ORIGIN OF THE PREGLACIAL WHIPPOORWILL FORMATION, NORTHERN MISSOURI
The Whippoorwill retains a strong, well-defined detrital remnant magnetization characteristic of a sedimentary deposit but not paleosols. The downslope margin (where exposed) appears lobate in form and possible ice-wedge casts are preserved in various exposures. Thus, the Whippoorwill is apparently a saturated mass-flow deposit, most likely from solifluction/gelifluction.
Recently we sampled the Whippoorwill for cosmogenic-isotopes (10Be and 26Al) at two sites to obtain ages (burial dates) of the overlying Atlanta-Formation till. Using the recently corrected decay constant for 10Be, we have obtained consistent dates of ~2.5 Ma. The concentrations of the cosmogenic nuclides are very high, reflecting long-term surface exposure prior to glaciation, but their concentration profiles are essentially constant with depth. If the Whippoorwill were an in-situ residual profile, an accretion deposit, or a mass flow that was exposed for a significant duration prior to burial, these concentrations would decrease exponentially with depth. Therefore, we propose that the Whippoorwill is the preglacial weathering- profile materials that were mobilized and homogenized under periglacial conditions shortly before glaciation by solifluction/gelifluction. Thus, the Whippoorwill could be considered either a sedimentary deposit or a buried Gelisol, the new soil order established for periglacial regions.