SPATIALLY VARIABLE GLACIAL EROSION REVEALED BY 10BE CONCENTRATIONS OF THE ORISKANY SANDSTONE

The landscape of Central New York experiences at least three Pleistocene glacial advances and is dominated by glacial landforms. If erosion occurs during a glacial advance or retreat, the column of rock moves towards the surface. If this rock traversed the zone where significant cosmogenic nuclides are produced, the concentration of cosmogenic nuclides, such as ¹⁰Be and ²⁶Al, that slowly build up tens of meters deep in bedrock due to muon production, can be used to estimate the amount of glacial erosion that has occurred in the area. In this study use the Oriskany Sandstone, a regionally extensive quartz Devonian sandstone, to explore the magnitude and timing of glacial erosion along the escarpment of the Appalachian Basin.

We collected five samples from active stone quarries that expose the Oriskany Sandstone over an E-W distance of nearly 140 km along with an additional sample collected from a road cut along interstate 88. Sampling depths below the modern day surface range between 35 and 8 m, a depth where cosmogenic nuclides are overwhelmingly produced by interactions with muons rather than spallation. The surface production rate of of ¹⁰Be by muons is ~0.4 atoms/(g*yr) at the surface and becomes > 0.001 atoms/(g*yr) at 110 m depth. All samples contain <6000 atoms/g, representing concentrations that barely detectable above laboratory backgrounds. Two of the samples do not contain measurable 10Be. For samples with a measurable concentration, all have apparent ages older than 24 Ka, implying a limited amount of LGM erosion.

We explore the amount of glacial erosion that occurred over the last 1 Ma by forward modeling of ¹⁰Be concentrations. We assume that Marine Isotope Stages 2, 6, 10, 12 and 16 correspond to periods when New York State was covered by the Laurentide Ice Sheet. Our forward model explores a model space that randomly prescribes an initial sample depth below the collection depth and an amount of glacial erosion at the end of each of the five glacial cycles. Our modeling results suggest erosion no greater than background continental erosion rates, while other sites clearly show at least 50 m of erosion across the northern edge of the Appalachian Plateau during MIS 6. Our results suggest that there is a major change in erosion N and S of the Valley Heads Moraine.