PALEOGEOGRAPHY OF THE HARTLEY MASTODON SITE, COLUMBIANA COUNTY, OHIO

The discovery of the Hartley Mastodon presented an excellent opportunity to investigate the paleogeography of the immediate deglacial environment of Columbiana County, Ohio. A lake was partly excavated into a pre-existing 70-meter wide depression interpreted as a kettle hole. It was from this depression that the mastodon was found. The kettle hole is in Lavery till, which was deposited by the Grand River Ice Lobe approximately 16,000 years ago. The till deposits therefore provide a maximum age of 16,000 BP for the specimen. The kettle hole is approximately 14 km behind the paleo-ice margin at its maximum extent in the region. A simple sequence of units was recorded at the site. The units are, from oldest to youngest, a dense gray clay, massive shelly organic clay, red fibrous peat, and black woody peat. The shelly organic clay layer contains abundant plant fibers, small wood fragments, molluscs, and gastropods. Fauna indicates that a pond or small lake existed, but water was shallow and contained abundant vegetation. The mastodon was found at the contact between this layer and the overlying red fibrous peat. This peat is rich in beaver chewed wood fragments, twigs, sedge, seeds, husks, coleoptera parts, small bones, and conifer cones. All evidence points to the pond shallowing, with vegetation replacing some of the zones of open water. The black woody peat contains coarser material ranging from small twigs to entire stumps, and indicates that the pond was shrinking and trees and shrubs colonized the marginal zones. The contemporary landscape at the site now contains swamp forest, cattail swamp, and some open water.