Mima-type mounds in southwest Missouri: Expressions of point-centered and locally thickened biomantles

Mima-type mounds, formed in gravelly soils of the Diamond Grove Prairie Natural Area near Joplin, Missouri, are the focus of this study. Emphasis is on the spatial and morphological aspects of the mounds, and more particularly on the analysis of mound soils and gravel distributions as a means for shedding light on mound origins in this region. The results strongly suggest that hierarchically dominant point-centered bioturbation by small vertebrates is the mode of mound genesis. Pocket gophers (Geomys bursarius), aided by other biota, create mounds as they burrow in residual gravelly soils that have evolved dense, relatively impermeable claypans that perch water during wet periods. Although pocket gophers do not presently inhabit the Diamond Grove area, evidence of past occupation, along with laboratory and field data, support them as the dominant role in forming the mounds. We conclude that these mounds are expressions of point-centered and locally thickened biomantles. Various subsidiary processes such as aeolian inputs, water erosion, and physical and chemical weathering also have genetically impacted Diamond Grove mounds.