Arkose, arkose conglomerate, shale, and some of the limestone of the Minturn formation, of Des Moines age (Pennsylvanian), near McCoy, Colorado, are red and yet on the basis of contained fossils are definitely marine beds. The red color is due to hematite which has been preserved because 1) the volume of hematite deposited with the beds was exceptionally high, 2) the reducing capacity of the marine environment was low, and 3) the sedimentation and subsidence rates were rapid.

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