MIDDLE WISCONSIN TO RECENT 14C CHRONOLOGY OF THE GENESEE RIVER BASIN IN WESTERN NY: AN EXTENDED CLIMATIC, ARCHAEOLOGICAL, FLORAL, FAUNAL, AND HISTORIC RECORD

Studies along 95 km of the Genesee River reveal a chronology extending back to Middle Wisconsin time, based on more than 140 ¹⁴C ages. Pleistocene and Holocene sediments record several important regional climatic signals or events. The oldest event includes glacially overridden spruce remains and Mammut spp. of the Middle Wisconsin Farmdale Phase of the Elgin Subepisode (Plum Point Interstadial) dated at >48,500 to 36,000 ¹⁴C years Before Present (yBP). Two deformation tills mark a glacial advance coincident with Heinrich Event H4 (~35,000 yBP) and rest disconformably on an interstadial floodplain containing organic remains with ages centered between 39,000 and 41,600 yBP. Although late Wisconsin deglaciation is not defined by this record, it is constrained between 12,600 (glacial Lake Iroquois) and 16,400 yBP by previous work. A peccary skeleton in a till-over-outwash moraine suggests rapid postglacial faunal repopulation. Reforestation occurred before 12,150 yBP as dated by trees in a paleolandslide, the base of which corresponds with the modern channel base near Avon, NY. A peat to marl transition in bogs beginning around 8200 yBP marks the regional cold event attributed to the final draining of glacial Lake Agassiz. The floodplain sediments contain leaf mats as old as 11,000 yBP that constrain lateral channel migration and vertical sedimentation rates (average 1mm/yr), which have doubled in the last 2 centuries, presumably due to agricultural practices and deforestation. Annual leaf mats are more accurate than wood fragments for defining point bar and archaeological stratigraphy due to reworking of wood.

An unusual aspect of the ¹⁴C stratigraphy is a concentration of charcoal debris in overbank deposits at a depth near 1.6 m with corrected calendar ages between 457 and 533 AD. The decade beginning around 536 AD is marked by world-wide climatic extremes, drought, and an unusual deviation in the ¹⁴C record coinciding with the beginning of the Dark Ages, summarized in the 2000 book, Catastrophe, by David Keys. An increase in forest fires caused by such widespread drought might explain the charcoal concentrations, which could be useful for regional correlations. The oldest floodplain fire pit age is 470±80 yBP at a depth of 1.2 m, but previous work has provided a range of archaeological dates back to 4746 yBP.