WHEN DID THE LAST, LATE WISCONSIN, CONTINENTAL ICE SHEET ACTUALLY RETREAT FROM WEST-CENTRAL NY?
R.A. Young, Geological Sciences, SUNY, Geneseo, NY 14454
The ongoing calendar year calibration of the radiocarbon timescale back to nearly 50,000 years ago, in conjunction with the detailed data sets obtained from the Greenland (GRIP) and Antarctic ice core projects, permit a more accurate revision of the timing of the last glacial events in New York State. In addition to documenting a mid-Wisconsin advance in both the Genesee and Cayuga (Six Mile Creek) Valleys (Young and Burr, 2006; Karig and Miller 2013), which corresponds closely with the age of Heinrich Event H4 at close to 39,000 years BP, there is significant new evidence which helps constrain the age of the Valley Heads moraine, as well as documenting a late glacial re-advance that coincides with the well documented Younger Dryas cold interval at ca 13,000 years BP (corrected calendar year ages). There are currently approximately 30 radiocarbon ages bearing on the Younger Dryas event, 18 of which can be used to document the Genesee Valley record. Additional radiocarbon ages that support a Younger Dryas event are part of an ongoing project for which the specific results have not yet been released for publication.
The Genesee Valley Younger Dryas record includes a complete peccary skeleton buried in quicksand along the crest of a small moraine near Linwood, NY, at the latitude of Fowlerville, NY. The geologic record at the peccary site is very instructive regarding how careful recording of stratigraphic information is essential for the accurate interpretation of the detailed geologic history. Thirteen additional ages from wood and organics enclosed in glacial till are located along the Genesee River channel south of Avon, NY, and immediately north of the informally named “Fowlerville moraine complex.” Four other ages extending from Caledonia, NY, southward to the Canaseraga Creek floodplain route of Interstate 390 (highway test borings near Sonyea, NY) demonstrate that the contact between glacial and postglacial sediments provides ages that fall within the 12,641 to 13012 year BP range. These data are consistent with re-vegetation shortly after ice withdrawal following the Younger Dryas cold interval. The Fowlerville moraine complex appears to mark the extent of the Younger Dryas advance in the Genesee Valley. This broad moraine system includes several sub-parallel ridges spread over a lateral distance of 3.5 miles (Geneseo, 1:24,000 topographic quadrangle)
A former glacial kettle pond, buried by katabatic(?) wind-generated sand dunes near Geneseo, NY, demonstrates that the ice had retreated to Geneseo by 16,545 ± 40 calendar years BP. This is consistent with the estimated age of the Valley Heads moraine in literature sources as being slightly older than this date.
The ability to provide a more accurate and concise framework for the last ice recession across western and central New York should improve the content of geologic and environmental project reports where this information has been the subject of poorly documented speculation for too long.