OSL-¹⁴C-¹⁰Be: A novel composite geochronometer for simultaneous quantification of timing and magnitude of change in bedrock outcrop erosion rate

Quantifying past changes in erosion rate is essential for deciphering earth surface processes and their driving mechanisms. Coupled in situ cosmogenic ¹⁴C-¹⁰Be has been shown to be a useful chronometer in detecting changes in erosion rate, but its detection ability is limited to rapidly eroding fluvial landscapes and changes greater than a factor of two; and in any case, it cannot uniquely quantify both the magnitude and the timing of change in erosion rate. Here, we establish a theoretical framework to show that this limitation can be overcome by combining the recently developed optically stimulated luminescence (OSL) rock surface exposure dating with the ¹⁴C-¹⁰Be chronometer. We demonstrate that the resulting OSL-¹⁴C-¹⁰Be composite geochronometer can determine both the magnitude and the timing of an abrupt change in bedrock erosion rate by a factor of < 0.8 or > 1.2 over 10⁰–10⁴ a timescales, where erosion rates are < 10⁻² cm a⁻¹.