T242 Dynamics of the Laurentide Ice Sheet

Wednesday, 13 October 2021
1:30 PM - 5:30 PM
Portland Ballroom 253 (Hybrid Room)

NEW RADIOCARBON CONSTRAINTS ON THE ADVANCE AND RETREAT OF THE LAURENTIDE ICE SHEET IN WESTERN NEW YORK, USA

Paper number: T242-12
Program: Technical Sessions
Time: 4:15 PM – 4:30 PM

Authors

Abstract

Enormous effort has been dedicated to determining when the southern Laurentide Ice Sheet (LIS) retreated after the Last Glacial Maximum (LGM); however, the timing of retreat in western New York (WNY) is poorly constrained. We address this data gap with multiple dating techniques. First, we mapped a stratified gravel deposit at the edge of the terminal moraine, which we interpret as a kame delta. From the gravel, we identified a reworked mammoth (Mammuthus sp.) tusk and use radiocarbon dating to provide a maximum-limiting constraint on the LGM advance. We also collected two samples for optically-stimulated luminescence dating to directly constrain delta emplacement (no results yet). Finally, we analyzed sediment cores from four kettle bogs and use radiocarbon dating for a minimum-limiting constraint of moraine abandonment. In addition, we measured loss-on-ignition and magnetic susceptibility to characterize the depositional environment. Preliminary results are reported as a 2σ age range for individual ages. The mammoth tusk dates from 30,940–30,128 cal yr BP, constraining the LIS advance into WNY after this time. The sediment cores capture transitions from gray pebbly diamicton to gray and tan silty clay to brown silt. Four ages from organic detritus within the grey and tan silty clay cluster between 16,200–15,500 cal yr BP, however, the oldest age comes from the overlying brown silt and is 19,587–19,348 cal yr BP. While this oldest age is out of stratigraphic order, it is based on a single macrofossil that appears terrestrial, and there is no measurable inorganic carbon in the bog sediments. As such, we believe the age is reliable and indicative of a deglaciated catchment at that time. Multiple radiocarbon ages date the transition from grey and tan silty clay to brown silt to around 14,600 cal yr BP, which coincides with the Bølling onset. This transition, characterized by a 30% increase in organic matter content, suggests a shift away from a mineral-rich, sparsely vegetated catchment to one with enhanced productivity. Together, our data show that the LIS advanced into WNY after 30,940 cal yr BP and retreated before 19,348 cal yr BP, and that Bølling warming influenced climate in WNY.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-366785

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