COSMOGENIC-ISOTOPE AGES FOR LAST-GLACIAL-MAXIMUM MORAINES OF THE LAURENTIDE ICE SHEET, SOUTHERN NEW ENGLAND

The advance of the southeastern margin of the Laurentide Ice Sheet to its maximum late Wisconsinan limit is marked by a series of prominent end moraines bordering the present coastline of southern New England. Thirteen 10-Be/26-Al analyses of boulders from the outermost moraine at Martha's Vineyard, MA indicate that the ice sheet reached its greatest extent about 25,000 cal yr B.P., approximately coeval with the coldest period of marine oxygen-isotope stage 2 and with Heinrich event 2. A further ten analyses from the Buzzards Bay Moraine to the north near Woods Hole, MA produced ages that cluster near 17,000 cal yr B.P. We found boulders with anomalously old exposure ages suggesting recycling of preexisting deposits in the outermost moraine, but boulder ages from the inner moraine are tightly grouped. These data and other radiocarbon dates from throughout New England indicate that fluctuations of this sector of the ice sheet were concordant with variations of North Atlantic climate: the ice sheet advanced rapidly to its maximum extent at the onset of coldest, glacial-maximum conditions ca. 25,000 cal yr B.P. and remained relatively close to this late Wisconsinan limit for ca. 8000 yr. before retreating.