North-Central Section - 47th Annual Meeting (2-3 May 2013)

Paper No. 5
Presentation Time: 2:55 PM


KERR, Phillip J., Iowa Geological Survey, IIHR - Hydroscience & Engineering, 340 Trowbridge Hall, Iowa City, IA 52242, BETTIS III, E. Arthur, Department of Geoscience, University of Iowa, 121 Trowbridge Hall, Iowa City, IA 52242 and BAKER, Richard G., Department of Geoscience, University of Iowa, Iowa City, IA 52242,

Investigations sponsored by the Iowa Museum of Natural History have discovered the remains of three mammoths eroding from alluvium in a small tributary of the South Skunk River in southern Iowa. Coring, examination of excavation walls, radiocarbon dating, and macrofossil analyses are providing a preliminary picture of the paleoenvironment occupied by the mammoths and the processes responsible for formation of the fossil deposit. Excavations to date have recovered fossils from early Holocene alluvium that filled a plunge pool cut into an older terrace fill that apparently contains in-situ mammoth remains. The pristine condition of bone recovered to date and a lack of size or density sorting suggests a very short transport distance. An exposure of the older terrace fill and cores from the terrace surface adjacent to the excavation show a sequence of fine-grained late glacial alluvium separated from sand and gravel by an organic-rich zone that yielded a radiocarbon date of 13,120+50 B.P. Plant macrofossils recovered from the organic zone indicate a marshy area within a spruce forest. On-going investigations are focused on refining a sedimentary model for the site and determining the location of the in-place deposition of the mammoth remains.