REFINING THE AGE OF GLACIAL DEPOSITS ON BLOCK ISLAND (RHODE ISLAND, USA) THAT PREDATE THE LAST GLACIAL MAXIMUM

Glacial advances tend to erase evidence of previous glaciations, making the Pleistocene record of ice sheet extent and global mean sea-level challenging to reconstruct. We rely on δ18O proxy records from benthic foraminifera and ice cores to determine global mean sea-level prior to the Last Glacial Maximum (LGM). However, the proxy records are convolved with other signals such as temperature change and confounding factors that contribute to widely varying pre-LGM ice volume and sea-level estimates. Recent ocean sediment studies from the Arctic have suggested that the Bering Strait may have been emergent prior to the LGM during MIS3. Recent archeological studies have uncovered new evidence for human migration into the Americas as far back as ~30 ka during MIS3. This begs the question: is there evidence for a significant MIS3 ice advance that could be related to pre-LGM human migration across the Bering Strait? The glacial deposits that make up Block Island (Rhode Island, USA) are continuous with terminal moraine deposits that extend from Long Island (NY) to Martha’s Vineyard (MA) and can be used to define the extent of the Laurentide ice sheet. The glacial deposits are categorized into two units: an upper New Shoreham Drift, which was deposited around 25-18 ka during the LGM; and a Lower Montauk Drift, which has yielded scattered 43–35 ka radiocarbon dates on woody material. One of the implications of the radiocarbon dates is that the Montauk Drift could be related to a poorly recognized MIS3 ice advance. To investigate and better define the timing of pre-LGM ice extent in eastern North America, we collected samples for radiocarbon and luminescence dating from the Montauk Drift on Block Island, and paired these dates with a new compilation of dated glacial deposits, to evaluate existing models of MIS3 ice extent and global mean sea level that might have permitted pre-LGM human migration into the Americas.