NEW, EXTREMELY OLD, 14C AGES ON BURIED CHARCOAL FROM PIT-MOUND TOPOGRAPHY IN NORTHERN MICHIGAN

We report on several new 14C ages, derived from charcoal and wood buried during the course of tree uprooting. These materials were either on the forest floor and subsequently buried by the root plate of the uprooted tree, or were derived from the burning of the tree trunk of the uprooted tree. Regardless, they provide excellent estimates of the age of the uprooting event. Previously, maximum longevities of pit-mound features like these have been derived using this type of dating. Our study site, in Michigan’s eastern Upper Peninsula, is a mixed hardwood-conifer forest, developed on sandy Spodosols, where uprooting and the resulting microtopography are commonplace. We excavated approximately 70 pit-mound pairs, and selected 14 pit-mound pairs as most appropriate for this type of dating. At each, we removed charcoal or wood fragments from the bottoms of the mounds, for radiocarbon dating. In these sandy soils, uprooting is often a straightforward process of simple folding, in which the upper profile is lifted up by the roots and laid down, more-or-less intact and with minimal mixing, on the adjacent forest floor. This type of uprooting, as well as the visually striking horizonation of the native soils, both favor the preservation of charcoal/wood and make it easy to locate. Prior to this study, the oldest reported date for a mound, also on sandy Spodosols in the Upper Peninsula, was 2420 + 70 years. We report on mounds that range from 50 to well almost 5300 radiocarbon years BP, calibrated to over 6000 calendar years in age. We attribute the extreme longevity of pit-mound topography in this landscape to the permeable soils, which minimize runoff and erosion, as well as to the rapidity with which a thick forest floor is developed in this cool, humid climate. The research was supported by Czech Ministry of Education and Sports and AMVIS (project No. LH12039).