22 July 2015

Oolitic soft sediment deformation in Helena Fm. limestone

Posted by Callan Bentley

Another gem from the Grinnell Glacier cirque:



Zooming in on the contact, showing the concentrically-zoned ooids:


Near the tip of the flame structure (?), I noted alignment of longer platy / flaky components within the oolitic layer:


This looks like a loading structure – soft sediment deformation due to a density inversion – perhaps when some high-energy event (a storm?) dumped a bunch of relatively coarse ooids atop some squishy micrite mud. The upper oolitic layer glooped down into the micritic lower layer, creating this convoluted contact.