POST GLACIAL ENVIRONMENTAL HISTORY FROM LAKES, BOGS AND ALLUVIAL FANS, NORTHEAST OHIO

The post glacial environmental history of Northeast Ohio is recorded in the sediments of lakes, bogs and alluvial fans. Preliminary analysis of cores from three basins include loss-on-ignition (LOI), magnetic susceptibility and radiocarbon dating. Basal dates from bogs and a lake record show that the region was deglaciated by 14,500 yr. BP and that there were abrupt transitions during the glacial-interglacial transition and throughout the Holocene.

Brown’s Lake Bog, a site that had been previously analyzed for pollen, was re-cored for its evaluation of Holocene variability. Abrupt lithologic changes were noted in the 11 meter-long interval that spans the Holocene. Two Holocene lithologic changes were dated at about 7880 yr BP and after 550 yr BP. The earlier transition corresponds with a dry interval indicated by pollen records and the later change is correlated with post European Settlement. Ongoing analyses are underway to better constrain the timing and character of these and other Holocene transitions.

A complementary set of ages on debris flows in eroding alluvial fans are providing ages on what we interpret as times of increased precipitation and mobilization of sediments. Six ages indicate a mid-Holocene (5800 yr BP) and late Holocene (1340 yr BP) increase in debris flows. The 5800 yr BP interval is consistent with a spike in beach pollen that has been interpreted to indicate increased precipitation. The 1340 yr BP increase in fan activity may correspond with an increase in precipitation associated with climate fluctuations during the first millennium AD, which are widely recognized from other parts of North America. More dates and inter-proxy comparisons are needed, however, the records from lakes can be analyzed for large-scale drought and human impacts associated with land use changes. The alluvial sediments appear to give information about shifts in precipitation. Together these records can help to better characterize Holocene environmental change for Northeast Ohio.