GSA QUATERNARY GEOLOGY AND GEOMORPHOLOGY DIVISION KIRK BRYAN AWARD: A COMPREHENSIVE DEGLACIAL TIME SCALE FOR THE NORTHEASTERN UNITED STATES: VARVES, RADIOCARBON AGES, PALEOMAGNETISM, AND COSMOGENIC-NUCLIDE EXPOSURE DATING

Terrestrial glacial sequences with continuously represented time are rare. In the northeastern US deglaciation is now tied to a reformulated and expanded North American Varve Chronology (NAVC) originally created by Ernst Antevs as the New England Varve Chronology. 54 ¹⁴C ages in the NAVC from terrestrial plant microfossils span ~4800 varve yr. Calibration of the NAVC has been formulated as the best fit (lowest mean sq. of weighted dev.) of the ¹⁴C age/varve year data to the Intcal09 data set assuming that varve and calibrated years are the same with only an offset of the time scales (Cal yr BP = 20,770 – AM yr). This avoids statistical treatment of individual ¹⁴C ages converted to calibrated ages. Basal varves in the Connecticut Valley have been used to precisely date deglaciation. Positions of readvances and delays in ice recession have been determined along with ice recession rates between these events. Ice recession rate increases northward to as high as 300 m/yr in northern New England. The NAVC has served as a means of intercalibrating cosmogenic nuclide (¹⁰Be) production rates, which accurately dates southern New England terminal thru early-recessional moraines. The NAVC also serves as a chronology for postglacial faunal succession (trace fossils of fish and crustaceans) in glacial lakes. Expansion of the time scale to NY State has been possible with correlation of varves in the Hudson Valley (Antevs 1922) and correlation of paleomagnetic declination records in varves from New England and NY. A declination maxima of 45-60° W occurs on both records at 14.5 cal kyr BP. The declination correlation shows synchronous glacial readvances across the region except for delays of 1-2 centuries in NY that may be the result of westward drift of the geomagnetic field. It has not been possible to directly correlate varve records in central NY with the NAVC because they are too short and often interrupted by mass movement events. Varve records have the added advantage of carrying a climate signal since glacial varve thickness variations are dominated by variations in glacial meltwater production (i.e. melting) making it possible to identify warming and cooling events that: 1) coincide with changes in ice recession rates and readvances, and 2) can be precisely matched to decadal-scale cooling and warming events in Greenland ice cores (GISP2 δ¹⁸O).