The Quaternary glaciation of western New England with correlations to surrounding areas

Abstract

Abstract Over the last 20 years there have been major improvements to our understanding of the Quaternary glaciation of New England. Numerous Accelerator Mass Spectrometer (AMS) 14C ages of terrestrial plant fossils have eliminated some of the errors associated with 14C ages of lake-bottom bulk sediment samples and marine fossils. The rebirth of Antevs' New England varve chronology and its 14C calibration have added precision to the Late Wisconsinan deglaciation chronology and a means of precisely testing correlations of deglacial events. Palaeomagnetic studies of both declination and polarity have allowed precise correlation between New England and adjacent areas. The exact chronology of pre-Late Wisconsinan glaciation is still poorly constrained because of difficulties in determining numerical ages. The terrestrial glacial record of New Jersey dictates that New England was glaciated at least twice in pre-Wisconsinan time, at least once when the geomagnetic field had a reversed polarity (pre-Illinoian, Marine Isotope Stage (MIS) 22 or older, 850 ka) and again during the Illinoian (160–180 ka BP, MIS 6). Controversy exists concerning pre-Late Wisconsinan till in central and northern New England with its weathering supporting an Illinoian age and amino acid ages from reworked marine fossils in Boston Harbor supporting an Early Wisconsinan age. In the Connecticut Valley of southern New Hampshire and Vermont the advance of Late Wisconsinan ice buried advance outwash and lake beds were deposited in tributaries impounded by advancing ice. Late Wisconsinan ice reached its limit on islands along the southern coast at 24.0-20.0 14C ka BP (28.0-23.7 cal ka BP). The overall pattern of deglaciation was one of spurts of ice recession punctuated by readvances and end moraine building, and acceleration of ice recession over time. The early chronology of deglaciation (20.0-15.0 14C ka BP, 23.7-18.0 cal ka BP) has been inferred from correlations to Greenland ice core records and varve sequences have been used to crudely constrain the chronology. The later part of deglaciation (15.0-11.5 14C ka BP, 18.0-13.4 cal ka BP) has been determined precisely where basal ice-proximal varves are matched to the 14C-calibrated New England varve chronology in the Connecticut, Merrimack, Passumpsic, and Winooski Valleys. The resulting precise chronology of deglaciation in central and northern New England is about 1500 years younger than in previous models largely based on bulk sediment lakebottom 14C ages. A comparison of terrestrial 14C ages for ice margins in the Merrimack Valley with marine 14C ages for contemporaneous marine ice margins in southern Maine suggest that a 600-1300-yr marine reservoir correction should be applied to the marine chronology. Correlations between New England and New York have been formulated with the matching of independent palaeomagnetic declination records from both areas and the connection of icefront positions that appear to align geographically. There appears to be a contemporaneity of readvances in both regions that also match cold intervals on Greenland ice core records. These observations support a rapid response of the last ice sheet's ablation system to cold events. Following deglaciation a delayed isostatic tilting occurred across central to northern New England with water planes dipping 0.85–0.94 m/km towards the south-south-east. The nonglacial remnants of glacial lakes in the upper Connecticut Valley persisted until at least 10.5 14C ka BP 12.5 cal ka BP) and may have been seen by the first humans in the area. While isostatic uplift was well underway in southern and central New England recession of ice in Canada allowed the invasion of marine water into the Champlain Basin at about 11.0 14C ka BP (13.0 cal ka BP). This age estimate is consistent with previous studies that attempted to remove a reservoir error from marine 14C ages of Champlain Sea fossils.