CORRELATION OF MAINE DEGLACIATION CHRONOLOGY WITH THE NEW ENGLAND VARVE CHRONOLOGY AND DEGLACIATION OF NEW HAMPSHIRE

The radiocarbon-dated chronology derived from varved glacial-lake clays is currently the most precise means of establishing the timing of deglaciation across much of New England (Ridge, 2004). This method has not been extended into adjacent southern Maine because of the scarcity of suitable varve exposures in the latter area. Maine's deglaciation chronology has been reconstructed chiefly from minimum-limiting radiocarbon ages of marine shells (below the marine limit) and terrestrial organics from lake sediment cores (Borns et al., 2004). The shell ages are assumed to be too old because of the marine reservoir effect. Corrections as large as -600 yr have been applied to them, but the adjusted ages still suggest a deglaciation chronology that is hundreds of years older than the isochrons that Ridge extrapolated from New Hampshire into SW Maine. It is also likely that some of the Maine terrestrial ages are too old because they were obtained from bulk sediment samples or from insects that may have inherited old carbon from pond waters. Recent and ongoing studies at a fossil-wood locality in Portland, Maine, suggest an answer to the dilemma of the marine radiocarbon ages (Thompson et al., 2008). Spruce logs in juxtaposition with marine shells in the Presumpscot Formation yielded ages for the shells that are 1000 yr older than the wood. If the large reservoir correction implied by these results is valid for other marine ages in SW Maine, it supports a deglaciation chronology consistent with Ridge's New England Varve Chronology to the west. Our proposed revision of the SW Maine chronology is also compatible with a tentative new correlation of ice-margin positions across the coastal moraine belt to the New Brunswick border. Farther inland, the series of moraines deposited in the northern White Mountains of New Hampshire during the Older Dryas cooling (13.8 cal ka BP) have now been traced to the Maine border. Limiting radiocarbon ages from Maine lakes suggest a northeasterly continuation of this ice margin across western and northern Maine, approximately coincident with the 12.0 14C ka (13.8 cal ka) isochron of Borns et al. (2004). No Older Dryas moraines have been identified in Maine, although the moraines flanking Mount Katahdin are close to the 13.8 cal ka isochron and warrant further study to determine their age and significance.