15 August 2013

Disconformity in northern Colorado

Posted by Callan Bentley

Orange sandstone overlying whitish limestone. The wiggly upper surface of limestone shows signs of dissolution, meaning that this is an unconformity.


52 mm lens cap for scale, at center.

Though the limestone beds are tilted, so are the sandstone beds, and at the same angle: so this is a disconformity (not an angular unconformity), as the stratification is parallel in the two units.

So, to produce this scene, the following events would have had to have taken place:

  1. Deposition of limestone (below sea level)
  2. Erosion of limestone (above sea level, presumably)
  3. Deposition of sandstone
  4. Tilting of the whole package

Somewhere in there (any time after step #1), sylolites formed parallel to bedding in the limestone. But this event isn’t constrained by relative dating to any of the other events (#2-#4).