Within the Pennsylvanian strata of Canyonlands National Park and Glen Canyon National Recreational
Area, eolian cross-strata are interbedded with marine carbonates. The white rocks along the creek and
the red strata are eolian; the grey rocks are cherty marine limestones.
Many of the crinoids and brachiopods in the marine limestones are replaced by red chert.
In some samples, it is possible to find both pyrite framboids (black spheres) and hematite.
Both chert and pyrite commonly form early replacements of invertebrate skeletal material. This
pyritized brachiopod is from the Devonian of New York.
The hematite in the Pennsylvanian rocks of Canyonlands is a product of pyrite oxidation.
When sea level dropped, the reducing pore water within the marine sediment was replaced by oxidizing,
meteoric water. Pyrite that had formed was oxidized to hematite So the diagenetic history of red chert-
replaced fossils appears to fit in well with what we know about the depositional history of these strata
(see Loope, D.B. and Watkins, D.K., 1989, Pennsylvanian fossils replaced by red chert: Early oxidation
of pyritic precursors: Journal of Sedimentary Petrology, v. 59, p. 375-386).