurrence; Naturally, it made me quite happy.