CALIBRATION OF A UNIFIED NEW ENGLAND VARVE CHRONOLOGY: DEGLACIATION RATES AND MORAINE BUILDING IN THE CONNECTICUT VALLEY OF NEW HAMPSHIRE AND VERMONT

A gap between the main sequences, lower and upper Connecticut (LC and UC) varves, of Ernst Antevs' New England Varve Chronology (NEVC) has been an obstacle to calibrating the NEVC as a whole. Hollow-stem auger continuous sampling of subsurface varves at sites in Westmoreland (Aldrich Bk.), Charlestown (3), N. Charlestown, Perry Hill Basin (2), and Claremont Junction, NH, and Weathersfield Bow, VT has provided a detailed chronology that consolidates the NEVC into a single sequence (LC 6268 = UC 6600) of over 5600 yr (LC 2701 to UC 8679). Corrections to the LC sequence based on a core at Amherst, MA (-10 yr; Rittenour, 1999) and 3 minor corrections to UC varves (-2/+1 yr) based on new cores has improved the accuracy of the NEVC and otherwise confirms Antevs' chronology. A unified numbering system for the NEVC is under construction. Along with 24 new ¹⁴C ages of terrestrial plant fossils and a snail fossil from varve outcrops at East Windsor, CT, Westmoreland and Walpole, NH, and Canoe Bk., Newbury, Wells River, and East Barnet, VT, the consolidation and corrections provide a new single calibration of the NEVC (LC 2701-UC 8679 = 17.9-12.3 cal ka), which is now available with all NEVC varve records and ¹⁴C ages (see web site below). New cores also indicate that there was a slow-down of ice recession (5 km in 250 yr or 20 m/yr) associated end moraine building and a minor readvance in Charlestown, NH at 14.7-14.45 cal ka. This event coincides with a subtle decrease in varve thickness, possibly reflecting lower meltwater and sediment input due to reduced summer melting. The Charlestown moraines may correlate with end moraines mapped by J.W. Goldthwait in the Lake Sunapee and Winnipesaukee basins. Prior to this time ice receded from Massachusetts to Charlestown at 90 m/yr. After the Charlestown event rapid ice recession abruptly started at 280 m/yr. This transition is easily recognized by a sudden (over 5 yr) 2 to 3-fold increase in varve thickness that signals much higher discharges of meltwater and sediment. The high recession rate was maintained for over 500 yr as ice receded to the northern Connecticut Valley. In numerous lacustrine, marine, and ice-core records this event (beginning of Bølling) has also been recognized as a time of dramatic warming in the northern hemisphere, and rapid ice sheet recession and sea level rise (mwp1A). Varve data are available at: http://ase.tufts.edu/geology/varves/.