Constrained age of Glacial Lake Narragansett and the deglacial chronology of the Laurentide Ice Sheet in southeastern New England

Abstract

The lack of radiocarbon ages and correlated varve sequences in southeastern New England has left the deglacial chronology of the region poorly constrained. A 265-year varve series from Glacial Lake Narragansett was constructed from eight continuous sediment cores collected from the Providence River, Narragansett Bay, Rhode Island. This varve series could not be correlated with either the North American Varve Chronology or other varve sequences from southern New England or southeastern New York. The uncorrelated varve sequences presented here represent the minimum time of deposition within the northern segment of Glacial Lake Narragansett. These sequences, used in conjunction with the calibrated North American Varve Chronology and cosmogenic exposure ages from recessional end moraines, provide minimum (>19,400 cal BP) and maximum (<20,500 cal BP) ages for Glacial Lake Narragansett. Correlations with the updated Greenland (NGRIP and GRIP) ice core records suggest that cold periods associated with moraine formation are 200–250 years older than the cosmogenic exposure ages. Whereas many studies refer to the last glacial maximum occurring from 20,000 to 18,000 cal BP, the constrained age of Glacial Lake Narragansett suggests that at least for the southeastern portion of the Laurentide Ice Sheet, deglaciation was well underway by this time.