THE MIDDLESEX READVANCE OF THE LATE-WISCONSINAN ICE SHEET IN CENTRAL VERMONT AT 11,900 14C YEARS BP

The study area in the Town of Middlesex is on the south bank of Culver Brook 5.85 km N2.5°W of the Vermont State Capitol Building in Montpelier. At each of two separate locations about 61 m apart, two tills are exposed. At the base of the first site is yellowish-brown, compact, sandy till, which is overlain by a 3.0-m thick package of blue-gray, compact and highly deformed clay-silt varves. The varves are overlain by loose to compact, yellowish-brown sandy till. At the second site lower till is very compact and has a dark greenish-gray color similar to rocks in the Moretown Formation from which it was largely derived. The upper one meter of lower till appears to have been weathered because it is light to dark yellowish brown and contains “phantoms”, pockets of loose grains formed by subsurface alteration of former solid pebbles transported by the ice sheet. The upper till is gravelly, loose to compact, brown to gray and overlies a sharp contact on lower till. It contains a slab of lower till and a 2.0-meter slab of fine-grained lacustrine? sediment. Lacking clear evidence for a local readvance such as moraines or ice-shove features, and the fact that the lower till at the second site appears to be deeply weathered, led to an initial interpretation that the lower till was Early Wisconsinan or older and the upper till was Late Wisconsinan. However, a sample of wood collected from the slab of fine-grained sediment in the upper till has a ¹⁴C age of 11,900 ±50 years BP (GX-26457-AMS). If the age is correct, the Late-Wisconsinan ice sheet readvanced across sediments of glacial Lake Winooski in Middlesex at about the same time that ice readvanced across glacial Lake Hitchcock sediments at the Comerford Dam site in Barnet, Vermont (Ridge and others, 1999).