19 Ice sheets, glaciers, and landscapes, oh my!

Glaciers and ice sheets shaped the landscape of the Northeast. Ice continues to shape the landscape of alpine and polar regions. We welcome submissions on glaciers &  ice sheets of any size, shape, age, and location.

Monday, 23 March 2026
8:00 AM - 12:00 PM
CCC, Room 26

Reconstructing Laurentide Ice Sheet Retreat in Northeast Pennsylvania Using Integrated Geological and Geochronological Evidence

Paper number: 19-2
Program: Technical Sessions
Time: 8:25 AM – 8:45 AM

Authors

Abstract

The timing of Laurentide Ice Sheet (LIS) recession in the northeastern United States has a long history of glacial geologic study, including extensive surficial geological mapping and the development of retreat chronologies using varved sediments, 14C, cosmogenic 10Be, and optically stimulated luminescence (OSL) ages. However, near the Last Glacial Maximum (LGM) terminal moraine complex, radiometric ages recording moraine stabilization and ice retreat disagree by thousands of years. In addition, there is limited geochronological data along the southeast margin of the LIS in northeast Pennsylvania, despite the prevalence of well-developed ice marginal landforms and deposits. As a result, the exact timing of regional LIS deglaciation is still debated. We address this by integrating: surficial geological mapping of ice margin deposits; collection, stratigraphic analysis, and 14C dating of lake and bog sediments; OSL dating of glacio-fluvial deposits; and 10Be exposure dating of moraine boulders and proximal bedrock outcrops. Preliminary results suggest that variations in basal 14C ages broadly reflects basin origin: lakes formed by subglacial erosion and containing varved minerogenic sediments are older, and suggest earlier deglaciation, than basins formed by meltout of detached ice blocks. 10Be ages from terminal moraine erratic boulders generally overlap with our 14C basal ages from erosional basins but are thousands of years older compared to kettle basins, supporting the notion that buried ice persisted within moraines for millennia. OSL ages on glacio-fluvial deposits ~50 km north of the terminal moraine are variable and generally older yet, suggesting a complicated history of LIS stagnation or insufficient bleaching of sands and subsequent re-working. We surmise the contrasting age estimates for LIS deglaciation in the northeastern United States may reflect regional-scale differences in topography, basin formation, ice sheet thermal regimes, and ice behavior along the terminal position, along with myriad inherent assumptions for each dating method. Ongoing surficial mapping and radiometric dating will further define the spatial distribution and age of glacial deposits. Our new data and synthesis shed important insights into LIS dynamics and retreat, where different geochronological models suggest contrasting ice retreat histories.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2

doi: 10.1130/abs/2026NE-411343

© Copyright 2026 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.