Saturday, February 16, 2013

Geo 365: Feb. 16, Day 47: Cut-and-Fill

Another loose boulder on the north side of Sunset Bay State Park This one shows a very nice cut-and-fill structure. Flow concentrated in a restricted area gouged out a small channel, which was later refilled with sediment. This is another structure that allows determination of stratigraphic "up." First, when a sequence is cut, the sequence is older than the feature doing the cutting- so in this case, the set of beds being cut into by the channel  is older than the channel doing the cutting. Second, in a stack of sedimentary  layers, the layer on top is younger. Combining those two principles makes it clear that from the perspective we're viewing it, the rock above is upside-down in a stratigraphic sense.

As it happened, we were at Sunset Bay as sunset approached; the low angle and warmer quality of of the light is apparent in this photo.

Photo unmodified. March 8, 2012. FlashEarth location.


Phil said...

It's kind of amazing to see this place I have been to so many times dissected geologically.
I do have to admit that I had noticed some strange geological formations there over the years but I had no idea just how active that place has been in the past.
It's pretty cool to see this from your viewpoint, things I had only glancingly noticed more fully explained and things I did not know at all that have been there staring me in the face for my fifty odd years.
Thanks for pointing them out.

Lockwood said...

My pleasure, literally! I've been having a great time with this series... and just think: 318 days to go yet.