[crusty old prospector]

The oil shale in Utah and Colorado (Green River Formation) is a little different in that it is the remains of a fresh water lake. Something similar to the Great Salt Lake but larger. The organic matter was laid down in yearly cycles like a tree ring such that you can count the layers and determine that it took about six million years to fill in. It is famous for its fossils and I have several fish in my office from there.

[zeestephen]

Re: Oil Shale

Thanks for your very interesting note.

I knew I should have researched that before commenting.

I assumed the organic material descended to the shale at the same time the shale was ascending back to the surface

The freshwater lake is a total surprise.

I recall that several times in geologic history salt water oceans have pushed all the way to the Rockies.

Is there also oil shale in the Burgess Shale deposits in the Canadian Rockies?