SIGNIFICANCE OF PARABOLIC RECUMBENT FOLDS IN PERMIAN ROCKS, SEDONA, ARIZONA
The cross-bedded portions of the Schnebly Hill, Coconino Sandstone and Toroweap Formations (Arizona, USA) are considered by most to be primarily eolian deposits. However, we have recently found multiple PRFs in all three of these formations. Deformed cross-bed sets occur over a wide area (>375 km2) at many different locations and horizons, particularly in the Sedona area. Some PRFs in single cross-bed sets can be traced for 400 m along ridge tops. Field evidence shows the folding was penecontemporaneous. The folds in these rocks are quite specific and are identical in scale and form to PRFs produced experimentally in subaqueous sand and PRFs observed in many deposits of known subaqueous origin. There are specific features that distinguish PRFs from deformation structures in slumping eolian dunes. Some of the PRFs we have discovered are large-scale, ranging in size up to 5 m high, while slumping eolian dunes produce only small-scale folds and faults, usually at cm scales. There does not appear to be any evidence that the deformed beds are fluvial deposits within an eolian sand sea or that the deformation occurred by post-depositional groundwater movement or by seismic activity, as has been documented in other sandstones. These features are distinctly different. Where these folds occur, it suggests these formations were deposited by strong underwater currents.