THE ENVIRONMENTAL MAGNETIC RECORD OF THE LAST GLACIAL-INTERGLACIAL TRANSITION FROM EKURD’S POND, URBANA, OHIO

Ekurd’s pond is a 1.5 square kilometer closed basin formed on an ice-contact ridge located in the interlobate morainal area of western Ohio. Three overlapping cores were extracted from the basin and together yield a 5 meter sequence of continuous sedimentation. AMS radiocarbon analyses from this site and four adjoining bogs suggest general ice retreat about 16,000 BP. The lower date at the core site shows ice retreated by about 15,800 BP. Total organics, total carbonate, grain size and a suite of magnetic analyses characterize this record of environmental change through the glacial-interglacial transition and much of the Holocene

Three distinct units are recognized based on the lithologic character, grain size, organic content and magnetic susceptibity. The lowest unit represents the changing landscape from the ice-contact, immediate postglacial setting to lacustrine deposition. A 2-meter sequence of lake silts was then deposited within a 2,000 year period, according to AMS radiocarbon dates. These lower two units are capped by a more organic-rich silt recording the transition into the Holocene.

Environmental magnetic analyses include ARM, IRM, and high and low frequency magnetic susceptibility parameters. Preliminary work shows that these measurements are consistent with the overall stratigraphy and may provide a detailed record of fluctuations in magnetic concentration, grain size and mineralogy that reflect changes in sediment fluxes into the pond. Fluctuations in erosion of soils within the basin as well as variations in eolian input external to the site will be interpreted in the context of the changing dynamics of the retreating Laurentide Ice Sheet, global climate fluctuations, and internal changes in the geological and ecological evolution of the basin.