April 24, 2012

Monday Geology Picture: K-T Boundary Exposure in Colorado

Posted by Evelyn Mervine

K-T boundary, with a famous astronomer's hand for scale and dramatic effect.

The field area where Phil observed the K-T boundary.

This week’s geology picture was sent to me by my friend Phil Plait aka “The Bad Astronomer.” This week’s picture– two pictures, actually– shows the famous K-T Boundary.

Phil explains,

I’ve attached the K/T pic. It was taken in Trinidad Park in southern Colorado, where the boundary is very distinct.

It’s my hand in the 0731 picture. 🙂  0732 puts it in context. The rock above is limestone, and below is coal and other friables. The coal erodes away easily with rain and wind, so it forms that slope, which is murder to climb, like trying to swim uphill. The limestone is much tougher so it forms a cap. As the coal erodes back, eventually the limestone breaks and rolls down the hill. There were big chunks of it lining the base of the slope. All of this used to be underwater a few million years ago.

Thanks for sharing, Phil! I had a busy day with thesis revisions, so I’m posting this week’s Monday picture just in the nick of time… here on the east coast of the USA it’s a few minutes to midnight.