Cosmogenic 3He and 10Be chronologies of the late Pinedale northern Yellowstone ice cap, Montana, USA

Cosmogenic ³He and ¹⁰Be ages measured on surface boulders from the moraine sequence deposited by the northern outlet glacier of the Yellowstone ice cap indicate that the outlet glacier reached its terminal position at 16.5 ± 0.4 ³He ka and 16.2 ± 0.3 ¹⁰Be ka, respectively. Concordance of these ages supports the scaled production rates used for ³He (118.6 ± 6.6 atoms · g⁻¹ · yr⁻¹) and ¹⁰Be (5.1 ± 0.3 atoms · g⁻¹ · yr⁻¹) (±2σ at high latitudes at sea level). Two recessional moraines upvalley from the terminal moraine have mean ages of 15.7 ± 0.5 ¹⁰Be ka and 14.0 ± 0.4 ¹⁰Be ka, respectively, and a late-glacial flood bar was deposited at 13.7 ± 0.5 ¹⁰Be ka. These cosmogenic chronologies identify a late Pinedale glacial maximum in northern Yellowstone that is significantly younger than previously thought, and they suggest deglaciation of the Yellowstone plateau by ∼14 ¹⁰Be ka.