Mima Mounds: The Case for Polygenesis and Bioturbation
“Pimple” mound microrelief in southern Saskatchewan, Canada
Published:October 01, 2012
L. Lee-Ann Irvine, Janis E. Dale, 2012. "“Pimple” mound microrelief in southern Saskatchewan, Canada", Mima Mounds: The Case for Polygenesis and Bioturbation, Jennifer L. Horwath, Donald L. Johnson
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Gravelly soil mounds less than 1 m high and up to 20 m in diameter, generally referred to as “pimple mounds,” are found in the prairies and aspen parklands of southern Saskatchewan, Canada. These low-relief mounds are the northernmost occurrence in North America of this geomorphic feature documented to date. When truncated by cultivation, former mounds are evident on air photos as a pattern of small, light-toned patches called “mound scars” that contrast with the surrounding darker soil. In many cases, these photographs are the only existing evidence of former mound topography.
Using air photos and direct field observation for identifying both intact and truncated mounds, the spatial distribution and characteristics of 10 pimple mound sites were examined, with mounds at the Little Manitou site studied in detail. Examination of the morphology and stratigraphy of multiple mounds indicates that bioturbation by burrowing animals has had, and continues to have, a major impact on the size, shape, nature, and origin of present-day mounds. Statistical analysis of 124 intact and 190 truncated mounds at the Little Manitou Lake site indicates that mounds form a more regular than random pattern, with strong biological implications. Saskatchewan mounds were compared to 30 other documented mound sites in North America. While most Saskatchewan mounds have greater relief and denser spacing, mounds from Texas, Wyoming, and Colorado are spatially most similar, also occur in predominantly prairie landscapes in areas with shallow soils, and are heavily bioturbated by burrowing animals.