HIGH-PRECISION ISOCHRON BURIAL DATING USING A GAS-FILLED-MAGNET

Cosmogenic ²⁶Al and ¹⁰Be in quartz can be used to date sediment burial over timescales ranging up to ~5-6 My based on their relative decay. However, burial dating has traditionally required deep burial in caves or beneath tens of meters of sediment, and the method has suffered from large uncertainties due to the difficulty in measuring ²⁶Al by accelerator mass spectrometry. This has now fundamentally changed due to the recent implementation of a gas-filled-magnet (GFM) at PRIME Lab. By suppressing the isobar ²⁶Mg, the GFM allows ²⁶Al to be injected into the accelerator as the molecular ion AlO^-, at more than an order of magnitude higher beam current. Precision of ²⁶Al measurements is now equal to that of ¹⁰Be, a few percent or better. We will present new data comparing burial dates to ⁴⁰Ar/³⁹Ar dates of overlying volcanic deposits at the 0.77 My Bishop Tuff, California, and at the Pulu site in the Tarim Basin of northern China where the uppermost Xiyu conglomerate is sandwiched by basalt flows that bracket its age to 1.2-1.4 My. In both cases the burial ages match the ⁴⁰Ar/³⁹Ar ages with precision of ~5%. Isochron burial dating has tremendous potential in archaeology and Quaternary geology, including for dating sites buried by only a few meters of sediment.