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.