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January 01, 1973

The age of the late Wisconsin maximum of the Laurentide ice sheet off the coast of New England and on Long Island, New York, is not closely designated. Radiocarbon and stratigraphic evidence from Martha’s Vineyard suggests that the glacier margin may have been close to its maximum position as late as 15,300 yrs ago; indirect evidence from Long Island infers that the ice sheet had reached a maximum and had begun to recede prior to 17,000 yrs ago. In any case, by at least 14,200 yrs ago the glacier margin had retreated from its maximum late Wisconsin position at the Ronkonkoma Moraine on Long Island, had constructed recessional frontal deposits, and had retreated north of Rogers Lake on the southern Connecticut coast. Subsequent readvances culminated near Middletown, Connecticut, some time after 15,000 yrs ago, and in Cambridge, Massachusetts, after 14,000 yrs ago. Whether these readvances were synchronous is unknown because of the absence of close limiting dates and because of the lack of evidence for readvance in the intervening area. The northwestward recession of the glacier margin from the present coast in eastern Maine was accompanied by a marine transgression and deposition of hundreds of submarine moraines between 13,500 and 12,500 yrs ago. This general recession was interrupted by a readvance which culminated at the Pineo Ridge Moraine approximately 12,700 yrs ago. Although it may have resulted from general climatic change, the Pineo Ridge readvance just as likely may have been caused by a vastly decreased calving rate associated with isostatic uplift and marine recession from coastal Maine. This is well documented as having occurred simultaneously with the Pineo Ridge readvance. Thereafter, the ice sheet thinned and separated over the highlands of northwestern Maine leaving residual ice to the southeast. Active ice, receding into the St. Lawrence Valley of southeastern Quebec deposited the Highland Front Moraine approximately 12,700 to 12,600 yrs ago. In summary, (1) a major amelioration of climate that began prior to 14,200 yrs ago resulted in very rapid dissipation of the ice sheet in New England at least by 12,500 yrs ago, with the exception of small glaciers that possibly persisted in the highlands; (2) no conclusive evidence has been recognized for any climatic reversals during the dissipation of the ice sheet in New England; and (3) although major events in New England compare with those of the Great Lakes region, no minor events have proven correlation with the possible exception of the Pineo Ridge and Port Huron readvances.

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Figures & Tables


GSA Memoirs

The Wisconsinan Stage

Robert F. Black
Robert F. Black
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Richard P. Goldthwait
Richard P. Goldthwait
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H. B. Willman
H. B. Willman
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Geological Society of America
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January 01, 1973




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