Soil Development on Monks Mound at the Cahokia Archaeological Site, Illinois

Abstract

The nearly level third terrace of Monks Mound had been constructed by prehistoric Cahokians (ca. AD 1100), who used this surface for approximately two centuries. After a 400-yr hiatus, during which the mound was probably vegetated by grass and/or trees, the third terrace was periodically occupied by aboriginal groups and Euro-American settlers. The primary objectives of this study were (i) to determine the nature and extent of diagnostic surface and subsurface horizon development during the past 900 yr and (ii) to determine if any tillage or mixing of the surficial soil horizons occurred during the historic period. The soil profile shows an extremely thick mollic epipedon and an A horizon were developed to depths of 0.9 to 1.2 m, respectively, during the last 900 yr. Magnetic susceptibility, magnetic minerals, fly ash, and organic C amounts and distribution within the surficial horizons suggest that the soil was disturbed by tillage after 1864, but not within the last 70 yr.