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Friday Field Foto #39: Prograding deltaic deposits

January 25, 2008

This week’s photo is from the Cretaceous of Utah. This is a unit called the Ferron Sandstone Member (Turonian), which is part of the Mancos Formation.

This photo is taken from Interstate 70 on the western limb of the San Rafael Swell (where the Ferron is exposed beautifully for several 10s of km).


It is hard to get a sense of scale on that photo … but the reddish-brown fallen block on the right side on the talus slope is probably the size of a bus (roughly).

Without going into too much detail, essentially you are looking at prograding delta-front deposits in the lower cliffs (notice the upward-coarsening and upward-bed thickening pattern) with fluvial channel deposits (the more buff-colored sandstone) overlying it.

Overall, the Ferron represents a clastic wedge that prograded into the Cretaceous Seaway. These strata are older than the more commonly visited outcrops of the Book Cliffs I’ve talked about before (here and here).

I visited the Ferron a few times when I was working on my master’s in Colorado. When I find a little time, I’ll put together a more comprehensive post…these are cool rocks!

Happy Friday!


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