VARVE RECORDS FROM GLACIAL LAKES IN SOUTHERN NEW ENGLAND: CONSTRAINTS ON THE TIMING OF LATE-WISCONSINAN DEGLACIATION

New varve cores from glacial Lake Hitchcock (GLH) at Turners Falls MA and glacial Lake Middletown (GLM) at Newfield CT record 433 years and 175 years of lake history at the respective sites. At Turners Falls, 26 m of gray varves overlie 1.3 m of red till, and the oldest varve resting on till correlates with the North American Varve Chronology (NAVC) at varve year 5072; this puts the ice margin at a position just north of the Connecticut River at Turners Falls at 15.8 cal ka (calibrated NAVC, Ridge, 2010). A core from the Matianuck Ave. site 85 km south in Windsor CT (Stone and Ridge, 2009) records basal varves of glacial Lake Middletown/Hitchcock that match the NAVC at varve year 2831, indicating that the ice margin stood at a position just south of the Farmington River at 17.9 cal ka. Four new cores at 2 sites in GLM in the Newfield area of Middletown CT are currently being studied. At the first site, side-by-side vertically offset cores penetrated 22.8 m of red varves overlying till; and at the second site, 12 m of red varves overlie till. Although varve analysis is ongoing, the 175-yr lake record for the Newfield basin of glacial Lake Middletown does not appear to overlap with the NAVC which begins at varve year 2700 (18.1 cal ka); however, mapped ice-margin positions indicate that this part of GLM immediately preceded that timeframe and thus existed from 18.3 to 18.1 cal ka. South of GLM, a 30-m core from glacial Lake Quinnipiac (GLQ) obtained by USGS in 1985 and recently analyzed by J. Ridge revealed 474 varves that match Antevs’ New Haven series at varve years 179-551; that series contains 700 years recorded at clay pits in Haverstraw NY and near New Haven CT (in GLQ). Thus, the mapped ice-margin position immediately preceding GLQ must have a minimum age of 19.0 cal ka; this ice margin position extends into eastern CT well north of the Old Saybrook and Ledyard moraines. To the south, the moraines extend beneath Long Island Sound as ridges of ice-marginal lacustrine fans that are overlain by more than 100 m of varved lake clay of glacial Lake Connecticut (GLC). A minimum estimate of time for direct meltwater-supplied varve deposition in GLC based on varve thicknesses in vibracores is 1000 years. Therefore, varves constrain the age of the moraines to at least 20.0 ka, and indicate that only the older range of the 20.2±1.0 ka ¹⁰Be date (Balco and others, 2009) is possible.