CONTRASTS IN EARLY AND LATE PLEISTOCENE GLACIAL RECORDS IN NORTHEASTERN U.S.A. RESULTING FROM TOPOGRAPHIC RELIEF, CLIMATE CHANGE, AND CRUSTAL DEPRESSION

The long buildup of the Wisconsin ice sheet ice, 71–30 ka, in the 100-kyr orbital climate interval, resulted in deep crustal depression as shown in geophysical models. In coastal New England detrital wood, peat, and shells dated >50–25 ka, derived from shallow marine basins, which required mid-Wisconsin crustal depression of 10’s of m’s during ice advance into glacio-regressed sea levels. Timing of the New England glacial event 32–12.9 ka is at the end of asymmetric marine isotope stage (MIS) MIS4-2, 71–14 ka. Ice-front terminal and recessional positions are based on new stratigraphic correlations, varve chronology, OSL ages, and ¹⁰Be dates. Terminal moraine segments vary in age, but may have a simultaneous age of 23.5 ka among seven ice lobes across the region. Early retreat of three eastern lobes to the Harbor Hill-Sandwich moraine line was complete by 22 ka. This line continues west to New York City and along the terminal moraine in NJ. Small recessional moraines in a 20–40 km-wide zone across NJ are correlated along traces in Long Island Sound basin to similar zones in southeastern CT, RI, and MA. This small-moraine zone records early slow ice retreat <10m/yr, at 22–20 ka; it sets a limiting age for lower varves in lakes Hackensack, Connecticut, and Narragansett. Glacial-lakes history and local moraines describe the regional pattern and increasing rates of ice-front recession, <100 m/yr to >100 m yr, in northern New England. Glacial-lake water planes slope upward to the north 0.5 m/km in the terminal zone, 0.9 m/km north of the coast, and decreasing in northern New England, recording uplift during ice retreat there.

Possible correlations of early-middle Pleistocene units in New England with midcontinent till units are: Wequobsque Drift (>MIS40-42); unit D1 (Georges Bank)-Dukes boulder bed-Manetto (MIS40-42? or MIS18?); unit D2-Moshup-Jameco-Port Murray Fm. (MIS 8-12). Large amplitude MIS events of relatively long duration produced ice buildup but perhaps not deep crustal depressions, leading to extensive flow of thinner ice sheets, compared to the late Pleistocene event. The mountainous barrier of >1 km relief in the northeastern U.S., and climate dominated by the 41-kyr period of Earth’s orbital obliquity may have helped to limit the number, duration, and crustal depressions of early Pleistocene glaciations compared to late Pleistocene events.