ALLUVIAL RECORDS OF ENVIRONMENTAL CHANGE FROM MID TO LATE HOLOCENE, NORTHEAST OHIO

Radiocarbon-dated alluvial sequences in Northeast Ohio preserved in alluvial fans and terraces are a record of complex fluvial responses to past climate and land use changes. Bog bottom radiocarbon ages show that the region was deglaciated at its southern margin by 15,400 yrs BP; this age also provides an estimate for the beginning of fluvial excavation of post-glacial bedrock gorges in the region that likely began within 1000 years of this age according to a transect of bog-bottom ages.

Radiocarbon ages at the base of one alluvial sequence suggest that general downcutting of bedrock gorges continued until approximately 6000 yrs BP when alluvium began to aggrade. Four radiocarbon ages from two sites provide additional evidence of environmental change at this time. These ages are from a forest buried in floodplain sediments from the Killbuck Creek and from logs buried in ephemeral lakes in wetlands. These dates span 6430-5770 yrs BP and are consistent with work done in the upper Mississippi Valley that has shown a changing flood regime around 6000 yrs BP followed by large-scale flooding events. In Northeast Ohio mid-Holocene warming is linked to a gradual increase in precipitation according to pollen records. Following this mid-Holocene transition, radiocarbon ages on wood in debris flows and alluvium cluster around 2500,1350 and 200 yrs BP and may suggest a millennial-scale pace to aggradation changes in Northeast Ohio during the Holocene.